A Submillimeter Imaging Survey of Ultracompact HII Regions

Home , Cosmic dust

A Submillimeter Imaging Survey

of Ultracompact HI I Regions

Thesis by

To dd R Hunter

In Partial Fulllment of the Requirements

for the Degree of

Do ctor of Philosophy

I T U T E O T F S N T E I C A I H

R O

O 1891 L

L G

A Y

California Institute of Technology

Pasadena California

Submitted Septemb er

To dd R Hunter

iii

Comet Hyakutake

photographed on March

at Joshua Tree National Park California

Acknowledgements

Much of the success of this thesis can b e traced to Larry Ramsey and Je Hall

for intro ducing me to instrumentation work at Penn State My exp erience as a

VLA summer student in also inuenced me immeasurably by bringing radio

astronomy to life in the Land of Enchantment where I made some lifelong friends

Lo oking back I am pleased that Craig Walker convinced me to apply to Caltech I

thank my graduate advisor Tom Phillips for teaching me how to tune SIS receivers at

CSO and welcoming me into the submillimeter group a unique collection of p eople

that always manages to nish rst when it counts Thanks to Pat Schaer and Jacob

Ko oi for the worlds b est receivers and all those lab to ols of theirs that I didnt steal

Sp ecial thanks go to Harvey Moseleys family and colleagues at NASAGo ddard for

all their help and hospitality For answering my frequent computer and scientic

questions Darek Lis deserves sp ecial mention Similar recognition go es to Gene

Serabyn for help with optics and for constructive comments on this manuscript and to

Ning Wang whose determination led to the timely commissioning of SHARC Thanks

also to Maryvonne Gerin and Peter Schilke for showing me all the neat features of

GRAPHIC For keeping the telescop e running thanks to the CSO sta esp ecially

Taco a dep endable source of advice and humorous stories To Greg Taylor thanks

for your lessons on VLA data and intro ducing me to the memb ers of the Arcetri

group Thanks to Natalie Merchant and the kM for audio encouragement during

long summer days of programming SHARC at the summit of Mauna Kea where by

the force of will my lungs were lled Thanks to Eric Howard for his nearinfrared

data on S Chris DePree for his radio data on K and Debra Shepherd and

Peter Hofner for sharing their millimeter and radio data on G and G Much of

the research rep orted here was augmented by the patient advice and frequent noggin

usage of Dominic Benford and Rob ert Knop Finally with all the encouragement and

help from my family back East these past ve years have b een well worth the eort

Abstract

This research explores the pro cess of massive star formation in the Galaxy through

submillimeter continuum and sp ectral line observations of ultracompact HI I UCHI I

regions First I describ e the design and op eration of the Submillimeter High Angular

Resolution Camera SHARCa pixel b olometer array camera for broadband con

tinuum imaging at and m at the Caltech Submillimeter Observatory CSO

Detailed information is included on the reective oaxis optical design and the in

strument control software interface Second I present to resolution SHARC

images of and m continuum emission from a sample of UCHI I regions

with dierent radio morphologies Although the dust emission typically p eaks at or

near the UCHI I region additional sources are often present sometimes coincident

with the p osition of H O masers The combination of submillimeter millimeter and

IRAS farinfrared ux densities forms the basis of greyb o dy mo dels of the sp ectral

energy distributions The average dust temp erature is K and the average

grain emissivity index is Using a radiative transfer program that

solves for the dust temp erature versus radius the distribution of dust around UCHI I

regions is mo deled with a p owerlaw spherical density prole to match the observed

radial ux density proles By xing the source b oundary at the outer limit of the

submillimeter emission the resulting density proles nr r can b e classied

into four categories regions exhibit p isothermal sphere exhibit p

dynamical collapse exhibit p in the outer regions and p in the inner

regions and exhibit p logatropic Although these simplied mo dels may

not b e unique a go o d correlation b etween the dust luminositytomass ratio and the

temp erature indicates that the more centrallycondensed sources exhibit higher star

formation rates Third I present to resolution CO maps which reveal bip olar

outows from out of UCHI I regions The outow mechanical luminosities and

mass ejection rates follow the scaling relations with b olometric luminosity established

for less luminous premain sequence stars However in contrast to lower luminosity

sources the momentum from stellar radiation pressure is comparable to that required

to drive the outows Many regions show evidence of separate overlapping outows

In a nal detailed study resolution images obtained with the Owens Valley Mil

limeter Array reveal multiple outows emanating from the molecular core containing

the UCHI I region G while simultaneous outow and infall motion is seen

toward the neighb oring lessevolved core containing G

vii

Contents

Acknowledgements iv

Abstract v

Intro duction and Background

Massive star formation

Thesis outline

The Submillimeter High Angular Resolution Camera SHARC

Instrument overview

Optical design

Optical p erformance

Instrument control system

Data reduction

Sensitivity

Submillimeter Continuum Images of UCHI I Regions

The characteristics of interstellar dust

Computation of dust column density and mass from submillimeter ux

density

HIRES IRAS images

Calibration and p ointing accuracy of the SHARC images

SHARC images of cometary UCHI I regions

SHARC images of shelllike UCHI I regions

SHARC images of unresolved UCHI I regions

SHARC image of the G Complex ON

Greyb o dy mo dels

viii

Density proles

Luminosity to mass ratios

Summary

Molecular Outows from UCHI I Regions

Characteristics of molecular outows

Possible mechanisms of jetdriven outows

Outows from highmass starforming regions

CO sp ectra

CO outow maps

Calculation of outow energetics

Scaling relations

Summary

Active Star Formation toward the G and G

UCHI I Regions

Intro duction

Observations

Molecular outows

Continuum emission

Discussion

Conclusions

Summary

References

App endix A SHARC Cryostat Manual

App endix B SHARC Software Manual

App endix C Input parameters for the OUTFLOW program

List of Figures

Photograph of the b olometer array detector

Layout of the ellipsoid reimager

Strehl ratios versus chopp er angle

Sp ot diagrams across the SHARC fo cal plane

Sketch of the internal cryostat optics

SHARC lter arrangement

Strehl ratio versus dewar rotation angle

CSOSHARC b eam map at m

SHARC lter transmission curves

SHARC Server computer display

OTF map computer display

SHARC NEFD s achieved at and m

SHARC sensitivity vs integration time at m

Mean ux densityweighted grain radius for the na a distribution

HIRES IRAS maps of G

HIRES IRAS maps of the K complex

HIRES IRAS maps of G

HIRES IRAS maps of WOH

HIRES IRAS maps of G

HIRES IRAS maps of Mono ceros R

HIRES IRAS maps of GGD

HIRES IRAS maps of the S complex

HIRES IRAS maps of G

cm radio continuum image of G

and m images of G

H CO map around GSE

H CO sp ectrum of GSE

cm radio continuum image of G

m image of G

cm radio continuum image of G

m image of G

cm VLA image of GGD

m image of the GGD

cm radio continuum image of Mon R

m image of the Mon R complex

VLA cm image of the K complex

m image of the K complex

SHARC m image of the K complex

cm radio continuum image of WOH

m image of WOH

m image of G

m image of the G complex

m image of the S complex

CS J image of the S complex

K band m image of SFIR

m image of G

cm radio continuum image of G

m image of the G complex

Histograms of the UCHI I greyb o dy mo dels

Sp ectral energy distribution of G

Sp ectral energy distribution of WOH

Sp ectral energy distribution of G

Sp ectral energy distribution of KA

Sp ectral energy distribution of KC

Sp ectral energy distribution of Mono ceros R

Sp ectral energy distribution of GGD

Sp ectral energy distribution of G

Sp ectral energy distribution of SFIR

Sp ectral energy distribution of G

Flux prole of Uranus as the instrument resp onse pattern

m image of Uranus in celestial co ordinates

Flux prole of G

Flux prole of WOH

Flux prole of KA

Flux prole of S FIR

xii

Flux prole of G

Flux prole of KC

Flux prole of G

Flux prole of GGD

Flux prole of G

Predicted sp ectral energy distributions

Predicted temp erature distributions

Dust core luminosity and L M ratio vs temp erature

FIR dust

CO outow sp ectra

CO J map of K

CO J map of KA

CO J map of WOH

CO J map of G

CO J map of the G complex

CO J map of G

CO J map of the S complex

CO J map of G

CO J map of the CepheusA complex

CO J map including G G

Outow mechanical luminosity vs b olometric luminosity

Outow force vs b olometric luminosity

xiii

Mass outow rate vs b olometric luminosity

CO J map of G G

CO sp ectra of G and G

CS sp ectrum of G and G

CO J maps of G

CO J map of G

C O J map of G

Channel maps of CO J toward G

CO J map of G

CS J map of G

CS J sp ectrum of G

CS J channel maps of G

and m continuum maps of the G complex

GHz continuum map of G

xiv

List of Tables

UCHI I regions analyzed with HIRES pro cessing

Observed prop erties of the dust clumps toward G

Observed prop erties of the dust clumps in Mon R

Greyb o dy mo del parameters of dust around UCHI I regions

Comparison of the one and twocomp onent greyb o dy mo dels

Summary of dust density proles

Observed and computed parameters of bip olar outows

Summary of CSO sp ectroscopic observations of G

Summary of OVRO observations of G

Observed prop erties of the CS J transition

Prop erties of the G molecular outow

Outow masses derived from the CO J maps

Millimeter and submillimeter continuum uxes of G

Greyb o dy mo del parameters of G and G

Chapter Intro duction and Background

Massive star formation

Massive stars exert a dominant force on the interstellar medium throughout their

lives Powerful outows stellar winds HI I regions and sup ernova explosions combine

to shap e the app earance of galaxies most notably the starbursts With this fact

in mind the understanding of massive star formation in our Galaxy b ecomes an

essential goal with universal application in astrophysics Traditionally this goal has

b een dicult to achieve due to the extreme optical extinction by interstellar dust in

active star formation regions In recent decades the discovery of ultracompact HI I

UCHI I regions at radio wavelengths has provided a promising target in this research

Observations indicate a link b etween UCHI I regions H O masers dust emission

dense molecular gas bip olar outows and massive star formation However these

dierent stages of activity cannot b e explained in detail by the theoretical mo del of

star formation that has develop ed from observations of nearby . kiloparsec low

mass starforming regions In contrast most of the highmass starforming regions

in the Galaxy lie much further away at kiloparsec distances As a result the bulk

of the problem in interpreting observations of massive star formation originates in

source confusion at the core of distant molecular clouds The presence of a young

stellar cluster in the nearinfrared or an UCHI I region in the radio must b e considered

in concert with the raw materials of star formation molecular gas and dust if the

formation pro cess is to b e understo o d

With the force of new technology submillimeter observations promise to clarify

the picture The spatial distribution of interstellar dust and molecular gas which

emit a signicant fraction of their energy in the submillimeter band may help to

explain the app earance of active star formation phenomena at other wavelengths To

explore this idea b oth wide eld and high resolution images will b e needed As bright

continuum sources at many wavelengths UCHI I regions provide a natural center of

attention in this quest

UCHI I Regions

Stars with high surface temp eratures emit a substantial numb er of photons at fre

quencies shortward of the Lyman edge sucient to ionize neutral hydrogen atoms in

the ground state The absorption of these photons by interstellar gas leads to ionized

nebulae known as HI I regions UCHI I regions are small versions of HI I regions with

diameters parsec p c b elieved to b e pro duced by newlyformed O and early

Btyp e stars at or near the dense cores of molecular clouds The size and shap e of

the compact ionized gas has b een studied in over UCHI I regions with the Very

Large Array VLA via their freefree radio continuum emission Wo o d Churchwell

Kurtz Churchwell Wo o d Several questions emerged from the radio

surveys of UCHI I regions What is the physical nature of their frequent cometary

morphology Why are there so many of them more than p er square degree in the

Galactic plane How is their expansion aected by the molecular gas and dust in

star formation regions

Radio morphologies

Five dierent radio morphologies have b een identied with UCHI I regions cometary

corehalo multiplyp eaked shelllike and spherical or un

resolved Most of the theoretical work to date concerns the cometary UCHI I

regions An early mo del of the cometary shap e presumed a density gradient in the

ambient gas into which the HI I region expands asymmetrically ie a nonspherical

Strmgren mo del Icke Gatley Israel Despite the plausibility of this mo del

the nearly p erfect parab olic symmetry revealed by more recent observations of re

gions like G spurred the development of b owsho ck mo dels in which the

young star moves through the ambient gas at high velo cities of km s Mac

Low et al Van Buren Mac Low However the discovery of a large

velo city gradient p erp endicular to the headtail axis of two cometary UCHI I regions

is incompatible with the b owsho ck mo del predictions Gaume Fey Claussen

Gaume et al Also multifrequency multiconguration VLA images of W

Main reveal velo city and linewidth gradients in the ionized gas which are indicative

of turbulent expansion into highly anisotropic and clumpy molecular gas Tieftrunk

et al As a consequence of ndings such as these current mo dels have found

renewed attraction in the idea of an initial density asymmetry in the gas surrounding

UCHI I regions Williams Dyson Redman

Lifetime

Related to the morphological question of UCHI I regions is their apparent longevity

The numb er of UCHI I regions found in the Wo o d Churchwell survey was

quite large compared to the small region of the rst quadrant of the galactic plane

that was imaged elds were observed with a primary b eam for a total coverage

of square degrees yielding a detection rate of p er square degree But b ecause

the Wo o d Churchwell elds were chosen with prior knowledge of the presence of

compact radio sources and strong farinfrared FIR emission the detection rate

could b e anomalously high In a volumelimited optical sample Conti et al

found only O stars within a kiloparsec kp c radius of the Sun Assuming

a constant disklike distribution of O stars within the central kp c radius disk of

the Milky Way one could then exp ect roughly O stars p er square degree toward

the inner half of the Galactic plane Together these results suggest that the lifetime

of UCHI I regions is a substantial fraction of an Ostar lifetime which is a few

million years Chiosi Nasi Sreenivasan Further evidence for the longevity of

UCHI I regions is the fact that their parsec scale height ab ove the Galactic plane

Churchwell Walmsley Cesaroni agrees well with the parsec scale height

of opticallyidentied O stars Mihalas Binney However the Conti et al

survey reaches only far enough to include parts of the Perseus and Sagittarius

arms adjacent to the lo cal OrionCygnus arm It misses most of the kp c ring seen

in CO surveys Clemens Sanders Scoville Scoville Solomon where

the concentration of O stars and UCHI I regions is probably higher A recent detailed

analysis of the IRAS database indicates that the surface density of UCHI I regions

at galacto centric radii b etween and kp c is only kp c Comern Torra

Using the initial mass function of stars in the solar neighb orho o d within

kp c tabulated by Humphreys McElroy the authors derive a birthrate of

massive stars M M to b e kp c yr The ratio of these values

yields an UCHI I region lifetime of yr or ab out of an Ostar lifetime

Though shorter than previous estimates this lifetime is still dicult to reconcile

with the rapid expansion timescale of standard HI I regions Spitzer The vol

ume of ionized gas which a star can maintain is determined by its total rate of photon

emission at frequencies ab ove the Lyman limit N compared to the recombination

rate of the gas excluding captures into the n level Captures into the

n level emit photons of sucient energy to ionize other excited hydrogen atoms

In the initial formation of an HI I region an ionization front pro ceeds rapidly into the

neutral medium following the relations

r t r exp n t

i S H

n n

e H

d N

Lyman

where r is the radius of the ionization front r is the radius of the Strmgren sphere

i S

n is the electron density n is the hydrogen ion density cm s in

e H

gas of T K and Hertz Hz Assuming an initial density

Lyman

of cm and N s typical of an O star Panagia Thompson

r will reach r p c at kp c in only years At this p oint a

i S

sho ck front forms and the HI I region will expand slowly toward pressure equilibrium

r C t

i HI I

r r

S S

where C is the sound sp eed km s in the ionized medium For the O HI I

star the dynamical timescale for the UCHI I region to double its angular diameter

is yr over an order of magnitude less than the average lifetime From this

remaining discrepancy one is led to the p ossibility that UCHI I regions reach pressure

equilibrium with their surroundings b ecause there is sucient ambient gas to supply

an essentially constant pressure at the ionization front DePree Ro drguez Goss

GarcaSegura Franco For example if the ambient gas outside the

front has density n cm and temp erature K then pressure equilibrium

with the ionized gas requires

P P

UCHI I ambient

n k T n k T

i i

n cm

In equilibrium the stagnation radius of the UCHI I region equals the radius of the

Strmgren sphere with density n

r p c

stagnation

Therefore for the O star at kp c the UCHI I region will stagnate at an angular

diameter of as long as there is sucient material present to keep n & cm

Molecular gas

To explore the problem of UCHI I region expansion studies of the molecular gas

around them have b een initiated Measurements of opticallythin molecular tran

sitions toward UCHI I regions yield typical column densities of N cm

Cesaroni et al Cesaroni Walmsley Churchwell Churchwell Walm

sley Wo o d Olmi Cesaroni Walmsley Millimeter interferometric

observations of G and G reveal gas densities of cm toward

the molecular cores Akeson Carlstrom In a survey of massive starforming

regions many of the UCHI I regions were detected in the CS J transition which

exhibits a critical density of cm Plume Jae Evans These

high densities supp ort the pressure equilibrium scenario as a solution to the problem

of UCHI I lifetimes Furthermore additional ram pressure may b e applied by the

infalling motion of molecular gas as suggested by the redshifted NH absorption fea

tures seen toward the UCHI I regions G Ho Haschick and WOH

Keto Reid Myers Bieging

Dust co co ons

Mixed with the molecular gas are dust grains which absorb short wavelength photons

from the central stars and in turn emit bright thermal radiation in the FIR and

submillimeter In fact the three brightest m sources in the IRAS Point Source

Catalog PSC coincide with UCHI I regions in the cores of well known molecular

clouds Sgr B NGC and G Although the dust comprises only

ab out of the mass its broadband emission dominates the b olometric luminosity

typically L escaping from these clouds In their survey of the IRAS

PSC Wo o d Churchwell found that the dust around radioidentied UCHI I

regions exhibits characteristic FIR colors which distinguish them from other classes of

ob jects Sp ecically they identify candidate massive emb edded stars satisfying

F F

the following criteria log and log The emission typically

F F

increases steeply from m to m indicative of co ol dust T . K A simple

mo del based on the IRAS data and millimeter ux densities of UCHI I regions

prop oses a small central region of warm dust T K near the star envelop ed by

a large cloud of co ol dust T K Garay et al

Luminosity estimates of the emb edded young stellar sources have b een made from

the relative ux densities in the four IRAS bands and from the ionizing photon rate

derived from radio continuum observations However the IRAS PSC suers from p o or

spatial resolution so it is p ossible that infrared emission from more than one young

ob ject contributes to the ux density of sources in the PSC Given this confusion

it is not surprising that IRAS luminosity estimates are higher than the luminosity

inferred from radio continuum emission in out of massive starforming regions

studied by Hughes Macleo d Also within HI I regions dust likely absorbs

many of the stellar ultraviolet photons resulting in a lower gas ionization rate and

less freefree emission than exp ected in a dustfree region Estimates for ultraviolet

UV absorption by dust within UCHI I regions run as high as Wo o d

Churchwell Armand et al Further observations of thermal dust emission

at high angular resolution are necessary to determine the amount of dust within

UCHI I regions

Emb edded protostars

Optical and infrared surveys of young clusters in the Milky Way such as NGC

reveal a strong p opulation of M premainsequence stars among OB clusters

Hillenbrand et al Massey Johnson DegioiaEastwo o d These obser

vations indicate that high mass and low mass stars form simultaneously at least to

some degree in clusters However to understand the formation pro cess we must

identify protostellar clusters in an earlier stage of development when they are still to o

emb edded to b e seen at wavelengths shorter than m The dust in young massive

protostellar cores should b e co oler than the dust in and around UCHI I regions since

the strong ionizing radiation has either not b egun or not had time to substantially

heat the surroundings even if the central luminosity source may already b e present

Protostellar cores in this stage and in the initial contraction stage should present

their p eak emission at wavelengths longward of m co oler than K Of course

lower mass protostars which never develop signicant ionizing radiation should lie

in co ol cores of lower mass which should b e detectable at submillimeter wavelengths

Deep surveys in the submillimeter will improve our knowledge of the numb er of young

protostars of all masses forming in these environments

In order to interpret submillimeter ux densities an imp ortant quantity to know

is the dust emissivity Q which varies as This prop erty causes the observed

emission to app ear as a mo died Planck sp ectrum with I in the submillime

ter range when the cloud is optically thin and in the RayleighJean limit such that

h k T Current mo dels of the dust emission around UCHI I regions are forced

to estimate by interp olation b etween the measured the m and millimeter

mm ux densities Chini et al Chini Krgel Wargau Clearly sub

millimeter uxes need to b e gathered in order to get more accurate measurements of

the color temp erature and the mass of the dust Furthermore if the emission can

b e spatially resolved much b etter constraints can b e set on the size of the dust cores

in relation to the ionized gas

H O Masers and preUCHI I regions

Interstellar masers are sources of intense line radiation amplied by stimulated emis

sion from molecules and radicals excited into p opulation inversion via collisional or ra

diative pumping Elitzur Twenty years ago the asso ciation of H O masers with

compact HI I regions was rmly established through singledish surveys in the GHz

transition Genzel Downes Cesarsky et al Genzel Downes

However the rst radio interferometric studies of starforming regions found

that H O maser sp ots were oset typically by several arcseconds p c

from compact HI I regions Forster Caswell These ndings led to the sp ec

ulation that the masers were actually tracing gas at the lo cation of massive stars

in an earlier stage of formation prior to the time when the UCHI I region b ecomes

detectable More sensitive high resolution VLA maps have revealed several

sources in which the maser emission is directly coincident with very weak mJy

unresolved . UCHI I regions such as WNB Hunter et al Also from

the continuing singledish H O maser surveys Brand et al Palla et al

there is evidence that the lifetime of the maser phase is quite short . yr In

the case of a massive protostar M the maser o ccurs during a brief stage of

evolution b efore the new UCHI I region has had time to expand signicantly eg

Co della et al To explore this idea Jenness Scott Padman surveyed

known H OIRAS sources with no asso ciated HI I regions or OB clusters and found

submillimeter continuum emission from of them Furthermore in a near

infrared imaging survey of H O masers all of the elds contain a high density

of K band sources Testi et al These high detection rates suggest a p opula

tion of deeply emb edded sources in an early protostellar phase In the UCHI I region

Cepheus A HW Hughes Wouterlo ot H O maser sp ots have b een re

solved spatially and kinematically into a disklike structure surrounding the UCHI I

region and p erp endicular to its asso ciated thermal radio jet Torrelles et al

Ro drguez et al This nding conrms the intimate connection b etween water

masers and protostars

Bip olar Outows

Further evidence that H O masers trace protostars comes from their asso ciation

with bip olar molecular outows Using verylong baseline interferometry H O maser

prop er motions have b een measured directly and indicate outow motion Genzel et

al Reid et al In addition singledish CO surveys of H O maser sources

have found a high detection rate of broad CO lines indicative of outowing gas Fukui

Fukui Surveys of CO outow sources also tend to reveal new H O masers

Henning et al Xiang Turner Furthermore the linewidths of CS and

NH transitions have b een found to scale with the H O maser luminosity suggesting

that masers trace regions undergoing a general increase in turbulent energy as can

b e exp ected from a molecular outow Anglada et al

An imp ortant development in the study of UCHI I regions has b een the recent

detection of massive molecular outows apparently asso ciated with them The earliest

examples are G Harvey Forveille DR Garden Carlstrom

and AFGL Mitchell Hasegawa Schella Dividing the length

scale of these outows by the mean outow velo city in the CO line wings yields a

typical dynamical timescale of yr However a recent survey of a welldened

sample of IRAS sources from the Class I or Class I ID phase of lowmass young stellar

ob jects as dened by Adams Lada Shu revealed a detection rate of

molecular outows Parker Padman Scott Similar high detection rates

are found by Fukui Because the combined duration of the Class I and I ID

phases is b elieved to b e yr Beichman et al Myers et al this

statistical evidence suggests that outows in lowmass starforming regions are much

older & yr than their dynamical timescale Since the outows observed in

more massive regions exhibit timescales similar to their low mass counterparts they

may also b e older than they app ear A dedicated singledish search for highvelo city

CO emission from UCHI I regions has recently b een completed with a success

rate Shepherd Churchwell a Further singledish mapping and interferometric

imaging is needed to determine if this CO emission corresp onds to outows from the

UCHI I regions or from younger nearby sources and to compare the dynamical and

statistical ages of these outows

Thesis outline

This thesis explores the app earance of highmass starforming regions by examining

two comp onents of the UCHI I region phenomenon dust co co ons and bip olar outows

As part of my research I help ed to build the rst facility b olometer array camera

for the Caltech Submillimeter Observatory CSO This instrument called the Sub

millimeter High Angular Resolution Camera SHARC is describ ed in Chapter

including details of my contribution to the optical design and software interface Im

ages at andor m of UCHI I regions taken with this camera are presented

in Chapter along with IRAS HIRES images The physical conditions of the dust

grain emissivity temp erature column density mass and luminosity are derived

from greyb o dy mo dels of the FIR to submillimeter sp ectral energy distributions The

submillimeter continuum ux density proles of the dust cores are compared to pre

dicted proles from radiative transfer mo dels Also the p ositions of the submillimeter

continuum sources are compared to radio continuum maps and H O maser p ositions

from the literature in order to search for new sources in the preUCHI I phase Maps

of bip olar molecular outows from many of these UCHI I regions are presented in

Chapter some of which are new detections Finally Chapter presents a detailed

study of a young cluster of outows and UCHI I regions in the G starforming region

using data from the CSO and the Owens Valley Millimeter Array

Chapter The Submillimeter High Angular

Resolution Camera SHARC

The successful deployment of array detectors on infrared telescop es has revolution

ized astronomy over the past two decades McLean Elston and driven

the development of longer wavelength arrays Beyond the midinfrared atmospheric

windows the longest infrared wavelengths observable from the ground are in the

m range often referred to as the submillimeter band A current goal in

astronomy is to gather high spatial resolution images using the new class of large

ap erture m groundbased submillimeter telescop es This includes the Caltech

Submillimeter Observatory CSO lo cated near the summit of Mauna Kea Hawaii

The CSO consists of a meter parab olic primary dish with excellent surface ac

curacy and a hyp erb olic secondary mirror which together form a classical Cassegrain

telescop e Op erating at frequencies from to GHz the telescop e employs

numerous cryogenic hetero dyne and b olometric instruments

During the past ve years the Caltech submillimeter group has develop ed a

b olometer array camera in collab oration with Dr S Harvey Moseley and his col

leagues in the infrared Xray and micro electronics fabrication groups at the National

Aeronautics and Space Administrations Go ddard Space Flight Center NASAGSFC

in Greenb elt Maryland Wang et al Installed at the CSO in Fall the

camera has b een in active use monthly since this date and has b een op ened for exter

nal prop osals b eginning in Septemb er The numerous advantages of the pixel

linear b olometer camera over the single channel b olometer system will revolutionize

the eld of groundbased submillimeter continuum observations Its main advantages

include A nearly twentyfold increase in mapping sp eed of extended sources such

as nearby external galaxies and Galactic molecular clouds Improved sky subtrac

tion by removing correlated noise and noise spikes from all pixels Doubling of the

ono integration time on p oint sources when p erforming p ointed observations In

this chapter I give a brief overview of the instrument followed by a more detailed

description of the optomechanical design which has b een accepted for publication

in the Novemb er issue of Publications of the Astronomical Society of the Pacic

under the authorship of TR Hunter DJ Benford E Serabyn Finally I explain

the camera control interface and data reduction software now in use at the CSO

Instrument overview

Bolometer theory

Bolometer can b e classied as thermal detectors Up on the absorption of incident ra

diation the temp erature of a b olometer rises causing a change in electrical resistance

of the active element Langley A b olometer has a heat capacity

where dQ is the additional thermal energy stored in the device after a temp erature

change of dT Because it is connected to a heat sink of xed temp erature T the

sink

heat will b e conducted away from the b olometer at temp erature T at the rate

b olo

P GT T

b olo sink

where G is the thermal conductance The magnitude of the b olometers temp erature

resp onse can b e increased by making G as small as p ossible with the constraint that

C is also reduced in order that the resp onse time dened as

remains b elow the value required in the exp eriment The change in resistance of the

active element is governed by its temp erature co ecient of resistance dened by

R dT

Unlike normal metals the resistance of ionimplanted thermometers in silicon b olome

ters at T K has empirically b een found to increase as T decreases eg Downey

et al

R R exp

where R and T are constants dep ending on the level of implantation This b ehav

ior is consistent with the prediction of the mo del for variablerange hopping with a

Coulomb gap Pignatel et al Zhang et al Hence incident radiation on

the b olometer causes a change in resistance

T T

T R exp R R T

T T

which can b e measured as a change in voltage at constant bias current I

T T

T IR exp V

T T

This equation simply illustrates the advantage of low temp erature op eration of ion

implanted silicon b olometers The b olometer resp onsivity R

R V T

increases with decreasing temp erature as long as the selfheating eect of the bias

current remains small

The fundamental sensitivity limit of a b olometer is determined by temp erature

uctuations in the active element Jones Low Mather Mather

In an optimal b olometer the dominant source of temp erature uctuations will b e in

the rate of absorption and emission of photons called the background limit In

the case of a practical submillimeter telescop e observation the detected radiation is

typically dominated by the atmosphere emitting as a greyb o dy a blackb o dy of nite

optical depth into the telescop e b eam Phillips The Noise Equivalent Power

NEP of a detector is dened as the signal p ower required to obtain a unity signal

to noise ratio in the presence of some known noise The background noise consists

of two terms the uctuations in the incident photon rate the particle term and

the uctuations in the squared amplitude of the incident electromagnetic waves the

wave term Lewis Fellgett Jones Twiss A detailed formula for

the background limit to the noise equivalent p ower of a b olometer op erating at the

fo cus of a submillimeter telescop e has b een compiled by Benford Hunter Phillips

valid in the limit that the emissivity of the atmosphere at the observed

frequency is constant across the detection bandpass

k T h k T

NEP

optics b olo

where T is the temp erature of the emitting material in the atmosphere is the

telescop e main b eam eciency is the net eciency of the lters and foreoptics

optics

and is the fractional absorptivity of the detector With the appropriate values

b olo

for SHARC

optics b olo

GHz GHz

MB GHz MB GHz

T K

the calculated background NEP s in the two highest frequency submillimeter windows

referenced to a p osition ab ove the atmosphere b ecome

Hz NEP Watt

GHz

Hz NEP Watt

GHz

In computing these values it is interesting to note that the contributions to the

background NEP from the particle and wave terms the additive terms in brackets

in Eq are comparable at a frequency of GHz and resp ectively

With appropriate consideration the NEP can b e related to a useful observational

parameter to the practicing astronomer the Noise Equivalent Flux Density NEFD

The NEFD provides a measure of the exp ected integration time required to attain

signal to noise ratio of on a source with a given ux density in Janskys Jy The

NEFD can b e estimated given the bandwidth of detection and the telescop e

geometric collecting area A

NEP

NEFD

demo d chop

where is the electronic demo dulation eciency of the lo ckin detection pro cess

demo d

and is the mechanical eciency of the chopping secondary mirror b eyond the fac

chop

tor of explicitly intro duced for standard optical chopping b ecause the onsource

b ecause the result is a dierenced measurement time is half the total time and

In p erio ds of go o d submillimeter transparency on Mauna Kea ab out of the

time can b e as low as across most of the and m lter bands Under

these conditions with A m the backgroundlimited NEFD

demo d chop

b ecomes

Hz NEFD Jy

GHz

Hz NEFD Jy

GHz

However b ecause varies with frequency within the lter bandpass increasing near

the edges and at several signicant absorption lines as can b e seen in Fig

Eq must b e integrated prop erly over frequency The resulting background

limited NEFD s can easily b ecome a factor of higher than those listed in equa

tions and In addition correlated sky noise not removed by the optical

chopping technique will raise the NEFD further

The backgroundlimited NEFD available to broadband b olometric detectors can

b e compared to that of the current generation of high frequency hetero dyne receivers

eg Ko oi et al Using the Dicke radiometer equation Kraus a system

noise temp erature of K a bandwidth of GHz and the same telescop e ecien

Hz at and cies listed ab ove the backgroundlimited NEFD s are and Jy

GHz resp ectively The advantage of a broad bandwidth is clearly evident in this

comparison

Optical coupling vs concentrating horns

Because photo conductive detectors are not available b eyond a wavelength of m

continuum detectors used in the submillimeter range have traditionally b een comp os

ite b olometers A comp osite b olometer consists of a separate thermistor physically

attached to a radiationabsorbing substrate which is susp ended from the cold bath by

leads of low thermal conductance eg Nishioka Richards Wo o dy Due to

the crowding of susp ension leads it is dicult to construct a closelypacked array of

comp osite b olometers In addition the low absorptivities of the b olometers typically

required the use of comp ound parab olic concentrating horns and integrating cavities

in order to collect light over a sucient diameter in the fo cal plane and deliver it

to the b olometer Winston Hildebrand At the same time these horns

commonly referred to as Winston cones limit the solid angle of ambient radiation

viewed by the detectors In a similar vein straightsided conical horns can b e used to

pro duce nearly Gaussian b eam proles with the appropriate horn ap erture d F

chosen to deliver high eciency Cunningham Gear Kreysa et al In

b oth cases however the large horn input diameter conicts by a large factor with

the goal of full sampling of the highest spatial frequencies available in the fo cal plane

pattern of a large ap erture submillimeter telescop e d F

On the other hand it is now p ossible to construct monolithic b olometer arrays

using micro electronic fabrication techniques Moseley Mather McCammon

In a monolithic b olometer array the substrate and thermalmechanical leads are

etched from a silicon wafer The thermistor and electrical leads are ionimplanted

directly into the silicon substrate This technology allows large b olometers mm

to b e manufactured in linear arrays on a single silicon wafer The closelypacked pixels

allow an optical conguration which fully samples the spatial frequencies available in

the fo cal plane With a prop er imp edancematching coating the large size of the

pixels enables them to eciently absorb radiation with d As at optical

pixel

and infrared wavelengths there is no inherent throughput limitation to this typ e

of coupling Richards Greenb erg This characteristic eliminates the earlier

requirement for a concentrating cone and indicates that the pixels can b e optically

coupled in the fo cal plane with geometric optics techniques

Monolithic b olometer array

The b olometer array detector used in SHARC is a monolithic silicon package of linear

geometry develop ed and fabricated by Harvey Moseley Christine Allen Brent Mott

and their colleagues at NASAGSFC Similar arrays have b een constructed there for

instruments own on the Kuip er Airb orne Observatory KAO Moseley and

the Advanced Xray Astronomical Facility AXAF Moseley Mather McCammon

McCammon et al McCammon et al Each array originates on a

silicon wafer large enough to supply several arrays Because the nal dopant concen

tration is dicult to predict a series of wafers are dop ed by increasing amounts in

order to obtain wafers with a range of values of R and T Sp ecically the SHARC

array came from the MIRA series MidInfraRed Array of by pixel arrays

After cutting and mounting the arrays a measurement of R and T determines their

optimum op erating temp erature for photon sensitivity In order that the background

photon noise dominate over thermal noise in the detector during broadband submil

limeter continuum observations the SHARC array was selected to op erate at K

A thin bismuth lm nm is applied as an absorb er to match the imp edance

of free space Each of the pixels is rectangular mm by mm by m with

four thermallyconducting supp ort legs of size mm by m by m see Fig

The total thermal conductance of the four legs at K was measured to b e W

Figure A closeup photograph showing the conguration of the b olometer array

detector in SHARC The minor divisions on the ruler at the b ottom are tenths of

inches Just ab ove the ruler is the rectangular invar blo ck co oled to K and sus

p ended from the rest of the housing via Kevlar cords for thermal isolation Mounted

in two rows near the top of the invar blo ck are the square M load resistors Below

these resistors lies a rectangular annulus of silicon with all of the interior etched away

except for the bisecting line of pixels and their narrow supp ort legs Manganin leads

inch diameter under tension bridge the thermal stages near the top and carry

the signals to the JFET stage mounted nearby

K Wang The heat capacity of the silicon plus the bismuth coating plus

the arsenic contact leads is estimated to b e approximately J K Benford

These two values yield a time constant of millisecond which is much

shorter than the typical telescop e b eam switching rate of several Hz Four of the

pixels were damaged during fabrication so there are working pixels in the current

version of the camera as of Summer

Cryogenics and electronics

The b olometer array has b een installed in a He cryostat backed by liquid He and

liquid N co oled shields The cryostat op erating manual is provided in App endix A

