DOCSLIB.ORG

FY1996 Q1 Oct-Dec NO

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
FY1996 Q1 Oct-Dec NO NATIONAL OPTICAL ASTRONOMY OBSERVATORIES NATIONAL OPTICAL ASTRONOMY OBSERVATORIES QUARTERLY REPORT OCTOBER - DECEMBER 1995 July 16,1996 TABLE OF CONTENTS I. INTRODUCTION 1 II. SCIENTIFIC HIGHLIGHTS 1 A. Cerro Tololo Inter-American Observatory 1 1. The Faintest Known White Dwarf 1 2. Evidence for a Black Hole in the X-ray Nova GRO J1655-40 2 3. The Stellar Metallicity Distribution in Omega Centauri 3 B. Kitt Peak National Observatory 3 1. Infrared Colors and Pre-Main-Sequence Evolution 3 2. Bargain Redshifts for Faint Galaxies 4 3. Weighing the Dwarf Spheroidal Companions to the Milky Way 5 C. National Solar Observatory 6 1. Fine Dark Threads and the Temperature of the Solar Corona 6 2. An Objective Test of Magnetic Shear as a Flare Predictor 7 3. Solar Particle Dynamics 7 D. US Gemini Program 8 m. PERSONNEL AND BUDGET STATISTICS, NOAO 9 A. Visiting Scientists 9 B. Hired 9 C. Completed Employment 9 D. Changed Status 9 E. Gemini 8-mTelescopes Project 10 F. Chilean Economic Statistics 10 G. NSFForeign Travel Fund 10 Appendices Appendix A: Telescope Usage Statistics Appendix B: Observational Programs Appendix C: US Sites Safety Report I. INTRODUCTION This document covers scientific highlights and personnel changes for the period 1 October - 31 December 1995. Highlights emphasize concluded projects rather than work in progress. The March 1996 NOAO Newsletter Number 45 contains information on major projects, new instrumentation, and operations. The appendices to this report summarize telescope usagestatistics and observational programs. II. SCIENTIFIC HIGHLIGHTS A. Cerro Tololo Inter-American Observatory 1. The Faintest Known White Dwarf The white dwarf luminosity function incorporates information on the age and star formation history of the Galactic disk which is independent of other techniques. In particular, the least luminous white dwarfs set lower limits on the disk age, and thus the age of the Universe. The faintest known white dwarfs have Mv ~ 16.2. Age estimates for these stars are in the range 6.5-11 Gyr, with the variation largely due to uncertainty in the core composition. The white dwarf luminosity function declines abruptly at this absolute magnitude, and this decline has been interpreted as beingdue to the age of the Galactic disk. The question remains, do even less luminous and older white dwarfs—however rare—exist? The search for very low luminosity white dwarfs is still very active. A concerted effort has been carried out for a number of years by Maria Teresa Ruiz and her colleagues at Cerro Calan Observatory (U. of Chile). Selection of promising candidates is done with a classic technique, blinking plate pairs from the ESO Schmidt telescope to identify faint stars with substantial proper motion. The magnitude limit is about mR ~ 21 and motions as small as 0.1 arcsec yr"1 are detectable with a few years' time base. Followup observations at CTIO and other facilities in Chile help winnow the most interesting objects out of the hundreds found on a plate pair. One such object is the cold DC type white dwarf ESO 439-26. Following its initial discovery in 1988, preliminary spectroscopic and astrometric data suggested it to be of very low luminosity. Several years' subsequent investigation at CTIO have now established this definitively. This result is based on another classic technique, the determination of trigonometric parallax, applied with modern CCD detectors in a program led by Claudio Anguita (U. of Chile). Observations were carried out on the CTIO 1.5-m telescope overa five-year period, using initially a 312 x 508 RCA CCDand morerecently a Tek IK device. With 0.3 arcsec pixels and seeing at 1.2 arcsec or better, 40 frames yield a parallax of 0.024± 0.003 arcsec, or Mv = 17.4—more than one magnitude fainter than the faintest previously known white dwarfs. The existence of such an extreme low-luminosity white dwarf may imply a very large value for the age of the local Galactic disk. Alternatively, the low luminosity of ESO439-26 couldbe accounted for if it is a massive whitedwarfwith a correspondingly small radius—also a rare beast, but not one implying greatage. Onlya detailed comparison of the observed absolute flux distribution with theoretical models can resolve the ambiguity. Ruiz and Anguita, together withS. K. Leggett (IRTF) and P. Bergeron (U. of Montreal), haveused BVRIphotometry obtained on the CTIO 1.5-m and 0.9-m telescopes and model atmosphere calculations by Bergeron and colleagues to make this comparison. They find the high mass interpretation to be the correct one, independent of details of atmospheric composition. The best fit to the photometiy gives Teff=4560 K, log g = 9.0, and M= 1.2 M solar masses—twice that of a typical white dwarf. Comparison with carbon core evolutionary models yields an upper age limit of 6.4 Gyr for the best fit solution. More complex interiors models would tend to reduce the age significantly, but are not yet available at appropriately cool temperatures. Infrared JHK photometry, in progress, will help constrain the atmospheric composition. Interestingly, spectroscopy does not. Even though Ha can be detected in low mass white dwarfs of comparable effective temperature, the large surface gravity of this small, massive object collisionally broadens hydrogen lines to the level of undetectability. Although not of great age, the high mass of ESO 439-26 makes it unique in one respect. Comparison withmodel isochrones indicate it is in an advanced stateof crystallization. 