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198 7ApJS. . .63. .645U hm © 1987.TheAmericanAstronomicalSociety.Allrightsreserved.PrintedinU.S.A. The AstrophysicalJournalSupplementSeries,63:645-660,1987March low mass,canbeobserved.Thesecloudsarecloseenoughto in theCO1-0lineofconspicuousobscurationsTaurus radio .Inthispaperwepresentacompletesurvey be studiedingreatdetail,notonlywithmoderate-aperture with theIC348cloud,onlylow-massstars,e.g.,TTauri While youngstarswithratherhighluminosityareassociated lated toIC348,NGC1333,andthePerOB2association; optical andinfraredtelescopesbutalsowithsingle-antenna clouds inwhichtheformationofstars,particularlythose in thedarkfilamentsouthwestofHeilesCloud2,nowsome- and Auriga;thestar-formingcloudcomplexinPerseusre- and Aurigaisoneofthebestexamplesnearbymolecular cm HCOabsorptionlinewasdiscoveredbyPalmeret al alongNGC1579andLkHa101wellintoAuriga. a cloudextendingfromtheCalifornianebula(NGC1499)in Heiles Cloud2),radiospectroscopy hasprovidedevidenceof Taurus (e.g.,inthewell-known sourceTMC-1,acoreof Heiles Cloud2andKutner’s cloud.Inafewlocationsin (1969); Kutner(1973)observedthislineatselectedpositions a regionofhighextinctionnearR.A438,decl.25°18', gan withHeiles’s(1968)detectionofnormalOHemission in and Herbig1979;CohenKuhi1979). are foundneartheTaurusandAurigaclouds(see,e.g.,Jones tions therewerelatermadebyHeilesandKatz(1976) and times calledKutner’scloud.MoreextensiveHCOobserva- afterward knownasHeilesCloud2.Inthesameregion, 6 a surprisinglycomplexchemistry (e.g.,Brotenetai1978; served weretooweaktoestablishaconnectionbetween Sume, Downes,andWilson(1975),butthelinesthey ob- 2 2 The extensivecomplexofdarknebulaeinPerseus,Taurus, Radio observationsofmoleculesintheTauruscloudsbe- -1 5 4 Taurus clouds,andtheL1558L1551cloudsinsouth.ThemassofeachIC348NGC1499 from nearly50%oftheobservedpositions;mostpositionswithemissionareinTaurus-Aurigadarknebulae, survey is250kHz,or0.65kms,andthermsnoiseperspectrometerchannel0.14K.Emissionwasdetected masses 10-30timestheirCOaresimilartothediffusemolecularcloudsathighGalacticlatitudes. equilibrium, buttheIC348andNGC1499cloudsaremoredynamicallyactive.Severalsmallwithvirial clouds surveyedisabout2x10Af.Onalargescale,theratherquiescentTaurusareclosetovirial clouds isabout5X10M,andthatoftheTaurus-Auriga3.5X10;totalmassall Other objectsseeninthissurveyareseveralsmallcloudsatGalacticlatitude—25°to—35°southwestofthe and NGC1579,whichoverlapsthenorthernTaurus-Auriganebulaebutisseparatedfromtheminvelocity. a cloudassociatedwithIC348andNGC1333,theCalifornianebula(NGC1499) surveyed inthe115GHz,J=l-0lineofCOatanangularresolution0?5.Thespectral Subject headings:interstellar:molecules—nebulae:generalHnregions 0 0 A regionof750squaredegreesincludingthewell-knowndarknebulaeinPerseus,Taurus,andAurigawas © American Astronomical Society • Provided by theNASA Astrophysics Data System A COSURVEYOFTHEDARKNEBULAEINPERSEUS,TAURUS,ANDAURIGA I. INTRODUCTION Goddard InstituteforSpaceStudiesandColumbiaUniversity Received 1986February20;acceptedSeptember4 H. UngerechtsandP.Thaddeus ABSTRACT 645 -1 long, extended,darkfilaments(Barnard1927). extinction whichtendtoappearonopticalphotographsas low-mass starshaveformedinornearasignificantfractionof J =1-0lineininterstellarspace(Wilson,Jefferts,andPenzias Toelle étal.1981;Thaddeusétal1985;Thaddeus,Vrtilek, highly desirableasaprerequisitetoreahsticestimatesofthe and Gottlieb1985),infraredobservations(Benson,Myers, have beenlimitedtoselectedareas,suchasthedarkfilaments