The rst stage electronics are three eightchannel FET eld eect transistor pack

ages which op erate at K inside the dewar and serve as imp edance transformers

of the signal Lo cated just outside the dewar are three fourlayer eightchannel

batteryp owered lownoise preamplier b oards These b oards yield a nominal gain

of from to Hz with a high gain setting of used for most astronomical

sources The amplied signals are subsequently sent to bit AD b oards with a

volt range and a sampling rate of kHz The digitized signals are transferred via

b er optic cables to a DSP digital signal pro cessor b oard inside a Macintosh Quadra

computer which p erforms digital lo ckin detection at the chopping frequency

During my graduate study at Caltech I have worked on several technical asp ects

of the b olometer array which will b e describ ed in detail in this chapter With Gene

Serabyn a senior research asso ciate in the submillimeter group I designed the helium

co oled oaxis reecting optics and the mechanical supp ort structure for these optics

Building on the Macintosh data display software package written for b olometer arrays

by Kevin Boyce of Go ddard I extended the package onto an Ethernet and digital in

putoutput interface with the CSO control computer and antenna computer Finally

I wrote tested and installed the complementary software interface on the telescop e

computer with helpful p ointers from Ken Young Raoul Taco Machilvich the CSO

sta astronomer and computer engineer The software manual is provided in Ap

p endix B

Optical design

Obviously in designing the optics for a new camera one must consider all of the

optical elements b eginning with the telescop e primary and secondary mirrors and

including any relay optics Here we briey describ e the tertiary relay optics at the

CSO the details of which are presented elsewhere Serabyn

Tertiary relay optics system

Array instruments including SHARC are mounted at the Cassegrain area of the

CSO where a large unvignetted eld of view is p ossible Padman Serabyn

However b ecause of the large fo cal ratio f at the Cassegrain fo cus a system of

relay optics was designed to reduce the fo cal ratio to a value f more suitable for

illuminating millimetersized detectors with an appropriatesized diraction sp ot As

constructed the relay optics provide dual mounting p orts each of which can supp ort

an instrument cryostat simultaneously A at steering mirror selects one of the two

p orts and an oaxis ellipsoidal mirror creates a tertiary image of diameter mm

of the primary mirror that lies mm ab ove the instrument mounting surface The

tertiary image of the fareld lies mm b eyond the image of the primary mirror

Design requirements for the camera

Many constraints on the camera optical design were necessary due to the imaging

requirements the geometry and cryogenic requirements of the detectors and the

limited volume available in cryostats First I briey describ e the array detector to b e

used in the camera as this sets the plate scale and sampling geometry

Optical requirements

Because the array detector is monolithically etched from a silicon wafer the detector

elements are closely spaced array elements of size mm by mm are aligned with

their long axes adjacent Wang et al There is only a small m gap

b etween the pixels so that the total size of the array is mm by mm In order

to provide Nyquist sampling of the sky brightness distribution along the array axis

the plate scale of the nal image must provide pixels p er telescop e diraction

b eamsize in the fo cal plane For simplicity and quick implementation the camera is

designed to op erate only in the and m atmospheric windows but an m

lter is available for limited observing and testing purp oses With this restriction

a single xed plate scale is sucient for the optical design In order for the CSO

diraction b eamsize at m to b e roughly mm in radius at the detectors

F mm they must b e illuminated by an f b eam Thus the camera

optics must transform the f relay optics input b eam to f With a meter

telescop e the f plate scale is p er mm Hence the mm b olometer array

subtends on the sky

In addition to the plate scale requirement the quality of the nal fo cus must b e

excellent Strehl ratio for secondary chop angles oaxis over a eld of

view as large as the available and foreseeable detector arrays To allow for expansion

of future arrays in the p erp endicular direction it was decided that the optics should

maintain high quality imaging over a square eld corresp onding to the linear size of

the current array or ab out by mm in linear units which translates

to a maximum radius of mm Also the distortion of the fo cal plane must b e

negligible with resp ect to the diraction b eamsize ie the separation of two p oint

source images must b e linear across the eld with resp ect to the angular separation

of the sources on the sky

Thermal requirements

Background radiative loading of the cold b olometer array must b e reduced to an

absolute minimum by prop er cold stops baing and bandpass and blo cking lters

Op erating at K the array is co oled by a He refrigerator With the exception of

a selected bandpass originating from the small solid angle of the sky targeted by the

b olometer array all ambient temp erature radiation entering the dewar window must

b e rejected by lters at liquid nitrogen and helium temp eratures Because they emit

as blackb o dies the stops and camera optics must lie within the helium work space of

the cryostat

Geometrical requirements

The total volume available to the camera optics is limited by the size of the helium

work space of the cryostat The diameter of the cold plate is cm and the height

of the helium stage radiation shield although extendable is limited to cm due

to mechanical stability concerns and cryogen usage In eect these sizes limit the

fo cal lengths of the optical imaging comp onents The use of folding mirrors must b e

avoided in order to minimize the numb er of optical elements and to reduce the eect

of stray light in the system Fewer elements also allow easier alignment

Rejected designs

In order to match the extensive requirements for the camera several reimaging designs

were explored All of the optical designs were mo deled on a VAXStation with the

software package CODE V Optical Research Asso ciates in order to determine

image quality and ray clearance The mo dels included all of the optical elements

b eginning with the CSO primary surface The automatic design features of CODE V

were used in many cases to vary the curvature of optical surfaces in order to optimize

the quality of the nal fo cal plane In the course of designing the camera optics

three general congurations were explored standard spherical lenses a pair of o

axis parab oloidal mirrors and a single oaxis ellipsoid In this section we briey

describ e our reasons for rejecting the rst two of these congurations

Onaxis lenses

Recently germanium lenses have b een successfully used in the reimaging optics of mid

infrared cameras Cowan et al Although cold lenses can provide distortionfree

elds with go o d imaging oaxis they require additional folding mirrors inside a cryo

stat b ecause the fo cusing elements are transmissive When using transmissive lenses

at submillimeter wavelengths an imp ortant consideration is the thickness and absorp

tion co ecient of the lens material When co oled to K b oth standard optical qual

ity germanium and silicon have fairly low but nonnegligible absorption co ecients

cm and high indices of refraction n n at

Ge Si Ge Si

m Lo ewenstein Smith Morgan The high refractive index of these ma

terials allows for lens surfaces with relatively large radii of curvature and thus small

thicknesses for a sp ecied fo cal length These qualities make them candidates for

submillimeter lenses Perhaps the biggest problem with using lenses is the diculty

of applying an antireection AR coating Recent work has b een done to coat hemi

spherical Si lenses with Stycast FT b erep oxy pro duced by Emerson Cum

ing Inc which has a refractive index n at K at millimetersubmillimeter

wavelengths Halp ern et al and to machine the cured layer to quarter wave

thickness Kaneshiro Although p ossible it is an exp ensive pro cess requiring

a diamond to ol lathe and the resulting ro otmeansquare RMS surface accuracy of

the coating is not well measured Despite the go o d imaging quality designs includ

ing lenses were rejected due to the reective and absorptive losses and the need for

additional at mirrors

Oaxis parab oloidal mirrors

After our research on lenses we grew to favor a mirror design for the camera b ecause

mirrors can redirect the incident b eam to a suitable lo cation in the cryostat while also

fo cusing In fact parab oloidal mirrors have b een used as the fo cusing element in mid

infrared cameras Gezari et al However with our f requirement a single

By using two oaxis parab oloid exhibits signicant coma on elds larger than

parab oloids in the prop er orientation as in an Eb ertFastie sp ectrometer mounting

one can correct for the eects of coma in the nal image James Sternb erg In

order to cancel coma in a planar arrangement the two concave oaxis mirrors must

face each other with their resp ective vertices b oth o to the same side of the chief ray

In this conguration the emergent chief ray crosses its incident path hence we lab el

it the crossed orientation for convenience This arrangement of parab oloids was

successfully used in the previous generation of relay optics at the CSO and provided

a Strehl ratio of over a diameter eld of view at a wavelength of m

Serabyn The rst design considered for the b olometer array optics consisted

of a pair of crossed parab oloidal mirrors inside the cryostat

In order to t into the limited volume of a cryostat relatively short fo cal lengths

mm and large b ounce angles are required Several crossed parab oloid

congurations were considered with separations of up to mm We found that al

though this mirror conguration pro duces go o d Strehl ratios the fo cal plane exhibits

a large barrel distortion across the eld If this design were implemented the re

sultant mapping of the b olometer array detectors onto the sky would b e signicantly

curved spread in azimuth with the array aligned in elevation In addition

the plate scale varies across the eld Both of these eects would necessitate detailed

measurements and corrections during optical alignment and astronomical observa

tions Although longer fo cal length parab oloids may b e ideal for small elds of view

they are not suitable in limited cryostat volumes

Selected design oaxis ellipsoidal mirror

The third design we considered for the array optics b egan with the realization that

larger mirrors can b e used if we include the relay optics ellipsoidal mirror in our

conception of the camera Since the tertiary relay optics already incorp orate one

oaxis ellipsoid p otentially sup erior imaging quality is then obtainable by using a

second oaxis ellipsoid in the camera optics similar to the crossed parab oloid case

However b ecause a fareld fo cus and primary image lie b etween two ellipsoids cold

ap erture and eld stops can b e provided with only one of the ellipsoidal mirrors inside

the cryogenic dewar see Fig Hence this single cold mirror can b e made much

larger As in the case of the parab oloids one can exp ect the ab errations induced

by the rst surface to b e partially cancelled by ab errations of opp osite sign induced

by the second surface the cancellation is only partial in the case of unmatched F

numb ers However in this case a fareld fo cus exists b etween the two ellipsoids Dewar Entrance Plane Final Focus Filters

Camera Cold Ellipsoid Aperture Stop Relay Tertiary Optics

Focus Ellipsoid

Figure Layout of the uncrossed ellipsoidal mirror reimager used for SHARC

The large ellipsoidal mirror is part of the CSO relay optics and the rest of the optics

are cryogenically co oled The rays plotted span a angle of on the sky

rather than a collimated b eam as in the case of the two parab oloids Since all the

rays cross the chief ray axis at the fo cus one exp ects the b est imaging to b e achieved

with the ellipsoid surfaces in the uncrossed conguration opp osite to the case with

parab oloids

Before discussing the shap e of the ellipsoidal mirror in the camera it is imp ortant

to review the shap e and illumination of the relay optics ellipsoid In geometric terms

elliptical surfaces can b e dened by two fo ci Optically rays emergent from one

geometrical fo cus of the ellipse are reected by the surface to the second fo cal p oint

But the imaging characteristics of the ellipse are not limited to these two p oints

Moving the ob ject p oint closer to the surface along the incident chief ray will displace

the image further from the surface along the reected chief ray This eect provides

an interesting exibility in using elliptical mirrors in which degradation of the onaxis

image is traded for improvements in the oaxis imaging

For example if it is required that the input and output fo cal ratios of the b eam b e

identical then using an ellipse in the standard conguration would require illuminat

ing the p ortion of the surface o the ma jor axis where the curvature is maximally

dierent in the two p erp endicular directions However by moving the ob ject p oint

relative to the geometric fo cus one can cho ose a dierent ellipse in which the p or

tion of the surface used is much closer to the axis and hence more symmetric This

ellipse is likely to achieve b etter imaging with the same p osition of the b eam fo ci

Of course the displacement of the ob ject p oint intro duces separate ab errations thus

there should exist a b est compromise b etween moving closer onaxis and deecting the

ob ject p oint Requiring a deection for mechanical clearances in the relay optics

the b est surface was found using CODE V optimization We carried out calculations

for nine eld angles lo cated at the center and on the corners and edgecenters of a

square grid The resulting relay optics ellipsoid has an eccentricity of an

input fo cal length of mm and an output fo cal length of mm The ob ject

distance the Cassegrain fo cus is mm

Since the camera optics require a small fo cal ratio change from f to f fo cal

displacement was again exploited in designing the camera optics ellipsoid In this case

a shorter fo cal length was necessary in order to t into the available cryostat length

Thus we chose mm as the fo cal length of the generating ellipse We also required

a deection angle on on the ellipsoidal surface to yield sucient clearance for

the detector assembly at the fo cal plane Determined from CODE V optimization

the ellipsoid giving b est imaging in this conguration has an eccentricity of

an input fo cal length of mm and an output fo cal length of mm With

for clearance the required size of the oaxis section of the ellipsoidal mirror

for the entire eld is cm square For two pixel linear arrays separated by

mm a feasible expansion of the current detector the required size is only by

cm which easily ts on the cm diameter cold plate This smaller section was

constructed for SHARC at Caltech with an automated milling machine p erforming

successive circular cuts ab out the axis of the ellipsoid

From analysis in CODE V the uncrossed ellipsoidal mirror conguration describ ed

ab ove provides excellent diractionlimited imaging Strehl in the nal fo cal

plane across a square eld even with the secondary mirror chopping rotated

at angles up to throw in the fareld Even with chopp er throws up to

the Strehl remains but this degradation is more due to the secondary mirror

than the camera optics The Strehl ratios as a function of secondary chop angle at

the eld center four edges and four corners of the eld are plotted in Fig All

the Strehl ratios rep orted in this pap er are taken at the b est comp osite fo cus of the

nine elds corners edgecenters and center of a square and hence the eects of

eld curvature are directly included However since the depth of fo cus F is

mm a small to mo derate amount of eld curvature is not a critical problem in

this application

Figure Strehl ratios across the eld of view of the camera fo cal plane as

a function of the secondary chopp er angle The solid and dashed lines represent

resp ectively the center and edges of the current linear array which is oriented in

zenith angle The graph shows the p erformance at the b est comp osite fo cus of the

nine elds at each setting of the chopp er

Sp ot diagram fo otprints of the by fo cal plane are given in Fig To

envision the diraction b eam these sp ot diagrams must b e convolved with a sp ot

size of mm at a wavelength of m There is essentially no distortion

in direction along the array A small distortion over exists across the

eld in the direction p erp endicular to the array but it is negligible compared to the

diraction b eamsize at the shortest op erating wavelength of m Distortion

b ecomes the most signicant ab erration at fo cal lengths less than mm for the

nal ellipse but the Strehl ratios also degrade

Optical stops

The pair of ellipsoidal mirrors is not the entire optical design however As shown in

Fig up on entering along the axis of the cylindrical cryostat the converging f

b eam delivers an image of the secondary mirror the secondary subilluminates the

primary lying cm inside the mounting surface The fareld fo cus lies an additional

cm b eyond the primary image After this fo cus the b eam reexpands to ll

the cold ellipsoid Up on reection the chief ray moves away from the dewar axis at

and is redirected by a small folding mirror onto the b olometer array mounted

p erp endicular to the helium work surface

With direct illumination as in any optical or infrared camera the ap erture must

b e carefully dened to avoid spillover past the edge of the primary mirror by using a

cold physical stop in the optics Hildebrand For this reason we place a mm

diameter cold ap erture stop at the primary image to dene the illumination pattern of

the array pixels ie to ensure that each pixel sees radiation originating only from the

secondary mirror Scattered ambient radiation which lowers b olometer sensitivity

and degrades the detector angular resp onse pattern b eam must b e prevented as

much as p ossible from entering the optical path after the stop To achieve this goal

we completely surround the reimaging optics with absorptive baing A sp ecial case

of baing is the eld stop which lies at a fareld image of the sky in order to precisely

dene the solid angle of the astronomical ob ject from which radiation is admitted to

the detector We place a eld stop in the form of a thin aluminum plate with a

rectangular slit machinepunched to match the scaled size of the b olometer array

at the fareld fo cus In this conguration the eld stop also limits the background

Primary beam 5.00 MM

Figure Sp ot diagram of the SHARC fo cal plane The sp ots lie at the center

corners and edges of a and a square eld corresp onding in the fo cal plane to

mm and mm resp ectively The diameter of the primary diraction b eamsize of

is shown

radiation transmitted to the detector By design the eld stop slit plate can b e easily

replaced by suitable plates as larger arrays b ecome available Because they lie b eyond

the bandpass ltering b oth the ap erture and eld stop must b e co oled to T K in

order to minimize the blackb o dy emission reaching the detector

Mechanical design

Because the optical design requires b oth the ap erture and eld stops to b e at low tem

p erature a signicant mechanical supp ort structure is needed to align and x these

elements with resp ect to the ellipsoidal and at mirrors and the detector array The

mechanical supp ort was designed to b e symmetric ab out a plane in order to simplify

the optical arrangement as much as p ossible and to allow for accurate p ositioning

of the mirrors and stops Thus the optical system is reectionsymmetric ab out the

plane dened by the linear array and the midline of the oaxis ellipsoid

In order to minimize the required dewar length without adding extra folding mir

rors the ellipsoidal mirror was placed directly on the helium work surface with the

chief ray aligned with the entrance window along the dewar axis see Fig All of

the optical elements including the rotation of the at mirror are xed in place Thus

there is no alignment to p erform other than the lateral p ositioning of the b olometer

array housing which is accomplished by means of a sliding surface As all mirror

surfaces are p olished this adjustment is p erformed with visible light

To insure prop er alignment of the ap erture stop and eld stop with the ellipsoidal

mirror the supp ort structure attaches directly to the mirror with selfconsistent stop

lo cations dened by tapp ed holes machined to sp ecication This arrangement also

allows easy removal of the entire optics assembly including the detector housing

either with or without the ellipsoidal mirror All sides of the main optics assembly

which resembles a sho e b ox with the ellipsoid at one end and the ap erture stop at

the other are covered with thin metal bae sheets to blo ck stray light from reaching

the detectors The baes are constructed from mm OFHC copp er sheet to

insure go o d thermal coupling to the helium bath

Vacuum Lid Polyethylene Window Filters Filter Wheel

Aperture Stop (Secondary Mirror Image)

455 Field Stop (Tertiary Focal

Plane) 424 Flat Mirror Liquid Nitrogen Final Stage Focal Shield Plane

Thermal Liquid Link to Helium Array Stage Shield

Ellipsoidal Mirror 4-Helium Work Surface 3-Helium Work Surface

254

Figure A scale drawing of the cryostat optics with dimensions in units of mil limeters

Filtering

Optical ltering is imp ortant in a submillimeter camera for two main reasons

to dene the bandpass of the observations and to limit the radiative heat load

on the cryogenic detectors The bandpass of the camera is dened by one of a pair

of narrowband metal mesh lters mounted on a liquid Heco oled lter wheel which

is lo cated just ab ove the ap erture stop According to measurements made by the

manufacturer Co chise Instruments the bandpass lters eectively blo ck all

wavelengths m outside of their sp ecied bandpass The bandpass lter

wheel is a mm diameter geared circular plate with four round milled slots that

can hold metalmesh bandpass lters of mm clear ap erture The lter wheel is

mounted at the top of the optics chamb er just b elow the lid of the He temp erature

shield Manually op erated from the outside the wheel drive shaft extends from the

b ottom of the dewar up along the inside of the helium shield to a mm diameter

gear The gear drives the lter wheel with a turn ratio

However b ecause of the broad wavelength resp onse of the detectors farinfrared

through optical radiation must b e rejected by a stack of prelters The preltering

o ccurs at the entrance to the liquid N and He shields of the cryostat A schematic

of the lter arrangement is shown in Fig First the vacuum window of the

cryostat is a mm thick disk of high density clear p olyethylene which provides

longterm durability and water imp ermeability Bussone coupled with low loss

at submillimeter wavelengths Birch Dromey Lesurf Sttzel Tegtmeier

Tacke Birch Next a longwavelengthpass quartz lter mm diameter

mm thick with a black p olyethylene AR coating on b oth sides is mounted at the

window of the nitrogen shield lid At this temp erature quartz is essentially opaque

to radiation b etween and m Eldridge b ecoming transmissive at longer

wavelengths Lo ewenstein Smith Morgan Randall Rawclie The

black p olyethylene also serves to blo ck optical and nearinfrared radiation A second

longwavelengthpass quartz lter mm diameter mm thick is mounted as the

window of the helium shield On its top surface is a diamond scattering layer opaque

Quartz Polyethylene Aperture window stop

32 mm

Bandpass filter CsI 77 K

4 K

Figure The lter arrangement at the entrance of the SHARC cryostat The

lters and thicknesses are high density clear p olyethylene vacuum window

mm quartz mm with black p olyethylene AR coating quartz mm with

a diamond scattering layer on the top and a black p olyethylene AR coating on the

b ottom Cesium Io dide mm with a clear p olyethylene AR coating on b oth sides

metalmesh bandpass lter mm The bandpass lters lie in a manuallydriven

lter wheel with space for four dierent lters

from ab out to m Infrared Lab oratories Again a black p olyethylene

AR coating is applied on the b ottom surface of the quartz to blo ck the nearinfrared

photons originating from the K lter and shield At this p oint photons shortward

of m are completely blo cked

The quartz lter on the helium shield lid is followed by a crystalline cesium io dide

CsI lter mm diameter mm thick with clear p olyethylene antireection

coating Josse Gerbaux Hadni on b oth sides The clear p olyethylene also

serves to protect the CsI from hydration As an ionic crystal CsI exhibits a reective

band in the farinfrared m due to lattice vibrations Mitsuishi Yamada

Yoshinaga Eldridge At K the CsI lter yields nearly zero transmis

sion of incident radiation b etween and m while rising to transmission

at m Hadni et al This combination of lters thus cuts o all radiation

shortward of m eliminating any p ossible third harmonic resp onse of the metal

mesh bandpass lters

Submillimeter black paint

As in all sensitive cameras it is imp ortant to minimize unwanted reections and scat

tered light inside the optical train When the detector pixels are similar in size to the

telescop e diraction b eam scattered light reaching the pixels will cause sidelob es in

their angular resp onse pattern and distort the instrument b eamshap e In addition

with cryogenic b olometers sensitive to broadband radiation all of the low temp erature

surfaces must b e highly absorptive so that only emission from low temp erature mate

rials can b e seen by the detector To ensure this prop erty we coated the inner surfaces

of the optics supp ort and baes with a sp eciallymixed submillimeter black paint

The farinfrared prop erties of various typ es of optical black coatings have b een mea

sured Smith Pomp ea et al The base of the mixture we chose is a black

p olyurethane paint Aeroglaze Z Lord Corp oration Industrial Coatings A

part wash primer was applied to the roughened grit sandpap er metal surfaces

prior to the black top coat Tests of the submillimeter absorptivity of the paint p er

formed by inserting metal samples coated with a layer of thickness millimeter

into the b eam of the GHz hetero dyne receiver at the CSO Ko oi et al

revealed that the paint absorbs less than of incident submillimeter radiation To

improve the absorption of the top coat base we added by volume carb on black

p owder Fisher Scientic ltered to remove large congealed clumps that could

clog the air brush used to apply the paint and solid glass b eads by volume with

a distribution of diameters from microns Potters Industries Carb on

black eectively absorbs optical and infrared radiation while dielectric glass b eads of

radius a extend the attenuation to longer wavelengths a Sato et al A

signicant amount of Aeroglaze paint thinner by volume was also added

to lower the viscosity of the total mixture suciently to b e sprayed with the air brush

Multiple coats were required to obtain sucient thickness of mm inch

With these additives the submillimeter absorptivity of the metal samples was raised

to The paint adheres well to aluminum and copp er surfaces of thickness over

mm inch When applied to thinner sheet metal thermal cycling causes

the paint to buckle and p eel

Field rotation

The current observing metho d employed with millimeter and submillimeter b olome

ters relies on rapid b eam switching in the azimuth direction in order to subtract sky

emission At the CSO this switching is accomplished by chopping the secondary mir

ror at a rate of several Hz Raster scan onthey maps are acquired by scanning

the telescop e in azimuth at successive elevation settings and restoring the individual

dual b eam pixel measurements to a single b eam image in celestial co ordinates Be

cause this rapid scanning metho d works well to combat correlated sky uctuations

the preferred observing mo de for SHARC is to align the array axis in the elevation

direction and have the CSO secondary mirror chop in azimuth Deep integrations

are p erformed by rep eated mapping scans This onthey mapping technique also

avoids the problem of eld rotation of altitudeazimuthmount telescop es

The option do es exist to maintain xed alignment of a linear detector array along

a sp ecial p osition angle on the source by rotating the dewar on its mounting plate

as the telescop e tracks However b ecause the optics contain oaxis elements this

rotation varies the imaging p erformance Best imaging is obtained when the two

ellipsoidal mirrors lie uncrossed in the same plane as discussed ab ove However

to align the linear b olometer array with the elevation direction the dewar must b e

rotated with resp ect to this conguration in order to comp ensate for an angular

oset intro duced by the two at mirrors of the relay optics which send the b eam

out of the symmetry plane of the primary mirror The imaging quality across the

b olometer array remains excellent in the elevationaligned conguration despite the

small disalignment of the mirror axes A plot of the Strehl ratios as a function of

dewar rotation is given in Fig The nine graphs plotted represent Strehl ratios at

the same nine elds as in Fig and with the secondary mirror rotated oaxis by

on the sky The allowance for dewar rotation was not a ma jor concern during the

original design given our xed orientation observing mo de However we note that the

Strehl ratios across the central line of the fo cal plane remain ab ove over of

p osition angle and b ecause sources are typically observed only within a few hours of

lo cal transit time with parallactic angles b etween this range of p erformance

is satisfactory for observations relying on eld derotation

Optical p erformance

Shown in Fig is a b eam map of SHARC obtained at the CSO at a wavelength

of m The map was constructed by scanning the b olometer array through the

planet Uranus in the azimuth direction at a rate of s stepping the array in

elevation by pixel and rep eating to allow all pixels to pass through the planet

A total of scans were added The sample size in azimuth was p er

second integration Because of the small angular size of Uranus and its

large ux density it is a go o d source with which to measure the b eam pattern The

brightness temp erature T of Uranus varies with wavelength such that at B

Figure The Strehl ratio of the camera optics across the eld of view in the

fo cal plane as a function of the dewar rotation angle The heavy and solid lines

represent resp ectively the center and edges of the currentlyinstalled array detector

The results plotted are with the secondary mirror rotated oaxis by on the sky

and m T and K resp ectively Hildebrand Orton et al

Serabyn Weisstein and at m GHz T K Ulich

Thus the exp ected blackb o dy ux density from Uranus at m GHz can b e

computed from the Planck function

F B T erg cm s Hz Jy

c exp

k T

Because SHARC uniformly illuminates the secondary mirror the resp onse to a

p oint source should b e an Airy pattern With a meter telescop e op erating at

m the theoretical fullwidth at halfmaximum FWHM of the main lob e of the

Airy disk is The underillumination of the primary by the secondary widens the

Figure A CSOSHARC b eam map at m constructed from a sum several

SHARC scans recorded while the telescop e was driven across the planet Uranus at a

rate of arcseconds p er second The secondary mirror was chopping arcseconds

in azimuth at Hz during the scans The solid contour levels are

by of the p eak ux density The dashed contour is The array fo otprint is

shown with nonfunctioning pixels marked by an X

CSOs Airy disk slightly while its central obstruction of roughly linear narrows

it slightly Schro eder In the case of the CSO these eects virtually cancel each

other so they are neglected here If we convolve the FWHM Airy disk over the

area of the rectangular detector the exp ected half p ower b eamwidths b ecome

along the long axis azimuth by along the short axis elevation

Fitting a single Airy pattern to the image of Uranus yields a size of in azimuth

by in elevation However the low level wings of b eam pattern evident in the

contour plot are not well tted by the single Airylike comp onents b ecause at this

short wavelength the surface roughness of the CSO primary and secondary mirrors

degrades the imaging p erformance Surface inaccuracies on the scale of

exure obstruction from the feed legs defo cus and decenter of the secondary divert

a p ortion of the ux into sidelob es called the telescop e error pattern which can have

a complex shap e We attempt to account for this error pattern by tting the azimuth

and elevation cuts through the image of Uranus with the sum of two comp onents

an Airylike main b eam and a wider and weaker Gaussian the error pattern

constrained to lie at the same p osition In this mo del the tted FWHM of the main

Airy lob e is in azimuth by in elevation containing of the ux while the

FWHM of the Gaussian comp onent is in azimuth by in elevation The tted

size of the Airy disk closely matches the theoretical prediction in azimuth and is only

larger than exp ected in elevation

Several eects could cause smo othing of the b eam in elevation including a

slow p ointing drift b etween successive scans or a slight oset b etween the and

b eams implying that this broadening may not b e signicant However the spatial

sampling of the current Uranus data set is not sucient to distinguish b etween the

causes Finer sampling p er integration of the signal in the inscan direction

together with smaller elevation increments b etween scans or less than the pixel

topixel spacing will improve the spatial sampling of the b eam pattern in the future

allowing further renement of our understanding of SHARCs p erformance However

it is already clear that SHARCs ultimate imaging p erformance will b e limited largely

by the quality of the telescop e surface rather than the camera optics The approach

871.4 µm (344.3 GHz) with 871.4 µm Effective Wavelength (Frequency): Filter: 870 µm 870.6 µm (344.6 GHz) with 870.6 µm 869.7 µm (344.9 GHz) with 869.7 µm Bandwidth 74.2 µm (29.4 GHz) Bandwidth 74.2 µm

applying geometric optics and planar arrays at submillimeter wavelengths has thus of Transmission (%) 100

10 20 30 40 50 60 70 80 90

b een quite successfully demonstrated 0

0 0 0 0 0 0 0 1000 900 800 700 600 500 400 300

The SHARC lter transmission curves are plotted in Fig along with the at

mospheric transmission over Mauna Kea as a function of frequency The bandwidths

and eective frequencies of the lters are also listed for sources with dierent submil

SHARC Filter Transmission Curves

limeter sp ectral indices where F Blackb o dies corresp ond to

Filter Transmission Atmospheric Transmission

while dust grains with p owerlaw emissivities generally corresp ond to or β β β = 0 = 1 = 2 Nominal 350µm, 450µm, 870µm Filters 870µm 450µm, Nominal 350µm, 448.9 µm (668.3 GHz) with 448.9 µm Effective Wavelength (Frequency): Filter: 450 µm 448.3 µm (669.2 GHz) with 448.3 µm 447.6 µm (670.2 GHz) with 447.6 µm Bandwidth 45.5 µm (67.9 GHz) Bandwidth 45.5 µm Frequency (GHz) β β β = 0 = 1 = 2 353.2 µm (849.4 GHz) with 353.2 µm Effective Wavelength (Frequency): Filter: 350 µm 352.4 µm (851.3 GHz) with 352.4 µm 351.7 µm (853.0 GHz) with 351.7 µm Bandwidth 42.6 µm (102.9 GHz) Bandwidth 42.6 µm β β β