2. Evidence for a Black Hole in the X-ray Nova GRO J1655-40 X-ray novae are binary systems in which a compact object accretes gas from a companion star. The observed velocity of the secondary starcan be used to determine the minimum mass of thecompact object. In six cases to date, the mass function of the compact object has been found to exceed 3 solar masses, confirming thepresence of black holes in these systems. These black hole X-ray novae (orBHXNs) provide a unique opportunity to study black holes, since one can observe both thesecondary starvia the absorption lines and the accretion disk surrounding the black hole via the emission lines. The unusual X-ray nova GRO J1655-40 is the newest and one of the most interesting of the BHXNs. Following its discovery in August 1994 by the Compton Gamma-Ray Observatory, Charles Bailyn (Yale U.) and collaborators located the optical counterpart using the CTIO 0.9-m telescope. Soon after, superluminal radio jets were discovered by Tingay et al. (1995, Nature, 374, 141) and Hjellming et al. (1995, Nature, 375, 464), making GRO J1655-40 the only galactic superluminal source which can be observed optically. The jet ejection, at 92% of the speed of light, appears to be episodic and asymmetric, and is so rapid that distinct motions can be seen from one hour to the next. Bailyn and collaborators returned to CTIO in 1995 to make further optical photometric and spectroscopic measurements of GRO J1655-40. Photometry was obtained on 18-25 March and 5-24 April with the 0.9-m telescope and CCD imager, and on 28 March to 2 April with the CTIO 1.5-m telescope and CCD imager. In addition, spectra were obtained with the RC spectrograph on the CTIO 4-m telescope on the nights of 30 April and 2-4 May. As the photometric data were obtained, it became clear that the light curve showed eclipses and was periodic on a timescale of approximately three days. The overall light curve shape was found to consist of a broad triangular primary minimum, and a shorter secondary minimum displaced by about 0.5 in phase from the primary minimum. By analogy with the eclipsing X-ray binary CAL87, it seems likely that aneclipse of a large accretion disk by the secondary staris responsible for theprimary minimum, and an eclipse of the secondary star by the disk explains the secondaryminimum. The spectra of GRO J1655-40 obtained by Bailyn et al. had less prominent Balmer emission lines and stronger high-excitation lines than X-ray novae in quiescence, presumably because the outburst was still underway. Nevertheless, it became immediately apparent from the individual spectra that a stellar F-type absorption spectrum was present. Cross-correlating the spectra against an F5 subgiant of known radial velocity revealed sinusoidal radial velocity variations with a period of 2.6days and a semi-amplitude of 227 km s"1. These parameters yield a minimum possible mass of the compact object of 3.16 ±0.15 solar masses. The maximum stable mass of a neutron star is 3 solarmasses for all possible equations of state, and below 2.5 solar masses for most plausible equations of state. Thus, in the absence of exotic matter and/or non-Einsteinian gravity, a mass function above 3 solarmasses requires thecompact object in GRO J1655-40 to be a black hole. The eclipsing geometry of GRO J1655-40 allows the possibility of using eclipse mapping techniques to explore the geometry of the system in further detail. Changes in the flux and spectral line shape during eclipse can be used to map the inner regions of the accretion disk. Hence, a multiwavelength campaign involving GRO, ROSAT, ASCA, XTE, and a variety of ground-based optical and radio observations (including 0.9-m time at CTIO) was organized for March 1996. One of the primary goals of this campaign was to use the eclipses to map the high-energy, optical, and radio emission. When successful, these observations allow the emission geometry near an accreting, jet-producing black hole to be explored in unprecendented detail. 3. The Stellar Metallicity Distribution in Omega Centauri Suntzeff (CTIO) and Kraft (UCO/Lick) have finished a project on stellar abundances and radial velocities for giant stars in the Galactic globular cluster co Centauri based on the Call infrared triplet.