and Wright1984;Beichmanetal1986)haveshownthat regions whereBaranhaddetected CO. 2.6 kms.Sofar,theOHsurveybyWouterlootandHabing Elmegreen (1978)fortheregionnearNGC1499.Themost eral understandingofthestructureanddynamics these densecores.Allcoresheinregionsofhighvisual extensive previousCOstudy(Baran1985)isseverelyunder- e.g., Sargent(1979)fortheIC348cloudandElmegreen and cover onlysomeactiveregionswithhighlineintensities; see, Baudry 1986).TheavailableCOmapsoftheotherclouds (e.g., Baudryetal1981;Myers1982;KleinerandDickman distribution ofmoleculargas.AlthoughCOemissionwas clouds. Duringthepastdecade,COmapshavebecome the cloudswithh>-20°,but theirmapwaslimitedtothe (1985) givesthebestpictureoflarge-scaledistribution of survey ofthisregionhasbeendone.MostCOmapsinTaurus 1970; Penziasetal1972),todatenocomplete,unbiased detected inHeilesCloud2soonafterthefirstdetectionof accepted asthebestcurrentlyavailabletooltosurvey total masses,interpretationsoftheIRASsurvey,andagen- ture nowusedontheColumbia 1.2mtelescopeallowsusto sampled andsuffersfromaratherpoorspectralresolution of 1984; MurphyandMyers1985;Duvert,Cemicharo, and A completesurveyofthemolecularcloudsinthisregionis A newSISreceiverwithan extremely lownoisetempera- 198 7ApJS. . .63. .645U 1 A fordetails).Integration times wereautomaticallysetto here areabout20%belowthetrueradiationtemperature (i.e., were abletosavetimebyfrequency switching(seeAppendix localized COsources(e.g.,peaks8a,12a,and27finTable 1). calibration. Pointingandcalibrationwerecheckeddailyusing for consistencyweretainthescaleusedCOmass Bronfman etal(1986)estimatedthattheintensitiesreported conversion fromintegratedCOintensitytoHcolumnden- was appliedtoobtainintensitiesthatareinagreementwith other Columbiadatareportedsince1980.Althoughrecently et al.1986),whichBloemenetal.(1984)usedtoderive the achieve anrmsnoise(after folding andsummingoverboth Since thelinesinallclouds surveyedarerathernarrow,we the temperatureofablackbodythatjustfillsmainbeam), sity fornearbymolecularclouds,andarewithin5%of all often whenitwasvariable.Acorrectionforbeamefficiency opacity ofatmosphericwatervaporweremeasuredbyan- perature blackbodychopperwheelinfrontofthefeedbefore the ColumbiasurveyofOrionandMonoceros(Maddalena each scan(Cohen1978;Kutner1978).Thetemperatureand corrected foratmosphericabsorptionbyrotatingaroom-tem- beamwidth. Telescopepointingwasestablishedtobetterthan tenna tippingdailywhentheweatherwasstableandmore raster ofpositionsseparatedby—slightlylessthanthe and wascheckedregularlybyradiocontinuumobservationof 1' byobservingstarswithasmall,coalignedopticaltelescope, stepping thetelescopeduringeachscanthrougha4Xsquare velocity resolutionof0.65kms~.Thefrontendwasa the Sun.Theintensityofspectrawascalibratedand tion ofthetelescopewasreducedtoa0?5x0?5beamby which hasafullbeamwidthathalf-maximumof8'7115 New YorkCitywiththeColumbiamillimeter-wavetelescope, temperature oftypically<90Kandatotalsystemnoise single-sideband SISreceiver(Pan1984),withanoise plains theanalysisoffrequency-switchedCOspectra,and in §II,thencommentonthemajorfeaturesourmapsand temperature <600K. trometer, a256channel,250kHzfilterbank,provided GHz, thefrequencyofCOJ=1-0transition.Thespec- given inAppendixB. more detaileddescriptionsofsomeindividualcloudsare estimates forthecloudsandourbestcurrentof on selectedindividualcloudsin§III.Theavailabledistance structure andmassarediscussedin§IV.AppendixAex- 2 646 (IRAS) surveys. resolution isadequateforcomparisonsonalargescaleofthe map