= 0 = 1 = 2

Figure The SHARC lter transmission curves sup erimp osed on the atmospheric

transmission over Mauna Kea during go o d weather The computed

GHz

bandwidths and eective frequencies of the lters are also listed for dierent submil

limeter sp ectral indices Figure courtesy of DJ Benford

Instrument control system

The other instrumentrelated pro ject of my thesis is the development and implemen

tation of the control software for the CSO b olometer array camera Traditionally

the hetero dyne sp ectrometers on millimeter and submillimeter telescop es have b een

managed by a small backend computer resp onsible for setting system parameters

and pro cessing and delivering data to the main telescop e computer In the case of

the continuum b olometer array system at the CSO the instrument control computer

or camera computer is an Apple Macintosh

System requirements

The requirements of the software package for the CSO b olometer array camera were

well dened at the outset of the pro ject First the digital signal pro cessing b oard

DSP that p erforms digital lo ckin of the b olometer signals was designed by engi

neers at the Go ddard Space Flight Center GSFC on a Macintosh NuBus b oard and

thus required a Macintosh computer for op eration Second much of the low level

communication to the DSP b oard was written by Kevin Boyce GSFC in the Lab

view software package a graphical programming language originally written for the

Macintosh but now available for PC and Unix platforms Rather than recreate this

co de the control software was based on the existing Labview architecture Third the

main CSO control program the User Interface Program UIP runs under the VMS

op erating system on a VAXStation lo cated in the telescop e building The UIP

exerts ultimate control over the based computer which controls the antenna

computer as well as the PowerPC Cetia backend computer for the acoustooptic

sp ectrometers used with the hetero dyne instruments For uniformity it was decided

in consultation with the CSO sta that the Macintosh computer that op erates the

DSP b oard would also b e controlled by the UIP over Ethernet in a manner similar to

the backend computer Finally since the Macintosh p erforms the actual data gath

ering rapid communication with the antenna computer is required in order to know

when the antenna has reached and acquired the selected p osition

Hardware

The control computer for SHARC is a Macintosh Quadra computer outtted

with Megabytes of RAM a Gigabyte hard drive and a Sup erMatch inch

color monitor The CPU in the Quadra is a MHz which currently runs

Labview version National Instruments The extra memory was required

to compile and run the complex virtual instruments VIs that communicate with the

VAX and display the data on the Mac Also purchased was a multipurp ose analog

and digital IO b oard the ATMIO b oard from National Instruments Inc to

allow the source acquisition status bit the acquire bit and the telescop e tracking

status bit the idle bit generated by the antenna computer to b e monitored in

real time by the Macintosh software The Quadra allows space for NuBus

b oards of which at least are required the DSP b oard and the IO b oard Since this

computer is planned to also run a b olometer sp ectrometer system or an upgraded

camera with a larger numb er of pixels additional b oards may b e required in the

near future The extra slots available in the Quadra plus its high pro cessor sp eed

inuenced the decision to buy it One imp ortant mo dication was needed to the

mechanical housing of the Quadra itself A second fan was added inside the case in

order to increase the convective co oling rate of the micropro cessors on the mother

b oard and the NuBus b oards in order to prevent the overheating problems frequently

faced by visiting groups using Macintosh computers at the CSO

Communication b etween the various computers

The communication b etween the Macintosh and the CSO control computer the

VAXStation is mo deled after the system congured for the hetero dyne receivers

by Ken Young at the CSO All of the communication o ccurs asynchronously using the

Transmission Control Proto colInternet Proto col TCPIP implemented over a lo cal

Ethernet Fortunately the Labview package supplies builtin VIs for TCPIP com

munication On the VAX side the communication software is written in C in order to

use the builtin TCPIP so cket routines for VAX C in the Multinet software package

Figure A sample of the SHARC Server display on the Macintosh Quadra at

CSO The font overruns in this image are an artifact of the screen dump pro cess

TGV Inc To initialize observing with the b olometer array the server VI

must b e started within Labview on the Macintosh which is congured as a Startup

item up on reb o ot of the system After initializing the display panel on the Macintosh

shown in Fig the server sits and waits for a connection to b e made on the

TCPIP p ort of the Macintosh Sometime later the observer issues the SHARC

command in the UIP which spawns a client program called SHARCCLIENT writ

ten in VAX C The client program creates two VMS mailb oxes called TOSHARC

and FROMSHARC which are used to transfer commands to and receive resp onses

from the Macintosh the server The client also assigns a communications channel to

a so cket to b e used for TCPIP communication to the remote Macintosh and initiates

a connection to p ort on the Macintosh When the server receives this connec

tion request it op ens the connection and returns a prompt character which the

client p erceives as the Connection OK resp onse The client then enters a p erma

nent lo op waiting for a message to app ear in the TOSHARC mailb ox as will o ccur

when SHARCrelated commands are issued in the UIP When a message app ears

it searches for the termination character and relays the message as a string to

the Macintosh over TCPIP then waits for a return string messages When the

client receives the prompt symb ol it stops waiting for further messages from the

Macintosh and instead waits for or acts up on the subsequent mailb ox message from

other UIP commands

Once the client has connected to the server the Mac initiates three more TCP

connections to the VAX one for error messages through p ort on b oth ma

chines event ags p ort and data p ort Multinet is congured on

the VAX so that when the Mac sends a connection request to these p orts the

appropriate server program will b e initiated on the VAX The connection to p ort

starts the program SHARCEVENTFLAGSERVER p ort starts the

SHARCERRORSERVER and p ort starts the SHARCSCANWRITER

All error conditions on the Mac are sent to the error server pro cess on the VAX and

app ear as messages on the UIP op erators terminal The event ag channel is used

to clear the backend wait BEWAIT status on UIP observing commands when the

Mac has gathered the appropriate numb er of data Finally data are sent to the scan

writer pro cess along with some header variables when appropriate

Data display on the Macintosh

The two main data acquisition mo des for b olometer observing at CSO are the scan

ning mo de known as OTFMAP and the p ointed observation mo de known as

CHOPSLEWY Both mo des involve the use of the CSOs chopping secondary

OTFMAP

The term OTFMAP onthey mapping refers to the observing mo de in which

the antenna computer directs the telescop e to scan across the source at a constant

rate usually in azimuth at a rate of a few arcseconds p er second while data is gathered

onthey Because rapid sampling of the lo ckin signal allows for the b est p ossible

sky noise subtraction we sample after each chop p erio d of the secondary mirror which

is the maximum rate p ossible This metho d allows extended maps to b e constructed

more rapidly than with a series of p ointed observations The raw signal is sampled

by the AD system at kHz and sent to the DSP via a b er optic link Performing

digital lo ckin detection the DSP demo dulates the data with a sine wave template

function and rep orts a signal level at the chopping rate The demo dulated b olometer

signals are displayed in real time on the Macintosh in the form of separate strip

chart graphs see Fig The basic display is mo deled on the Display Data

mo dule written by Kevin Boyce of GSFC As integrations are obtained they are sent

back to the VAX over Ethernet in real time The data are accumulated at the so cket

on the VAX and written to disk all at once at the end of each row of the map This

strategy has the advantage of requiring only a single op en and close of the data le

for each OTFMAP row The data consist of byte integers in DSP units The data

header of each scan contains the scale factor for the prop er conversion from DSP units

to millivolts The conversion from DSP units to actual voltage p ostamplication

DSP units f

V volts

c T

where f is the chopping frequency in Hz c is the numb er of chop cycles p er integration

usually T is the unitless amplitude of the sine wave template defaults to

and s is the right shift in bits applied to the data by the DSP defaults to The

chopping frequency is generated on the DSP b oard in the Macintosh in the form of a

to volt square wave and can take on quantized values satisfying the equation

where n f Hz

The chopp er throw is determined by the amplication and oset applied to the square

wave signal by the chopping secondary control circuitry built by Martin Houde at

CSO Currently the throw must b e tuned manually However a simple closedlo op

circuit has b een designed and is b eing built that will interface with the IO b oard in

the Macintosh to enable it to automatically set and monitor the chopp er throw via

the standard UIP command SECONDARY on the VAX Figure arra large y sw on eep the autoscales same This scan scale of with The Jupiter the graphical signal is a sample la from y out the of of reference the the displa SHAR pixel y C w OTF as while originally mapping the grid conceiv displa of ed y sw b on y eeps Kevin the sho Macin Bo ws yce tosh the at signals Quadra NASA from oddard Go at CSO the en The tire

CHOPSLEWY

The term CHOPSLEWY refers to the standard p ointed observation combining two

motions constantly chopping the secondary mirror at a few Hz while frequently

no dding the telescop e every few seconds to move the target source b etween the

p ositive and negative b eams and provide b etter subtraction of atmospheric uctua

tions and b eam asymmetries As in OTFMAP mo de the demo dulated b olometer

signals are displayed on the Macintosh as strip charts Up on the completion of each

no dding segment data are sent to the VAXStation which immediately app ends it to

the current le At the conclusion of the sp ecied numb er of chopping cycles the av

erage and RMS value of the data in each channel are written to the le after the scan

data Since the multiplex advantage of a continuum linear array is b est exploited in

mapping mo de the p ointed observing mo de of SHARC was not fullycommissioned

until August It is exp ected to b e used more in the future for deep integrations

on p oint sources

Data reduction

Since all demo dulated SHARC data are stored on the VAX it is most convenient for

this machine to run the data reduction software Using the NOD dual b eam restora

tion algorithm Haslam Emerson Klein Haslam Darek Lis has written

an OTF data reduction program called CAMERA The program interactively pro

ceeds through the various steps of data reduction pixeltopixel gain calibration

automatic or manual despiking destriping constant oset or linear baseline

removal airmass correction dual b eam restoration azimuthelevation p oint

ing correction and transformation to equatorial celestial co ordinates In standard

mo de images of the source are created by restoring a map from each pixel of the array

separately A separate mo de of the software is available for automatically analyzing

p ointing scans and pixel gain scans In a separate FORTRAN program called RE

GRID the restored images written by CAMERA are summed together into a regular

grid in equatorial co ordinates with sigmaweighting and ux calibration applied The

output image le from REGRID is in FITS format Wells Greisen Harten

and can b e read into a variety of software packages

Pixel gain calibration

Because of small dierences in the thermal prop erties of each pixel and in the optical

eciency across the fo cal plane each pixel of the b olometer array exhibits a slightly

dierent level of resp onse when centered on a given source Although the magnitude

of the eect is generally less than in the SHARC pixels it is a go o d practice to

measure and remove it from the data The relative gains of the pixels are measured at

the CSO by scanning a bright planet quickly through the array such that atmospheric

changes are minimal during the scan This is accomplished with elevation scans

invoked by the UIP command OTFSIDEWAYS The planet is placed in the p ositive

b eam for several scans followed by the negative b eam for several scans Each scan is

analyzed in the gain mo de of CAMERA which writes out a le with the computed

gains normalized to unity These gains are then averaged to create the gain le named

CAMERADAT to b e subsequently used in data reduction

Despiking

Cosmic ray hits and static electronic glitches are o ccasionally manifest in the data

as temp oral spikes in the scans Spikes may app ear in a single pixel or in all pixels

at once Fortunately these spikes can b e automatically identied and agged in

CAMERA by their magnitude with resp ect to the RMS background level The value

of the spike is replaced by the average of four values the two adjacent integrations

from that pixel and the integration from the two adjacent pixels if they are not

already agged An avoidance range can b e sp ecied within which spikes will not b e

removed by the automatic pro cedure Alternatively spikes can b e agged manually

in CAMERA

Destriping

After despiking any correlated noise remaining on the array app ears as strip es in the

scan data along the direction of the array On nights of unstable or windy conditions

the dominant source of correlated noise originates ab ove the telescop e Most likely the

correlation is due to cells of water vap or blowing through the two b eams faster than

the chopping p erio d seconds Removal of these strip es is a riskier pro cess

than despiking esp ecially when extended emission is present For this reason an

avoidance region in the scan can b e sp ecied in CAMERA within which the data

will not contribute to the calculation of the destriping correction and within which

no destriping correction will b e made This feature enables one to ensure that the

structure of sp ecied sources will not b e altered by this noise reduction algorithm

Oset or baseline removal

During long scans a drift in the signal zero level may o ccur Although this eect is

usually not detectable in SHARC scans CAMERA allows the removal of a constant

oset or a baseline computed from a sp ecied numb er of integrations on each end of

the scan Of course if destriping has already b een invoked no oset should remain

at this p oint

Airmass correction

Even in excellent conditions on Mauna Kea the zenith optical depth of the atmo

sphere at and m is always greater than This optical depth corre

sp onds to an emissivity via the relation e As a source rises

and sets the airmass At through which it is observed changes causing the signal

strength S t to rise and fall signicantly as a function of time t

S t S exp At where At sec zenith anglet

where S is the signal that would b e recorded ab ove the atmosphere In order to

prop erly calibrate the continuum ux density of all the sources observed it is essential

to measure the optical depth each night preferably on several sources observed at

many dierent airmasses Once the optical depth has b een computed the scans of

each source can b e calibrated to a xed airmass with CAMERA b efore summing into

a map

Dual b eam restoration

Once the scans are calibrated they can b e restored from a dual b eam resp onse pattern

into a single b eam sky intensity This is accomplished in CAMERA with the NOD

libraries The raw dual b eam scan is essentially a derivative of the sky intensity The

restoration pro cess uses the edges of the scan as a zero level which is propagated

across the scan intro ducing some additional noise in order to prop erly reconstruct

the extended emission Both b efore and after the restoration the scans are written

to GREG format RGDATA les named CAMERADUAL and CAMERAREST

Pointing correction

Occasionally it necessary and valid to correct the p ointing osets listed in the scan

header For example if the p ointing is not rechecked after a change in reference pixel

the op erator may have erred in the sign of the change to the xed zenith angle oset

of the telescop e Or a thermal p ointing shift of the telescop e may have o ccurred

since the most recent p ointing scan Because the OTF scans are recorded in azimuth

elevation co ordinates these telescop ebased p ointing shifts can b e corrected in data

reduction after the observation The osets to shift the image should b e sp ecied in

CAMERA as the direction you wish the image to move in azimuth and elevation

Co ordinate transformation

After restoration each integration of each scan is transformed by CAMERA from

azimuthelevation co ordinates to celestial equatorial co ordinates using the appropriate

header information of the lo cal sidereal time and telescop e osets Space exists in

the raw data le header for individual motor enco der readings but these are not

currently written by the antenna computer The data are treated as if the telescop e

was p ointed at the requested lo cation during the scan The transformed integrations

are then output to the le CAMERARADEC

Regridding summing and ux calibration

Multiple maps of a given source in the form of multiple CAMERARADEC les

can b e summed by the program REGRID A center p osition in right ascension and

declination and a grid of pixels ab out that p oint must b e sp ecied Each integration

of each map is placed into the appropriate pixel and added in with sigma weighting

Each map can b e given an absolute ux calibration conversion from millivolts mV

to Jy which will b e applied individually The ux calibration changes smo othly with

opacity with larger opacities causing fewer mV p er Jy Like the optical depth it is

vital that the ux calibration b e computed for each night at some consistent reference

airmass typically In REGRID additional pixels can b e agged in any or all

maps if necessary The pixeltopixel gain calibration can also b e invoked at this p oint

if it has not already b een applied The output of REGRID is a FITS image At the

CSO smo othing and customized display of these images is achieved in the GRAPHIC

package develop ed at the Insitut de Radio Astronomie Millimtrique IRAM

CHOPSLEWY data reduction

A software package called the Bolometer Array Data Analysis Software has b een

develop ed by Dominic Benford to read sum display and calibrate data obtained in

CHOPSLEWY mo de The command line interface resembles the CLASS package

develop ed at IRAM for hetero dyne sp ectroscopy

Sensitivity

Finally this chapter concludes with a demonstration of the sensitivity achieved with

SHARC at the telescop e in the case of short and long integrations

Short integrations

Shown in Fig are SHARC OTF scans taken with the same pixel under

stable atmospheric conditions on April With calibration based on Uranus

the NEFD achieved in a one second integration on blank sky adjacent to the planet

is Jy at m and Jy at m These values are ab out a factor of ve ab ove

the most optimistic background limits computed in Eq and

Long integrations

In order to test the camera sensitivity during long integrations it is necessary to

consider a series of data taken during constant sky conditions The longest integration

p erformed to date with SHARC is the CSO deep eld survey for protogalaxies which

contains the sum of second pixel integrations This corresp onds to

seconds of integration in each resolution element in the map Therefore

the RMS noise achieved in the nal map mJy at m implies an average

Hz However these data are spread over a large eld and NEFD Jy

acquired over many nights with varying weather conditions and may not represent the

eective NEFD for long integrations on a single p osition with the CHOPSLEWY

mo de

Because the CHOPSLEWY observing mo de mo de was only recently commis

sioned no comprehensive sensitivity measurements exist yet However we can con

struct long OTF integrations by adding together scans from dierent pixels over

adjacent patches of sky during the same map thereby insuring that the data are

taken during similar sky conditions For this purp ose we use a map of Uranus for in

trinsic calibration and use only those scans which do not pass near the planet

Figure The SHARC NEFD measured at CSO on the night of April

UT during which the optical depth in the m lter band was The inte

gration time along the xaxis is seconds corresp onding to one secondary mirror

chop cycle at Hz

away A plot of the RMS noise versus integration time on the blank sky in this map

is shown in Fig For the timescales prob ed by these data the decrease of inte

Figure The RMS noise in a single SHARC pixel is plotted as a function of

integration time at m The data at the upp er left come from raw dual b eam

scans of Uranus taken within the same hour The solid square at the right marks

the RMS noise achieved in the nal restored map of the deep eld survey The op en

square represents the estimated noise prior to single b eam restoration

grated noise with time closely follows the theoretical prediction Representing a much

longer integration time the deep eld p oint lies ab ove the trend partly due to added

noise from the dual b eam restoration pro cess explained further in section and

partly due to the fact that the data were taken during varying weather conditions

Chapter Submillimeter Continuum Images of

UCHI I Regions

The characteristics of interstellar dust

Over the past decade the development of large infrared and submillimeter telescop es

along with sensitive detectors has allowed astronomers to measure thermal emission

from co ol interstellar clouds Comp osed primarily of invisible molecular hydrogen

gas these clouds can b e studied only through emission from other molecules or dust

Contrary to many common sp ectral lines from molecular sp ecies thermal dust emis

sion has an optical depth of much less than one at wavelengths longer than m in

most interstellar clouds Hildebrand Hence the total submillimeter continuum

ux density is prop ortional to the numb er of grains present in the telescop e b eam

With instruments like the Submillimeter High Angular Resolution Camera SHARC

at the CSO the spatial distribution of dust can now b e mapp ed at high resolution

However the determination of the mass of dust from ux density measurements de

p ends critically on the farinfrared emissivity of dust grains Thus in order to quantify

the physical conditions of dust in interstellar clouds it is necessary to understand the

comp osition and shap e of individual grains and how they resp ond to incident ra

diation For this purp ose a brief review of cosmic dust grains is presented in the

following subsections

Dust comp osition

The shap e and comp osition of interstellar dust grains have b een inferred from astro

nomical observations and lab oratory measurements of their probable constituents A

review of the observed extinction from dust at UV to FIR wavelengths is given by

Mathis The detailed comp osition of grains such as the presence or absence of

ice mantles likely varies b etween dierent typ es of regions To explain the bulk of the

observations standard ingredients in dust grain mo dels of the interstellar medium in

clude graphite and silicate particles One of the early and oftenquoted mo dels of dust

includes a mixture of six dierent materials graphite silicon carbide SiC enstatite

FeMgSiO olivine FeMg SiO iron and magnetite Fe O Mathis Rumpl

Nordsieck hereafter referred to as MRN In order to calculate the extinction

due to a spherical grain of a given material one must know the complex indices of

refraction at each wavelength considered Of the six materials listed graphite ex

hibits the additional complexity of anisotropic refraction The geometry of graphite

is describ ed by two axes in the basal plane with a third axis the caxis p erp endicular

to this plane The refractive indices for light with the electric eld Evector parallel

to the caxis are dierent from that for light with the Evector p erp endicular to

the caxis Taft Philipp Tosatti Bassani Although no rigorous

theory exists for computing the optical cross sections of such a material the common

approximation as in the MRN mo del is to assume that of the grains exhibit

and exhibit In general the resp onse of a grain to incident radiation is

mo deled with the dip ole approximation as the grain radius a . Note that this

approximation likely fails in the inner parts of protostellar and protoplanetary accre

tion disks The result of the MRN mo del for b oth spherical and cylindrical grains

is that of the six materials graphite is present in all the mixtures which provide the

b est t to the observed interstellar extinction in diuse clouds from UV wavelengths

to m The required distribution of grain sizes follows the p ower law distribution

na a over the range m to m

Dust extinction in the infrared

The extinction predictions of the MRN graphitesilicate grain mixture have b een

computed and extended to longer wavelengths In a comprehensive pap er Draine

Lee compiled the dielectric prop erties of graphite and silicate dust grains

including the scattering and absorption cross sections as a function of wavelength

from m They nd that the MRN mo del matches the observed near

infrared extinction of diuse clouds with graphite grains mostly the comp onent

contributing a factor of several more extinction than the silicate grains At longer

wavelengths m silicate grains dominate the extinction particularly in the

and m bands in which absorption features have b een conrmed observationally

Dyck Simon By m extinction due to graphite grains mostly the

comp onent again exceeds silicate grains Draine Lee predict the m

thermal emission from the MRN mixture and show that it matches the IRAS ux

density observed toward clouds of infrared cirrus Low Thus the MRN mixture

has proved to b e successful in predicting dust extinction and thermal emission across

the infrared range

Dust extinction in the submillimeter

At submillimeter wavelengths the extinction from b oth graphite and silicate grains

increases as a p owerlaw with frequency

ext

where N is the column density of molecular hydrogen gas In the mo del of Mathis

Mezger Panagia graphite grains exhibit silicate grains exhibit

and a mixture of the two yields Draine Lee predict

for b oth sp ecies Recent lab oratory measurements of millimeterwave absorption

in silicate grains yield values of b etween and Agladze et al The

essential reason for this steep drop in extinction is that as the wavelength b ecomes

much larger than the radius the dust grain b ecomes a p o or radiator Purcell

notes the corresp ondence of this eect to the diculty of constructing an ecient

broadband longwavelength radio antenna of small size The absorption eciency Q

of a grain is dened as the ratio of the absorption cross section to the pro jected abs

geometric area

abs

Often is rewritten in terms of a mass opacity co ecient and the grain mass

abs

density assuming spherical grains

grain

Q a

a a

A simple derivation of the exp ected p ower law dropo of the absorption eciency of

a grain is given by Knacke Thomson and Wright using formulae from

van de Hulst for small ellipsoids In this derivation Q can b e approximated

by the expansion

Q Im Im Re

where a c a is the particle radius is the complex index of refraction and

is the frequency The rst term represents the Rayleigh absorption cross section

which dominates in the low frequency limit In a dissipative mo del of atomic os

cillators where the restoring force is prop ortional to velo city the imaginary part of

the dielectric constant is prop ortional to With another factor of coming from

the emissivity Q is then prop ortional to Andriesse This relation can

b e exp ected to hold for frequencies lower than the structural resonant frequencies of

the grains which are generally ab ove GHz Gezari Joyce Simon Mea

surements of the emissivity of interstellar grains as a function of frequency should b e

compared to the exp ected value of derived here

Measurements of dust emissivity in the submillimeter

Despite the exp ected value of measurements of at submillimeter wavelengths

exhibit a broad range from to over Helou Why is there such a variation

One explanation for ob jects with low values of is that the emission comes from very

ne grains in which surface vibration mo des dominate the bulk vibration mo des lead

ing to Seki Yamamoto Lab oratory measurements conrm this result

for grains of olivine obsidian and fused quartz with a . m Koike Hasegawa

Hattori A p ossible explanation for the values of is the presence of

ice on grains The absorptivity of ice has b een measured from to m Bertie

Labb Whalley At the longest wavelengths from ab out to m the

absorptivity scales as much steep er than the exp ected value of This dep endence

is predicted by a theory of light absorption by the vibrational mo des of the crystal

in which the density of states and the vibration intensity are b oth prop ortional to

Whalley Labb

The relevance of ice to dust grains was established by the detection in dense clouds

of absorption features at Soifer Russell Merrill m

in combination with the silicate band at m These lines have b een attributed to

ice in the form of a mantle surrounding the silicate core of a grain Tielens

Calculations on olivine quartz and lunar ro cks by Aannestad show that the

presence of ice mantles of radii & a on grains of these materials steep en

core

to values of to For this reason ice mantles have b een invoked to explain

measurements of at millimeter wavelengths Schwartz The presence of

ice is likely to b e augmented on colder grains and there is some evidence that is

inversely correlated with dust temp erature in dust clouds around HI I regions Gordon

A go o d overview of the optical constants and opacity of ice organic metallic

and comp osite grains compiled by Pollack et al shows that the exp ected value

of varies signicantly with the grain material Thus the large variation in observed

values of may b e real and may reveal the underlying comp osition and physical

condition of the grains Also fractal mo dels of dust grains suggest that the long

wavelength absorption of grains dep ends strongly on their shap e and asp ect ratio

Wright Further accurate measurements of in the submillimeter range such

as the data presented in this thesis are necessary to explore these p ossibilities

Computation of dust column density and mass

from submillimeter ux density

The general result of the dust mo dels discussed in the previous section is that the

emissivity of the grains decreases with decreasing frequency causing them to emit a

mo died Planck sp ectrum With this information the ux density F at frequency

from a opticallythin cloud of N dust grains at uniform temp erature T with a

geometric cross sectional area can b e immediately written Hildebrand as

follows

N Q B T N Q h

D D c exp h k T

where D is the distance to the source As seen in Eq Q a and thus F

a v the volume of a single grain As mentioned in section a distribution

g r ain

of dust grain radii na a is present in an interstellar cloud Truncating this

distribution at a m and a m the dust mo del of Mathis Mezger

l u

Panagia nds go o d agreement with the observed interstellar extinction A

at optical and infrared wavelengths One can compute a ux densityweighted mean

grain radius a over this size distribution

R R

a a

u u

anaa da aa a da

a a

l l

R R

a a

u u

naa da a a da

a a

l l

da a

a a

a da

m for a m and a m

u l

A contour plot of a as a function of a and a is included in Fig

l u

The value of a can b e used as an eective grain radius in the formula for ux

density Essentially a cloud of N identical grains of radius a would emit the same

ux density as N grains having the sp ecied p owerlaw distribution of radii Assuming

spherical grains one can then compute the total ux densityweighted volume of dust

Figure Mean ux densityweighted grain radius for the na a grain dis

tribution as a function of the lowercuto radius a and the upp ercuto radius a

l u

The p oints lab elled MRN and MMP corresp ond to the mo dels of Mathis Rumpl

Nordsieck and Mathis Mezger Panagia resp ectively

in the cloud

V N v N a

g r ain

This relation can b e used to eliminate N from Eq and arrive with

M a F D

a B T Q

where is the grain mass density The total mass of a cloud with ux density F

b ecomes

F D a

B T Q

R a F D

B T Q

a F D R

Q J T m g cm Jy kp c GHz

where R is an empiricallydetermined gas to dust mass ratio and J exp h k T

Using the telescop e b eam size this equation can b e rewritten in terms of the

gas column density

m D

a F R

Q J T m g cm Jy GHz

By applying the following empirical expression for Q valid at submillimeter and

longer wavelengths Hildebrand

THz

the formulas for column density and mass b ecome

a F R

N cm

J T m g cm Jy THz

a F D R

M M

J T m g cm Jy kp c THz

In reality a distribution of dust temp eratures will b e present in a starforming cloud

with the warmest grains lying near the young emb edded stars and co olest grains lying

in the outer parts of the cloud in the absence of external heating sources For this

reason we cannot exp ect to b e able to t the entire infrared through submillimeter

sp ectrum with a mo died Planck function of a single temp erature Multitemp erature

mo dels have b een constructed to t the continuum sp ectra of starforming dust cores

Hobson Padman Xie et al Grtler et al Pa jot et al

These mo dels include a comp onent of small warm grains T K which signif

icantly increase the emission in the and m bands of IRAS As discussed later

in section radiative transfer mo dels indicate a smo oth distribution of temp er

ature with cloud radius Goldreich Kwan Scoville Kwan However

b ecause the bulk of the luminosity from UCHI I regions emerges at m accu

rate estimates of the dust mass can b e obtained by tting only the cold comp onent

of dust Measurements at and m are essential to characterize

this comp onent of the sp ectrum Many m ux density measurements of UCHI I

regions exist in the literature eg Chini et al and low resolution m

data are available from the IRAS database IRAS images of UCHI I regions are pre

sented in the next section followed by new high resolution submillimeter images in

the subsequent sections

HIRES IRAS images

In order to link the new submillimeter images presented in this thesis to the far

infrared analysis of the IRAS database was undertaken With the ultimate goal of

spatially resolving the dust surrounding UCHI I regions I conducted a HIRES sur

vey of elds surrounding the UCHI I regions in the Wo o d Churchwell survey

along with others from the literature A NASA Astrophysics Data Program ADP

grant was obtained in order to pursue the research The HIRES algorithm employs

the maximum correlation metho d to enhance the spatial resolution of IRAS images

b eyond the standard IRAS Sky Survey Atlas ISSA plates which have to resolu

tion and approach the diraction limit of the telescop e Aumann Fowler Melnyk

The pro cessed elds are one square degree in size with pixels at the

wavelengths of and m The images were analyzed using the Skyview

software package develop ed at the NASA Infrared Pro cessing and Analysis Center

IPAC The eective resolution achieved by HIRES is approximately at m

and at m with signicant variation from eld to eld Ap erture photometry

was p erformed on the sources in these elds which could b e identied with radio

detected UCHI I regions The list of these sources together with their measured IRAS

ux densities within a radius of the centroid and blackb o dy color temp eratures

b etween and m are given in Table

In general the FIR emission remains unresolved at the two longest wavelengths

despite the improved resolution of the HIRES maps In a few cases including

G G G G and KA KC

the FIR ux has b een resolved b etween a pair of adjacent UCHI I regions This allows

more accurate blackb o dy ts when combined with submillimeter data However the

overall lack of real detail in the HIRES images emphasized the need for higher resolu

tion submillimeter studies at CSO As a sample of the HIRES results contour plots

of the sources later imaged with SHARC are included as Figs through All

of the maps are in presented in equatorial B co ordinates

Table UCHI I regions analyzed with HIRES pro cessing

Co ordinates IRAS ux density Jy T

col

Source RA Dec m m m m K

h m s

WOH

h m s

MONRIRS

h m s

GGD

h m s

NGCA

h m s

NGCB

h m s

NGCC

h m s

NGCD

h m s

NGCE

h m s

NGCF

h m s

AFGL

h m s

AFGL S

Co ordinates IRAS ux density Jy T

col

Source RA Dec m m m m K

h m s

Co ordinates IRAS ux density Jy T

col

Source RA Dec m m m m K

h m s

Co ordinates IRAS ux density Jy T

col

Source RA Dec m m m m K

h m s

Co ordinates IRAS ux density Jy T

col

Source RA Dec m m m m K

h m s

NGCS

h m s

Average

Figure HIRES pro cessed IRAS maps of G Contour levels are

to by of the p eak intensity in each eld m m

m m MJysr

Figure HIRES pro cessed IRAS maps of G Contour levels are

to by of the p eak intensity in each eld m m

m m MJysr

Figure HIRES pro cessed IRAS maps of G Contour levels are

to by of the p eak intensity in each eld m m

m m MJysr

Figure HIRES pro cessed IRAS maps of G The two UCHI I regions

G and G have b een resolved Contour levels are to

by of the p eak intensity in each eld m m m

m MJysr

Figure HIRES pro cessed IRAS maps of the K complex Radio comp onents

A B and C have b een resolved Contour levels are to by of the

p eak intensity in each eld m m m m

MJysr

Figure HIRES pro cessed IRAS maps of G The two UCHI I regions

G and G have b een resolved Contour levels are to

by of the p eak intensity in each eld m m m

m MJysr

Figure HIRES pro cessed IRAS maps of WOH Contour levels are

to by of the p eak intensity in each eld m m

m m MJysr

Figure HIRES pro cessed IRAS maps of G Contour levels are

to by of the p eak intensity in each eld m m

m m MJysr

Figure HIRES pro cessed IRAS maps of G Contour levels are

to by of the p eak intensity in each eld m m

m m MJysr

Figure HIRES pro cessed IRAS maps of Mono ceros R Contour levels are

to by of the p eak intensity in each eld m m

m m MJysr

Figure HIRES pro cessed IRAS maps of GGD Contour levels are

to by of the p eak intensity in each eld m m

m m MJysr

Figure HIRES pro cessed IRAS maps of the S complex The extension to

the southwest of the eld center coincides with S Contour levels are to

by of the p eak intensity in each eld m m m

m MJysr

Figure HIRES pro cessed IRAS maps of G Contour levels are

to by of the p eak intensity in each eld m m

m m MJysr

Calibration and p ointing accuracy of the SHARC

images

The data reduction scheme used to prepare the SHARC images was describ ed in

Chapter Before presenting and interpreting the images a discussion of the ux

calibration dynamic range and p ointing accuracy should b e considered

Flux calibration

The absolute ux calibration of groundbased submillimeter continuum observations

is ultimately limited by the stability and uniformity of the atmosphere Even on

relatively calm nights the zenith optical depth across the frequency band of the lter

can change signicantly on short timescales minutes to hours Beyond the

regular increase with airmass can b e a signicant function of azimuth and elevation

dep ending on the p osition of clouds and weather systems The most accurate metho d

of measuring through the desired lter is to record the signal strength of a source

as it rises or sets through dierent airmasses By nature this measurement requires

several hours during which can b e changing In the and m bands in

go o d weather Thus a change in will cause change in the signal strength

The calibration conversion factor from volts to Janskys dep ends on the signal recorded

from a standard source including planets and secondary sources previously calibrated

to planets eg Sandell taking into account the fact that planetary brightness

temp eratures vary as a function of frequency Hildebrand Orton et al So

if changes by b etween the observation of the calibrator and the observation of

the source then the source ux density will b e in error by plus the additional

measurement uncertainties Several scans of the source taken at dierent times and

intersp ersed with the calibrator can help reduce this uncertainty If the source is

extended spatially the extended ux has additional uncertainty b ecause the resp onse

of the telescop e b eam to an extended source diers from the resp onse to a p oint

source The b est estimate of the accuracy of the ux calibration on a given night can

b e made from the disp ersion in several measurements of on dierent sources The

frequent readings from the CSO GHz meter can also b e considered if it was

op erating dep endably at the time With these eects the ux calibration of a single