Load more

Recommended publications
  • A Search for Ionized Gas in the Draco and Ursa Minor Dwarf Spheroidal Galaxies
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by CERN Document Server A Search for Ionized Gas in the Draco and Ursa Minor Dwarf Spheroidal Galaxies J.S. Gallagher, G. J. Madsen, R. J. Reynolds Department of Astronomy, University of Wisconsin–Madison, 475 North Charter Street, Madison, WI 53706-1582; [email protected], [email protected], [email protected] E. K. Grebel Max-Planck Institute for Astronomy, K¨onigstuhl 17, D-69117 Heidelberg, Germany; [email protected] T. A. Smecker-Hane Department of Physics & Astronomy, 4129 Frederick Reines Hall, University of California, Irvine, CA 92697-4575; [email protected] ABSTRACT The Wisconsin Hα Mapper has been used to set the first deep upper limits on the intensity of diffuse Hα emission from warm ionized gas in the Draco and Ursa Minor dwarf spheroidal 1 galaxies. Assuming a velocity dispersion of 15 km s− for the ionized gas, we set limits of IHα 0:024R and IHα 0:021R for the Draco and Ursa Minor dSphs, respectively, averaged ≤ ≤ over our 1◦ circular beam. Adopting a simple model for the ionized interstellar medium, these limits translate to upper bounds on the mass of ionized gas of .10% of the stellar mass, or 10 times the upper limits for the mass of neutral hydrogen. Note that the Draco and Ursa Minor∼ dSphs could contain substantial amounts of interstellar gas, equivalent to all of the gas injected by dying stars since the end of their main star forming episodes &8 Gyr in the past, without violating these limits on the mass of ionized gas.
    [Show full text]
  • Enrichment in R-Process Elements from Multiple Distinct Events in the Early Draco Dwarf Spheroidal Galaxy*
    The Astrophysical Journal Letters, 850:L12 (6pp), 2017 November 20 https://doi.org/10.3847/2041-8213/aa9886 © 2017. The American Astronomical Society. Enrichment in r-process Elements from Multiple Distinct Events in the Early Draco Dwarf Spheroidal Galaxy* Takuji Tsujimoto1,2 , Tadafumi Matsuno1,2 , Wako Aoki1,2, Miho N. Ishigaki3 , and Toshikazu Shigeyama4 1 National Astronomical Observatory of Japan, Mitaka, Tokyo 181-8588, Japan; [email protected] 2 Department of Astronomical Science, School of Physical Sciences, SOKENDAI (The Graduate University for Advanced Studies), Mitaka, Tokyo 181-8588, Japan 3 Kavli Institute for the Physics and Mathematics of the Universe (WPI), University of Tokyo, Kashiwa, Chiba 277-8583, Japan 4 Research Center for the Early Universe, Graduate School of Science, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan Received 2017 October 11; revised 2017 October 26; accepted 2017 November 1; published 2017 November 16 Abstract The stellar record of elemental abundances in satellite galaxies is important to identify the origin of r-process because such a small stellar system could have hosted a single r-process event, which would distinguish member stars that are formed before and after the event through the evidence of a considerable difference in the abundances of r-process elements, as found in the ultra-faint dwarf galaxy Reticulum II (Ret II). However, the limited mass of these systems prevents us from collecting information from a sufficient number of stars in individual satellites. Hence, it remains unclear whether the discovery of a remarkable r-process enrichment event in Ret II explains the nature of r-process abundances or is an exception.