COrapidlywithfullsampling.Thispaperpresentsthe results ofasurveyforwhichtheangularresolution CO distributionwithy-ray(COSB),A,HI,andinfrared ture, e.g.,thedarkfilamentsinTaurus.Further,thisangular sufficient resolutionwasretainedtoseesignificantsubstruc- the completeregiontobefinishedwithinfourmonths,while wasreducedto0?5,allowingtheobservationsfor v In ordertocoveralargeareaquickly,theangularresolu- The observationsweremadein1985February-May We describetheinstrumentandobservationalmethods © American Astronomical Society • Provided by theNASA Astrophysics Data System II. OBSERVATIONSANDANALYSIS UNGERECHTS ANDTHADDEUS -1 mo m m probably fromseparateemittingcloudsratherthan rion adoptedissufficientlystringentthatalldoublefinesare self-absorption byforegroundmatter. exception oftheconfusedregionnearNGC1499,crite- fines, asopposedtoblends,andwasthereforeusedcon- with asubjectiveandqualitativediscriminationofdouble sistently atallpositionsinthissurvey.Withthepossible well asforthetotalemission.Wedefinetwospectralpeaks eral CatalogueandtheIndex Catalogue(Dreyer1888,1895, locations ofselectedwell-known nebulaefromtheNewGen- To showtherelationtooptical objects,inFigure4the somewhat arbitrary,theyprovideacriterionwhichagreeswell channels andaminimumlowerthan60%ofthe where T>=0.14K.Atpositionswithmultiplelines ity =jT(v)dv/W.Theintegralsareovertherange 30% ofthehigherpeakintensity.Althoughthesevaluesare observed spectrumhasatleastonedetectedline:thepeakline Four parameterswerecalculatedforallpositionswherethe 0.5 Kkms;ifitisnotasinglestrongchannel,orspike; because thestructureoflinesisgenerallysimple.We 1908; SulenticandTifft1973), Sharpless’s(1959)catalogof in Figure1andasafalse-colormaptheupperpart of two distinctlinesiftheyareseparatedbyatleastthree these parameterswerecalculatedforeachlineseparatelyas greater than0.3Kanditsintegratedintensityis good weatherconditionstypicallyrequired1minute. false-color map,followingthestandardastronomicalconven- Figure 2.Thebestformattodisplaythevelocitystructure isa the equivalentwidthAi;=W/T,andaverageveloc- and ifitisnotatthevelocityexpectedfortelluricline. consider aspectralfeaturetobelineifitspeakintensityis northeast coveredintheColumbiasurveyofsecond No dataweretakenatdeclinationsbelow16°,aregion was detected.ThetotalareacoveredisoutlinedinFigure1. western comersareundersampled,4XI,sincenoemission frequency-switched components)of<0.14K,whichunder tion ofredforredshiftandblue(Fig.3,top[PI.45]). Figure 2(Plate44);forcomparison,thefinepeaktempera- temperature T,theintegratedlineintensityW=}Tdv, Monoceros survey,orwithin4°oftheGalacticplaneto extensively mappedbyMaddalenaetal.(1986)intheOrion- dechnation. Samplingisonthefull2X0?5gridformostof ture, T,isalsoshowninfalsecolorthelowerpart of generally simple,withsinglefinesatabout90%oftheposi- our survey,becausethevelocitystructureoffines is velocity giveafairlycompletesummaryoftheresultsfrom Galactic quadrant(Gottlieb,Brock,andThaddeus1986). correction wasapplied,sothestepinrightascensionis the survey,butsmallareasinnorthwesternandsouth- somewhat lessthan0?5intrueangle,decreasingslightlywith every 2inrightascensionand0?5declination.Nocosine tions whereCOwasdetected.WeshowWasacontour plot square degrees.Allpositionsareonaregularcoordinategrid R Rco equcoR Rco r co Most ofthespectrainoursurveyarereadilysummarized A totalof3817COspectraweretaken,covering-750 Maps ofvelocity-integratedintensityandaveragefine III. RESULTS 198 7ApJS. . .63. .645U PLATE 44 to a0?1X0?1raster wasappliedtothemeasureddata toproduceasmoothcolordistribution. Ungerechts and Thaddeus(seepage646) Fig. 2.