OTF map recorded in one session is probably no b etter than accurate Since the

images in the following sections were constructed from a sum of or maps the

estimated calibration accuracy is

Dynamic range

Due to the presence of sidelob e resp onse in the and m b eams there is a

dynamic range limit for genuine features surrounding bright sources in the SHARC

maps As can b e seen in the m b eam map in Fig the brightest feature outside

the central b eam lies at the intensity level Consistent results have b een found

with maps of bright compact galaxies such as Arp When several maps taken at

dierent parallactic angles are summed the eect of the sidelob es will tend to smear

which will raise the dynamic range further Thus the dynamic range is at least

All of the sources identied in the maps presented in the following sections easily fall

within this criterion It should b e noted that the b eam is signicantly cleaner at

than at m due to the telescop e surface accuracy and hence the dynamic range

in maps at the longer wavelength is nearly a factor of larger

Pointing accuracy

The CSO is an altitudeazimuth mount telescop e Pointing correction is accomplished

with two sets of osets in this co ordinate system tilt terms which vary as a function of

elevation and xed terms which remain constant in the ideal case and vary only due

to small dierences in the mounting p osition of the selected instrument Additional

corrections in azimuth and elevation result from a formula containing several constants

designed to account for deviations b etween the radio and optical p ointing of the

telescop e These socalled optical p ointing constants are p erio dically measured and

up dated using an optical telescop e attached to the radio telescop e backing structure

and lo oking through a hole in the primary Finally a signicant refraction correction

. to the elevation angle is computed from the current humidity reading The

details of these formulas will not b e discussed but they provide an idea of the level

of complexity required in the p ointing of a submillimeter telescop e

Even when these systematic terms correct well for p ointing errors other eects

can disturb the p ointing accuracy of the telescop e Thermal changes at sunset and

sunrise can cause small distortions in the telescop e surface which cause changes

in the xed terms For this reasons observations during these times cannot b e relied

up on for absolute p ointing accuracy The b est p ointing accuracy is achieved when the

xed terms are measured on a calibrator lo cated near the target source in b oth axes

of motion particularly in elevation Unfortunately in the and m wavebands

very few bright p ointlike sources exist Planets of small angular size such as

Uranus Neptune and much of the time Mars are b est Nearby evolved stars with

dust shells and wellknown p ositions such as IRC are also go o d p ointing

sources Bright starforming regions with a dominant comp onent of compact emission

have also b een used by assuming the submillimeter emission p eak coincides with

infrared or radio p ositions Sandell UCHI I regions have b een used for this

purp ose even though the presence of extended emission and the lack of a pr ior i

knowledge of the submillimeter p osition makes them less reliable p ointing sources

Because UCHI I regions themselves are the sub ject of this work I chose to use

only sources with the most reliable p eak p ositions Uranus IRC Orion KL

IRAS and KA for correction of the xed p ointing terms For this

reason the angular distance b etween the p ointing source and the target source was

in many cases larger than recommended in azimuth or in elevation

The absolute p ointing accuracy of a single map is estimated to b e For many

of the regions studied more than one map was acquired and summed which should

improve the accuracy of the p eak p ositions of sources in the map

SHARC images of cometary UCHI I regions

Since the installation of SHARC at CSO in Septemb er over a dozen UCHI I re

gions have b een imaged at andor m The sample includes regions of various

radio morphology The cometary UCHI I regions studied are GA G

G G and GGD Similar to the cometary shap e is the

classic blistertyp e HI I region Mono ceros R Mon R The shelllike or spher

ical UCHI I regions studied are WOH KA and KC Also studied are

a group of UCHI I regions unresolved at radio wavelengths including G

G G G and a group of sources in the S

complex The nal ob ject presented is the G complex which contains several UCHI I

regions of cometary and corehalo shap es These sources will b e discussed individ

ually in the following sections with the exception of the two G sources which are

presented in greater detail in Chapter Also prior to the installation of SHARC

maps of m emission from many of these UCHI I regions were made at the CSO

with the single channel b olometer equipp ed with a Winston cone These maps

are included in the following sections Although most of the sources are unresolved

at the limited signal to noise level of these maps they do provide m uxes which

are used in the greyb o dy mo dels computed in section All of the maps in the

following sections are in presented in equatorial B co ordinates

G Complex W AFGL I

p c ex At a distance of kp c Kuchar Bania G is a

tended shelllike HI I region as seen in Fig Fey et al Fey et al Just

b eyond the northwest edge of the extended HI I region lies the prototypical cometary

UCHI I region G see Fig The discovery of this source prompted

sp eculation that the cometary tail was due to relative motion of the central ionizing

source with resp ect to the interstellar medium Reid Ho Higher sensitivity

observations show that the tail is at least p c in length and that it curves

back on itself Gaume Fey Claussen Theoretical mo dels prop ose that this

Figure cm radio continuum image of the G complex repro duced

from Fig of Fey et al

kind of cometary shap e could b e explained if the young O star was moving at a rate

of km s through the natal molecular cloud Mac Low et al Van Buren

Mac Low Also two unresolved radio comp onents lab elled A and B lie

southeast and northeast of the cometary region C resp ectively The lo cation

of the OH masers Garay Reid Moran and the primary concentration of

H O masers Benson Johnston Downes et al lie b etween the radio

comp onents directly opp osite to the direction of the cometary tail VLA images of

the NH and inversion transitions indicate a concentration of dense gas in

timately asso ciated with the H O masers Heaton Little Bishop Keto

reaching densities of cm in the central region Garay Ro drguez

Such high densities are conrmed by the presence of a CH CN core Akeson Carl

strom Maser emission has also b een observed in the

and GHz transitions of H O Melnick et al

In a JCMT GHz sp ectral line survey transitions of ethanol have b een

detected indicating a rotational temp erature of K and a large column density

cm consistent with grain surface chemistry Macdonald Habing Mil

lar Observed with the BerkeleyIllinoisMaryland Array BIMA millimeter

Figure cm radio continuum image of G repro duced from Fig

of Gaume Fey Claussen

interferometer the p osition of the complex molecules in the region also lies a few

arcseconds east of the UCHI I region Mehringer Snyder Together these ob

servations suggest that the UCHI I region expands preferentially to the west away from

the dense molecular gas Additional H O maser sp ots lie at an oset

from the UCHI I region Fey et al and probably trace a separate center of star

formation activity at a pro jected distance of p c

Shown in Fig are m and m images of the G complex

The p osition of the cometary UCHI I region is marked by a triangle and the two

sites of H O maser emission are marked by crosses Essentially the dust emission

p eaks on the UCHI I region The half p ower width of the dust core is p c

identical to the size of the CS J emission mapp ed with the IRAM m telescop e

Churchwell Walmsley Wo o d Extensions of dust emission protrude to the

southwest and northwest bracketing the ionized tail of the cometary UCHI I region

on a large scale The dust clump northwest of the UCHI I region coincides with

the secondary concentration of H O masers Fey et al Blueshifted CO

emission near this p osition was once interpreted as an extension of an outow from

the UCHI I region Matthews et al but the coincidence of the dust clump and

Figure Bottom panel m image of G d kp c with the

p osition of the UCHI I region marked by the triangle and the two H O maser con

centrations marked by crosses The contour levels are

and Jyb eam Top panel m image of the same region

with contour levels and

Jyb eam The asterisks mark the p osition of the submillimeter sources identied in

Table

masers provides overwhelming evidence that it is a separate core Two additional

dust sources GSE and GSW lie to the southeast and southwest

of the UCHI I region There is no compact radio continuum nor maser emission at

these p ositions However the ux in these ob jects imply large molecular masses

and M resp ectively see Table Thus they may contain younger massive

protostars forming on the outskirts of the dust core containing the UCHI I region

Table Observed prop erties of the dust clumps toward G

Src UCHI I oset B Co ordinates S S M

m m gas

RA Dec Jy Jy M

h m s

Sum of clumps

Total emission

To conrm the protostellar nature of the isolated continuum source GSE

a map of the H CO transition at GHz around its p osition

was obtained with the CSO see Fig Emission in this transition indicates

a high volume density of molecular gas Wang et al Mangum Wo oten

GSE clump in Table was chosen b ecause it is suciently separated

from the UCHI I region to avoid confusion in the CSO b eam at this frequency

The p osition of an H CO core coincides with the m source conrming the

presence of a dense starforming molecular core asso ciated with the dust core The

sp ectrum closest to the p eak is shown in Fig The core of emission on the

northwest edge of the map originates from the vicinity of the UCHI I region

G WS AFGL I

At a distance of kp c Churchwell Walmsley Cesaroni G is

a cometary UCHI I region similar in app earance to G The main radio

comp onent lies on the edge of a shelllike envelop e ab out p c in diameter

Figure H CO map integrated over the velo city range to km s

of the submillimeter dust clump that lies southeast of G d kp c in

Fig The p osition of the dust clump is marked by the asterisk Contour levels

are to by K km s on the main b eam brightness temp erature scale

Megeath et al Cesaroni et al As seen in Fig diuse radio emission

extends up p c to the north where a faint lament ab out p c in length

turns toward the west Fey et al Another lamentary structure emerges from

the southern edge of the shell and extends to the east

The m CSO single channel b olometer map shows a compact dust core Fig

The total FIR IRAS luminosity of the dust core is L Wo o d Churchwell

Strong emission from the molecular sp ecies CH CN CS and CO is present to

ward the core Observed with an b eam at the IRAM m telescop e the half

Figure The H CO sp ectrum observed with a b eam at the CSO at

the oset of from G within a few arcseconds of the p eak dust

emission from GSE The vertical axis is main b eam brightness temp erature

in units of Kelvin

p ower width of the core in the CS J transition is in RADec co or

dinates p c Churchwell Walmsley Wo o d The core contains a

nearinfrared cluster of stars roughly across and centered on the UCHI I region

Fey et al In the other direction p c west of the core lies a dense

NH clump Cesaroni et al coincident with two H O maser sp ots Hofner

Churchwell and a rare cm H CO maser Pratap Menten Snyder The

Br line exhibits large linewidths b oth ahead of the b ow and in the tail Lumsden

Hoare This velo city structure is inconsistent with the b ow sho ck mo del but can

b e explained by the streaming motions toward low density regions in a champagne

ow in which the ionization front reaches the edge of the cloud in one direction

causing the ionized gas to ow away at velo cities of order km s Bo denheimer

TenorioTagle Yorke TenorioTagle In this picture the G

UCHI I region encounters a high density medium on its western side The photo evap

orated material is swept back to the east along the cometary tail where it expands

into a less dense but anisotropic medium Fey et al

The m image of G shown in Fig reveals that the dust emission

p eaks near the core of the UCHI I region The half p ower diameter is p c

Figure cm radio continuum image of G repro duced from Fig of

Fey et al

slightly smaller than the CS core But as in G an extended comp onent

of dust emission lies along the general direction of the ionized cometary tail to the

east and also to the north along the extended radio lament Lo oking back at the

m map Fig the faint clump of emission in the east matches the northeast

tail of emission seen in the m image The coincidence of the extended radio

and submillimeter continuum suggests that there exists a diuse comp onent of warm

dust asso ciated with the expanding HI I region The diuse m emission to the

southwest is not identied with any radio continuum emission

Figure m image of G Contour levels are to by Jyb eam

The p osition of the UCHI I region is marked by the cross Wo o d Churchwell

Figure m image of G d kp c Contour levels are to

by Jyb eam The p osition of the UCHI I region is marked by the triangle and

the direction of the cometary laments are indicated by arrows Fey et al

G I

G is a compact cluster of UCHI I regions see Fig the most promi

nent of which is comp onent A a cometary UCHI I region asso ciated with strong H O

maser emission Churchwell Walmsley Cesaroni The UCHI I regions lie

within a compact core of m continuum emission as seen in the CSO single chan

nel b olometer map in Fig At a distance of kp c Wo o d Churchwell

the total FIR IRAS luminosity of the region is L Wo o d Churchwell

Figure cm VLA radio continuum image of G repro duced from Wo o d

Churchwell

Figure m image of G Contour levels are to by Jyb eam

The p osition of radio comp onent A is marked by the triangle Wo o d Churchwell

The p osition angle of the cometary radio tail of comp onent A is as indicated

by the arrow on the SHARC m image in Fig Analogous to G

and G the radio p osition of the main UCHI I region is consistent with the

p eak dust p osition with a slight extension of dust along the radio tail In this case

all ve radio comp onents lie within the Jy contour

Figure m image of G d kp c Contour levels are

to by Jyb eam The p osition of the ve UCHI I comp onents are marked

by letters Wo o d Churchwell

GGD complex I

GGD is a cluster of HerbigHaro ob jects identied from the Palomar Sky Survey

Gyulbudaghian Glushokov Denisyuk A large molecular outow originating

from these ob jects was rst identied in the CO J transition by Ro drguez

Cant Torrelles A cometary UCHI I region see Fig p owered by a

B star lies at the core of GGD with a water maser lo cated p c

to the northeast Tofani et al OH maser emission has also b een detected in

this region Ro drguez et al along with a core of NH with a molecular gas

mass of M Torrelles et al Despite higher resolution CO J maps

obtained at the James Clerk Maxwell Telescop e JCMT the p owering source of the

molecular outow remains uncertain Little Heaton Dent but the outow

axis lies closer to the H O maser source than the UCHI I region Although the UCHI I

region dominates the FIR emission it do es not have a prominent counterpart in the

nearinfrared At a distance of kp c Ro drguez Cant Torrelles the FIR

and submillimeter luminosity of the entire region is L Little Heaton Dent

Figure A cm VLA image of GGD repro duced from Tofani et al

An m JCMT map p eaks on the UCHI I region with some extended emission

surrounding the H O maser p osition A cluster of nearinfrared sources lies around

the lower contours of the submillimeter emission including the L source M

coincident with the H O maser Harvey et al With higher angular resolution

than the JCMT map the m SHARC image of GGD reveals a distinct sub

p eak of emission at the p osition of the maser source see Fig

Figure m image of the GGD complex d kp c Contour levels

are to by Jyb eam The p ositions of the H O maser and UCHI I region are

marked Tofani et al

Matching an extended m source Harvey et al the main submillimeter

p eak o ccurs a few arc seconds northwest of the UCHI I region in front of the cometary

head of ionized gas As in G the absolute p ointing of the SHARC image

is strengthened by the go o d corresp ondence of the H O maser and the subp eak of

continuum emission Hence the magnitude and direction of the oset from the UCHI I

region is likely to b e real This oset supp orts the mo del of cometary UCHI I regions

discussed in section as the result of a streaming motions in an asymmetric

medium As in G and G faint extended dust emission lies along

the direction of expansion of the HI I region

Mono ceros R complex I

At a distance of p c Henning Chini Pfau Mon R is a reection neb

ulosity containing a blistertyp e UCHI I region see Fig imaged at the VLA

by Massi Felli Simon Early FIR observations revealed a young cluster

of infrared sources with a total FIR luminosity of L Beckwith et al

Thronson et al Infrared p olarimetric studies have b een p erformed Ho dapp

Aspin Walther More sensitive nearinfrared observations revealed the

ionizing source to b e IRS consistent with a B star Howard Pipher Forrest

The infrared cluster is asso ciated with a core of dense gas identied in maps

of the CS J and transitions Heyer et al and in NH Torrelles et

al A gas kinetic temp erature of K was derived from observations of the

NH and transitions in a b eam Takano

The brightest nearinfrared source in the cluster is IRS a premain sequence

ob ject undetected in radio continuum or in Br emission VLA observations pinp oint

an H O maser coincident with IRS Tofani et al Previously H O maser

emission was detected at another lo cation oset from IRS Ro drguez

Cant but this source was not detected in the more recent observations of

Tofani et al IRS has b een resolved into two comp onents at nearinfrared

wavelengths including a conical reection nebula AU in length and a p ossible

circumstellar disk Koresko et al A giant molecular outow p c in

extent has b een mapp ed in CO J Wolf Lada Bally Due to the large

dimensions of the outow it is unclear whether IRS IRS or some other source is SW

the source of the outow High resolution CS and CO observations indicate dense

clumps in the outow Tafalla Bachiller Wright

Figure cm radio continuum image of Mon R repro duced from Fig of Massi

Felli Simon

An early submillimeter map at m with p c resolution obtained at

the Swedish ESO Submillimeter Telescop e SEST revealed seven dust clumps in the

Mon R cluster Henning Chini Pfau which were interpreted as remnants

of star formation The SHARC m image of Mon R is shown in Fig The

p eak emission o ccurs southeast of the UCHI I region whose cometary tail expands

to the northwest along a minimum ridge in the dust emission As in the case of

G and GGD the condence in the absolute p ointing accuracy of the

SHARC map is b etter than judging by the go o d corresp ondence of the H O maser

coincident with IRS and the subp eak of continuum emission Thus the magnitude

and direction of the oset from the UCHI I region is signicant and strongly conrms

Figure m image of the Mon R complex d kp c Contour levels

are to by Jyb eam The arrow marks the expansion direction of the blister

UCHI I region whose cometary p eak is marked by the triangle Massi Felli Simon

The squares mark the p osition of the two H O masers Tofani et al

Ro drguez Cant the eastern one b eing coincident with IRS The asterisks

mark the p osition of submillimeter sources identied in Table

the blister mo del for the HI I region In addition to the two main sources a dozen

other dust clumps surround the cloud core Some of the clumps can b e identied

with the Henning Chini Pfau sources A list of source p ositions and uxes

is compiled in Table Some of the sources have no infrared counterpart in a deep

K band image of the region Carp enter As this is the nearest UCHI I region

in the survey the complex submillimeter structure evident here suggests that similar

structure may b e present but unresolved in the submillimeter images of the more

distant sources

Table Observed prop erties of the dust clumps in Mon R

Src Oset B Co ordinates S M

m gas

RA Dec Jy M

h m s

Sum of clumps

Total emission

Osets measured from the H O maser asso ciated with IRS

Summary of cometary UCHI I regions

The dust surrounding cometary UCHI I regions is generally extended on arc minute

scales In most cases the p osition of the p eak dust emission coincides with the

dominant compact radio source with extended emission present along the direction of

the tail One exception is the blistertyp e HI I region in Mon R which clearly expands

asymmetrically from the edge of the dust core of IRS into a cavity relatively empty of

dust In most sources additional subp eaks of dust emission have also b een identied

some of which are asso ciated with known H O maser clusters and some of which are

heretofore unknown sources

SHARC images of shelllike UCHI I regions

K complex I

At a distance of kp c Ro elfsema Goss Geballe K is a complex

of compact HI I regions asso ciated with the W molecular cloud Neugebauer

Garmire VLA observations with p c resolution of the K radio

comp onents A and C reveal shelltyp e morphologies Turner Matthews On

a larger scale of p c comp onent A shows an ionized bip olar structure with

evidence for outow in radio recombination lines while comp onents B and D are diuse

HI I regions roughly p c in diameter lying to the northeast and southeast

resp ectively DePree et al The FIR luminosity of the entire region is L

Thronson Harp er By comparing the radio continuum to the infrared Br

line ux the visual extinction toward A B C and C has b een measured at A

and mag resp ectively averaged over a ap erture Ro elfsema Goss

Geballe Comp onent D lies b ehind only magnitudes of extinction and is visible

in optical images Comp onent A V km s is likely to b e lo cated toward

HI I

the front side of the molecular cloud WynnWilliams et al while comp onents

B C and C V km s are situated on the far side In a ap erture at the

HI I

p eak radio p osition the extinction toward C rises to A mag implying a large

hydrogen column density in a compact molecular envelop e surrounding the ionizing

star H images of KC reveal an outow of ionized gas from this source

DePree Ro drguez Goss As a whole comp onent C also corresp onds to

ON an OH maser source WynnWilliams Werner Wilson A recent deep

cm image of K see Fig revealed a new faint ultracompact comp onent

called C p c south of C and C DePree This ob ject may

b e coincident with a faint nearinfrared source Howard et al K3-50 3.6 cm Radio Continuum

K3-50 C2 33 26 00 C1 3.6 cm Continuum

25 30 C58.75

B 00

24 30

A (core) A (lobes)

00 DECLINATION (B1950)

23 30

00 D

22 30

20 00 02 0019 59 58 56 54 52 50 48

RIGHT ASCENSION (B1950)

Figure VLA cm image of the K complex courtesy of Chris DePree

With the exception of comp onent D all of the radio sources exhibit m con

tinuum emission with comp onent A b eing the dominant source see Fig The

m image of K in Fig provides a more detailed picture of the dust emis

sion from the HI I regions The brightest dust source is coincident with KA with a

strikingly round distribution conrming its frequent use as a submillimeter p ointing

source Sandell Some faint extended emission lies to the northeast near the

diuse HI I comp onent B Another ridge of dust is seen toward comp onents C and

C and brightening toward the south at the newlydiscovered radio source C A

CO J map taken at the CSO also reveals a molecular outow emerging from

the p osition of C These three ndings indicate that C is probably the

youngest massive protostar in the region Fortunately KA and C are suciently

separated to b e resolved in the IRAS HIRES images shown in Fig Separate

greyb o dy mo del ts to their sp ectral energy distribution indicate that comp onent C

is co oler than A K vs K Because the dust is heated internally this temp era

ture dierence is consistent with the higher extinction measured toward comp onent C

and may indicate that the emb edded stars there are younger than those of comp onent A

Figure m image of the K complex Contour levels are to

by Jyb eam Triangles mark the p osition of the ve radio comp onents

ABCCC lab elled in Fig

Figure SHARC m image of the K complex Contour levels are

to by Jyb eam The radio continuum comp onents are marked

by triangles and lab els DePree et al DePree

WOH G IC

Discovered during the Westerhout radio survey W is a complex of three

HI I regions Schraml Mezger Lying ab out southeast of the main radio

comp onent WOH is the prototypical shelltyp e UCHI I region Dreher Welch

with emb edded concentrations of OH masers Reid et al Fouquet Reid

Norris Bo oth Diamond and CH OH masers Menten Evidence

for gravitational infall has b een seen in the form of redshifted NH absorption features

Keto Reid Myers Bieging Lying p c east of the UCHI I

region is a group of GHz H O masers see Fig coincident with a faint

millimeter continuum source known as the TurnerWelch TW ob ject Turner

Welch Maser emission in the GHz transition Menten

Figure cm radio continuum image of WOH repro duced from Reid

Moran

Melnick Phillips and the GHz transition Cernicharo et

al has also b een detected from this source Frequently dubb ed as a massive

protostar this as yet unresolved ob ject was recently measured to b e mJy and

AU in diameter at GHz with the BIMA array Wilner Welch

Forster

At a distance of kp c Humphreys the FIR luminosity of WOH is

approximately L Harp er Thronson Harp er As shown in the

CSO m map in Fig the dust emission from WOH p eaks at the p osition

of the UCHI I region However some contribution of dust emission no doubt comes

from the TW ob ject When compared with the GHz IRAM ux measurement of

mJy Wink et al the millimeter ux from the TW ob ject is consistent

with opticallythin dust emission with a submillimeter sp ectral index implying

a dust mass in the range of to M This mass estimate is barely compatible

with the M C O clump identied at the same p osition Wink et al The

dust interpretation is also easily compatible with the upp er limit of mJy at GHz

Wilson Johnston Mauersb erger

Shown in Fig the SHARC image of WOH gives a more sensitive picture

of the region Similar to an unpublished JCMT m map Sandell the

m dust emission p eaks near the UCHI I region with noticeable extension toward

the east and northeast The ux at the p osition of the TW ob ject is Jyb eam

Since the TW ob ject is subarcsecond in size this measurement is an upp er limit to

its submillimeter ux The total angular extent of the dust emission in the region

ab out p c matches well with the size of the molecular cloud measured from

VLA H CO observations Dickel et al The FWHM of the m emission

is p c As observed with the Kuip er Airb orne Observatory KAO the

deconvolved FWHM sizes of the FIR emission are and at and m

resp ectively Campb ell et al

An interesting feature is the lament extending to the northeast which matches

the shap e and lo cation of the NH lament imaged by Wilson Gaume Johnston

Although the authors oer several p ossible explanations for the lament we

note that the feature is analogous to the lamentary structures seen in C O emission

Figure m image of WOH Contour levels are to by Jyb eam

The p osition of the UCHI I region is marked by the triangle Dreher Welch

and the TW ob ject is marked by the cross Turner Welch

in the Ophiuchus complex de Geus Burton and to the laments emerging

from the core of Orion A seen in b oth molecular line Tatematsu et al and

continuum emission Wiseman Ho Lis et al The nature of these

laments remains unclear though they seem to b e common in molecular clouds

Summary of shelllike UCHI I regions

As is the case in the cometary UCHI I regions the dust surrounding the shelllike

UCHI I regions is concentrated ab out the p osition of the radio sources Elongations

in the dust cores match the distribution of the compact sources Lower level dust

emission also comes from the more diuse HI I regions in the vicinity of the compact sources

Figure m image of WOH d kp c Contour levels are

to by Jyb eam The p osition of the UCHI I region and TW

ob ject are marked Turner Welch A lament of dust emission matches the

NH imaged at the VLA by Wilson Gaume Johnston

SHARC images of unresolved UCHI I regions

G I FIRSSE

At a distance of kp c G was discovered to b e a H O maser source with

the Eelsb erg m telescop e Henning et al Subsequently it was found to

exhibit broad CO J line wings and a GHz p oint source with a ux consistent

with a B star McCutcheon et al The total FIR luminosity of the IRAS

source is L consistent with an O star Shepherd Churchwell a A

bip olar molecular outow from the UCHI I region G was resolved in a CO

J map by Shepherd Churchwell a This discovery prompted further

interest in this source The m SHARC image in Fig shows a compact dust

core coincident with the UCHI I region

Figure m image of G d kp c Contour levels are to

by Jyb eam The triangle marks the UCHI I region McCutcheon et al

G G AFGL W

East I

The molecular cloud ICA lies at the b order of the extended HI I region S

W at a distance of kp c Emb edded in this cloud are the radio continuum

sources G and G which have b een imaged with the VLA

Kurtz Churchwell Wo o d In a b eam H O maser and NH emission

has b een detected from this region Churchwell Walmsley Cesaroni which

is asso ciated with the infrared cluster Air Force Geophysical Lab oratory AFGL

AFGL Price Murdo ck An optical and nearinfrared study of the

cluster reveals over young B stars the most massive of which ionizes the UCHI I

region G near the center of the cluster Deharveng et al The

luminous L highlyreddened A mag ob ject AFGL IRS

corresp onds to the radio source G which is likely to b e an ionized stellar

wind accompanied by a high velo city optical jet A CO outow is also identied with

this source Snell et al

The m SHARC image shows that the bulk of the dust emission is asso ciated

with G and lies in a short ridge that is elongated northsouth The

ridge runs p erp endicular to the CO outow see Fig in Chapter There is no

signicant dust emission at the p osition of G and the nearinfrared clus

ter Apparently the bulk of the dust lies around the younger source G

which probably accounts for the H O maser and NH emission as well

Figure m image of G and G d kp c

Contour levels are to by Jyb eam The triangles mark the p ositions of the

UCHI I regions from Kurtz Churchwell Wo o d

G AFGL I

AFGL is a compact cluster of a few dozen young stars and a reection nebula over

p c in diameter in the nearinfrared Weintraub Kastner Near the

center of the cluster lie two UCHI I regions imaged with the VLA Kurtz Churchwell

Wo o d and an H O maser Torrelles et al H O maser and NH emission

has b een detected by Churchwell Walmsley Cesaroni At a distance of

kp c Arquilla Goldsmith the total FIR IRAS luminosity of the

cluster is L A wide apparently p o orlycollimated molecular outow emerges

from the center of the cluster Gmez et al From p olarimetric imaging of

the outow cavity Weintraub Kastner suggest that the young stellar ob ject

WK which coincides with the H O maser p osition illuminates the reection

nebula and drives the outow In Fig we see that the m emission extends

around the p osition of the UCHI I region and the WK source with an additional

p eak to the east near the other UCHI I region The further extent of the submillimeter

emission may originate from other emb edded memb ers in the cluster Weintraub et

Figure m image of the G complex d kp c The

large triangle marks the p osition of the main UCHI I region while the smaller triangle

marks a fainter GHz source Kurtz Churchwell Wo o d The cross marks

the H Oinfrared source WK Torrelles et al Weintraub Kastner

Contour levels are to by Jyb eam

S complex AFGL I

Lying at a distance of kp c Mezger et al the S molecular cloud is

asso ciated with a cluster of red nebulae SS Sharpless with extended

radio continuum emission Also present in the cloud b etween two of the extended

HI I regions S S are several UCHI I regions see Fig lab elled S

G Israel Rengara jan Ho and three fainter mJy

sources called Sabc Snell Bally

Figure GHz VLA image of the S molecular cloud complex repro duced from

Fig of Snell Bally

A p ossible tracer of sho cked gas in outows blueshifted OH absorption app ears

in front of G Ruiz et al Comp onents Sb and c coincide

with the m sources IRS and IRS Beichman Becklin WynnWilliams

Asso ciated with S is a cluster of nearinfrared sources all but of which

are invisible on the Palomar Observatory Sky Survey POSS plate Tamura et al

Early FIR and submillimeter maps revealed two p eaks separated by in

declination and coinciding with the two sources S and S Jae et al

Richardson et al Higher resolution mm continuum maps with the IRAM

m telescop e resolved the dust emission into distinct clumps including a third source

south of the rst two cores called FIR Mezger et al All three sources are

seen in the SHARC image in Fig

Also visible in the SHARC image signicant extended emission lies b etween S

FIR and SFIR Four extensions of dust match with extensions in the CS

J emission of the region shown as indicated by the stars in Fig

The S region has b een studied in detail in the nearinfrared by Howard

Shown in Fig is an enlargement ab out the source SFIR with the m

contours overlaying a K band image in greyscale More than any other this image in

dicates the great p otential of detailed comparison of submillimeter and infrared data

The submillimeter emission lo cates the raw materials of star formation while the near

infrared emission identies the emb edded young stellar ob jects The main structure

at m is a b owllike feature extending to the northeast In the nearinfrared the

central core region of SFIR shows a limbbrightened shell of molecular hydrogen

emission centered on the central core with an additional enhancement of emission

along the lane of reection nebulosity that extends from IRS to IRS The lower

half of the b owl seen in m emission is also seen in H as the southeastern exten

sion of the shell Howard The northern half of the b owl is not as clearly seen

however the northern extension of the shell lies in the direction of the northern half

of m b owllike feature

Figure m image of the S complex d kp c Contour levels are

to by and to by Jyb eam The three radio sources of SFIR are

marked by triangles Snell Bally along with G Israel

Figure Left panel CS J image of the S complex Four p ositions in

the extended envelop e of gas are marked by stars Contour levels are

to by K km s Right panel m image of the same region with the

same p ositions marked

Summary on unresolved UCHI I regions

Most of the unresolved UCHI I regions presented here coincide with compact dust

cores with little extended emission except in the case of S where there is evidence

for faint unidentied submillimeter sources Compared to the rest of the sample

these UCHI I regions are of lower luminosity and hence lower ionizing ux which may

explain why they are unresolved at radio wavelengths Typically asso ciated with the

regions are rich clusters of young nearinfrared stars mixed in and around the dust emission

Figure Shown in greyscale is the nearinfrared K band image Howard

centered on SFIR Overlayed are the m contours with and

Jyb eam shown in white contours and and Jyb eam shown in dark

contours The dark contours surrounding white blotches are K band contours

SHARC image of the G Complex ON

At a distance of kp c Wo o d Churchwell the G complex contains several

centers of compact and extended HI I emission As shown in Fig G

is an extended doublep eaked corehalo HI I region lying several arcminutes to the

north Garay et al

Figure cm VLA radio continuum image of G repro duced from

Wo o d Churchwell

As shown in Fig G ON N is a cometary UCHI I region lying

several arcminutes to the south with asso ciated OH maser emission and a group of