    [Show full text]
  • Search for Ultra-Faint Satellite Galaxies in the Milky Way Halo
    Search for Ultra-faint Satellite Galaxies in the Milky Way Halo filtering techniques and first results Helmut Jerjen SkyMapper Workshop April 2014 Cold Dark Matter Simulations of the Milky Way (Millennium II or Aquarius project) 0.5 Mpc Cold Dark Matter Simulations of the Milky Way (Millennium II or Aquarius project) predict ~1000 dark matter subhalos in the MW potential (e.g. Diemand et al. 2006, 2008) distributed spherically symmetric ⇒optical manifestation: satellite dwarf galaxies Milky Way Satellite Census (2004) The Disk of Satellites • Only 11 dwarf satellite galaxies known within the gravitational influence of the MW • 10 satellites are distributed in a common plane (Lynden-Bell 1976; Kroupa et al. 2005; Metz, Kroupa & Jerjen 2007, 2009) -> result of a major merger? Known Satellite Galaxies in Milky Way Halo (2014) SDSS Footprint 2004-10: 14 new Milky Way Satellites discovered out to 250 kpc (-7.9<Mv<-2.7), many consistent with DoS and 9 out the 11 brightest share the same dynamical orbital properties (Metz et al. 2008; Palowski & Kroupa 2013). More Results and Open Questions Strigari et al. 2008 •How many MW satellites are in the southern hemisphere? •What is their distribution and are there satellite galaxies that do not follow the DoS? •How much dark matter is in these MW satellite galaxies? (some may not be virialised) •Are there possibly two different types of satellites (tidal and cosmological origin)? •Do all MW satellites have the same total mass? •What is the evolutionary link between satellites and MW? The Stromlo Milky Way Satellite Survey SkyMapper key project SkyMapper Search for satellite galaxies to similar depth as SDSS over 20,000 sqr degrees.
    [Show full text]
  • Does the Fornax Dwarf Spheroidal Have a Central Cusp Or Core?
    Research Collection Journal Article Does the Fornax dwarf spheroidal have a central cusp or core? Author(s): Goerdt, Tobias; Moore, Ben; Read, J.I.; Stadel, Joachim; Zemp, Marcel Publication Date: 2006-05 Permanent Link: https://doi.org/10.3929/ethz-b-000024289 Originally published in: Monthly Notices of the Royal Astronomical Society 368(3), http://doi.org/10.1111/ j.1365-2966.2006.10182.x Rights / License: In Copyright - Non-Commercial Use Permitted This page was generated automatically upon download from the ETH Zurich Research Collection. For more information please consult the Terms of use. ETH Library Mon. Not. R. Astron. Soc. 368, 1073–1077 (2006) doi:10.1111/j.1365-2966.2006.10182.x Does the Fornax dwarf spheroidal have a central cusp or core? , Tobias Goerdt,1 Ben Moore,1 J. I. Read,1 Joachim Stadel1 and Marcel Zemp1 2 1Institute for Theoretical Physics, University of Zurich,¨ Winterthurerstrasse 190, CH-8057 Zurich,¨ Switzerland 2Institute of Astronomy, ETH Zurich,¨ ETH Honggerberg¨ HPF D6, CH-8093 Zurich,¨ Switzerland Accepted 2006 February 8. Received 2006 February 7; in original form 2005 December 21 ABSTRACT The dark matter dominated Fornax dwarf spheroidal has five globular clusters orbiting at ∼1 kpc from its centre. In a cuspy cold dark matter halo the globulars would sink to the centre from their current positions within a few Gyr, presenting a puzzle as to why they survive undigested at the present epoch. We show that a solution to this timing problem is to adopt a cored dark matter halo. We use numerical simulations and analytic calculations to show that, under these conditions, the sinking time becomes many Hubble times; the globulars effectively stall at the dark matter core radius.
    [Show full text]
  • National Optical Astronomy Observatories
    E NATIONAL OPTICAL ASTRONOMY OBSERVATORIES Preprint Series NOAO Preprint No. 834 WFPC2 OBSERVATIONS OF THE URSA MINOR DWARF SPHEROIDAL GALAXY KENNETH J. MIGHELL CHRISTOPHER J. BURKE To Appear In: The Astrophysical Journal March 1999 Operated for the National Science Foundation by the Association of Universities for Research in Astronomy, Inc. To appear in the Astronomical Journal (accepted 1999 March 1) WFPC2 OBSERVATIONS OF THE URSA MINOR DWARF SPHEROIDAL GALAXY 1 KENNETH J. _'IIGHELL 2 AND CHRISTOPHER J. BURKE 3'4 Kitt Peak National Observatory, National Optical Astronomy Observatories 5, P. O. Box 2673:2, Tucson, AZ 85726 mighell@noao, edu, chrislopt_ r. burk_ @yale.cdu 1Based on observations made with tile NASA/ESA Hubble Space Telescope, obtained fl'om the data archive at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS5-26555. 2Guest User, Canadian Astronomy Data Centre, which is operated by the Dominion Astrophysical Observatory for the National Research Council of Canada's Herzberg Institute of Astrophysics. ZBased on research conducted at. NOAO as part of the Research Experiences for Undergraduates program. 4 Current address: Department of Astronomy, Yale University, P. O. Box 208101, New ttaven, CT 06520-8101 SNOAO is operated by the Association of Universilies for I/esearch in Astronomy, Inc., under cooperative agreelnent with the National Science Foundation. _ ABSTRACT \Ve present our analysis of archival Hubble Space Telescope Wide Field Planetary Canlera 2 (WFPC2) observations in F555W (,-_V) and F814W (_I) of the central region of the Ursa Minor dwarf spheroidal galaxy.