—False-colormapsofintegrated COintensity,W(top),andpealelinetemperature,T (bottom). Atwo-dimensionalsplineinterpolation coR © American Astronomical Society •Provided bythe NASAAstrophysics Data System 198 7ApJS. . .63. .645U m (bottom). Hereno interpolationwasapplied,andthe samplingpixels(2X0?5)are clearly seen. Ungerechts and Thaddeus(seepage646) Fig. 3.—False-colormapsofthe averageCOlinevelocity,v(averagedoverallvelocitycomponents; top),andthelineequivalentwidth,Aü ay equ © American Astronomical Society •Provided bythe NASAAstrophysics Data System PLATE 45 198 7ApJS. . .63. .645U © American Astronomical Society • Provided by theNASA Astrophysics Data System (0S6D8

1 Fig. 1.—Velocity-integrated intensity of CO emission, Wco. The lowest contour is 0.5 K km s \ and the separation between contours is 1.5 K km s . The border of the surveyed region is indicated by the outer, solid Une; in the small regions beyond the dashed Une the map is undersampled, with a spacing of 4m XIo. 198 7ApJS. . .63. .645U © American Astronomical Society • Provided by theNASA Astrophysics Data System 198 7ApJS. . .63. .645U -1 hm -1 -1 -1 _1 -1 -1 h -1 hm hm hm l -1 photographs ofTaurus.Amoderatelystrongpeakinthe km sandadistanceof140pc;(3)theIC348cloud, long northerncloudatnegativevelocitiesinPerseusand interacting withthePleiades(FedermanandWillson1984). largely differingvelocities;oneofthese,at342,23°30', is higher velocity,~10kms.SouthwestoftheTaurusand IC lies inthisdirection.ThebipolaroutflowcloudL1551(Knapp northern ridgeisinHeilesCloud2,whichcontainsTMC-1 in aregionofactivestarformation.Afairlylargeisolated located mainlyintheareafreeofCOtonortheastwith because itisbelievedtoberelatedthePerOB2association Aries, atadistanceof350pcwithvelocitiesvaryingrather which lieswestoftheTaurusclouds,mainlyinPerseusand Auriga, whichisassociatedwiththeCalifornianebula(NGC logs ofdarknebulaeareshownagainstthelowestW cantly larger,5-8kms,in regionsofdoubleandmultiple false-color mapinthelower partofFig.3),butitissignifi- equivalent widthoftheCO line isonly2-3kms(seethe map appearsconnectedtothembyaratherlargecloud with km sliessouthoftheTaurusfilamentsandin W partially mapped,iswellseparatedinvelocityat8-10km s km sformsanarceastandsoutheastofthecentralTaurus A chainofcloudswithvelocitiesmostlybetween5and7 close toTMC-2inKutner’scloud(B18).Thenorthernridge map, a=4-5,020°-32°. connected tothemainTauruscloudsincenterofour dark clouds(L1492)at4-5kms,whicharesmoothly 445, 35°,thenegativevelocitycloudoverlapsAuriga near NGC1579,anebulasurroundingLkHa101.Near This cloudisassociatedwiththeCalifornianebulaNGC multiple lines,mostlyatnegativevelocities,near350,39°. Taurus darkcloudsinthecenterofoursurveywithamajor region. Thelastcloudinthechain,L1558,whichwe only extends fromHeilesCloud2throughL1495(B7)northwestto distance estimatessee§IVa).TheIC348cloudisalsoknown extension northintoAuriga,whichhavevelocitiesof5-8 contour fromFigure1. H iiregions,andBarnard’s(1927)Lynds’s(1962)cata- 348 cloudsisagroupofsmallclouds,partlyinAries,with et al.1976;Snell,Loren,andPlambeck1980)at 7 survey (Maddalenaetal.1986);theopenclusterNGC1647 and extendssouthintotheregionofOrion-Monoceros 340, 31°,whereitappearsconnectedtotheIC348cloud. and IC2087;theeasternmostpeakinsouthernridgeis spond tothetwoprominent,filamentarydarknebulaein structure, southeastintoAuriga,withanotherstrongpeak IC 348towardtheopenstarclusterNGC1342. cloud (L1434)atvelocity0-3kms~liesabout6°northof only afewstarsinthedirectionofcloud.BothWand as thePerOB2cloud(Sancisietal.1974;Sargent1979), systematically from10to0kms(foradiscussionof 1499) andNGC1579hasadistanceof350pc;(2)the 1499; itextendsnorth-northeastandthen,inaveryelongated around PerOB2thereisstrongCOemissionwithbroad T arestrongestatthepositionofNGC1333,abrightnebula co co co r Two emissionridges,clearerinTthanW,corre- Northeast oftheIC348cloudbeyondlargeCOhole Three majormolecularcloudsdominatethemaps:(1) In mostofthemolecularclouds coveredbyoursurveythe Rco © American Astronomical Society • Provided by theNASA Astrophysics Data System CO SURVEYOFDARKNEBULAE 2 hm-1 -1 hm -1 1 related. understand thethree-dimensionalspatialstructureof the kinetic energy(virialmass).Bothmethodsrequireknowledge mass) ortheassumptionofvirialequilibriumbetween complexes andtodecidewhetheroverlappingobjectswhich of theclouddistance/*,becauseCOmassscaleswith r ratio oftheCOfineintensitytoHcolumndensity(CO observations intwodistinctways,usingeitheranempirical appear smoothlyconnectedinWandvelocityactually are and thevirialmasswithr.Distancesalsoarerequired to gravitational potentialandthetotalinternalthermal and photometric distancestostars thoughttobeassociatedwith reflection .Thesecond methodisphotometryoffield highly accurate.Thefirstand generallythebestisbasedon the cloudbecausetheyexcite anembeddedHuregionor tances tonearbymolecularclouds,allindirectandnone 2 co lumbia secondquadrantandOrionsurveys,aredefinedin passes throughthemaximanearNGC1333andIC348 within onecloudaredesignatedbythenumberof prominent WorTmaxima(peaks).Severalpeaksfound velocities, passesnearNGC1579,and,atrightascension fines orrapidspatialvariationofaveragevelocity. Figures 4and5bythinbrokenfines. only partiallymapped,becausetheyarecoveredbytheCo- bers toallextendedstructures(clouds)andthemost a =420,withvelocity~kmsisoverlappedbythe evident fromFigure6cthat(1)theTaurusandIC348clouds near +5kms;thetwovelocitycomponentsareclearly 436-50, cutsthroughtheAurigacloudsatvelocities lows theridgeoflongNGC1499cloudatnegative velocity structureisshownexplicitlyinthespace-velocity rather smallcloudcomponentsbetween-8and-f3kms, in Auriga,wheretheTaurus-Aurigacloudsatpositivevelocity and thedefinitionofsomecloudsisfairlyarbitrary.Clouds Taurus clouds. overall velocityvariationintheIC348cloudaremuchlarger contour ofWforallcloudcomponentswellseparatedin ond, theL1449regionnearNGC1499,whichincludesmany Two majorareasfoundwithdoubleormultiplefinesare,first, lines andstarformation,e.g.,nearIC348NGC1333. accuracy forthepeaksisoforderourbeamsize,0?5, and aletter,asinTable1Figure4.Thepositional are connectedinvelocity,(2)thefinewidthsaswell then followsthenorthernridgeofTaurusclouds.Itis separated byadeepminimum.Thesecondfine,B'-B”-B, diagrams ofFigures66and6c.ThefineA'-A"-A'"fol- space orvelocity,withshadingtoindicateregionsofmultiple some wellresolved,otherspartiallyblended.Tosummarize overlap theNGC1499cloudatnegativevelocity;and,sec- the velocitystructure,inFigure5weplot0.5Kkms“ than intheTaurusclouds,and(3)asmallregionnear coR co The massofamolecularcloudcanbeestimatedfromCO Three methodsarecommonlyusedtodeterminethedis- Along thetwofinesdefinedinFigure6a,detailed For quickreferencetoindividualclouds,weassignednum- IV. DISCUSSION a) Distances 649 198 7ApJS. . .63. .645U © American Astronomical Society • Provided by theNASA Astrophysics Data System (0561)8 650 -c x: x: E E E O ro m O ro O ro CD ro ro ir> O} ID O