H O maser sp ots Cato et al Walker et al Downes et al Dense

thermal gas has also b een seen in the form of NH emission Churchwell Walmsley

Cesaroni G is a doublep eaked HI I region comp onents A and

B lo cated ab out southwest of G Matthews et al

Figure cm VLA radio continuum image of G repro duced from

Wo o d Churchwell

Both clusters exhibit and m continuum emission see Figs and

but G is quite diuse matching its radio morphology G is also

much fainter at m relative to G suggesting that much of the ux is

from freefree emission Also G was undetected in H O and NH in the

survey of Churchwell Walmsley Cesaroni conrming that it is a more evolved

region with no dense gas nor compact sources In contrast the G complex

contains several compact sources in the m SHARC image shown in Fig

Overlayed on the map are the p ositions of the UCHI I regions the millimeter CO SiO

and SO p eaks Shepherd Churchwell b Haschick Ho Apparently

G contains a string of sources within a ridge of dust while the HI I regions

GA and B are unasso ciated with prominent dust emission Two additional

submillimeter sources lie to the southwest G recently detected as an H O

maser Hofner b and G unknown at other wavelengths Like the

submillimeter clumps in Mon R and G these sources are candidates for

massive protostars which should b e observed in depth at nearinfrared wavelengths

Figure m image of the G complex ON Contour levels are to by

Jyb eam Triangles mark the p ositions of the radio continuum sources asso ciated

with the northern cluster G Megeath et al Pipher Soifer Krassner

and the southern cluster G Matthews et al

Figure m image of the G complex d kp c with contour levels

to by Jyb eam Plus symbol G UCHI I region and H O

maser cluster Hofner b Fil led square CO J p eak Open square SiO

J blob Fil led triangle GHz continuum p eak Open triangle SO blob

Shepherd Churchwell b Asterisk H O masers Hofner b Crosses HI I

region comp onents of G Pipher Soifer Krassner Garay et al

The letters A and B mark the p ositions of the two comp onents of the HI I

region G Matthews et al Newlydetected submillimeter sources

G and G are indicated by arrows Dashed lines mark the edge

of the map

Greyb o dy mo dels

Onecomp onent mo dels

In a simple rstorder analysis greyb o dy functions have b een t to the sp ectral energy

distribution of the regions imaged with SHARC A greyb o dy function is simply a

blackb o dy function multiplied by the factor e which accounts for the nite

optical depth of the dust cloud at all frequencies The three free parameters are

the dust temp erature optical depth and grain emissivity index The source solid angle

and distance is input to the program to convert to observed ux units Using a grid

search leastsquares tting routine Bevington a single temp erature greyb o dy

mo del was used to t the IRAS and m uxes and the SHARC andor

m uxes In most cases and m uxes available from CSO observations

or from the literature were also included in the t Assuming a sp ectral index of

from radio wavelengths an estimate of the freefree emission contribution to the

m ux was subtracted prior to the t Plots of the sp ectral energy distribution

and greyb o dy mo dels for the regions are given in Figs through A

summary of the mo del t parameters is compiled in Table and in Fig The

data marked by crosses in the top panels of Fig corresp ond to sources which

do not have ux measurements at m G G and

G The average dust temp erature in the remaining regions is

K This is degrees co oler than the average mm color temp erature of all

UCHI I regions studied in the HIRES survey see Table Because the mo del

ts are less aected by the excess ux in the m band contributed by warm dust

the co oler dust temp eratures derived here by including the submillimeter data b etter

p ortray the condition of the co ol dust grains which account for the bulk of the cloud mass

Twocomp onent mo dels

As can b e seen in Figs through the single comp onent greyb o dy mo dels do

not t the observed and m uxes Emission at these wavelengths must come

from warm dust with either low optical depth or small solid angle ie primarily scat

tered light In the former case the warm dust could lie in a diuse comp onent more

extended than the submillimeter chopp er throw which would not aect the submil

limeter ux measurements However if the warm dust is compact escaping at only

certain geometries from the core then it could p otentially aect the submillimeter

measurements The HIRES IRAS maps generally show the emission to b e compact at

these wavelengths Therefore to check whether emission from this warmer comp onent

of dust aects the submillimeter p ortion of the sp ectrum twocomp onent greyb o dy

mo dels were also constructed Five free parameters were used the temp erature emis

sivity index and optical depth of the cold dust and the temp erature and optical depth

of the warm dust Because the warm dust probably consists of smaller grains without

ice mantles the emissivity index of the warm dust was held constant at In

Figs through the twocomp onent mo dels are overlayed in dashed lines with

the onecomp onent mo dels for the sources with ux measurements at more than

frequencies In nearly every source the twocomp onent mo del is indistinguishable

from the onecomp onent mo del at submillimeter wavelengths Thus the warm dust

do es not aect the dust prop erties derived from the onecomp onent mo dels A com

parison of the temp eratures grain emissivities and optical depths derived from the

one and twocomp onent mo dels is given in Table

Grain emissivity results

From the onecomp onent greyb o dy mo dels the average grain emissivity index in

the regions with complete submillimeter data is with a total range of

to These results are very consistent with those from a previous study of

star formation regions where Chini Krgel Kreysa As

shown in the top right panel of Fig there app ears to b e a correlation b etween

the emissivity index and the dust temp erature with a b est t line of

T Because the errors are signicant on b oth axes the prop er

linear regression b etween two random variables was p erformed Trinchieri Fabbiano

Bandiera The data from a survey of warm clouds with larger HI I regions are

included as op en squares in panel of Fig Gordon Adding these data the

correlation attens slightly to T Because it includes

data from warmer clouds in OMC this function is probably more indicative of the

underlying trend of interstellar dust One explanation for this correlation is that the

dust grains in the co oler clouds are more likely to have ice mantles which steep en the

grain emissivity index ab ove At the same time warmer clouds have smaller

grains which could atten the grain emissivity index toward However the

correlation may simply reect the fact that warmer sources exhibit a broader range

of dust temp eratures such that their sp ectral energy distributions b ecome broader

via a sum of several Planck functions Single temp erature greyb o dy mo dels will then

underestimate in order to simulate a broader Planck function Lis Carlstrom

Keene

Finally one of the denitions of a Class protostar Bachiller Barsony

Andr is that it exhibits the ratio L L where L is

submm b ol submm

the luminosity measured at m or equivalently logL L

submm b ol

The average ratio over the UCHI I regions is only slightly lower than the

Class criterion Evidently UCHI I regions are the high mass equivalent to young

low mass protostars at least in their app earance at submillimeter wavelengths This

agreement simply reects the fact that b oth classes of ob jects lie deeply emb edded in

molecular clouds The G G G WOH ceros Mono GGD SFIR G KC KA G G G G G G G Source Av erage last three of R sources D pc kp lac k T T millimeter K able ry dy o Greyb ux measuremen m FWHM odel mo ts parameters making d c p the log of dust computed L L

around log parameters L submm CII UCHI L log regions less M M

constrained M LL M

log cm N H log cm n H

Figure Histograms of the temp erature submillimeter grain emissivity column

density diameter numb er density luminosity mass and luminositytomass ratio

derived from greyb o dy mo dels of the sp ectral energy distribution of the regions

studied regions with nonexistent long wavelength mm ux measurements

are marked by crosses in the top panels Op en squares in the top right panel are

data from Gordon The vertical dashed line in each panel marks the average

value of the sources with complete submillimeter ux data WOH ceros Mono GGD SFIR G KC KA G G G G G G G Source R T able T K One Comparison oponen comp t of m the T Cold one K and t Cold w oponen ocomp Cold Tw o oponen comp t m ry dy o greyb T Hot K ts odels mo Hot Hot m

Figure Sp ectral energy distribution of G with the onecomp onent

solid line and the twocomp onent dashed line greyb o dy mo dels overlayed Listed

parameters corresp ond to the onecomp onent mo del

Figure Same as Fig for WOH

Figure Same as Fig for G

Figure Same as Fig for K comp onent A

Figure Same as Fig for K comp onent C

Figure Same as Fig for the Mono ceros R complex

Figure Same as Fig for the GGD complex

Figure Same as Fig for G

Figure Same as Fig for SFIR

Figure Same as Fig for G

Figure Sp ectral energy distribution of G With only ux mea

surements a twocomp onent greyb o dy t was not p ossible

Figure Sp ectral energy distribution of G With only ux mea

surements a twocomp onent greyb o dy t was not p ossible

Figure Sp ectral energy distribution of G The ux measurements

at and m rep orted by Gezari et al are from the AFGL survey

Density proles

Signature of collapse

Numerical analysis of the gravitational collapse of an initiallyuniform density spher

ical gas cloud reveals that the cloud quickly acquires a density prole

nr r

which resembles an isothermal sphere Bo denheimer Sweigart Larson

Penston Hunter This prole allows the cloud to approach hydrostatic

equilibrium b etween the outward force of gas pressure and the inward force of self

gravitation However there exists an upp er limit to the cloud mass ab ove which

equilibrium is imp ossible in the presence of external pressure from the interstellar

medium Bonnor

M c G P

crit ext

where the sound sp eed c is given by

k T

c km s for K gas

and the external pressure of neutral interstellar gas is given by

P nk T dyn cm for gas with n cm

ext

With these particular parameters M M If the mass exceeds this critical

crit

value dynamical collapse will follow pro ceeding most rapidly in the central regions

where the density is largest and the freefall timescale is shortest Mestel

freefall

In the outer parts of the cloud the sound travel timescale is less than the gravitational

timescale and subsonic motions can pro duce pressure gradients that opp ose and slow

the freefall For example in an isothermal cloud of mass M M and radius

r p c n cm the initial gravitational acceleration at large radius is

GM r GM

a km s yr

r r

Thus subsonic motions can redistribute material within the outer radii of the cloud

for at least yr and thereby slow the collapse b efore the gravitational velo city

approaches the sound sp eed Because the cloud is already centrally concentrated

M r r r dr r

a r

and hence the gravitational collapse acts more quickly on the inner parts of the

cloud leading to an insideout collapse This simple prediction is vindicated by more

detailed solutions to the selfgravitating isothermal ow problem In particular Shu

showed analytically and numerically that in the course of selfsimilar dynamical

collapse the r density prole breaks down at small r such that

nr r

and the infall velo city is given by

v r r

This conguration is consistent with a steady mass accretion rate onto the core

M r r nr v r r

Some observational results match these collapse predictions The earliest measure

ments of the density prole of molecular cores were determined from extensive maps of

two H CO transitions Fo cusing on the nearby lowmass starforming clouds Oph A

B and R CrA to get the b est spatial resolution Loren Sandqvist Wo otten

found that the maps were consistent with radiative transfer mo dels in which the

density proles ranged from r to r More recently radio and millimeter sp ec

troscopy has b een used to search for kinematic evidence for collapse For example red

shifted NH absorption has b een rep orted toward the UCHI I regions WOH Keto

Reid Myers Bieging G Keto and G where

the infall velo city scales as v r Keto Ho Haschick Similarly

redshifted HCO absorption and blueshifted emission from WIRS and We are

consistent with largescale dynamical collapse Rudolph et al By mo deling

line proles Zhou Evans show that infall will create an asymmetry b etween

the strength of the blueshifted and redshifted emission as a function of the optical

depth of the molecular transition This eect has b een observed toward B and

IRAS Similar results have also b een found in the dark clouds Lynds

L and L Myers Bachiller Caselli

In addition to sp ectroscopy continuum observations of dust provide evidence for

collapsing structures For example the and m continuum prole of the massive

starforming region Cepheus A is consistent with the r density prole Colom

Harvey An IRAS study of Bok globules yielded density proles in the range

from r to r Yun Clemens In a higher resolution study the millimeter

and submillimeter dust emission prole from the Bok globule B was consistent

with an r density prole Chandler Carlstrom Tereb ey Similar results

are found in L Motte Andr Neri L and L Ladd et al

and in LIRS Butner et al In LB the density prole approaches

r in the outer regions of the cloud and b ecomes at least as at as r within

p c Andr WardThompson Motte m observations of NGC

match an r density prole Evans Observations of the lowmass protostellar

source VLA in the Oph A cloud indicate an even shallower density prole of

r Barsony Clearly further highresolution observations of dust continuum

emission from a larger sample of sources are needed to measure how common each

typ e of density prole is

The case of massive stars

Current evolutionary mo dels of massive stars M M predict that hydrogen

burning b egins b efore protostellar accretion has ended precluding a premain se

quence phase Palla Stahler Beech Mitalas Thus it is likely that

the protostellar cloud is still collapsing on a large scale even after the app earance

of the rst stars Larson In attempts to mo del the dust distribution around

UCHI I regions Churchwell Wolre Wo o d found that constant or very shal

low density proles r provide the b est t to the nearinfrared to m sp ectral

energy distributions of these ob jects However emission at these wavelengths is most

sensitive to warm dust near the central star which accounts for a small fraction of the

total dust mass By spatially resolving the dust clouds the maps presented in this

chapter allow a more direct measure of the density prole In the following subsec

tions I mo del the density prole of the dust clouds surrounding the UCHI I regions via

radiative transfer simulations in an attempt to match the observed dust continuum

ux prole from the submillimeter maps

Flux density proles of UCHI I regions

Although the greyb o dy mo dels characterize the global prop erties of the dust they do

not immediately indicate the distribution As seen in Table the m optical

depth of the dust cores is typically much smaller than This means that the ux

density in a given ap erture is prop ortional to the temp eratureweighted mass in the

b eam Because the dust emission is resolved in many of the SHARC images there is

more information to b e gleaned Ap erture photometry was p erformed on each of the

UCHI I regions recording the ux density in ap ertures of logarithmically increasing

radii ab out the centroid of the source The average ux density p er pixel in the

outermost ring inscrib ed in the map was subtracted as a background value from all

pixels in the inner ap ertures but typically there was no signicant oset present

Radiative transfer mo dels

One can compare the submillimeter ux density prole to predicted proles from

radiative transfer mo dels To avoid confusion with the particle density proles ux

density proles are hereafter referred to as ux proles For this purp ose I have

mo deled the app earance of dust co co ons around UCHI I regions with the radiative

transfer program CSDUST which solves for the dust temp erature at all radii within

the co co on Egan Leung Spagna

Input parameters

Even with the assumption of spherical symmetry a complete mo del requires many

input parameters the dust emissivity index the normalized mass opacity of the

dust at some sp ecied frequency an initial dust temp erature distribution

T r the outer b oundary of the cloud r the inner core radius of the cloud where

the p owerlaw density prole levels o r the p owerlaw index of density prole p

the optical depth at from the center to the surface the luminosity L and eective

b ol

temp erature T of the internal heat source and the external radiation eld intensity

In the following simulations and L are taken from the greyb o dy mo dels

m b ol

for each source and a normalized dust emissivity of at m is assumed

Hildebrand At wavelengths shorter than m the dust emissivity index is

set to to match the typical observed values in the midinfrared Hildebrand

Q Q for m

m m

Q for m

where Q

A nal constraint is placed such that Q at short wavelengths T is taken

from the zero age main sequence values for a star with the appropriate value of L

b ol

Thompson Panagia An external radiation eld of one standard ISRF is

also assumed

Mo del pro cedure

Because of sensitivity limitations in the maps esp ecially to emission structures larger

than the chopp er throw the true outer b oundary of the cloud r is uncertain and

should b e varied to obtain the most accurate mo del eg Mundy et al How

ever as a simplication to the mo del pro cedure owing to time constraints on this

research the value of r has b een xed at the radius where the intensity of the sub

millimeter emission vanishes usually equal to or close to the size of the map Mo dels

were then run for dierent p owerlaw density prole indices p and The

results are compared to the observations and the value of p most consistent with the

data is assigned to the source As a selfconsistency check the predicted sp ectral

energy distributions of the mo dels are compared to the measured FIR and sub

millimeter ux densities to conrm that the assigned value of p provides the b est

Regarding the starting p oint for T r radiative transfer mo dels of infrared sources

in molecular clouds have previously revealed that T r r Goldreich Kwan

Scoville Kwan where q Harvey et al Adams

Thus the input temp erature distribution was computed for each source using the

value of from the greyb o dy mo del and normalizing the temp erature at the half

p ower radius to the greyb o dy temp erature The program CSDUST mo dies this

distribution slightly after each iteration while converging toward equilibrium Because

p owerlaw density proles b ecome singular at the origin it is necessary to cap them at

small radii The program achieves this requirement by smo othly matching the input

p owerlaw density prole to a Gaussian density prole The match p oint r is set

to the radius inside of which of the optical depth lies Typically this o ccurs at a

fractional radius of Rep eated mo dels with the match p oint set to revealed

that the mo del ux proles are fairly insensitive to the match p oint over the range of

fractional radii prob ed by the observations

Convolution with the instrumental b eam pattern

Once the radiative transfer mo del has converged the result must b e convolved with

the telescop e b eam to obtain a prediction of the observed ux prole at a sp ecic

wavelength To do this prop erly I have mo deled the instrumental b eam resp onse

to a p oint source from images of Uranus Because its angular diameter is

much smaller than the b eamsize it can b e taken as a go o d approximation to a p oint

source Shown in Fig is the integrated ux prole extracted from the m

image of Uranus obtained with a chopp er throw of Fig Overlayed on the

observations is the ux density prole of a Gaussian b eam which matches the full

width halfp ower diameter in the Uranus image but fails to match the broad wings

of the resp onse As discussed in Chapter the SHARCCSO b eam resp onse can b e

describ ed by a sum of two functions a diractionlimited comp onent convolved with

the pixel size and a larger sidelob e comp onent In Fig I have also overlayed the

ux prole predicted by the sum of two Gaussian b eams a b eam with of the

p ower and a b eam with of the p ower Although the main b eam eciency of

the CSO is known to b e only at m much of the sidelob e p ower evidently

lies in an even more extended error pattern which is either chopp ed out or to o faint

to b e seen in the b eam map Thus the emergent intensity at each impact parameter

of the radiative transfer mo del has b een convolved with the sum of these two b eams

in order to derive the predicted ux prole

In Figs through I compare the observed ux prole with predicted ux

proles from the CSDUST radiative transfer mo dels with particle density proles of

nr r nr r and in some cases nr r Mon R is excluded from this

analysis as it is clearly a nonspherical cluster of individual sources primarily b ecause

it is the nearest source in the survey The rest of the sources can b e characterized

into four categories isothermal central collapse bulk collapse and logatropic

Figure Observed ux prole of Uranus measured from the m image and

compared to predictions from a Gaussian b eam which matches the halfp ower

diameter and the sum of a Gaussian main b eam and a Gaussian sidelob e

b eam which provide a b etter match to the resp onse pattern

Figure m SHARC image of Uranus in celestial co ordinates from which the

ux prole of Fig was measured Contour levels are to by

The dashed contours represent the halfp ower levels of the and Gaussian

b eams that comprise the mo del of the resp onse pattern

Sources resembling an isothermal sphere

At all scales the ux prole of G closely matches the n r density

prole of the isothermal sphere suggesting that it is in an early stage of star formation

development b efore substantial collapse has o ccurred As discussed in section

so far there is evidence for only a single ob ject forming in this core

Figure Observed ux prole of G measured from the m image

and compared to predictions of radiative transfer mo dels

Like G G resembles the isothermal sphere throughout most

of the cloud although the slop e app ears to b ecome shallower in the outermost regions

This broadening may b e due to fainter sub clumps in the halo esp ecially since a cluster

of UCHI I regions is seen in this source see Fig in Section

Figure Observed ux prole of G measured from the m image

and compared to predictions of radiative transfer mo dels

The ux prole of G matches the isothermal sphere through most of

the cloud though it app ears to deviate slightly in the inner regions However small

p ointing and tracking errors b etween subsequent scans of the map may broaden the

prole up to This eect will b e esp ecially noticeable at small radii Thus within

the estimated error the observed prole is consistent with the isothermal sphere at

all scales The presence of the UCHI I region a separate concentration of H O masers

and a small nearinfrared cluster indicates several sites of star formation already exist

at the core

Figure Observed ux prole of G measured from the m image

and compared to predictions of radiative transfer mo dels

Sources resembling the collapse prole at the center

The ux prole of WOH matches the isothermal sphere in the outer parts of the

cloud but rapidly approaches the nr r law at the innermost radii This prole

is consistent with collapse in the central core r . or p c while the outer

regions r & or p c remain isothermal and have not yet felt the collapse To

estimate the time since the collapse b egan I assume uniform gravitational acceleration

and set the collapse velo city at r p c equal to the sound sp eed Eq Using

the mass and temp erature from Table this yields a timescale of yr virtually

identical to the typical dynamical timescale of UCHI I regions derived in Chapter

Note that there are at least two young ob jects already formed in this core the UCHI I

region and the TurnerWelch ob ject

Figure Observed ux prole of WOH measured from the m image and

compared to predictions of radiative transfer mo dels

Like WOH the ux prole of KA matches the prediction of the isothermal

density prole in the outer regions of the cloud and approaches the collapse prole

in the inner regions Like WOH there is evidence for several young ob jects in this

core the UCHI I region an outow source lying to the east identied in Chapter

and a p ossible nearinfrared cluster Howard et al

Figure Observed ux prole of KA measured from the m image and

compared to predictions of radiative transfer mo dels

Sources resembling the collapse prole

Throughout the cloud the ux prole of S FIR matches the prediction from

the collapse mo del density prole suggesting that the bulk of the cloud is currently

undergoing collapse Several radio sources and a nearinfrared cluster show that

substantial star formation has already o ccurred at the core

Figure Observed ux prole of S FIR measured from the m image and

compared to predictions of radiative transfer mo dels

On all scales the ux prole of G lies b etween the predictions from

the isothermal and collapse mo del density proles It app ears to b e consistent with a

prole of r however the mo dels are not easily distinguishable due to the limited

spatial resolution achieved on this source Nevertheless it will b e classied here as

a collapse prole Like WOH and KA there is evidence for more than one

young ob ject forming in this core Shepherd Churchwell b

Figure Observed ux prole of G measured from the m image

and compared to predictions of radiative transfer mo dels

In the outer half of the cloud the ux prole of G matches the pre

diction from the collapse mo del density prole suggesting that the entire cloud is

currently undergoing collapse As in G the slight broadening of the pro

le at small radii is consistent with a tracking error To date only the UCHI I

regionH O maser source has b een identied in this distant source

Figure Observed ux prole of G measured from the m image

and compared to predictions of radiative transfer mo dels

Based on the image in Fig the outer parts of the ux prole of G

is obviously widened due to contamination from of additional p oint sources in the

extended halo Without this confusion the prole would likely exhibit the collapse

prole throughout the cloud as it do es in the inner regions The UCHI I region H O

maser sites and submillimeter sources reveal multiple cores of star formation in this

cloud

Figure Observed ux prole of G measured from the m image and

compared to predictions of radiative transfer mo dels

Sources resembling logatropic spheres

The prole of KC a ridgelike source containing UCHI I regions is consistent

with a shallower density prole of nr r This typ e of prole is known as a

logatropic sphere Lizano Shu and implies equal column density on all scales

The structural analysis of dark clouds by automatic starcounts yields an internal

density structure of nr r Stwe and in particular for the Taurus

Auriga complex nr r Cernicharo Bachiller Duvert Similarly the

distribution of the average densities of molecular clouds of varying radius follows the

relation n r Larson Therefore this density prole may b e the signature

of either a cluster of dust cores consistent with the UCHI I regions found here

Figure Observed ux prole of KC measured from the m image and

compared to predictions of radiative transfer mo dels

The prole of G exhibits a similar shallow prole to that seen in K

C Including the UCHI I region this source contains at least young ob jects with

outows see Chapter

Figure Observed ux prole of G measured from the m image

and compared to predictions of radiative transfer mo dels

Like G and KC GGD matches the nr r p owerlaw At

least two sources the UCHI I region and H O maser have formed in this relatively

lower luminosity ob ject L L

Figure Observed ux prole of GGD measured from the m image and

compared to predictions of radiative transfer mo dels

G also matches the nr r law throughout the cloud Although

only a single dominant radio source has b een detected there is an infrared cluster as

well as faint radio and submillimeter emission to the north Like GGD it is one

of the lowest luminosity sources in the sample

Figure Observed ux prole of G measured from the m image

and compared to predictions of radiative transfer mo dels

G also matches the nr r law throughout the cloud As dis

cussed in section this cloud contains two radio sources and an infrared cluster

of at least stars Like GGD and G it is one of the lowest

luminosity sources in the sample

Figure Observed ux prole of G measured from the m image

and compared to predictions of radiative transfer mo dels

Finally G also matches the nr r law Like G

this lower luminosity cloud contains more than two dozen young stars and p ossibly

as many as ve dozen Weintraub Kastner Weintraub et al

Figure Observed ux prole of G measured from the m image

and compared to predictions of radiative transfer mo dels

Conrmation of the sp ectral energy distributions

Besides predicting the ux proles discussed in the preceding section the radiative

transfer mo dels also predict the total source ux as a function of wavelength For

a selfconsistency check these predictions can b e compared to the measured uxes

that were used to t the greyb o dy mo dels in section Plotted in Fig are

the predicted sp ectral energy distributions SEDs from the radiative transfer mo del

for each source Separate curves are plotted for the r r and the r density

proles In nearly every case the measured farinfrared and submillimeter uxes lie

within the error bars on the appropriate curve that matches the ux prole Like

the onecomp onent greyb o dy mo dels the curves tend not to match well with the mid

infrared and m uxes Apparently the dust mo del is not detailed enough to

treat these wavelengths prop erly Since only a single dust grain size was used this

shortcoming is not surprising A more complex mo del would b e necessary to treat

features such as the midinfrared silicate bands However the simple mo del presented

here do es serve well at the wavelengths of interest

Temp erature distributions

Plotted in Fig are the equilibrium temp erature distributions from the radiative

transfer mo dels As can b e seen by the thin straight lines overlayed the simple scaling

laws of T r r or r corresp onding to or are go o d approximations

to the mo del temp erature distributions in the outer parts of the cloud The general

upturn in the mo del temp erature o ccurs ab out the radius at which the mo del p ower

law density prole is matched to a Gaussian prole

Figure The predicted sp ectral energy distributions from the radiative transfer

mo dels are plotted as curves dotted r dashed r dashdot r The b oxes

mark the observed uxes from each source corresp onding to IRAS submillimeter and

millimeter measurements

Figure The predicted temp erature distributions from the radiative transfer

mo dels are plotted as curves dotted r dashed r dashdot r The

straight lines mark the simple scaling laws of T r r r and r from top

to b ottom The upturns in the mo del temp erature at small radii corresp ond to the

core radius where the p owerlaw density prole is matched to a Gaussian prole

Luminosity to mass ratios

With the density prole analysis complete a nal relation to explore in these UCHI I

regions is their FIR luminosity to dust mass ratio L M versus dust temp era

FIR dust

ture As evident in Table a large range exists in the L M ratio to

FIR dust

Because the FIR dust emission derives from repro cessed starlight originating at the

core of molecular clouds the L M ratio has b een quoted as a measure of the

FIR CO

star formation rate of whole galaxies and individual giant molecular clouds Young et

al Mo oney Solomon Scoville Go o d Carp enter Snell Schlo

erb Typically the mass has b een determined from CO observations but in

this case we can measure the dust mass directly from the greyb o dy mo dels Because

the FIR dust luminosity is prop ortional to dust mass and the frequency integral of

the mo died Planck function the L M should b e prop ortional to the latter

FIR dust

quantity Cox Mezger

Z Z

FIR

B T Q d B T d T

dust dust

dust

As exp ected Fig indicates a strong correlation b etween the L M ratio

FIR dust

and the dust temp erature of UCHI I regions No correlation is seen in the L versus

FIR

T diagram due to the range of masses present in the source sample A simple

dust

explanation for the observed L M vs T relation is that it represents an

FIR dust dust

evolutionary track That is the more evolved sources lie to the upp er right b ecause

they have formed a greater numb er of hot stars that have b o osted the luminosity

and heated the dust to a higher temp erature over a longer p erio d However the

sources tend to group together on the L M vs T diagram as a function

FIR dust dust

of their density prole with isothermal cores showing the largest L M ratios

FIR dust

and temp eratures and logatropic cores showing the smallest In other words the

more centrallycondensed cores contain warmer dust A similar correlation is seen in

extragalactic studies in which merging and interacting galaxies lie to the upp er right

and isolated galaxies lie to the lower left of the L M vs F F diagram

FIR CO m m

Figure Upper panel The luminosity plotted against the dust temp erature from

the onecomp onent greyb o dy mo del Letters denote the UCHI I regions whose density

proles indicate the isothermal I collapse C isothermalcollapse IC and logat

ropic L proles Filled triangles mark the UCHI I regions with no long wavelength

ux measurements and op en triangles mark Mon R and G for which den

sity proles could not b e reliably measured Squares mark HI I regions from Gordon

There is little correlation due to the range of masses in the sample Lower

panel Same as the upp er panel for the luminosity to dust mass ratio a measure

of star formation eciency which correlates with dust temp erature Overlayed is a

p ower law t consistent with a mo died StefanBoltzmann law with

Young Thus p erhaps the range of values is not established directly by the

time evolution in the star formation rate from lower to higher values of L M

FIR dust

Instead a range of initial conditions may determine the collapse density prole which

in turn sets the star formation rate and the dust temp erature Sp ecically clouds

with steep er radial density proles yield higher star formation rates and warmer dust

A further argument against simple time evolution is that b ecause all of the sources

contain UCHI I regions they may all b e of similar age and in a similar evolutionary

stage

Summary

The dust cores surrounding a sample of UCHI I regions are resolved for the rst

time in the highresolution submillimeter continuum images presented in this chapter

The rst impression left by the images is the presence of clusters of dust emission

Undoubtedly the UCHI I regions dominate the p eak emission due to the warm dust

surrounding them However in many cases cores of lower level emission lie in their

vicinity H O masers are often found in these subcores although many are not as

so ciated with any known maser or radio continuum source These newlyidentied

sources should b e followed up with deep nearinfrared surveys to search for the coun

terparts of these massive p ossibly protostellar sources

As a sample the sources cover a fairly wide range of b olometric luminosity

to L and temp erature to K Onecomp onent and twocomp onent

greyb o dy mo dels show that the submillimeter emission can b e characterized accu

rately by a single temp erature and grain emissivity index The average temp erature

is K and the average grain emissivity index is consistent

with results from prior mm surveys Using p owerlaw density proles of the form

nr r radiative transfer mo dels successfully predict the ux prole of the

dust Three of the sources are consistent with r resembling an isothermal cloud

In two sources the outer parts of the cloud are consistent with the r prole while

the inner parts approach the shallower r prole indicative of dynamical collapse

The app earance of these two sources is likely to b e shortlived as the collapse has

b een o ccurring for only yr Four sources are consistent with the r prole

throughout the cloud p ossibly indicating a more advanced state of collapse The nal

six regions are shown to exhibit a density prole approaching the r law similar to

that seen in nearby extended dark clouds

It should b e noted that of the six logatropic sources four are the least distant

d kp c regions in the sample These four are also the lowest luminosity sources

in the sample L L corresp onding to stellar typ es later than B In most

cases these regions show evidence for a cluster of young emb edded stars on scales

larger than the b eamsize Hence it is no surprise that they app ear more like lo cal

lowmass starforming dark clouds than the rest of sample When these four sources

are discarded from the statistics over half out of UCHI I regions exhibit the

collapse density prole to some degree These results are summarized in Table

Table Summary of dust density proles

p owerlaw sources with of sources with

Density prole index sources L L L L

isothermal r

isothermalcollapse r r

collapse r

logatropic r

Finally an interesting discovery is that sources with similar density proles lie in

similar areas of the L M star formation rate vs T diagram Isothermal

FIR dust dust

clouds lie to the upp er right where the star formation rate is high while logatropic

clouds lie to the lower left where the rate is low Apparently clouds with more

highly concentrated density proles develop star formation more rapidly than other

congurations Because all the clouds contain UCHI I regions with typical lifetimes of

yr it is p ossible that this dierence arises from dierent physical conditions

such as the relative imp ortance of magnetic eld supp ort rather than b eing dierent

evolutionary states of a general track

As exp ected from the relative timescales the inner region and in many cases the

bulk of the dust cloud is still collapsing even after the rst OB stars have formed near

the core Opp osing the collapse motion are bip olar molecular outows from young

emb edded ob jects in the core It has b een prop osed that outows may ultimately

limit the mass of an accreting star Silk Measuring the strength of outows

from these clouds and determining whether the UCHI I regions or asso ciated sources

drive the outows is the sub ject of the next chapter

Chapter Molecular Outows from UCHI I

Regions

Characteristics of molecular outows

At some p oint during the formation pro cess of a new star an outow phase b egins

which can manifest itself in various observational forms including the bip olar molecu

lar outow Lada Bachiller GmezGonzlez Bachiller Molecular

outows are most commonly observed as high velo city wings in the rotational tran

sitions of CO the most abundant interstellar molecule after H These line wings

usually extend to velo cities of km s away from the systemic velo city but can

reach to velo cities km s in the case of extremely high velo city EHV bullets

such as in HH Lizano et al Masson et al Bachiller Cernicharo

Although not yet fully understo o d the acceleration mechanism of the molec

ular gas must b e intimately related to the star formation pro cess Shu et al

When the high velo city CO emission can b e resolved spatially it usually exhibits a

collimated bip olar morphology analogous to the ionized jets sometimes seen at visible

and radio wavelengths from young stellar ob jects eg Reipurth Heathcote

Staude Elssser In many cases the CO outows align with bright knots

of emission nebulae known as HerbigHaro HH ob jects which often exhibit large

prop er motions implying velo cities of km s away from the driving source see

references in Schwartz The similar morphology of these phenomena suggests

a common driving mechanism and invites a comparison of their physical attributes

Momentum comparison b etween jets and outows

An imp ortant physical measure of a jet or outow is the force or the rate at which

momentum is dep osited into the ow Usually the force F is expressed as the pro duct

of the mass loss rate m and the ow velo city v In the case of optical jets v can b e

determined from high resolution sp ectroscopy of the H line With H imaging one

can measure the length of the jet and compute a kinematic age t the dynamical

crossing timescale The electron density n can b e estimated from the intensity ratio

of forbidden lines such as the and lines of ionized sulfur Hartmann

Raymond Combining n with the linear dimensions of the jet leads to an

estimate of the mass m of ionized gas in the ow Combining these parameters yields

the outow force

mv mv mv

F mv

t r v r

In the case of molecular outows v can b e determined from CO sp ectra r from

the CO maps and m from the integrated CO emission Lada In the case

of L IRS the force observed in the optical jet Sarcander Neckel Elssser

is to orders of magnitude less than the force required to drive the molecular

outow MoriartySchieven Snell This result has b een typical of young

stellar ob jects the force exerted by the ionized gas of optical jets is ab out orders

of magnitude to o small to drive the molecular outows Mundt Brugel Bhrke

Consequently it was widely sp eculated that the two phenomena had separate

origins with the optical jet b eing driven by a collimated stellar wind while the larger

molecular outow was driven by a wideangle wind from the accretion disk Pudritz

Pudritz Norman

However the discrepancy in momenta of jets and outows has b een eased by the

discovery of two key facts First it was realized that the outows may b e much older

than previously assumed The typical kinematic age of molecular outows is yr

Masson Chernin However in a survey of a welldened sample of IRAS

sources from the Class I or Class I ID phase of lowmass young stellar ob jects as

dened by Adams Lada Shu out of emb edded IRAS p oint sources

contained outows Parker Padman Scott The combined duration of the

Class I and I ID phases is b elieved to b e yr Beichman et al Myers

et al Therefore the statistical lifetime of the outows is

numb er of sources with outows

yr yr

numb er of sources

A similar lifetime has b een derived by comparing the numb er of outow sources with

the numb er of opticallyidentied T Tauri stars in the nearby dark cloud L Fukui

Second calculations suggest that much of the optical jet material is

neutral gas Hartigan Morse Raymond Raga Binette Cant The

presence of neutral gas in jets has b een conrmed by the detection highvelo city HI

emission in the cm line from HH km s Lizano et al and L

km s Giovanardi et al The combination of these two facts can close

the gap in momentum b etween the two dierent phenomena Raga Padman

Richer For example it has b een observed that the HH jet may provide

sucient momentum to drive the surrounding CO outow in L Cernicharo

Reipurth Similar results are found in the red nebulous ob ject RNO Bence

Richer Padman Finally the fact that b oth jets and outows are high

velo city and highlycollimated structures p oints to a common driving and collimation

mechanism near the central source Masson Chernin They could well b e

dierent manifestations of the same phenomenon

Conservation of momentum in outows

One of the observational constraints on molecular outow mo dels is that they app ear

to b e driven by a pro cess that conserves linear momentum Because outows generally

exhibit strong bip olarity in b oth velo city and space the transverse velo city of material

must b e small compared to the radial velo city along the axis of the ow This feature

is a natural characteristic of a momentumdriven ow In contrast a pressuredriven

ow that conserves energy would tend to inate bubbles of ambient gas leading to

larger transverse velo cities than are observed MeyersRice Lada Such a ow

would also exhibit backward moving material in each lob e which is generally not seen