    [Show full text]
  • Dark Matter Searches Targeting Dwarf Spheroidal Galaxies with the Fermi Large Area Telescope
    Doctoral Thesis in Physics Dark Matter searches targeting Dwarf Spheroidal Galaxies with the Fermi Large Area Telescope Maja Garde Lindholm Oskar Klein Centre for Cosmoparticle Physics and Cosmology, Particle Astrophysics and String Theory Department of Physics Stockholm University SE-106 91 Stockholm Stockholm, Sweden 2015 Cover image: Top left: Optical image of the Carina dwarf galaxy. Credit: ESO/G. Bono & CTIO. Top center: Optical image of the Fornax dwarf galaxy. Credit: ESO/Digitized Sky Survey 2. Top right: Optical image of the Sculptor dwarf galaxy. Credit:ESO/Digitized Sky Survey 2. Bottom images are corresponding count maps from the Fermi Large Area Tele- scope. Figures 1.1a, 1.2, 1.3, and 4.2 used with permission. ISBN 978-91-7649-224-6 (pp. i{xxii, 1{120) pp. i{xxii, 1{120 c Maja Garde Lindholm, 2015 Printed by Publit, Stockholm, Sweden, 2015. Typeset in pdfLATEX Abstract In this thesis I present our recent work on gamma-ray searches for dark matter with the Fermi Large Area Telescope (Fermi-LAT). We have tar- geted dwarf spheroidal galaxies since they are very dark matter dominated systems, and we have developed a novel joint likelihood method to com- bine the observations of a set of targets. In the first iteration of the joint likelihood analysis, 10 dwarf spheroidal galaxies are targeted and 2 years of Fermi-LAT data is analyzed. The re- sulting upper limits on the dark matter annihilation cross-section range 26 3 1 from about 10− cm s− for dark matter masses of 5 GeV to about 5 10 23 cm3 s 1 for dark matter masses of 1 TeV, depending on the × − − annihilation channel.
    [Show full text]
  • Constraints on the Parameters of Radiatively Decaying Dark Matter from the Dark Matter Halos of the Milky Way and Ursa Minor
    A&A 471, 51–57 (2007) Astronomy DOI: 10.1051/0004-6361:20066774 & c ESO 2007 Astrophysics Constraints on the parameters of radiatively decaying dark matter from the dark matter halos of the Milky Way and Ursa Minor A. Boyarsky1,2,3, J. Nevalainen4, and O. Ruchayskiy5,2 1 CERN, PH-TH, 1211 Geneve 23, Switzerland e-mail: [email protected] 2 École Polytechnique Fédérale de Lausanne, Institute of Theoretical Physics, FSB/ITP/LPPC, BSP 720, 1015 Lausanne, Switzerland 3 On leave of absence from Bogolyubov Institute of Theoretical Physics, Kyiv, Ukraine 4 Helsinki University Observatory, Finland e-mail: [email protected] 5 Institut des Hautes Études Scientifiques, 91440 Bures-sur-Yvette, France e-mail: [email protected] Received 20 November 2006 / Accepted 19 April 2007 ABSTRACT Aims. We improve the earlier restrictions on parameters of the warm dark matter (DM) in the form of a sterile neutrinos. Methods. The results were obtained from not observing the DM decay line in the X-ray spectrum of the Milky Way (using the recent XMM-Newton PN blank sky data). We also present a similar constraint coming from the recent XMM-Newton observation of Ursa Minor – dark, X-ray quiet dwarf spheroidal galaxy. Results. The new Milky way data improve on (by as much as the order of magnitude at masses ∼3.5 keV) existing constraints. Although the observation of Ursa Minor has relatively poor statistics, the constraints are comparable to those recently obtained using observations of the Large Magellanic Cloud or M 31. This confirms a recent proposal that dwarf satellites of the MW are very interesting candidates for the DM search and dedicated studies should be made to this purpose.