_1 Fig. 5.—Schematic representation of cloud components separated in space or velocity. Cloud outlines correspond to the 0.5 K km s level of Wco and are the same as in Fig. 4. Continuous light and dark lines represent fully mapped clouds discussed in this paper. Light dashed lines delineate clouds close to the Galactic plane and in Orion not fully mapped in this survey. Regions of double or triple lines, double-peaked single lines, and steep velocity gradients are indicated by shading. 198 7ApJS. . .63. .645U © American Astronomical Society • Provided by theNASA Astrophysics Data System -10 0 10 LSR RadialVelocity (km s') Fig. 6a Fig. 6c 651 -1 -1 contour forTis0.25K,thelowestsolid0.5and the lowest contourfor}Vis0.5Kkms(asinFigs.1,4,and5), the separation betweensolidcontours is0.5K. separation betweencontoursis6Kkms.(b,c)Thelowest,dashed two cutsshowninFig.6awithWcontoursforcomparison,(a) The R co co Fig. 6.—Space-velocitydiagramsoflinetemperatureTalongthe R Fig. 6b 198 7ApJS. . .63. .645U American Astronomical Society •Provided bythe NASA Astrophysics Data System 22*. 20 .. 24b. 24a... 442 23 .. 21c* 21b. 21a. 19* 17 .. 14 .. 13 . 12e .. 12c .. 11 ... 18 .. 16* 15 .. 12f * 12d.. 12b.. 12a*. 10 ... Peak 6 . 4 . 2 . 7 . 9 . 5 . 3 . 8e 8c 8b 8a . 8f 8d ha hn hn h hn 254 4 38 4 12 326 3 42 350 3n 3 24 3 38 3 18 3 10 3 08 3 42 346 3 42 (1950) 4 02 24 38 38 32 18 12 26 02 16 54 44 46 a 38 54 32 02 28 02 00 41 00 43 00 41 30 43 30 40 30 42 00 43° 00' 23 20 21 22 22 20° 00' 30 002.6 31 30 33 00 35 00 37 00 39 30 34 30 38 00 31 30 29 30 27 30 26 30 28 30 23 31 303.7 38°00' 38 00 35 00 39 30 38° 30'2.2 37 00 37° 30' 32 00 31° 00' (1950) 8 00 00 30 30 30 30 Small CloudsinSouthwest(TaurusandAries) T R (K) 0.9 0.9 0.7 2.0 2.3 2.6 4.1 2.8 2.2 7.8 2.8 2.3 2.7 3.5 3.2 2.3 3.6 3.2 1.2 6.2 3.2 1.9 1.8 1.6 1.0 1.8 1.0 3.2 3.1 1.4 1.2 1.0 1.5 1.8 Small CloudsinNorth(Perseus) 1 Dark CloudsinAuriga (km s)(Kkm CO EmissionPeaks y NGC 1499Cloud -9.4 + 4.7 -0.4 + 2.0 + 9.7 + 8.1 + 8.0 + 1.8 + 1.1 -1.2 + 4.3 + 5.7 -3.9 + 4.3 + 3.1 -7.0 -9.3 -8.6 -8.9 + 3.4 + 6.3 -1.0 -2.7 -5.7 -5.9 -5.0 + 4.2 + 1.1 + 2.4 + 8.9 + 1.2 -0.3 + 8.5 + 6.8 + 8.9 -1.5 -2.1 L1434 andL1446 av ^CO i IC 348Cloud TABLE 1 40.1 12.4 11.9 18.1 12.7 12.8 16.5 13.8 12.1 12.5 12.7 18.4 4.0 4.8 6.3 2.3 4.2 4.1 4.6 4.0 1.8 9.3 2.1 2.0 7.1 6.6 8.3 3.8 3.9 3.7 2.0 7.1 3.0 1.7 5.3 5.2 1.0 NGC 1333,L1452, IC 348,L1472,B3-B5 L1503 =B23, L1522 =B222(?), L1512 (?) L1492 L1488 LI505, L1496=B221, L1481 L1479 (?),[L1481] L1492 L1459, L1447 [L1443] L1449, NGC1499= L1434, NGC1342(?) L1453, L1454, S214, S215 L1478, L1482, L1478, L1473 L1446 Merope (Pleiades) HH 4-HH12,14-HH18 Bl, B2,B202-B206, [B26, B27,B28= L1523 =B29(?) NGC 1579=S222 LI 507=B24 L1517, L1519] LkHalOl, L1457, L1458 S220 (Californianebula) Related Objects 198 7ApJS. . .63. .645U nearby standardfield.An approximate upperlimittothe ity inE_atthedistanceofcloud.Inthirdmethod, used todeterminethevisualextinction^4orcolorexcess distance canalsobederived for cloudsfarfromtheGalactic tude intervaltowardthecloud andthoseinanunobscured, estimated bycomparingthe number ofstarsineachmagni- opacity ofamolecularcloudwillcausesteplikediscontinu- E_ asafunctionofthedistancetostars;generally, the withspectralorphotometricluminosityclassification, the distanceaswell extinction ofadarkcloudare bv K Bv © American Astronomical Society • Provided by theNASA Astrophysics Data System hm hmo 1 26* ..4222800 27c ...4142800 27b... 4282700 27a ...4322930 25 ....4231°00' 27d ...4082530 27f ...4362530 27e ...4282400 27g ...4442500 27i ...5142630 27h ...4522730 29 ....4281800 28 ....4102200 27j ...5262330 30 ....43620 33 ....5001830 32 ....5042030 31 ....4402130 34.... 