Furthermore such a ow cannot b e collimated by the ambient cloud without inducing

substantial transverse motion in the collimating mass Takano et al Thus

outows must b e driven in a momentumconserving manner by a bip olar collimated

wind at the central source Masson Chernin

Momentum transfer in jetdriven outows

In parallel with these new conclusions unied mo dels of jetdriven molecular outows

have b een develop ed Raga et al Raga Cabrit Masson Chernin

Chernin et al In general the mo dels must transfer momentum P from a

sup ersonic jet to the dense ambient gas that will comprise the molecular outow The

rate of momentum transfer can b e written

P mv m v

outow jet

where is the entrainment eciency which equals if the jet is completely stopp ed

by the ambient material The physical device used in the mo dels to accomplish the

momentum transfer from the jet to the outow is a b ow sho ck When a sup ersonic jet

impacts stationary gas the jet rapidly decelerates in a jet sho ck while the ambient gas

is accelerated by a forward b ow sho ck Blandford Rees Following Chernin

et al the rate of momentum transfer P at the working surface ws of a b ow

sho ck is

P A v v A v

jet ws jet ws BS jet jet

jet

where is the entrainment eciency of the b ow sho ck A is the geometrical area

BS jet

of the jet A is the geometrical area of the working surface of the b ow sho ck and

is the gas density in the jet One can solve this equation for in terms of the

jet BS

observable parameters

A v

ws ws

A v

jet jet

In the limit that all of the energy released in the b ow sho ck is immediately radiated

away there is no additional thermal pressure and the ram pressure in the jet equals

the ram pressure of the sweptup medium at the working surface of the b ow sho ck

m v m v

jet jet ambient ws

A v v A v

jet jet jet ws ambient ws

Using the quadratic formula one can solve for the velo city of the working surface

v v

ws jet

jet

where

ambient

jet

and

In this case the b ow sho ck entrainment eciency then b ecomes

Chernin et al have computed threedimensional smo othed particle hydro dy

namic simulations of jets in which the jet area and b ow sho ck areas are equal

and with several dierent values of density contrast and jet Mach numb er M

The jet radius was r cm and the sound sp eed in the jet was km s

jet

appropriate for ionized gas with T K from Eq These simulations show

that in the case of a high Mach numb er jet M v km s and

the jet is not decelerated signicantly until it reaches a radius of r or p c

jet

corresp onding to at a distance of kp c Ambient gas is entrained only at the

end of the jet a pro cess called prompt entrainment DeYoung This pro cess

leads to a parab olicshap ed nebula with the vertex at the b ow sho ck and the curve

op ening toward the driving source However in a low Mach numb er jet M

v km s is a factor of a few smaller than and the jet is decelerated

by by the time it ows a distance r In this case called steadystate or

jet

turbulent entrainment the ambient gas is entrained essentially along the entire jet

Because the transverse motion of gas remains roughly constant this pro cess creates

a conical outow of increasing radius with distance

Comparison to observations

The detection of EHV features in outows is the most imp ortant piece of evidence for

jetdriven outows EHV gas requires that protostellar jets have high Mach numb ers

suggesting that prompt entrainment dominates the ow This pro cess can explain

the common observational nding that the highest velo city gas shows the highest

degree of collimation as in the outows of NGC FIR Richer Hills Padman

and NGCG Lada Fich A sp ecic numerical mo del of Chernin

et al with high Mach numb er and actually predicts the existence

of a small clump of gas M moving at km s in the p ostsho ck region

In this case implying that the momentum transfer is ecient

Another observational nding that may supp ort the b ow sho ck mo del is the frequent

presence of infrared reection nebulae near the origin of molecular outows Ho dapp

Hunter et al Although they may b e illuminated by radiation from young

stellar clusters these nebulae could also b e p owered in part by the co oling radiation

from b ow sho cks Testi et al

Even though the jetdriven outow mo del of Chernin et al is promising

it do es p ossess a few shortcomings First the mo del do es not treat the evolution of

the cavity region left b ehind by the outwardlymoving b owsho ck thus alone it may

not prop erly predict the app earance of older outows Raga et al prop ose

a similar jet mo del but with a large numb er of internal working surfaces along the

length of the jet that eject mass sideways to form a turbulent isothermal envelop e

of jet material mixed with entrained ambient gas This envelop e can then rell the

trailing cavity left by the b owsho cks and preserve the continuous app earance of the

molecular outow Evidence for this scenario comes from the morphology of the near

infrared vibrationallyexcited H line emission which traces hot gas T & K

Frequently as in NGC Garden Russell Burton and IRAS

Bachiller et al the hot H gas lies in a collimated structure along the axis of

the ow tracing the turbulent interface where kinetic energy from the jet heats the

molecular cloud

A shortcoming ascrib ed to jetdriven outow mo dels in general is that they cannot

explain the existence of p o orlycollimated HH ows Numerical simulations show that

sup ersonic jets develop a radiativelyco oling dense shell of gas b etween the jet sho ck

and the leading b ow sho ck which may b e the source of the optical emission from HH

ob jects Blondin Knigl Fryxell Wolre Knigl But in L the

ob jects HH and HH lie far from the outow axis emanating from IRS yet they

b oth have high prop er motions and radial velo cities Davis et al Also rather

than tracing the jet the H emission extends over most of the H cavity which co

incides with the blue CO outow lob e These phenomena suggest a wideangle wind

from the central source Snell Loren Plamb eck however they could con

ceivably b e explained by wandering of the central jet Recent observations of RNO

show unambiguous evidence for jet wandering in the form of pairs of symmetric HH

ob jects lying at various p osition angles within the total op ening angle of the outow

Bence Richer Padman This evidence supp orts an app ealing idea that the

various morphologies of molecular outows simply represent the integrated eect of

a wandering central jet over a long timescale

Possible mechanisms of jetdriven outows

Radiation pressure

If molecular outows are driven by stellar jets then what is the ultimate driving mech

anism of the jet Assuming a central star has already formed one obvious mechanism

for a momentumconserving outow is radiation pressure on the surrounding dust en

velop e The radiation pressure from a star of luminosity L has the p otential of driving

a mass outow M at velo city V r

L L

MV r r P M km s yr

rad

c L

where is an eciency factor amounting to some measure of the optical depth of dust

in the envelop e with corresp onding to the opticallythick case Knapp et al

Radiation pressure acts primarily on the dust comp onent rather than the gas

b ecause the mass absorption co ecient of the dust is much higher than that

dust

of the gas For example in ionized gas a ma jor comp onent of the continuum

gas

opacity comes from Thomson scattering o the free electrons giving a mass absorption

co ecient

cm g

gas

where is the Thomson cross section Rybicki Lightman For dust the

mass absorption co ecient from the geometric cross section is

gr gr

cm g

dust

m r m

gr gr

gas

assuming spherical grains with density g cm and a gas to dust mass ratio

R However the gas mixed with the dust will presumably acquire a similar

outow motion through collisions with grains Shull The timescale for collision

t of a gas particle with a grain Goldreich Kwan in the high density coll

cm ionized gas near the star is

n m c

H H dust s

t n c c

coll dust gr s dust dust s

n R c r

H s gr

cm km s m

outow

Higher densities smaller grains and a smaller gas to dust mass ratio R will all lead

to a shorter collision timescale

Using Eq one can compare the observed values of the outow momentum

supply rate with the maximum amount available from radiation pressure In the case

of RNO the central source has a b olometric luminosity of L and the momentum

ux in the outow is M km s yr Bence Richer Padman

This value is orders of magnitude larger than radiation pressure can supply This

discrepancy is typical of outows from lowmass stars Lada Mozurkewich

Schwartz Smith and remains signicant even with a factor of correction

for the outow age as discussed in section Empirically the mass loss rate

of outows scales as M L over the range of to L Levreault

Thus the large discrepancy b etween radiation pressure and outow momentum ux

may disapp ear in suciently massive stars if the driving mechanism remains the

same This p ossibility must b e checked with observations of outows from highmass

stars In either case a dierent source of outow momentum must b e considered for

lowmass stellar outows

Disk winds

In order to explain the large observed values of momentum ux in outows theories

of particle winds from accretion disks have b een develop ed The formation of disks

around protostars has b een shown to b e inevitable b ecause the excess of angular

momentum in a typical molecular core over that of a premain sequence star leads to

a nonradial collapse Tereb ey Shu Cassen Boss Recently elongated

disks of radius AU p erp endicular to the outow axes in L IRS and HL Tau

have b een resolved in submillimeter continuum with the CSOJCMT interferometer

Lay et al Presumably accretion pro cesses in the disk allow mass to move

inward and angular momentum to move outward Pringle Ejection of this

angular momentum is a p ossible source of jets and molecular outows however a

plausible mechanism requires b oth strong magnetic elds and rapid rotation Shu et

al Shu et al The basic mo del of a magneto centrifugally driven ow

provides for a wind of magnitude M

M f M

w d

where M is the accretion rate and f is an eciency factor related to the angular

momentum of the inowing and outowing matter Na jita Shu The wind

presumably emerges at the radius where the gravitational and centrifugal accelera

tions balance the socalled X p oint For this reason the wind is referred to as an

X wind with a linear velo city V of the same order of magnitude as the angular

velo city in the plane of the disk

V GM

R R

V R

X X X

For a M protostar if R R then V km s typical of HH jet

X X

velo cities The resulting momentum supply rate to the wind can b e estimated by

assuming the accretion pro cess takes place during the typical outow timescale

M V f M V

w X d X

M R t

X acc

f M yr km s

M yr R

This value is sucient to drive the observed outow in RNO with values of f

The luminosity carried by the wind will consist of two parts one comp onent carried

by the gas and the other carried by the magnetic eld The upp er limit to the wind

luminosity can b e expressed simply as the energy released during accretion

GM M M R M

d d X

L . L

R M M yr R

Clearly in the case of lowmass stars the wind luminosity has the p otential to

greatly exceed the radiative luminosity of the central star However in the case

of a M Ostar accreting at a rate of M yr the limiting wind luminos

ity is L which is only comparable to or less than the stellar luminosity Because

the wind will pro ceed into a jetdriven outow in a momentumconserving fashion

much of this luminosity will b e reradiated at sho cks Draine McKee Nev

ertheless this calculation parallels the prediction given in the previous section that

radiation pressure will eventually dominate over an accretion disk wind in the most

luminous stars

Outows from highmass starforming regions

All of the sp ecic outow sources discussed in the previous section are examples from

lowmass starforming regions Outows are known to exist in highmass starforming

regions and generally have signicantly larger mass ow rates and momenta How

ever there is insucient evidence to conclude that the nature of the outow driving

mechanism is the same as in lowmass outows One reason for this uncertainty is

that far fewer massive outows have b een studied at comparable spatial resolution

due to their larger distance Also the co eval formation of lowmass stars with high

mass stars will likely lead to a confusing cluster of outows present simultaneously

in the host molecular cloud The typical result that highmass outows app ear less

collimated than their lowmass counterparts may b e due to a simple sup erp osition

of ows A dedicated singledish search for highvelo city CO emission from UCHI I

regions has recently b een completed with a success rate Shepherd Church

well a Further singledish mapping and interferometric imaging is needed to

determine if this CO emission is bip olar and if it corresp onds to outows from the

UCHI I regions or from younger nearby sources Analogous to the prior studies of low

mass outows a comparison of the dynamical and statistical ages of these outows

should also b e made In the following sections results derived from the observation

of outows toward UCHI I regions are presented followed by a discussion of their

implications

CO sp ectra

Prior to the installation of SHARC at CSO I p erformed a search for molecular out

ows from UCHI I regions in transitions of CO Most of the sources mapp ed

were also imaged with SHARC including KAC WOH G

G G G G G G

and the S complex The outow maps of G and G are

presented separately in Chapter Outow maps already exist in the literature

for GGD Little Heaton Dent and Mono ceros R Wolf Lada

Bally Other sources not imaged with SHARC were mapp ed in CO includ

ing G G G and the Cepheus A complex All of the

sources studied in this survey were found to exhibit mo derate to high velo city CO

emission A mosaic of the CO sp ectra recorded at the central p osition of each source

dened by the UCHI I region are shown in Fig In all cases a designated refer

ence p osition was used typically ab out away to avoid contamination of the prole

from the host giant molecular cloud GMC Constant or linear baselines have b een

subtracted to set the continuum level to zero Many of the sp ectra contain dips near

the LSR velo city of the molecular cloud which can b e attributed to selfabsorption of

the line radiation by co ol molecules on the front side of the GMC Another common

feature is a shoulder of emission adjacent to the line p eak on either the redshifted or

blueshifted side

Figure CO sp ectra of the outows mapp ed at the CSO The horizontal scale

is LSR velo city in units of km s and the vertical scale is main b eam brightness

temp erature in Kelvins

CO outow maps

The pro cedure of sp ectral line OntheFly OTF mapping employed at CSO is similar

to continuum OTF mapping discussed in section The three main dierences

are the secondary mirror do es not chop during the scanning of the rows

reference p osition integrations are acquired b etween row scans and scans are made

in celestial co ordinates The absolute p ointing accuracy is generally The CSO

b eamsize in the transition is and in the transition is Contour

maps of the redshifted and blueshifted CO wings are presented in this section along

with a brief description of the results on each source All maps are given in B

celestial co ordinates

Two compact outows have b een detected in the K region Fig A faint

outow app ears to originate from the UCHI I region C The outow is barely

resolved into an eastwest direction which is p erp endicular to the direction of the dust

ridge Fig A second more luminous outow lies near the UCHI I region A

Although only marginally resolved the bip olarity in the CO matches that of the radio

recombination line outow DePree et al However the origin of the outow

is displaced ab out to the east of the UCHI I region and the bip olarity of the

highvelo city molecular gas disagrees with older Kitt Peak m CO maps Phillips

Mampaso These facts prompted a followup map at higher frequency to

obtain higher angular resolution

Figure CO J map of the K complex Blueshifted emission to

km s is shown in solid contours and redshifted emission to km s is

shown in dashed contours Levels are and

K km s Triangles mark the p ositions of the UCHI I regions DePree et al

and straight lines indicate the suggested outow axes

In this resolution map of KA Fig the northsouth bip olarity is

conrmed as well as the oset of the ow axis from the p osition of the UCHI I region

A The magnitude of the oset is ab out p c which equals the absolute p ointing

accuracy From this map the driving source of the outow is consistent with KA

but the fact that b oth maps show a consistent oset suggests that the outow may

originate from a separate emb edded source The redshifted lob e seems to indicate a

broad conical op ening angle

Figure CO J map of KA Blueshifted emission to km s is

shown in solid contours and redshifted emission to km s is shown in dashed

contours Levels are to by K km s The triangle marks the p osition of

the UCHI I region DePree et al and the straight line indicates the estimated

outow axis identical to the line in Fig

WOH

As shown in Fig the high velo city CO emission toward WOH is complex

There are two directions of bip olarity evident in the map a northeastsouthwest

outow that lies parallel to the NH and m lament Fig and a p ossible

eastwest outow north of the core With the p ointing uncertainty the northeast

southwest outow could originate from either UCHI I region or the TW ob ject

Figure CO J map of WOH Blueshifted emission to km s

is shown in solid contours and redshifted emission to km s is shown in

dashed contours Levels are to by K km s Two suggested axis of outow

are indicated by straight lines

As seen in Fig a prominent eastwest outow originates from within of the

UCHI I region G Also a fainter more extended northsouth outow

app ears to originate from the adjacent radio source G As shown in

Fig a dust core envelop es G It is interesting that the bright

source with the more compact outow is asso ciated with the strong dust emission

while the extended outow source is not suggesting that the dust source is younger

Figure CO J map of the G Blueshifted emission to

km s is shown in solid contours and redshifted emission to km s

is shown in dashed contours Levels are to by K km s Triangles mark

the p ositions of the radio sources G to the east G at the

center Kurtz Churchwell Wo o d The lines suggest outow axes from each source

In the CO J map of G Fig we see why the outow was

originally classied as a wide lowcollimated outow Gmez et al However

in this map the multiple p eaks in the lob es suggest overlapping outows from a

cluster of young stars as is seen in IRAS Bachiller Fuente Tafalla

One outow app ears to originate from the main UCHI I region while another

outow may emerge from an unknown source ab out p c to the east Higher

resolution imaging is necessary to disentangle the emission

Figure CO J map of G Blueshifted emission to

km s is shown in solid contours and redshifted emission to km s is

shown in dashed contours Contour levels are to by K km s The triangles

mark the p osition of the two UCHI I regions Kurtz Churchwell Wo o d The

cross marks the H O maser Torrelles et al asso ciated with the infrared source

WK Weintraub Kastner

In Fig a prominent outow is resolved toward G In the lowest

contours there is marginal evidence for a second outow axis The UCHI I region lies

within p c of the central p oint of b oth axes Interferometric observations

will b e necessary to conrm the UCHI I region as the driving source of one or b oth

outows

Figure CO J map of UCHI I region G indicated by the triangle

McCutcheon et al Blueshifted emission to km s is shown in solid

contours and redshifted emission to km s is shown in dashed contours

Contour levels are to by K km s Straight lines suggest the axes of the main

outow and a p ossible second outow

G Complex ON

As shown in Fig two strong compact outows are detected in the ON region

One outow is lo cated p c northeast of the UCHI I region G

Higher resolution BIMA observations show this region to b e comp osed of multiple

outows Shepherd Churchwell b A second outow is asso ciated with the

H O masersubmillimeter continuum source G see Fig and shows

an extended tail of blueshifted emission to the southwest

Figure CO J map of the G complex Blueshifted emission

to km s is shown in solid contours and redshifted emission to km s is

shown in dashed contours Levels are to by K km s The triangle marks the

UCHI I region G Wo o d Churchwell and the crosses mark H O

maser p ositions Hofner a

Lying ab out p c north of G the extended HI I region G

also exhibits an outow consistent with b eing centered on the p eak radio p osition An

additional redshifted lob e crosses the region with a faint blueshifted counterpart sug

gesting a second outow originating from a source p c east of the UCHI I

region

Figure CO J map of G Blueshifted emission is shown in solid

contours and redshifted emission is shown in dashed contours Levels are to

by K km s The triangle marks the p eak p osition of the HI I region Wo o d

Churchwell

S Complex

As shown in Fig the high velo city CO emission is complex in the S region

Though displaced ab out p c southwest from the origin the westernmost

UCHI I region of SFIR triplet lies on the outow axis generated by connecting

the p eak p osition of the redshifted lob e with the lower contour ridge of the blueshifted

lob e Another outow lies b etween SFIR and G and may b e driven

by the faint submillimeter continuum source detected there in the SHARC image see

Fig

Figure CO J map of the S complex Blueshifted emission to

km s is shown in solid contours and redshifted emission to km s is

shown in dashed contours Contour levels are to by K km s Triangles

mark UCHI I regions Snell Bally and lines mark two suggested outow axes

In Fig the high velo city CO emission shows compact lo cal maxima at the

p osition of the cometary UCHI I region G comp onent A The blueshifted

lob e shows an extended tail in the general direction of the radio tail Diuse emission

contaminates the redshifted lob e to the north and east

Figure CO J map of G Blueshifted emission to km s

is shown in solid contours and redshifted emission to km s is shown in

dashed contours Levels are to by K km s The letters mark the p osition of

the UCHI I regions from Wo o d Churchwell

As seen in Fig extended emission dominates the high velo city channels toward

G The p eak in the blueshifted wing o ccurs within of the UCHI I region

but there is no clear evidence for a bip olar outow

Figure CO J map of G Blueshifted emission is shown in solid

contours and redshifted emission is shown in dashed contours Contour levels are

to by K km s

Although not imaged with SHARC G is an interesting UCHI I region near

the O V star Herschel Her lo cated west of the Hourglass Nebula in M At

a distance of kp c Georgelin Georgelin a AU jet from Her

has b een detected in K band with a groundbased adaptive optics camera and in H

with the Hubble Space Telescop e Planetary Camera Steckum et al The jet

p oints toward the UCHI I region lo cated ab out p c to the southeast Wo o d

Churchwell Evidence for a corresp onding molecular outow is shown in

Fig However although the blueshifted CO lob e extends along the extrap olated

direction of the jet it is oset from Her and the UCHI I region while the redshifted

lob e b ends northeast Thus this outow is probably driven by a dierent source in

the core ab out p c northeast of the UCHI I region and Her

Figure CO J map of G indicated by the triangle Wo o d

Churchwell Blueshifted emission to km s is shown in solid contours

and redshifted emission to km s is shown in dashed contours Levels are

to by K km s

Cepheus A G I

The Cepheus A complex was not imaged with SHARC as it has b een mapp ed in the

past at wavelengths of and m at JCMT MoriartySchieven Snell Hughes

Emb edded in the dust core lie discrete radio continuum sources Hughes

Wouterlo ot Hughes Cohen Garrington one of which HW is a

p owerful thermal radio jet Ro drguez et al Surrounding the jet origin

H O maser sp ots have b een resolved spatially and kinematically into a disklike

structure Torrelles et al Clusters of H O and OH masers also coincide with

several of the other UCHI I regions Cohen Rowland Blair Lada et al

and the H O masers show rapid variability Mattila et al Maser emission

in the GHz transition of H O has also b een detected Cernicharo et al

Lying adjacent to the Cep OB asso ciation at a distance of kp c Blauuw

Cepheus A was the rst source after Orion to exhibit high velo city CO emission

Ho Moran Ro drguez Further observations led to the suggestion that

the outow was quadrup olar Torrelles et al Shown in Fig is a CSO

map of the region clearly showing two distinct outows an extended northsouth

outow and a compact eastwest outow with dierent origins The submillimeter

dust emission is closely asso ciated with the origin of the compact outow However

neither outow origin cannot b e uniquely identied with any particular compact radio

comp onent Rather the radio sources seem to lie along ridges of the CO gas For

example the four radio sources abcd lying in a line to the southeast align with

a faint arm of redshifted CO J emission This arm also passes through the

central cluster of radio sources and With VLA maps separated by a

year baseline a tentative outward eastsoutheasterly prop er motion of km s

has b een rep orted in comp onent c consistent with the typical velo cities of HH jets

Hughes The bip olar CO emission coincides with an H S emission

nebula Hoare Garrington and a bip olar NH structure Torrelles et al

Gsten Chini Neckel These ndings supp ort the jetdriven outow mo del

as the CO emission is likely tracing the warm entrained gas surrounding the jet

b ow sho cks much like vibrationallyexcited H line emission is b elieved to do

Figure Left panel CO J map of the CepheusA complex Blueshifted

emission to km s is shown in solid contours and redshifted emission to

km s is shown in dashed contours Contour levels are to by K km s

Triangles mark the p osition of compact radio continuum comp onents Hughes

Wouterlo ot Hughes Cohen Garrington Right panel CO J map

of the central region Blueshifted emission to km s and redshifted emission

to km s contour levels are to by K km s

G G GAB

Shown in Fig is a map that covers the two UCHI I regions of G and

G which lie at a distance of kp c Kuchar Bania Unresolved

at radio wavelengths the UCHI I region G lies ab out southwest of the

center of what app ears to b e a compact outow The origin of this outow coincides

with a faint clump of SiO emission imaged by Wilner Ho Zhang so p erhaps

it traces a young emb edded source From interferometric imaging of the HCO

J and SiO J transitions these authors found no evidence of spherical

collapse in the UCHI I region The sp ectral index of the centimeter radio emission

suggests that it may b e a partially ionized stellar wind The cometary UCHI I

region G coincides with the p eak blueshifted CO emission However it is

dicult to discern additional bip olar outows in this complex

Figure CO J map of the UCHI I regions G and G

marked by triangles from left to right Wo o d Churchwell Blueshifted emis

sion to km s is shown in solid contours and redshifted emission to

km s is shown in dashed contours Contour levels are to by K km s

Calculation of outow energetics

From maps presented in the previous section the energetics of the outows can b e

calculated The outow radius pro jected on the sky r D combined with the

o o

observed velo city b can b e used to compute the observed dynamical timescale t

o o

r D

o o

v v

o o

The intrinsic dynamical timescale of the outow is related to the observed value via

the inclination angle i of the ow via the trigonometric relation

t t cot i cot i

Unfortunately since prop er motions of molecular outows are to o small to detect i is

a dicult parameter to measure For an outow with i the observed timescale

equals the intrinsic timescale so this value is conveniently assumed when no other

information is available

With some basic assumptions including lo cal thermo dynamic equilibrium the

integrated ux of the line emission from a linear rigid rotor molecule can b e converted

into a column density of molecules within the solid angle of the telescop e b eam

Following App endix A of Garden et al the column density can b e expressed

as follows

k f T hB k exp hB J J k T

ex l l ex

dv N

B J exp h k T

l ex

where B and are the rotational constant and p ermanent dip ole moment of the

molecule J is the rotational quantum numb er of the lower state of the observed

transition T is the excitation temp erature of the molecule and f is the b eam

lling factor of the source For CO Debye esu cm and

B GHz Townes Schawlow The antenna temp erature T recorded a

on the source is related to f and the microwave background temp erature T by the

following formula

T f h

exp

k exp h k T exp h k T

MB ex bg

where is the main b eam eciency of the telescop e Combining these two equa

tions reduced formulas for the lowest four rotational transitions of CO are listed

b elow

T T

ex v

N dv cm

exp

T T

v ex

dv cm N

exp

T T

v ex

dv cm N

exp

T T

v ex

dv cm N

exp

where v is in units of km s From the column density of CO the mass of H gas in

a cloud of angular size at distance D is simply

H H

M M D N d

H CO CO

CO CO

where d is the telescop e b eamsize and the factor H CO is an empirical abundance

ratio Blake et al With a measurement of the gas mass one can compute

the momentum P and the energy E of the outow

P mv

cos i

m v mv

cos i

Knowing the age of the outow the mass outow rate m the momentum supply

rate or force required to drive the ow P and the mechanical luminosity L

mech

can also b e computed If the age of the outow t is taken as the dynamical timescale

then

m mv tan i

t r

m sin i v mv

P mv

t cos i r

v m sin i E

L E

mech

t r cos i

In reality gas molecules with a range of v contribute to the sp ectral line prole

For this reason the integrals over velo city and solid angle must b e shifted from the

column density equations to the momentum and energy equations These

equations are numerically integrated over a sp ecied velo city range to compute the

total value of each parameter Selecting the velo city range is inevitably an arbitrary

pro cedure in which one tries to avoid including emission from the line center b ecause

it primarily traces the large mass of ambient gas unasso ciated with the outow This

selection can b e a signicant source of error in the outow mass Masson Chernin

Fortunately it is less of a concern to the velo cityweighted parameters in which

the highvelo city emission contributes more heavily to the integral As another source

of p otential error the fact that statistical lifetimes of molecular outows may b e up

to a factor of longer than the dynamical timescales Parker Padman Scott

will cause all of the computed parameters that include the age m P L to b e

mech

overestimates Fortunately the momentum and energy values are unaected by this

uncertainty as they simply reect the observed state of the gas

A computer program was written to p erform the prop er numerical integration of

these equations over a given velo city range from a CO data cub e input as a set of

les in tabular format To b e exible the program accepts a set of inputs including

the sp ecic CO transition and isotop omer observed Other required inputs are the

source distance gas excitation temp erature generally taken from the p eak CO

brightness temp erature the velo city limits of the outow and estimates of the optical

depth and inclination angle of the ow The format of the input le is sp ecied in

App endix C The results of the program for the observed outows are presented in

Table In order to ensure consistent measurements the outow angular size is

dened as half the angle along the outow axis b etween the outer halfp ower CO

contours in the red and blueshifted lob es In all cases an intermediate inclination

angle of has b een assumed Thus the length l rep orted in column of

Table is the source distance times the computed halflength depro jected to this

inclination angle Because highsensitivity maps of the less abundant sp ecies CO

are not available to estimate the optical depth the highvelo city gas is assumed to

b e optically thin

The average dynamical timescale of these outows is yr which roughly

matches the statistical age of outows from lowmass stars Parker Padman Scott

Also this timescale is a factor of greater than the statistical lifetime of UCHI I

regions Comern Torra Apparently the typical outow b egins b efore the

star develops a signicant ionized region This nding supp orts an accretiondisk

winddriven outow rather than an outow driven purely by radiation pressure at

least in the early stages of accretion G WOH G SFIR GS G G CepheusA CepheusA G G KC KA G G G G G source Outo w NS EW pc kp D v lsr T able v blue km s Observ v red ed M and m computed km v s M parameters P km s log L E yr of i olar bip M log km P yr s outo l c p ws log yr t log L L mec h log M yr

Scaling relations

From the data in Table one can search for correlations in the outow parameters

that scale with the luminosity of the driving source Fig shows that the outow

mechanical luminosity scales with the p ower of the b olometric luminosity

where the quoted uncertainty is computed assuming that the data on b oth axes

are random variables with error Clearly only a small fraction of the

total luminosity is ultimately converted into mechanical motion of the molecular gas