    [Show full text]
  • Structure of the Draco Dwarf Spheroidal Galaxy
    CORE Metadata, citation and similar papers at core.ac.uk Provided by CERN Document Server Structure of the Draco Dwarf Spheroidal Galaxy Slawomir Piatek Dept. of Physics, New Jersey Institute of Technology, Newark, NJ 07102 E-mail address: [email protected] Carlton Pryor1 Dept. of Physics and Astronomy, Rutgers, the State University of New Jersey, 136 Frelinghuysen Rd., Piscataway, NJ 08854–8019 E-mail address: [email protected] Taft E. Armandroff National Optical Astronomy Observatory, P.O. Box 26732, Tucson, AZ 85726 E-mail address: tarmandroff@noao.edu and Edward W. Olszewski1 Steward Observatory, University of Arizona, Tucson, AZ 85721 Email address: [email protected] ABSTRACT This article studies the structure of the Draco dwarf spheroidal galaxy with an emphasis on the question of whether the spatial distribution of its stars has been affected by the tidal interaction with the Milky Way, using R- and V-band CCD photometry for eleven fields. The article reports coordinates for the center, a position angle of the major axis, and the ellipticity. It also reports the results of searches for asymmetries in the structure of Draco. These results, and searches for a “break” in the radial profile and for the presence of principal sequences of Draco in a color-magnitude diagram for regions more than 50 arcmin from the center, yield no evidence that tidal forces from the Milky Way have affected the structure of Draco. Subject headings: galaxies: dwarf — galaxies: individual (Draco) — galaxies: stellar content — galaxies: structure — galaxies: Local Group 1Visiting Astronomer, Kitt Peak National Observatory, National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy, Inc.
    [Show full text]
  • Your Guide to Planets, Stars, and Galaxies by Richard Talcott
    FACTS500 INSIDE! Your guide to planets, stars, and galaxies by Richard Talcott A supplement to Astronomy magazine © 2012 Kalmbach Publishing Co. This material may not be reproduced in any form 618129 without permission from the publisher. www.Astronomy.com Saturn Saturn’s rings consist of icy particles ranging in size from tiny motes to house-sized icebergs. NASA/THE HUBBLE Planets HERItaGE TEam (STSCI/AURA) of the solar system arth may seem extraordinary to those who call it home, but it’s not a land of superlatives. Earth is neither too hot nor too cold, too big nor too small. It’s just right in so many ways — the perfect “Goldilocks” planet. Of course, as the only known abode of life in the universe, Earth doesE have one major claim to being special. The other planets in the solar system leave their marks in different ways. The planets divide into two broad categories: terrestrial and jovian. The small, rocky terrestrial planets include Mercury, Venus, Earth, and Mars. Mercury, the closest to the Sun, bakes Mars at temperatures up to 800° Fahrenheit at noon. But Mercury’s razor-thin atmosphere can’t hold heat; at night, the temperature plummets far below freezing. Venus most resembles Earth in mass and diameter, but a thick atmosphere of carbon dioxide has led to a runaway greenhouse effect. Venus’ surface remains a scorching 865° F year-round. Earth and Mars are the water worlds of the solar system. Our home planet is the only one with liquid water at the surface now, but spacecraft observations during the past 15 years leave no doubt that Mars once had loads of surface water.