4421730'2.7+7.911.8L1558,NGC1647(?) Peak (1950)(K)(kms“)(Kkms“RelatedObjects Note.—Spectra towardthepeaksmarkedwithanasteriskshowadditionallinesasfollows: a 8Ti;W ravco CO SURVEYOFDARKNEBULAE 1 26.. . 2.5+6.84.3 22.. . 0.5+7.4 21c... 1.0-2.73.5 12a... 0.6+3.11.3 19.. . . 0.8+0.61.6 16.. . . 2.4-1.33.8 12f ...2.9+5.04.5 Peak (K)(kms)(Kkm 6.4 +6.920.6 2.6 +3.87.9 3.8 +4.610.7 1.3 +2.04.6 4.8 +6.114.6 5.0 +5.914.2 4.6 +5.911.6 3.9 +8.18.1 4.0 +10.712.0 4.0 +7.06.2 5.8 +6.015.3 4.0 +6.17.1 0.7 +4.23.0 3.9 +7.08.6 3.5 +7.67.1 3.5 +6.08.5 1.2 +8.54.3 1.0 +3.52.7 Dark CloudsinTaurus TABLE 1—Continued Tr vWco av L1558 Perseus OB2associationlocated towardtheIC348cloud, CO-free regionnorthofIC 348, andNGC1499;theyoung associations withintheregion surveyed:theveryextended within roughly1kpc,those20°fromtheplane600 pc, plane than3a,where-65pcisthezdispersionin the plane, becausefewcloudsareexpectedtobefartherfrom the and those30°fromtheplane within400pcoftheSun. Galactic distributionofmoleculargas(DameandThaddeus 1985). Thus,clouds10°fromtheplaneareexpectedto he z Good opticaldataareavailable forsixstarclustersor L1500 =B219 L1495 =B7,L1484, L1521 =B19 L1497 (?) L1501, L1498,L1499, L1528, L1534,B14, L1529 =B18,L1542, L1538 L1545, L1547-L1549, L1537, L1539,L1540, L1559 L1551, S239,L1543, LI 541(?) HH 31 IC 359,B209,B211, L1506, B207,B208, [B212, B215],L1536 L1531, L1535,TMC-2, B210, [B212,B215] B22, B220,TMC-1, L1552, L1554 IC 2087 L1542, L1544 [S238, TTau] L1546, HH28-HH30, 653 198 7ApJS. . .63. .645U o hm hm peak 12e)maybeaslarge as800pc.TheCOvelocity (1971) estimatedthatthedistance ofLkHa101(NGC1579, uncertain: onthebasisofphotometry oftwoBstars,Herbig relation forstarsina2X2°fieldaround3C111nearpeak adopt 350pcforclouds12-20, butthisdistance,too,is 200-300 pc.Ungereretal(1985)derivedAversus r end oftheNGC1499cloudatnegativevelocities(peak12f). Auriga at300-380pcisplausiblyidentifiedwiththeeastern pc layerwiththemolecularcloudatpositivevelocitiescon- 12d, andtheyfindthatthemolecularcloudisat380pc. We sorption intheregionofourcloud12occursalayer at Heeschen (1951)concludedfromstarcountsthatmost ab- cloud followstheminimallineacrossconnectingbridge 21-33. Forthecalculationofmasseswearbitrarilyassume nected totheTaurusfilaments.Weadopt140pcas distance ofthedarknebulaeinTaurusandAuriga,i.e.,clouds follow WouterlootandHabing(1985)inidentifyingthe115 using photometryoffieldstars,foundtwoabsorbinglayers, pc (StraizysandMeistas1980). An Aversusrdiagramfor74starsinthefielda= through thesaddlepointnear345,31°. that theborderbetweenTauruscloudsandIC 348 one at115pc,theother300-380pc.Itseemsreasonableto 420-48, 5=24?5-27°alsoimpliesadistanceof140 Taurus clouds(GottliebandUpson1969),aswellwith versus rrelationforstarsinaverylargefieldincludingthe value, firstestimatedfromstarcountsbyGreenstein(1937) ing Elias(1978),generallyadoptadistanceof140pc.This layer isnearerthan300pc.Weadopt350pcasthemean pc (Racine1968).Schreur(1970)concludedfromstarcounts NGC 1499,£Per,aswelloPerandBD+31°643nearIC distances toexcitingstarsofsmallnebulosities(Racine1968). (L1449). reflection nebulositiesinthenorthernpartofcloudis330 (Frederick 1956).Themeandistancetofourstarsexciting distances of400pc(Seyfert,Hardie,andGrenchik1960; widely extendedoverthesoutheasterncloudsinoursurvey. and