Both of these results are consistent with the outows measured from lower luminosity

premain sequence stars also plotted Levreault

Figure The mechanical luminosity of the outow is plotted against the b olo

metric luminosity of the driving source Solid squares UCHI I regions Open squares

premain sequence stars from Levreault where the triangle represents T Tau

The linear function with the b est t to all of the data is plotted solid line along

with the ultimate limit from the law of conservation of energy in which the two lu

minosities are equal dashed line The larger value for G comes from the

CO map presented in Chapter

Shown in Fig the momentum supply rate required to drive the UCHI I out

ows scales with the p ower of the central source luminosity Also plotted

are outows from lower luminosity L L sources from the Levreault

survey which clearly cannot b e driven by radiation pressure alone However in the

case of the highest luminosity sources the UCHI I regions the momentum supply

rate available from radiation pressure b ecomes sucient to drive the outows This

crossing p oint reects the simple theoretical predictions made in sections that

radiation pressure from the central star rivals the maximum momentum supplied by

the accretion disk wind The fact that Orion IRc lies so far ab ove the curve suggests

that it is a sp ecial case or simply that it is near enough to prop erly resolve all of the

outowing gas Indeed when the correction is made for the signicant optical depth

in the wings of the CO transition see Chapter the force required to drive

the G outows compares well with Orion IRc Further study of CO

in UCHI I region outows will b e necessary to determine if all of the mass estimates

should raised by a similar factor

Figure The momentum supply rate force required to drive the outows is

plotted against the b olometric luminosity of the central source Solid squares UCHI I

regions from this work Open squares premain sequence stars from Levreault

where the triangle represents T Tau The solid line is the linear function with the

b est t to the UCHI I regions and the dashdot line is the b est t to all the data The

dashed line is the total momentum available from the radiation eld and the dotted

line is the reduced momentum available to a jetdriven outow with a b ow sho ck

conversion eciency of The larger value for G comes from the CO

map presented in Chapter

For UCHI I regions the mass outow rate of the molecular gas scales with the

p ower of the central source luminosity as shown by the solid line in

Fig Combining these data with those of Levreault the scaling b ecomes

over the luminosity range from to L The extent of the correlation

from sources of to over L sp eaks p owerfully for a common underlying outow

mechanism

Figure The mass outow rate plotted against the b olometric luminosity of the

driving source Solid squares UCHI I regions from this work Open squares premain

sequence stars triangle T Tau from Levreault The linear functions with

the b est t to the UCHI I regions solid line and to the combined data set dashed

line are included The larger value for G comes from the CO map

presented in Chapter

Summary

Of the UCHI I regions mapp ed show evidence for bip olar outows in the form

of a spatial oset b etween the redshifted and blueshifted emission centered ab out a

p osition within of the p eak radio p osition The other two regions also show high

velo city CO emission but with a nonbip olar distribution The mass outow rate

and mechanical luminosity of the outows b oth scale with the b olometric luminosity

of the central source The agreement of the scaling across the full range of proto

stellar luminosities suggests a common driving mechanism In contrast to outows

from lowmass stars radiation pressure cannot b e ruled out as the ultimate source

of momentum for the molecular outows from the UCHI I regions presented here

Because stellar luminosities scale steeply with stellar mass the momentum available

from the radiation pressure of an Ostar rivals that from the accretion disk wind

mo dels develop ed to explain jetdriven outows from lowmass stars

Much like the submillimeter continuum images presented in Chapter many of

the highvelo city molecular line maps of UCHI I regions show evidence for multiple

sources In G two distinct outows can b e identied with two indi

vidual radio sources In the G complex and the S complex individual

outows are seen toward a known radio source and toward an adjacent radioquiet

submillimeter source In nearly all cases the outow sources coincide with areas of

strong dust emission However in several cases including G G

and KA the origin of the outow is displaced by or more from the UCHI I

region suggesting a separate driving source When multiple outows are present

as in CepheusA G and K the most compact outow lies closest

to the center of the dust core consistent with the idea that the youngest outows

emerge from the most deeply emb edded sources

The results presented in this chapter parallel the growing literature on multi

ple outows in starforming regions Some examples include IRAS

Bachiller Fuente Tafalla AFGL Hunter et al and DR

Garden et al all of which lie within kp c of the Sun Due to their larger dis

tances many of these individual outows tentatively identied here with the UCHI I

regions may consist of further multiplicity like that seen in the striking dual outow

from the nearby Cepheus A core Thus to explore this p ossibility and to complete

the research presented in this thesis Chapter presents a detailed highresolution

molecular line and continuum study of a complex region of outow asso ciated with

the UCHI I regions G and G

Chapter Active Star Formation toward the

G and G UCHI I Regions

Prologue Recently reviewed by a referee for The Astrophysical Journal the results

presented in this chapter have b een revised for publication under the authorship of

TR Hunter TG Phillips and KM Menten This pap er contains a detailed study of

bip olar outows from two UCHI I regions in a giant molecular cloud of high b olometric

luminosity L L at a distance of kp c

Abstract

A multiwavelength study of the molecular cores containing the ultracompact HI I

UCHI I regions G and G reveals a series of phenomenological

dierences that distinguish the age of these cores in terms of their development of

high mass star formation First we rep ort the discovery of massive bip olar molecular

outows from b oth UCHI I regions The G UCHI I region lies centered on

a spatially extended km s outow that we have mapp ed in the CO J

CO and C O transitions at the Caltech Submillimeter Ob

servatory CSO The broad bip olar structure is opticallythick in the CO line The

CO measurements imply a large outow mass of M of the total cloud

mass Interferometric observations with the Owens Valley Millimeter Array in the

CO line resolve the gas into at least two outows one of which emanates from

the Jy GHz source identied with the UCHI I region An additional outow is

driven by an adjacent young emb edded ob ject which contributes to the extended sub

millimeter continuum emission imaged with the CSO b olometer array camera Lying

in a separate core a few arcminutes away the G UCHI I region contains

H O masers and presents higher velo city km s yet more compact CO emis

sion An outow has b een detected in the CO transition along with a compact

submillimeter continuum source OVRO observations in the CS J transition

conrm a compact outow centered on the GHz continuum source toward which

infall is also seen in the form of redshifted absorption The multiple outows higher

CO antenna temp eratures more extended submillimeter and radio continuum emis

sion and lack of H O masers all distinguish the core containing G as a

more advanced site of massive star formation than the neighb oring core containing

Intro duction

The bright compact Galactic radio sources known as UCHI I regions are thought to

b e p owered by massive young stars still emb edded in their parent molecular cloud

Wo o d Churchwell Generally the large column densities of molecular gas

N cm toward these ob jects prohibit the optical identication of

their ionizing stars and hide the early stages of massive star formation Churchwell

Walmsley Wo o d While nearinfrared imaging provides a deep er view of the

young stars emb edded in the cloud sometimes in the form of reection nebulae eg

NGC FIR Mo ore Yamashita the study of the molecular gas and dust

surrounding UCHI I regions at submillimeter wavelengths oers the most direct to ol

for understanding the distribution and kinematics of the material from which stars

are forming in these regions

At some p oint during the accretion pro cess of a new star an outow phase b egins

which can manifest itself in various observational forms including H O masers Genzel

et al Reid et al Gwinn Moran Reid and bip olar molecular out

ows Lada Bachiller GmezGonzlez Tofani et al Although

most known bip olar molecular outows have b een observed in nearby lowmass star

forming regions Staude Elssser they have also b een detected from young

massive ob jects as well such as G Harvey Forveille DR Garden

et al and WN Hunter et al Bip olar outow has also b een seen in

radio recombination lines toward the UCHI I region KA DePree et al A

wider search for outows from massive protostars is b eing pursued to determine the

rate of o ccurrence of outow in highmass starforming regions Shepherd Church

well a In recent years multiple outows emanating from a protostellar clus

ter have b een identied in several starforming regions including IRAS

Bachiller Fuente Tafalla L Bachiller et al and AFGL

Hunter et al Given that the statistical ages of the oldest outows must b e

yr Parker Padman Scott it is reasonable to exp ect outows from sev

eral young emb edded sources to b e present simultaneously in an evolved starforming

cluster Outow surveys of highmass starforming regions should help determine the

ep o ch of the outow phase relative to the UCHI I phase of massive stars Also the

discovery of outows from UCHI I regions themselves are imp ortant for comparison of

their energetics to outows from lower mass ob jects in terms of theoretical jetdriven

mo dels Masson Chernin

Because most UCHI I regions lie at distances of several kiloparsecs past CO sur

veys have had insucient spatial resolution to identify distinct molecular outows

For this reason we have p erformed a higher resolution search for molecular

outows in the submillimeter CO transitions at the CSO Followup observations at

the OVRO millimeter array are b eing obtained to study sp ecic sources in greater

detail In this pap er we present a comprehensive picture including maps of molec

ular outows and submillimeter continuum emission from the cores containing the

luminous UCHI I regions G and G Shown in Fig is the

integrated CO emission from these two cores The most striking features of the

map are the sp okelike structures of gas that protrude from the northern core The

southern core app ears more compact Given their proximity in the plane of the sky

and similar LSR velo cities G and G probably lie at the same

distance kp c derived from recent HI absorption studies of G Kuchar

Bania The sp ectral typ es derived for the ionizing stars are O and O

and the farinfrared luminosities based on the IRAS uxes are and L

resp ectively Wo o d Churchwell

Nearinfrared photometry of G reveals a sp ectrum rising steeply with

increasing wavelength consistent with a deeply emb edded source emitting most of

Figure Contour map of the CO J transition observed with a b eam

with levels to by K km s The p ositions of the UCHI I regions are marked

by triangles Wo o d Churchwell Note the several sp okelike protrusions of

gas from the core containing the UCHI I region G

its energy at farinfrared wavelengths Chini Krgel Wargau Imaging of

the Br line reveals an ionized nebula extended to a scale of Lumsden Puxley

signicantly larger than the radio UCHI I region Multitransition CO and CS

observations imply large H column densities toward the G core N

cm Churchwell Walmsley Wo o d and NH observations indicate

a rotational temp erature of K Olmi Cesaroni Walmsley The millimeter

continuum ux of G rises with decreasing wavelength Jy at mm

in a b eam Wo o d et al Jy at mm in a b eam Wo o d Churchwell

Salter and Jy at mm in a b eam Chini et al consistent

with a mixture of freefree emission and dust emission Likewise the millimeter

continuum ux of G rises steeply from Jy at mm Jy at

mm Jy at mm and Jy at mm Sandell indicating a dust

core Both regions also exhibit broad nearinfrared Br and HeI lines suggestive of

outow motion Doherty et al

Despite their similarities at infrared through millimeter wavelengths these two

regions exhibit rather dierent radio prop erties thus they provide excellent targets

for comparative research The radio continuum emission from G app ears

spherical or unresolved while G app ears cometary Wo o d Church

well Both regions contain Typ e I OH masers Goss et al but only

G contains H O masers Genzel Downes which have b een re

solved into several spatial and velo city comp onents coincident with and adjacent to

the UCHI I region Hofner a G has not b een detected as an H O

maser source to a level of Jy Felli Churchwell Walmsley Cesaroni

These contrasting prop erties drive our interpretation of the extensive multi

wavelength observations presented here

Observations

Caltech Submillimeter Observatory

Our submillimeter observations were p erformed with the onthey mapping mo de

using the facility receivers and acoustooptical sp ectrometers AOS of the CSO A

summary of the sp ectroscopic observations of G and G is given

in Table All sp ectra were analyzed with the CLASS software package and are

molecular main map total time b eam AOS month of

Source transition b eam grid p er p oint eciency MHz observation

G CO ! sec March

CO ! sec July

C O ! sec July

CO ! sec April

CS ! sec April

CO ! sec May

G CO ! sec May

CO ! sec May

Table Summary of CSO sp ectroscopic observations of G

presented on a main b eam brightness temp erature T scale We estimate our

calibration to b e accurate to and our p ointing to

In Septemb er we obtained an onthey m continuum map of b oth

UCHI I regions using the CSO singlechannel b olometer equipp ed with a Win

ston cone Rep eated azimuth scans were spaced by in elevation the chopping

secondary frequency was Hz and the central frequency of the lter was GHz

Lis Carlstrom Extinction correction and calibration were based on frequent

observations of Saturn and Uranus at various airmasses The zenith optical depth in

the lter band was

In March we obtained onthey continuum maps of b oth sources at m

and of G at m using the new Submillimeter High Angular Resolution

Camera SHARC at the CSO SHARC contains a linear monolithic pixel b olome

ter array op erating at K Wang et al Illuminated directly by cold optics

The Caltech Submillimeter Observatory is funded by the National Science Foundation under

contract AST

the pixels subtend by on the sky for a total size of by Hunter Serabyn

Benford The array was aligned in elevation and scanned in azimuth at s

with a secondary throw of at Hz scans were obtained on each region

stepping by in elevation on each subsequent scan The relative gains of each pixel

were calibrated by rapid elevation scans of Jupiter The central frequencies of the

lters were and GHz for sources with F The maps were smo othed to

an eective angular resolution of The zenith optical depth at GHz was

as measured by the CSO tipping radiometer Because the submillimeter optical depth

was changing during the observations a direct measurement of the optical depth in

the observed lter band was not p ossible Instead the continuum ux was corrected

for atmospheric extinction using an estimate of the optical depth in the lter band

computed by scaling up the GHz optical depth measurements by a factor of

Absolute calibration is based on scans of IRC during the same night Sandell

and the p ointing accuracy is estimated to b e

Owens Valley Millimeter Array

A summary of the observations made with the sixelement OVRO Millimeter Array is

listed in Table The bright compact nature of the continuum sources asso ciated

with the UCHI I regions allowed us to p erform selfcalibration and apply the solu

tions to the sp ectralline data The rst few CLEAN comp onents of the continuum

source were used as an initial mo del for phase selfcalibration using the Difmap soft

ware package Shepherd Pearson Taylor After several iterations of phase

selfcalibration and further CLEANing the amplitude gains for each antenna of each

subarray were computed using GSCALE Finally the amplitude gains were allowed

to vary on slowly decreasing timescales over each track in an iterative phase and am

plitude selfcalibration pro cess Due to the signicant amount of extended emission

only a minimal amount of CLEANing was p erformed on the sp ectral line channels

Extended emission limits the noise achievable in most of the sp ectralline channel maps

Source G

Observing season Fall

Pointing centers and relative to

h m s

Transits observed

Total baselines

Phase calibrator

Primary b eam

Synthesized b eam PA

CO J bandwidthresolution km s km s

C O J bandwidthresolution km s km s

Continuum frequencybandwidth GHz GHz

Continuum sensitivity mJyb eam

Continuum dynamic range

Source G

Observing season Spring

h m s

Pointing center B

Transits observed

Total baselines

Phase calibrator

Primary b eam

Synthesized b eam PA

CS J bandwidthresolution km s km s

Continuum frequencybandwidth GHz GHz

Continuum sensitivity mJyb eam

Continuum dynamic range

Table Summary of OVRO observations of G

Molecular outows

CSO observations

CO and CS sp ectra

CSO sp ectra of the various CO transitions observed toward the central p ositions of

G and G are presented in Fig Both sources exhibit high

velo city emission in all of the lines signifying molecular outow In G

there is a rapid increase in brightness temp erature with CO transition Since all

of the CO transitions are signicantly extended on the scale of the b eamsize this

increase cannot b e due entirely to b eam lling factor eects and instead indicates

the presence of a hot core In contrast G shows very little increase in

brightness temp erature with CO transition level indicating co oler gas Also a steep

drop in emission from the three lower J CO lines o ccurs in G near

km s a km s redshift from the LSR velo city of the molecular cloud Cesaroni

et al No such drop is seen in the line suggesting that the feature is a

characteristic of only the co ol comp onent of the gas

Figure CSO sp ectra of several CO transitions observed toward the UCHI I

regions G and G calibrated on the main b eam brightness tem

p erature scale

Source v km s v km s T K I K km s

LSR MB CS

Table Observed prop erties of the CS J transition

Sp ectra of the CS J emission observed simultaneously with the CO J

toward b oth sources are shown in Fig G exhibits signicantly brighter

emission than G in this high densitytracing transition The line parame

ters are summarized in Table

Figure CSO sp ectra of the CS transition observed toward the UCHI I regions

G solid histogram and G dashed histogram calibrated on the

main b eam brightness temp erature scale

CO maps

We now compare the spatial app earance of the CO emission toward b oth sources

Shown in Fig are contour maps of the high velo city emission from G

in dierent isotopic transitions of CO J all at resolution The C O

map reveals a ridge of high column density gas that p eaks a few arc seconds northeast

of the UCHI I region In the two more abundant sp ecies a distinct northsouth oset

is present b etween the bulk of the redshifted and blueshifted emission Although the

p ositions of the redshifted and blueshifted CO lob es are roughly symmetric ab out the

UCHI I region the additional structure in each lob e indicates that the outow is not a

simple bip olar nebula Furthermore the resolution CO J map shown in

Fig suggests that the outow has a broad op ening angle and may not b e centered

on the UCHI I region

Figure Left panel Contour map of the CO J transition toward

G with the blueshifted emission to km s shown in solid con

tours to by K km s the redshifted emission to km s shown in

dashed contours and the radio p eak p osition indicated by a triangle Wo o d Church

well Center panel Same as a for CO contours to by K km s

Right panel Contour map of the integrated C O J emission contours to

by K km s

Figure Contour map of the CO J transition toward G with

blueshifted emission to km s shown in solid contours to by

K km s and redshifted emission to km s shown in dashed contours

to by K km s The triangle marks the p osition of the UCHI I region

Wo o d Churchwell

In the case of G the CO J map not shown revealed an unre

solved outow in the high velo city channels A higher resolution followup map

of the CO J transition is presented in Fig In contrast to G

the outow is barely resolved in this map with the axis along a p osition angle of

The UCHI I region coincides within of the outow origin consistent with

the absolute p ointing uncertainty of the map

Figure Contour map of the CO J transition toward G with

blueshifted emission to km s shown in solid contours and redshifted

emission to km s shown in dashed contours to by K km s

The triangle marks the p osition of the UCHI I region Wo o d Churchwell

Line T v l log t log M log M log M v log L log M v

exc m

M M

km km

p c yr M L M K

s yr yr s s

CO !

Table Prop erties of the G molecular outow

Outow prop erties

The mass momentum and energy contained in the molecular outows are computed

by integrating each sp ectrum channel by channel over the line wings to and

to km s with the appropriate LSR velo city moment jv v j applied

LS R

eg Garden et al To prop erly compute the mass the excitation temp erature

and the optical depth of the outowing gas must b e known The temp erature is

approximated by the p eak main b eam brightness temp erature of the CO transition

Regarding the optical depth it is a common practice to assume the highvelo city CO

gas to b e optically thin However in the case of G the outow app ears

prominently even in the less abundant CO transition To estimate the CO optical

depth the CO CO line ratio was computed at each p osition in the maps for

the redshifted and blueshifted wings separately The ratio varies b etween and

implying CO optical depths b etween and from the simple relation

T COT CO e where is the abundance ratio

MB MB

b etween CO and CO at a galacto centric distance of kp c from Wilson Ro o d

Using the appropriate factor from the optical depth at each map p osition

the column density measurements were increased accordingly in the calculation of

the outow parameters listed in the rst row of Table The most striking result

is the large outow mass of M making it one of the most massive protostellar

outows yet discovered

A separate estimate of the outow mass can b e made by assuming the highvelo city

CO gas is optically thin This assumption is consistent with the mo derate optical

depths derived for CO and the fact that the outow do es not app ear in the C O

transition The outow mass computed in this way for the CO line is M

ab out twice that computed from opticallythick CO transition We b elieve this

larger value to b e the most accurate measurement of the mass in the outow thus

surpassing even the DR outow Garden et al Because CO data are not

available in the higher transitions the values listed in rows and of Table are

computed for comparison under the opticallythin assumption likewise in Table

for the G outow

To measure the total molecular gas mass in the cloud we use the integrated ux

in the C O line The average C O column density over the map is cm

Using the conversion formula of Frerking Langer Wilson for dense cores

this value corresp onds to an average H column density of cm and hence

a total mass of M The fraction of the total cloud mass participating in the

outow is similar to the recently measured in the Mon R outow Tafalla

et al

Is there a precedent for such a massive bip olar outow To explore this question

we consider the mechanical luminosity and momentum input rate required of the

driving source These quantities require an estimate of the age of the outow a lower

limit to which is the dynamical timescale The dynamical timescale of the outow

is derived from the outow halflength half the distance b etween the halfp ower

contours at the two ends of the ow divided by the mean massweighted velo city

In this way the dynamical timescale refers to an inclination angle of The wind

mechanical luminosity of the outow L lies b elow the value predicted L

for a source of this b olometric luminosity based on the trend from lower luminosity

sources Levreault

L L

mech b ol

L L

b ol

Similarly the momentum input rate force required to drive the outow log M v

is within the range observed in outows from other sources with L L

Lada As in the case of lowmass protostellar outows Bally Lada

this momentum input rate is nearly an order of magnitude higher than that available

Line T v l log t log M log M log M v log L log M v

exc m

M M

km km

p c yr M L M K

s yr yr s s

CO !

Table Prop erties of the G molecular outow

in the radiation eld from the central source if one assumes single scattering

of photons from an O star on the basis of the the L b olometric luminosity

from the region Thompson Panagia

Another physical measure of an outow is its total kinetic energy Past work on

molecular outows has revealed a correlation b etween outow kinetic energy and the

mass of the driving source Levreault The slop e b of the correlation is a steep

function of mass b logM M If we extrap olate the trend the kinetic energy

of the G outow erg implies a central mass of M If we use

the largest slop e and oset allowed by the errors in the b estt line of Levreault the

implied mass can b e as low as M not unreasonable considering the b olometric

luminosity of the source Thus despite the large mass it app ears that the prop erties

of the G outow are by no means incongruent with other outows

OVRO interferometric observations

C O absorption toward G

The integrated C O ux from G is shown in Fig The ma jor

feature in this eld is gas seen in absorption against the UCHI I region The spatial

extent of the C O absorption feature matches well with the GHz continuum

source see Fig In addition faint emission lies northeast of the UCHI I region

matching the p osition of the C O core

CO emission toward G

Interferometric observations of G in the CO J transition with a

synthesized b eam are shown in channel maps in Fig These images provide

a more detailed picture of the complex distribution of outowing gas Since there

Figure Integrated ux of the C O J transition observed toward

G with a synthesized b eam of contours

to by mJyb eam with dashed contours representing negatives

The p osition of the GHz continuum source is indicated by the triangle

is much extended emission from this source in the CO transition the nearLSR

velo city channels suer from spatial ltering Thus only the channels from the line

wings are presented They are divided into four velo city regimes relative to the LSR

velo city km s In the upp er panels of Fig the lowvelo city redshifted

emission is plotted next to the highvelo city blueshifted emission A linear north

south structure app ears to b e symmetric ab out a p oint oset by from

the UCHI I region We interpret this structure as a bip olar outow from a separate

emb edded source which we designate G West The average LSR velo city

of these velo city ranges is km s blueshifted by km s from the bulk

of the cloud At b oth ends of the structure a small kink of emission extends out

symmetrically on opp osite sides of the main axis This feature along with the curved

app earance of the southern lob e suggests wandering of the outow direction The

lack of radio continuum emission at the p osition of G West in the maps of

Wo o d Churchwell suggests that the driving source of the outow is either a

younger massive star or a co oler lower mass star than that which p owers the UCHI I

region

In the lower panels of Fig the highvelo city redshifted emission is plotted

next to the lowvelo city blueshifted emission In this case the emission app ears to b e

mostly symmetric ab out the p osition of the UCHI I region as indicated by the conical

surface drawn on the map Therefore we identify this emission with an outow from

the star p owering the UCHI I region The average LSR velo city of these velo city

ranges is km s redshifted by km s from the bulk of the cloud

Estimates of the individual outow masses can b e made from the CO maps

Assuming the same excitation temp erature and abundance ratio noted in the previous

section we derive a conversion factor of M Jy km s for an opticallythin

source at a distance of kp c eg Snell et al By dening narrow b oxes

around the emission we carefully measured the integrated ux in each of the four

outow lob es app earing in Figure The results listed in Table indicate that we

have recovered only ab out of the outow emission in the interferometer maps

Nevertheless we can conclude that the two outows app ear to b e similar in mass

Source wing velo city range Integrated ux Mass

km s Jy km s M

G red

blue

total

G West red

blue

total

Total

Table Outow masses derived from the CO J maps

Figure Channel maps of the CO J transition Top left panel Low

velo city redshifted emission contours b egin at and increase by Jyb eam

with dashed contours representing negatives The triangle marks the UCHI I region

and the cross marks the susp ected origin of the outow from G West

The large b ounding circles mark the halfp ower primary b eam Top right panel

Same as left panel for the highvelo city blueshifted emission contours by

Jyb eam Bottom left panel Same as top panels for the highvelo city redshifted

emission contours by Jyb eam Bottom right panel Same as top panels

for the lowvelo city blueshifted emission contours by Jyb eam

Having seen the interferometer maps it is interesting to reexamine the single

dish data Channel maps of the CO J transition observed with resolution

are shown in Fig Also plotted are the two outow origins and axes identical to

those in Fig Many of the extended ridges in the map are aligned with the axes

consistent with the multiple outow interpretation

Figure Channel maps of the CO J transition with blueshifted emission

to km s shown in solid contours and redshifted emission to km s

shown in dashed contours to by K km s The UCHI I region G

is marked by the triangle and the second outow origin G West is marked

by the cross

The CS map shown in Fig traces the warm dense molecular core which

is elongated parallel to the separation of the two outow sources The UCHI I region

G lies closest to the p eak CS emission and may b e the main heating source

of the gas The other outow origin G West lies along the ridge near the

edge of the core

Figure Contour map of the integrated CO J transition with contour levels

to by km s The UCHI I region G is marked by the triangle and

the second outow origin G West is marked by the cross

CS emission toward G

The OVRO baselineaveraged sp ectrum of CS J toward G is shown

in Fig A broad blueshifted wing indicates molecular outow while a redshifted

absorption feature suggests infalling motion in the foreground gas

Figure The OVRO baselineaveraged sp ectrum of the CS J transition

observed toward G The amplitude unit is Janskys

Contour maps of the high velo city CS emission are shown in Fig The

spatial oset b etween the red and blueshifted emission matches the structure seen in

the CO J transition and provides further evidence for molecular outow from

the UCHI I region along a p osition angle of Redshifted absorption app ears

against the continuum source in the three channels covering to km s The

curved app earance of the lowest p ositive contours around the UCHI I region indicates

that some of the redshifted CS gas lies in front of the source and is infalling At this

spatial resolution the outow app ears to have a large op ening angle In contrast to

the outows toward G the high velo city gas is not very extended

The outow dynamical timescale is yr nearly an order of magnitude less than

the G outows Consequently the outow driving source of G

is likely to b e a younger ob ject than either G or G West

Interestingly the velo city pattern of the H O masers on a scale imaged at the

VLA Hofner a roughly matches the orientation and direction of the outow seen

here in thermal CO and CS molecular gas on a scale This agreement strongly

supp orts the theoretical ideas that a protostellar jet from a massive young star can

concurrently p ower H O masers Mac Low et al and drive a molecular outow

Masson Chernin In this case it app ears that the H O masers originate in

the warm dense gas lo cated in b etween the jet sho ck and the leading b ow sho ck

Blondin Knigl Fryxell interior to the brightest CS J emission

Figure Left panel redshifted km s emission of the CS J

transition observed with a synthesized b eam Contour levels are to

by Jy b eam dashed contours represent negative emission The outow

axis is plotted at a p osition angle of Right panel Same as the left panel for

the blueshifted km s emission

Continuum emission

CSO maps

Maps of the submillimeter continuum emission at and m are shown

in Fig Like the C O line the submillimeter continuum emission from

G p eaks a few arcseconds northeast of the UCHI I region In the m

map a ridge of emission extends to the southwest of the UCHI I region and con

tains the outow source G West identied in the OVRO maps adding

weight to our identication of the separate outow source G West To

ward G the submillimeter emission is compact and coincides with the

UCHI I region in agreement with the m ndings of Sandell

Figure Contour maps of the and m continuum emission of the

region Contour levels are to by Jy at m to by Jy at m and

to by Jy at m The UCHI I regions G and G are

marked by triangles and the outow source G West is marked by a cross

The integrated continuum uxes of b oth regions are listed in Table Combining

these uxes with the and m IRAS uxes and the mm ux Chini et al

a mo died Planck function of some nite optical depth can b e t to the sp ectral

energy distribution The three free parameters in the mo del are the dust temp erature

Source Frequency Integrated Flux Instrument

GHz Jy

G OVRO

CSO

SHARC

G OVRO

CSO

SHARC

Table Millimeter and submillimeter continuum uxes of G

T the grain emissivity index and optical depth at the reference wavelength

dust

of m The grain emissivity at m was matched to the value of Hildebrand

A summary of the b estt mo dels is listed in Table The mass estimate

from the dust M is remarkably consistent with that derived from the C O

emission

Source T K logM M logLL

dust m

Table Greyb o dy mo del parameters of G and G

millimeter OVRO maps

The GHz emission observed at OVRO is shown in Fig The only source

h m s

reliably detected in the eld is lo cated at

consistent with the radio p osition of the UCHI I region Wo o d Churchwell

The deconvolved size of a single twodimensional Gaussian t to this source is

at p osition angle The ma jor axis of the UCHI I emission is oriented roughly

p erp endicular to the bip olar molecular outow axis from the UCHI I region The

p eak intensity is Jyb eam and the integrated ux density is Jy Since the

integrated ux at GHz is Jy Wo o d Churchwell the sp ectral index

b etween and GHz is Extrap olation from the submillimeter sp ectral

index implies that Jy of the GHz ux is from opticallythin dust emission

Subtracting this dust emission from the GHz ux then implies that the sp ectral

Figure Contour map of the GHz continuum emission observed toward

G with a synthesized b eam Contour levels are

and mJyb eam with a p eak intensity of Jyb eam

The UCHI I region G is marked by the triangle and the outow source

G West is marked by the cross

index of the remaining emission b etween and GHz is reasonably consistent

with opticallythin freefree emission

No emission is seen at the susp ected p osition of the outow source G West

down to a level of mJy In the m map G West lies on the Jy

contour To estimate an upp er limit to the ux of a p oint source at this p osition an

elliptical Gaussian source was freelytted and removed from a subset of the m

image containing the emission around G The residual map contained a

p eak intensity of Jyb eam in a compact source essentially coincident with the

UCHI I region with a tail extending past the p osition of G West Based

on the mo del sp ectral energy distribution this limit corresp onds to an mJy dust

source at GHz Therefore we cannot detect the source at GHz with the

present data More sensitive ie higher dynamic range millimeter observations will

b e necessary

The GHz map of G is presented in Fig The p eak intensity of

the central source is Jy b eam and the integrated ux density is Jy The

h m s

tted p osition of a single Gaussian mo del is

with a deconvolved source size of at p osition angle In this case the

ma jor axis is away from the axis of the CS molecular outow Extrap olation

from the submillimeter sp ectral index implies that Jy of the GHz ux is from

opticallythin dust emission Subtracting this ux yields Jy of freefree emission

and a sp ectral index of b etween GHz and GHz Wo o d et al Compared

to G the continuum emission is three times more compact The contrast

in sizes presents another piece of evidence that G is a younger source whose

central star is just b eginning to ionize the molecular gas and heat the surrounding

dust envelop e

Discussion

The nature of the multiple outows of G

In G the single dish and interferometer data show evidence for at least two

separate bip olar outows The total mass swept up by these outows is quite large

M M and their dynamical timescale is rather long at yr The age

of the outows may b e even older than the dynamical timescale as rapid deceleration

of the outow may o ccur during the sweepingup pro cess of ambient gas Masson

Chernin In fact the absence of H O masers in the G cloud core

suggests that b oth of the outow sources have evolved b eyond the H O maser phase

Figure Contour map of the GHz continuum emission observed toward

G with a synthesized b eam Contour levels are

and mJyb eam with a p eak intensity of mJyb eam

Statistical studies of masers toward HI I regions indicate that H O masers are much

more common during the earliest phases of formation of an HI I region Co della et

al and last p erhaps a few yr Co della Felli Natale Because

neither of the driving sources is lo cated exactly on the highest column density of the

O core there seems to exist additional material for future star formation dustC

there The CS linewidth at the core of G is km s implying

a virial mass of only M within a b eam Since the virial mass falls a factor

of short of the total gas mass computed from the submillimeter dust and C O

measurements the molecular cloud is not suciently supp orted against further

collapse The UCHI I region and the outow source G West may represent

the result of the rst ma jor burst of star formation in this molecular cloud

From the agreement of the outow energetics with trends from lower mass exam

ples we can conclude that these outows dier only in scale from lower mass outows

and likely share the same driving mechanism at the central star Recently theories of

jetdriven molecular outows Masson Chernin Raga et al have b een

put forth to unify the observed phenomena of stellar jets and molecular outows

as manifestations of the same ow seen over dierent length scales and integrated

over dierent timescales As high mass analogues of low mass outows the outows

of G and other massive sources like G and G Shepherd

Churchwell a indicate that these unied theories may apply over the entire mass

range of protostellar outows

Age contrast b etween G and G

In G b oth the CO and the CS maps indicate bip olar out

ow from the UCHI I region The lower antenna temp eratures from the highJ CO

lines suggest that the bulk of the gas is co oler than it is in G The

energy and momentum in the G outow is signicantly lower than the

G outows Sp ecically the momentum input rate in the G

outow is roughly equal to the amount available from the radiation eld while the

outow mechanical luminosity L is only L In addition the CS

b ol

map reveals redshifted absorption toward the UCHI I region In fact this absorption

manifests itself in the lowJ singledish CO sp ectra as a steep drop in emission near

km s Interestingly this drop is not present in the CO transition despite

the smaller b eamsize Apparently very little of the absorbing gas exists in the J

state therefore it must b e co oler than the outowing gas With this evidence we

attribute this absorption feature to co ol infalling gas

We prop ose that G exists in a p erhaps brief phase in which b oth

outow and infall are o ccurring simultaneously The smaller momentum shorter

timescale smaller amount of sweptup mass and the presence of H O masers suggest

that the G outow is younger than the outows in the G region

Also the agreement of the molecular outow in b oth p osition angle and velo city

with the H O masers imply that b oth phenomena are b eing p owered concurrently in