    [Show full text]
  • A Search for Ionized Gas in the Draco and Ursa Minor Dwarf Spheroidal Galaxies J
    The Astrophysical Journal, 588:326–330, 2003 May 1 # 2003. The American Astronomical Society. All rights reserved. Printed in U.S.A. A SEARCH FOR IONIZED GAS IN THE DRACO AND URSA MINOR DWARF SPHEROIDAL GALAXIES J. S. Gallagher, G. J. Madsen, and R. J. Reynolds Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, WI 53706-1582; [email protected], [email protected], [email protected] E. K. Grebel Max-Planck-Institut fu¨r Astronomie, Ko¨nigstuhl 17, D-69117 Heidelberg, Germany; [email protected] and T. A. Smecker-Hane Department of Physics and Astronomy, 4129 Frederick Reines Hall, University of California, Irvine, CA 92697-4575; [email protected] Received 2002 December 6; accepted 2003 January 13 ABSTRACT The Wisconsin H Mapper has been used to set the first deep upper limits on the intensity of diffuse H emission from warm ionized gas in the Draco and Ursa Minor dwarf spheroidal galaxies (dSphs). Assuming À1 a velocity dispersion of 15 km s for the ionized gas, we set limits of IH 0:024 R and IH 0:021 R for the Draco and Ursa Minor dSphs, respectively, averaged over our 1 circular beam. Adopting a simple model for the ionized interstellar medium, these limits translate to upper bounds on the mass of ionized gas of d10% of the stellar mass, or 10 times the upper limits for the mass of neutral hydrogen. Note that the Draco and Ursa Minor dSphs could contain substantial amounts of interstellar gas, equivalent to all of the gas injected by dying stars since the end of their main star-forming episodes e8 Gyr in the past, without violating these limits on the mass of ionized gas.
    [Show full text]
  • Supernova-Driven Outflows and Chemical Evolution of Dwarf Spheroidal Galaxies
    Supernova-driven outflows and chemical evolution of dwarf spheroidal galaxies Yong-Zhong Qiana,1 and G. J. Wasserburgb,1 aSchool of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455; and bThe Lunatic Asylum, Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 Contributed by G. J. Wasserburg, January 30, 2012 (sent for review October 13, 2011) We present a general phenomenological model for the metallicity Recent observations (14) give results for eight dSphs with rather distribution (MD) in terms of ½Fe∕H for dwarf spheroidal galaxies detailed structure of their MDs and provide a basis for exploring (dSphs). These galaxies appear to have stopped accreting gas from models of their chemical evolution (e.g., ref. 15). Among the key the intergalactic medium and are fossilized systems with their stars issues that we try to address are MDs exhibited by stellar popula- undergoing slow internal evolution. For a wide variety of infall his- tions of dSphs. Our general approach follows that of Lynden-Bell tories of unprocessed baryonic matter to feed star formation, most described in his incisive and excellent article on “theories” of the of the observed MDs can be well described by our model. The key chemical evolution of galaxies (16). It will be shown that the me- requirement is that the fraction of the gas mass lost by supernova- tallicity at which the MD peaks is directly related to the efficiency driven outflows is close to unity. This model also predicts a relation- of SN-driven outflows and that the MD of a dSph and the rela- ship between the total stellar mass and the mean metallicity for tionship between the stellar mass and the mean metallicity for dSphs in accord with properties of their dark matter halos.
    [Show full text]
  • Kinematics of the Dwarf Spheroidal Galaxies Draco and Ursa Minor
    University of Groningen Kapteyn Astronomical Institute Kinematics of the dwarf spheroidal galaxies Draco and Ursa Minor MSc Thesis in Astronomy by Johanna Hartke Groningen, August 14, 2015 Supervisors Second Reader Prof. Dr. Eline Tolstoy Prof. Dr. Scott Trager Dr. Shoko Jin Dr. Maarten Breddels Abstract The aim of this thesis is to study the kinematics of the Local Group dwarf spheroidal galaxies Ursa Minor and Draco. These two galaxies are an interesting pair to study, since they are similar in terms of mass, extent, and distance. However, while Draco appears to have a perfect, undisturbed stellar distribution, Ursa Minor shows signs of tidal disturbance. We use new optical spectroscopy of individual red gi- ant branch stars from the AF2-WYFFOS fiber spectrograph on the William Herschel Telescope. We observed several hundred stars in the CaII triplet region. The data have been pipeline-processed at CASU in Cambridge using prototype WEAVE pro- cessing. We combine our dataset of Draco with data published by Walker, Olszewski & Mateo (2015) and apply orbit-based Schwarzschild modeling to the velocity data in order to constrain the dwarf spheroidal's (dark) matter distribution. We are able to determine the dark matter halo mass distribution for a NFW and a cored profile. Page 1 of 58 Contents 1 Introduction 4 1.1 Galaxy Formation . .5 1.2 Local Group dSph galaxies . .6 1.2.1 Draco . .7 1.2.2 Ursa Minor . .8 1.3 Dynamical modeling . .8 1.3.1 Early attempts to model dSphs . .8 1.3.2 Jeans modeling . .9 1.3.3 Schwarzschild modeling .
    [Show full text]