G with the masers forming at the inner edges of the outow lob es at the

site of the sho cked dense gas

Further evidence for the age distinction b etween the two regions comes from

the submillimeter continuum images Toward G at least two sources

are present in a region of extended dust emission with the p eak emission coincid

ing with the C O molecular core to the northeast of G In contrast an

unresolved dust core is seen toward G consistent with the conclusion that

G is a more evolved region in which the dust and gas have b een heated

over a greater volume

Conclusions

With extensive high resolution molecular line and submillimeter continuum obser

vations of the ultracompact HI I regions G and G we present a

detailed picture of massive star formation toward these regions We have discovered

bip olar molecular outows from b oth sources marking them as memb ers of a grow

ing class of UCHI I regions observed to exhibit this phenomenon In G

the singledish CSO maps reveal a main northsouth bip olar outow with additional

complicated structure OVRO ap erturesynthesis images resolve the system into at

least two outows The highest velo city outow app ears centered on the UCHI I re

gion which is emb edded in an extended nearinfrared Br nebula We identify an

additional bip olar outow with a dynamical center lying oset from the

UCHI I region This source called G West can b e identied with ex

tended m emission that most likely represents dust emission from a younger

or lower mass protostar that formed during the same ep o ch as the ionizing star of

the UCHI I region From these observations it is apparent the molecular cloud core

containing G has already formed a numb er of stars

In contrast G exhibits a single compact outow observed in the CO

line emerging from a dense core traced by bright CS emission OVRO

observations of the CS line conrm that the origin of the bip olar outow is

centered on the UCHI I region and that its axis is aligned spatially and kinematically

with the H O maser sp ots in this source Redshifted absorption at km s in

the CS and lowJ CO lines is seen toward the continuum p eak which is identied

with an unresolved m source These phenomena along with the more compact

radio continuum emission and the presence of H O masers lead us to conclude that

G is in an earlier evolutionary phase in which b oth infall and outow

are visible and only a single prominent star has b een formed More sensitive infrared

images and submillimeter synthesis maps of b oth regions will b e required to conrm

the identication of the young stars p owering the molecular outows and heating the

dust grains

Chapter Summary

In this dissertation I explore the phenomenon of massive star formation in the Galaxy

via a submillimeter imaging survey of UCHI I regions After describing the design and

p erformance of the b olometer array camera SHARC now op erating at the CSO I

present submillimeter continuum images of UCHI I regions which show that the

dust emission p eaks at or near the p osition of the compact radio source Often

asso ciated with H O masers outlying cores of dust typically lie on the p eriphery of the

main core The ux measurements from the submillimeter images are combined with

m measurements IRAS m uxes and millimeter uxes from the literature

to obtain greyb o dy mo dels of the sp ectral energy distribution The average dust

temp erature in the UCHI I regions with complete wavelength coverage is K

The average grain emissivity index in the regions is very consistent

with previous studies based solely on mm and IRAS uxes

Radiative transfer simulations of dust clouds with p owerlaw density proles can

successfully mo del the observed submillimeter ux prole of the UCHI I regions How

ever the mo dels presented here may not b e unique due to the uncertainty in the radius

of the outer source b oundary which was xed from the images rather than prop erly

mo deled Of the regions will L L three resemble the isothermal sphere

b ol

prole nr r four exhibit the prole of dynamical collapse nr r two

resemble an isothermal sphere in the outer part of the cloud and approach the collapse

prole toward the inner part and two regions exhibit a shallower prole nr r

indicative of a cluster of sources This evidence for collapse in more than half of the

UCHI I regions b olsters the collapse interpretation from sp ectral line observations of

many UCHI I regions in the literature A go o d correlation exists b etween the den

sity prole the dust luminosity to mass ratio and the dust temp erature The most

centrallycondensed sources exhibit the warmest dust and the high luminosity to mass

ratios indicative of a higher star formation rate

In addition to the dust continuum images many of the UCHI I regions have b een

mapp ed in the J or rotational transitions of CO in search of molecular

outows Of the UCHI I regions mapp ed in CO show evidence for bip olar

outows in the form of a spatial oset b etween the redshifted and blueshifted emission

centered ab out a p osition within of the p eak radio p osition In some cases

separate outows can b e identied with dierent compact radio sources in the same

general region The mechanical luminosity and mass outow rate of the outows

follow the scaling relations with b olometric luminosity established for less luminous

sources by Levreault In contrast to less luminous sources the momentum

supply rate required to drive the molecular outows from UCHI I regions is comparable

to that available from the radiation eld demonstrating that accretion disk winds are

eventually dominated by radiation pressure

Perhaps the most striking asp ect of the data presented in this thesis is the in

evitably complex app earance of massive starforming regions due to the presence of a

cluster of young stars forming from multiple dust cores and driving multiple outows

However the general app earance of the regions seem to b e similar when observed on

dierent size scales Distant sources like the G complex are found to contain

several molecular cores of a few hundred to a thousand solar masses If one could

observe one of these cores at higher angular resolution it would probably lo ok like the

nearby Mon R core which is shown here to contain dozens of clumps of a few tens of

solar masses in addition to the main core As shown in Chapter a similar hierar

chy exists in the molecular outow observations A distant source like G

app ears to have a single giant outow when observed at resolution but when the

resolution is increased by a factor of the outow breaks up into multiple indi

vidual outows similar to those seen from nearby isolated protostars Both of these

ndings suggest a scaleinvariant app earance of massive protostellar clusters This

idea will no doubt b e further tested in the future by combining wideeld surveys

from instruments like SHARC and hetero dyne array receivers with high resolution

studies from millimeter and submillimeter interferometers

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App endix A SHARC Cryostat Manual

Last revised on August

Pumping the cryostat to vacuum

Connect the vacuum gauge controller to the blue sensor on the top plate of the

dewar

Start the rough pump and pump out the line in front of the dewar valve

If the dewar has NOT b een op ened since the last time it was cold then

turn on the turb opump and wait until the pump gauge go es b elow the

current dewar pressure b efore op ening the dewar valve

Else if the dewar has b een op ened then dont turn on the turb o pump

yet First slowly op en the dewar valve and rough out the dewar with the

rough pump Due to the large diameter of the bandpass lters you should

pump slowly no more than torrsec Once the dewar gauge reads

less than torr you can fully op en the valve When the pressure reaches

ab out torr you can turn on the turb o pump

Let the turb opump run for hours until pressure is b elow mTorr on the

dewar gauge

Initial Co oldown to K

Op en b oth heat switches counterclo ckwise They jam if left closed while

co oling from ro om temp erature They have ab out turns of travel

Op en the knurled green valve counterclo ckwise on the He tank ab out

turns but not so far as to have it come lo ose in your hand

Pour LN with a funnel into the nitrogen can Be careful not to scrap e the

sides of the ll tub e when you insert and remove the funnel Filling this jacket

rst causes any remaining water and hydro carb ons to condense on the nitrogen

jacket rather than the helium jacket hence less helium will b e required to co ol

the helium jacket

Pour LN into the helium can It will take liters l and hour to ll

b oth tanks

Plug separate rubb er hoses onto b oth ll tub es to prevent ice plugs from forming

Ab out hours later close b oth heat switches clo ckwise

It takes another hours to get everything inside down to K The longer you

wait the less helium you will use later

Co oling to K

Close the dewar vacuum valve and disconnect and p ower o the turb opump

Dump out the LN by ipping the dewar upside down on the cart Have

containers ready to catch the liquid You can raise the elevator to the highest

p osition for convenience

Ro ck the dewar a couple times to get the last drops out

Right the dewar retighten the rotation stage plug He ll tub e with the stopp er

and rell the nitrogen can with LN

Ho ok up the pin military connector cable from the Housekeeping p ort on

SHARC to the aluminum BNCIEEE housekeeping breakout b ox

Connect an ohmmeter across pins g j which reads the charcoal pump heater

resistor

Connect the IEEE cable to the Lakeshore thermometer readout

Set the Lakeshore to p osition B and the rotating switch on the breakout b ox

to DE This selects the DT thermometer on the lter wheel which is quite

far from the helium cold plate and thus will lag a lot in temp erature during the

co oling pro cess It should read around volt

Connect a voltmeter in parallel with the small blue microamp current source

across pins NP using a BNC tee and cables This selects the dio de ther

mometer mounted directly on the helium cold plate which gives a go o d measure

of the instantaneous cold plate temp erature If you reverse the cables by mis

take this will read volts otherwise it should read ab out volt

Unstopp er the He ll tub e and start a slow transfer of liquid He Immediately

after removing the stopp er use the initial warm gas from the transfer tub e to

blow out any remaining LN in the helium can Remove the transfer tub e from

the ll tub e after a few seconds When you see a liquid ame reinsert it to the

b ottom

It takes l to preco ol the He tank to K and another to get it full the

rst time for a total of l on the initial transfer In the following section is a

typical log for the co oling pro cess to use as a guide to see how it is going

Typical log for the initial co oldown to K

AM Blow out any remaining LN with warm He

AM Begin LHe transfer at psi pressure Prevent LHe transfer tub e

from resting on the b ottom of the can or else things may stop co oling at some

p oint Rub ice o the tip of the transfer tub e if necessary b efore inserting it

Time Transfer Thermometer readings

AM rate NP g j DE lter wheel

HST psi He plate charcoal pump Lakeshore channel B

FULL

This should have taken minutes and L of He

If it is humid then place the long rubb er hose on He ll tub e

Disconnect the pin military connector cable and mount dewar on telescop e

After it is full leave at K for hours to equilibrate The hold time will b e

less if you allow less time b efore starting the cycling of the He The dewar can

b e mounted on the telescop e during this equilibration p erio d

After the dewar has b een mounted on the telescop e rotate the stage until the

small red indicia are aligned correctly with the b olt heads on the mounting plate

and the preamp b ox facing front Connect the small housekeeping breakout b ox

to the dewar where the pin military cable used to b e It will rotate freely a

bit when it is on b ecause I didnt make the thread depth exactly right

Mount the blue AD b ox on the relay optics in front of the dewar by placing

the long screws through the available holes and fastening them with the

nuts supplied

Attach the pin military cables hanging from the hex plate to the Analog and

Digital p ower input p orts on the AD b ox It do esnt matter which is which

Attach the shield ground lines from the cables under one of the screws holding

the AD p ower input p orts

Attach the DB connector to the preamp p ower input p ort screwing down the

connector The ground do es not need to b e attached Dont lo osen any screws

on the top of the preamp b ox b ecause there are nuts on them inside the b ox

Detach the silver b er optic hose from the railing and undo the duct tap e

holding the end section on Carefully pull this section o revealing the ends

of the b er Place the b ers through the shorter green hose for protection and

retap e the joint

Cable tie the silver hose to one of the lower relay optics struts Cable tie the

green hose to the black bracket on top of the relay optics so that the b ers

emerge near their p orts on the AD b ox

Pull o the plastic b er end protectors and screw them into the p orts The

b ers are lab elled and and should b e attached to the prop er numb ered

p ort Keep the plastic protectors in a safe place

Attach the black DB cables from the preamp b ox to the AD input They

are lab elled and

Pumping on liquid He start here on succeeding afterno ons

Make sure b oth the p ot and the pump heat switches are closed clo ckwise

Tilt the telescop e to zenith angle for convenience If the observatory is

running low on liquid He or you want the longest p ossible hold time leave

the telescop e at zenith angle to keep the dewar vertical during transfer and

pumping

Turn on the Lakeshore thermometer and attach the IEEE cable from it to the

housekeeping breakout b ox on the back topside of the dewar In this mo de the

Lakeshore reads the temp erature of a germanium resistor on the He p ot

Move a fo ot step ladder next to the relay optics

Move the LHe storage dewar on the gold cart into p osition next to the ladder

Tighten the extension on the transfer tub e b efore inserting it into the storage

dewar You may have to use one of the longer transfer tub es To conserve

helium use the shortest one that isnt soft

Retop the He can of the dewar from the storage dewar until it is full audible

pluming It may take ab out minutes dep ending on the transfer rate Prevent

the LHe transfer tub e from resting on the b ottom of the can or else ice may

form on the tip and the transfer rate may slow way down

Put away the transfer tub e and move the storage dewar out of the way

Tilt the dish back to zenith angle so the dewar is vertical while pumping

Be sure the roughing pump next to the CTI compressors is p owered on and

the red ball valve next to it is op en Be sure the small valve on the pumping

assembly is closed the valve on the p ort you use to repressurize the He tank

with He gas

Put the pump tting on the He ll tub e You may have to align the Oring in

the b ottom section if it do es not t easily dont force it to o hard Tighten

the base

Begin pumping by cracking op en the large ball valve on the pumping assem

bly while monitoring the Lakeshore thermometer At LHe temp erature the

Lakeshore should read Crack the valve slowly until the Lakeshore read

ing rises at a rate of to p er up date will give the b est

holdtime use if you are in a hurry

Monitor this rate every minutes and continue op ening the valve to maintain

this rate You can watch from the control ro om If it is humid use the heat gun

to deice the pump tting if it gets heavy ice on it Wip e away the resulting

water with a Kimwip e

Retop the LN jacket while you wait After it is full place the long hose over

the tip of the ll tub e so that LN wont spill onto the b er optics when you

start observing near the zenith later It is easier to put the hose on if you wait

a couple of minutes until the ll tub e has warmed up a bit

After minutes of monitoring the thermometer and op ening the pump

valve you will reach a pressure of torr the lamb da p oint At this p oint the

Lakeshore reads Op en the pump valve all the way

After another minutes the Lakeshore thermometer will rise ab ove

The He pump pressure will probably b e b elow torr At this p oint all the He

should b e condensed in the charcoal sorption pump The He pump pressure

will eventually go down to torr

Condensing He

Connect an ohmmeter with a BNC cable to the pump thermometer p ort on the

housekeeping breakout b ox The pump thermometer will b e ab out k

Connect a BNC b etween the JFET thermometer p ort on top of the preamp

b ox to the small blue microamp current source Put a BNC tee to the Fluke

meter Voltage will b e V

Close the knurled green valve clo ckwise on the He tank outside the dewar

Be sure the p ot heat switch is closed clo ckwise Op en the pump heat switch

counterclo ckwise The pump thermometer will drop quickly to k

Connect the long BNC from the battery b ox hanging from the hex plate to

the pump heater BNC p ort on the housekeeping breakout b ox on the backside

of the dewar

Connect the other end of this long BNC to the BNC p ort on the battery b ox

lab elled Heater Charcoal pump

Be sure the AC line is plugged into the battery b ox and press the big green

button on the battery b ox to switch into op eration mo de Unplug the AC line

Turn on the preamp switch and AD switch on the battery b ox near the top

center and top right of the front panel The preamp takes the raw and

V from the batteries The AD voltages are preset through a regulator

to and volts They can b e read with the lower voltmeter on the

battery b ox

Turn on the meter and meter backlights on the battery b ox Set the lower

meter rotary switch to Pump heater The lower meter then displays the

pump heater voltage

Turn on the pump heater switch on the battery b ox and adjust voltage to

Volts

After ab out minutes the pump thermometer will drop to You will

notice that the He stage thermometer Lakeshore will have dropp ed to

due to thermal conduction from the pump heater IMMEDIATELY turn

o the pump heater switch on the battery b ox

Disconnect the pump thermometer cable and ohmmeter from the dewar to

prevent noise pickup

Move the long BNC cable from the pump heater to the JFET heater p ort on

the housekeeping breakout b ox on the top backside of the dewar

Wait for minutes until the Lakeshore thermometer again reads

At this p oint all the He will b e liqueed in the p ot

Op en the p ot heat switch counterclo ckwise

Close the pump heat switch clo ckwise The Lakeshore reading will now rise

While you are still on the ladder turn on the preamp p ower switch on the top

of the preamp b ox b olted to the dewar The JFET thermometer reading drops

as the JFETs warm up from bias current

Setting up the electronics

Move the BNC from the pump heater output on battery b ox to the JFETs

heater output

Set the lower meter rotary p osition switch to read the heater voltage

JFET heater

Turn on the JFET heater switch on the battery b ox and adjust the meter voltage

to V to start with

When the JFET thermometer reaches after a few minutes immediately

turn the JFET heater voltage down to V This will give a stable temp era

ture reading near V If you oversho ot and drop b elow V turn o the

JFET heater and allow it to rise to b efore turning it back on

Turn o the meter switch and the meter backlight switch on the battery b ox

Turn o the microamp current source and the Fluke meter to prevent noise

pickup

Unplug the JFET thermometer cable from the preamp b ox to prevent pickup

When the Lakeshore thermometer reading go es ab ove in ab out an

hour the array will b e at op erating temp erature Turn o the Lakeshore ther

mometer and unplug at the dewar side the IEEE cable going from the dewar

to the thermometer

Note If you turn on the AD while the Lakeshore is still on a strange ground

lo op will cause the Lakeshore reading to plateau at This is OK it is

just an anomalous reading

The only cable plugged into the dewar housekeeping p ort at this p oint should

b e the JFET heater

He valve on the dewar For safety op en counterclo ckwise the knurled green

ab out turns but not so far as to have it come lo ose in your hand

Turn on the AD p ower switch on the AD b ox mounted on the relay optics

Dont b other turning on the AD heater switch as it is not needed Note that

the chopping secondary TTL signal is ultimately generated on the logic b oard

in the AD b ox so p owering it on starts the chopping secondary if the BNC

cables are connected in the control ro om

If it is humid b e sure the fan is running to keep ice o the dewar window mm

p olyethylene If there is ice gently melt it with your ngers and wip e the water

away with a Kimwip e

Uncover the at tertiary mirror and the big ellipsoidal mirror b efore observing

During your rst ZA slew monitor the movement of the b er optic cable conduit

to ensure that it never gets caught on anything or gets to o tight

At the end of the night or when the helium runs out

If prop erly cycled the limiting cryogen in the dewar will b e the He When

the He has all b oiled the He will quickly follow and you will no longer detect

sources The data will lo ok much less noisy since the b olometers are no longer

sensitive to radiation as they warm up Also the pump gauge will b e p egged

b elow mTorr essentially at meaning that all the He has b een pump ed out

The He will typically last hours from when you start pumping in the

early afterno on On the rst night it may only last hours

Cover the at tertiary mirror with the plexiglass cover and cover the ellipsoidal

mirror with the foam pad

Turn o the preamp switch on the preamp b ox on the side of the dewar

Turn o the AD p ower switch on the AD b ox on the relay optics

Turn o the preamp switch on the battery b ox

Turn o the FET heater switch on the battery b ox

Turn o the AD p ower switch on the battery b ox

Plug the AC line back into the battery b ox and switch it to recharge by pressing

the big red zero button

If it is the last night observing with SHARC you can simply leave the He can

on the pump and let the day crew deal with it Op en the pump heat switch

counterclo ckwise and press the telescop e STOP button b efore you leave Be

sure the green He valve is op en b efore you leave

If the dewar is to b e used tomorrow then you must immediately backll it with

warm He gas and rell the can with liquid He as describ ed b elow

Tilt the telescop e to zenith angle

Connect the hose from the He gas b ottle to the inlet valve to the pumping line

b eing sure to blow out the hose with He gas rst and have some pressure on

the line

Close the big pump valve

Slowly op en the small inlet valve and watch the pressure gauge

Bring the pressure up slowly over the course of minute to b etween and

torr on the vacuum gauge next to the big valve

Close the small inlet valve

Move a fo ot step ladder next to the relay optics

Get the helium storage dewar in transfer p osition next to the ladder

If it is humid use a heat gun to deice the pumping xture on the helium ll

tub e

Unscrew the base of the pumping xture enough so that you can lift it o as

unit you may get a blast of helium overpressure when you do this which is

nethis actually prevents air b eing sucked in and causing an ice plug

Tighten the extension on the transfer tub e b efore inserting into the storage

dewar

Immediately transfer helium into the dewar until it is full pluming out of the

ll tub e

Put away the transfer tub e carefully and move the storage dewar out of the

way

Put the short rubb er hose over the helium ll tub e

Fill the nitrogen can with LN

Put the long rubb er hose over the nitrogen ll tub e

Close the p ot heat switch clo ckwise

A few minutes after it is full put the short rubb er hose onto the nitrogen ll

tub e

Tilt the telescop e to zenith angle to conserve cryogen

Be sure the knurled green He valve is op en b efore you leave

Press the STOP button and you can safely leave

App endix B SHARC Software Manual

This manual describ es the function and op eration of the system hardware and Labview

and VAX software required to p erform the prop er instrument setup for astronomical

observing at the CSO

Go ddard Space Flight Center AD and DSP Hardware

The AD unit consists of a logic b oard and AD b oards each with up to channels

contained in an isolated electronics b ox DC p ower and V is connected via two

pin cables from the battery b ox containing four V deep cycle marine batteries

The AD inputs are two pin cables from the dewar preamp b ox The AD output

is sent via two meter b er optic cables encased in a wirereinforced plastic hose

to the control ro om where they connect to a small interface b ox attached to the

Macintosh Quadra The interface b ox connects via a short cable to the DB

input p ort on the DSP NuBus b oard in the Quadra In order to eliminate capacitive

coupling in the particular b ers and detectors at washers are inserted such that

the b ers attach only through a single screw thread Also lo cated on the interface

b ox are BNC p orts for Chop Outthe output TTL chopping signal from the DSP

b oard and Chop Inthe input TTL chopping signal Typically these two p orts are

connected together via a short BNC cable such that the output signal is pip ed right

back in as the input A BNCTee is added so that the Chop Out signal can b e sent to

Martin Houdes chopping secondary control b ox to the TTL input p ort Another

Tee can b e added to monitor the TTL signal on the HP digital oscilloscop e

Labview on the Macintosh

Labview is an ob jectoriented graphical programming language designed to sim

ulate a multitude of scientic instruments The building blo cks of the language are

called Virtual Instruments VIs and are analogous to functions or subroutines in

other programming languages like C or FORTRAN Each Labview VI consists of a

frontpanel display and a programming diagram The frontpanel is a window that

can b e used to display data in the form of numb ers graphs strip charts lights etc

andor to accept input from the user in the form of data control switches dials etc

VIs have the handy feature that they can b e emb edded as subVIs with their input

and output parameters wired into other VIs Thus each VI can b e run standalone

or can b e called and executed by other VIs The programming diagram for a VI is

a separate window that is congured by the application programmer to p erform the

appropriate tasks including arithmetic le IO etc required of the VI Diagrams

can contain typical programming structures such as FOR and While lo ops and Case

and Sequence structures Op erations and conversions on all common datatyp es in

teger long integer oat double extended precision string array bundle etc are

provided Communication over GPIB Serial and TCPIP networks is simplied with

the use of builtin VIs

Getting Started SHARC Server

Many of the Labview VIs for SHARC based up on similar VIs written by Kevin

Boyce for the Kuip er Airb orne Observatory infrared b olometer sp ectrometer instru

ment Small mo dications have b een made to suit our needs at the CSO The main VI

for the b olometer array system is called SHARC Server Currently this VI must b e

started manually on the Macintosh by clicking on the desktop alias SHARC Server

in the top righthand corner of the display Alternatively it can b e started by pulling

down the Apple menu to To dds Labview moving right and releasing on SHARC

Server The refers to the date of the last ma jor revision of the co de It is

p ossible to place this VI in the Startup Folder of the System Folder so that it will b e

started up on reb o ot of the Macintosh But b ecause the Macintosh is a multipurp ose

machine and Labview takes a signicant amount of resources this is not advised on

a p ermanent basis When this VI is executed it go es into a wait mo de and lis

tens for a TCPIP communication request from the CSO control computer Poliahu

VAXStation This request is issued by a client routine activated on the VAX

by the UIP command SHARC Like all UIP commands the SHARC command is

implemented by a Pascal subroutine When the request is received from p ort

on the VAX SHARC Server in eect b ecomes a server program running on the

Mac which in turn op ens new TCPIP connections to the VAX for clearing event

ags p ort displaying error messages on the op erator terminal p ort and

sending scan data p ort All commands sent to the Mac must have a standard

length due to the apparent constraints of the TCPIP software available within Lab

view Currently characters is the standard length that I have chosen The

character serves as a command delimiter and the character serves as a command

terminator See HELP SHARC from within the CSO UIP program for a descrip

tion of the available commands When in the default PRINT mo de the SHARC

command will send any new values to the Mac then immediately requery it for all

of the current values and print them on the control terminal so the user knows the

current conguration Occasionally one of the values printed will b e bizarre p erhaps

to do some communication glitch In this case reissuing the command usually clears

up the problem On rare o ccasions the DSP will get screwed up and rep ort an error

during a SHARC command If it continues to do this try turning the setup display on

and o with the commands SHARCSETUP followed by SHARCNOSETUP This

should reset the DSP

Bad andor Dark pixels

As in all array detectors not all of the pixels are working In SHARC pixels

and are dead These are dened as dead by running the subVI SHARC Set Bad

Pixels which up dates a le on the Mac containing the current array conguration

When data are taken the subVI SHARC Read Bad Pixels returns the numb ers of the

dead channels which are subsequently agged in the header of the data le so that the

data reduction software will ignore them Also we have a dierent eld stop slit that

darkens pixel in case you would like to get an idea of the level and nature of the

correlated pixel noise not asso ciated with sky radiation Dark pixels are also dened

in the subVI SHARC Set Bad Pixels Once you know the current array conguration

you should run this routine to store any changes in the conguration

Pointing

Perhaps the rst thing to do at the b eginning of the night is to lo cate and p oint on

a bright source like a planet Partly for this purp ose the VI SHARC Setup Display

has b een written Essentially it p erforms the duties of an analog stripchart while

you p oint up on a source and center the b eams using the JOYSTICK command in

UIP Fixed p ointing osets and the nominal fo cus oset have b een measured with

SHARC mounted on the righthand p ort of the Cassegrain relay optics of CSO and

the array aligned in zenith angle with pixel the highest in the sky These osets

are stored in a standard UIP p ointing le called SHARC and can b e loaded with

the UIP command POINT SHARC Rough values are for FAZO and for

FZAO for reference pixel Although a stepp er motor controls the rotation of

the dewar plate so far we have always manually aligned the dewar in elevation by

using ducial marks on the relay optics which should b e set by the day crew that

mounts the dewar These ducial marks apply only to the righthand p ort of the

relay optics WARNING If the dewar is ever mounted on the lefthand side then

the dewar rotation will have to b e readjusted Rep ointing and refo cus would also b e

recommended in this case Generally only small adjustments of a few arc seconds

are needed to optimize the p ointing during the night As a sup erior alternative to

JOYSTICK for OTF acionados p ointing can b e done rapidly by making a single

row OTF map of the calibrator and displaying the resulting map in p ointing mo de

in the CAMERA software written by Darek Lis The p ointing corrections can then

b e read from the p eak p osition of the planet in the map

Fo cus

The nominal fo cus of the array is stored in the SHARC p oint le but

should b e checked o ccasionally esp ecially if p eople or other instruments have b een

standing on the relay optics The p eak intensity of the image is fairly insensitive

to fo cus oset changes of However the shap e of the image due to ab errations

do es vary noticeably over such a range Thus it is b est to optimize the fo cus for the

roundest image and hence the b est b eamshap e At prop er fo cus the observed half

p ower contour of a resolved planet matches well with the almanac values with the

p olar attening of the Jovian planets easily visible The halfp ower contour on p oint

sources should b e close to the diraction b eamsize Note if someone ever removes

the secondary mirror get them to verify the XPOS and YPOS b efore your observing

run

Phasing the pixels

After p ointing it is wise to phase the pixels individually on a bright source

From the UIP executable command les have b een created to p erform this task

automatically in communication with the Macintosh They are stored in the directory

USERHUNTERNEWUIP and are named using the format PHASECOM where

indicates the reference pixel b eing used A dierent COM le is needed for each

choice of reference pixel For obvious reasons it is useful esp ecially for mapping

an extended source to cho ose a pixel near the center of the array as the reference

pixel ie the pixel whose lo ckin signal is used to p oint the telescop e These COM

les command the telescop e to move to one pixel after another At each p oint the

Macintosh gathers a data sample and computes the arc tangent of the inphase and

quadrature data and determines the phase This pro cess is accomplished by the

subVI SHARC Phases Allor The computed phase is stored in the DSP memory

for subsequent lo ckin detection It is imp ortant to rememb er that this calculation

is valid only for a sinewave template the current default If a dierent template

function is loaded such as the mo died square wave that we have created the results

of this calculation will not b e as accurate A manual switch on the VI allows you to

select a dierent calculation path for the mo died square wave

After phasing one should make at least two more scans on the calibrator source

at dierent airmasses in order to measure a go o d millivolts to Janskys conversion

factor for the night Also you should consider issuing the useful UIP command

SHARCSAVEPHASE in order to save your current phases to disk on the Mac in

case the Mac crashes and needs to b e reb o oted If this happ ens the UIP command

SHARCLOADPHASE can b e used to reload the last phases that were saved

Pixel Gain Calibration

After phasing it is necessary to measure the relative gains of the pixels The

pixels vary in their resp onsivity to astronomical sources for several reasons diering

thermal conductivity of the pixel supp ort legs varying quality of the optical fo cal

plane diraction eects near the ends of the eld stop and p ossible misalignment

eects The metho d for removing these eects from imaging data is referred to as at

elding Our metho d for atelding is to p erform scans through a bright calibrator

ie Saturn measure the relative signals among the pixels and create a gain le

to b e used in data reduction of subsequent target source observations There are of

course several metho ds to accomplish this goal In the OTF mapping mo de zenith

angle scans are used for gain calibration b ecause the array is aligned in zenith angle

and scanned in azimuth in OTF mo de These calibration scans are accomplished

using the SIDEWAYSALTAZ option of OTFMAP in UIP and provide a rapid

comparison of the signal from each pixel thus minimizing sky changes during the

time of the measurement

OntheFly Mapping

Onthey mapping is a useful pro cedure that allows you to p oint p erform gain

calibration and observe real sources The preferred metho d for observing of the CSO

b olometer crew is OTF OnTheFly mapping The OTF pro cedure is similar to

that used in hetero dyne sp ectroscopy with the main dierence b eing that continuum

OTF is p erformed in altitudeazimuth co ordinates to optimize the sky subtraction

p erformance of an azimuth chopp er See HELP OTF under UIP for details on the

UIP command parameters A minor dierence b etween hetero dyne OTF mapping

and SHARC OTF mapping is in the denition of the longitude resolution of the

map Because the chopping secondary is run during b olometer mapping the data are

quantized in units of chopp er cycle typically Hz Then the longitude resolution

is calculated from the current values of the chopping frequency and the numb er of

chops p er integration The calculated value is displayed when the OTF command is

issued Occasionally the Mac will sp eeze and return a for one of the imp ortant

OTF parameters The OTF command now traps this case instead of dying with a

dividebyzero error Simply reissue the OTF command and it will work prop erly

On the Macintosh the subVI SHARC OTF Accumulate handles the datataking

At the b eginning of each row the Mac awaits the IDLE bit from the antenna computer

which indicates that the antenna has reached the b eginning of the map after the ramp

up p erio d The Mac then takes data and sends it to the VAX over the data so cket

until it has acquired the prop er numb er of data p oints Even when sampling each

chop cycle at Hz the Mac can keep up with the data rate If the map is ab orted

by issuing ControlC under UIP the Mac do es not know this and will continue to

nish the row Once it nishes it should b e in a healthy state ready for the next UIP

command

There is one remaining known bug in the OTF command Actually the problem

seems to b e in the TCP data channel but so far has only b een seen during the rapid

data rate of OTF maps After a couple of hours of mapping the antenna computer

will die at the end of an OTF row To recover from this situation you must stop

the main SHARC Server VI on the Mac by clicking on the little STOP sign on the

window menu bar Then restart the VI by clicking on the rightarrow button On the

VAX controlY out of the UIP and typ e EXIT to kill the image Finally reenter the

UIP and typ e the SHARCRESTART command to restart the connections If this

command hangs go es more than seconds without a resp onse then the SHARC

Client on the VAX was not killed prop erly Just controlY out of UIP typ e EXIT

and go back in and issue the SHARC command which should now work As always

b e sure to issue the SHARC command b efore trying to op en a new data le b ecause

this requires that the Mac connection already b e established

Pointed Observing

For those observers who are interested in making deep integrations on p oint

sources the routine CHOPSLEWY is available In this mo de the telescop e ex

ecutes a sequence of chops and no ds in the form In other words a sp ecied

numb er of chop p erio ds are integrated in the p ositive b eam then in the negative

b eam the negative b eam and back to the p ositive b eam This sequence is rep eated

for the numb er of CHOPSLEWY cycles sp ecied The data le format is dierent

from the OTF map les which is why you must always sp ecify which typ e of le

you wish to op en in the UIP DATAFILE command The data reduction package

for CHOPSLEWY data is the Bolometer Array Data Analysis Software BADAS

written by Dominic Benford Resembling the CLASS package develop ed at IRAM

for hetero dyne sp ectroscopy BADAS will read sum calibrate and plot scans For

p ointed observing the option exists to align the array in azimuth or elevation or

to track the parallactic angle of the source Tracking the rotation has not yet b een tested

App endix C Input parameters for the OUTFLOW

program

The FORTRAN program OUTFLOW reads the input parameters from a text le with

the following example format The mark simply represents the VMS comment

delimiter

K source name

CO isotop e or for CO CO or C O

upp er J level of the transition

numb er of sp ectra to b e summed

LSR velo city in kilometerssecond

lower and upp er velo cities of blue wing

lower and upp er velo cities of red wing

distance in kiloparsecs

angular size in arcseconds of the red lob e and blue lob e

optical depth

excitation temp erature in Kelvin

inclination angle in degrees p oleon

ksp ectrum lename of sp ectrum

The list of lenames included at the end identify the les containing the sp ectral line

data in ASCI I format where the rst column is the channel velo city and the second

column is the line strength in Kelvin at that velo city The columns are delimited by

spaces Such les can b e created with the following CLASS command

CLASS GREG lename FORMATTED

Column densities are computed by assuming that the sp ectra have b een obtained

on a regular grid corresp onding to half the b eamsize