McCuskey(1938,1939),isconsistentwiththeE_ distance oftheIC348cloudandthatNGC1499 that allextinctionnearNGC1333occurswithin500pcofthe other estimatesare316pcfromphotometry(Strom,Strom, Morgan, andRoman(1954)derivedadistanceof380pc; Becker andFenkart1971),322pc(BorgmanBlaauw of PerOB2.PhotometricobservationsOB2imply 348, wereconsideredbyBlaauw(1952)aspossiblemembers The Hyadesaresoclose,r=40pc(BeckerandFenkart cluster atIC348;theopenclustersNGC1342and Sun, andheobtainedthebestfittohisdataifobscuring and Carrasco1974)480pcfromproper-motionstudies the distanceofPerseusOB2association.Thestarexciting 1971), thattheyareprobablyforegroundstarsunrelatedto try offourearly-typestarsintheIC348cluster,Harris, the molecularcloudsintheirgeneraldirection. 1964; Lesh1969),and413pc(Guetter1977).Fromphotome- 1647; thePleiadesnearcloud7;andHyadescluster, 654 v v Bv The secondabsorbinglayerfoundbyEklöf(1958)in In theregionofL1492andL1488inAuriga,Eklof(1958), For thedarkTaurusfilamentsmolecularobservers,follow- Most authorsadoptforIC348,NGC1333,and1499 © American Astronomical Society • Provided by theNASA Astrophysics Data System UNGERECHTS ANDTHADDEUS 1 8 _1 -1 hm 8 basis ofthedistancetoPleiades.Thedistancesother visual extinction;and,finally,r=125pcforcloud7on the versus rrelationtoward3C111,andstudiesofthelarge-scale simply beenassumed. clouds arepoorlyknownandforthesakeofcalculationhave pc fortheIC348cloudonbasisofphotometry Per nebulae, andE_versusrdiagramsforfieldstars;= 350 A -02mag(BeckerandFenkart1971;CrawfordPerry OB2 andIC348stars;r=350pcfortheNGC1499cloud on clouds onthebasisofstarcounts,distancesreflection cluster’s beingbehindthecloud,andweadoptafairlyuncer- our surveyWiscloseto6Kkms',consistentwiththe but theratherhighGalacticlatitude(-25°to-35°)sug- the basisofPerOB2distanceforNGC1499, Ay and Fenkart1971),theage1.3XlOyr(Gray1965).In distance is550pc,theaverageabsorption1.2mag(Becker parently, noinformationisavailablepertainingtoclouds1-6, Willson 1984),soweadopted125pcasitsdistance.Ap- plane isatmost200pc)possible. maps ofvisualextinction(McCuskey 1938,1939),aswell tain r=500pcforcloud34. 34) maybeanalogoustothatofNGC1342L1434:the gests thattheyarenearby.Weuse125pcforalltheseclouds, cloud 10isindirectlyrelatedtoPerOB2and12) ment (L1495)totheIC348 cloud haslongbeenknownfrom the scatterindistancesprobablybeinghigh. from undersampledorincomplete molecular-linemaps(CO: r =125pc,towardwhichtheextinctionisvariablebutlow: ated withacloudinoursurveyisthatforthePleiades, 350 pc,withthereservationthatanyvaluebetweenpc(if 1342 isinfrontoforbehindthecloud.Weuseadistance 1976). Cloud7isinteractingwiththePleiades(Federmanand 800 pc(ontheassumptionthatdistancefromGalactic be estimatedwithsufficientaccuracytosaywhetherNGC BV v km s),theextinctioncausedbymolecularcloudcannot km s.Iftheseconnectionsarerealandnotmerelya velocity transitionbetweentheAurigaandNGC1499 co yr. Thisgreatage—andtheabsenceofanyapparentinterac- visual extinctionof0.84mag(Johnsonetal1961;Beckerand unrelated. Onthebasisofourpresentdata(W=2-10K determined istheopenclusterNGC1342at550pc,witha clouds isseennear430,38°,whereWlessthan2K components areconnectedbyweak(0.25-0.5K)COemis- connected insomedirections:thespace-velocitydiagram tion betweenclusterandcloud—suggeststhatthetwoare Fenkart 1971),whoseageaccordingtoGray(1965)is5X10 the twolayersisprobablysmall. superposition oflinewings,thedifferenceindistancesto cutting throughthedouble-lineregion(Fig.6b)two distribution indicatesthatthetwolayersmaybespatially sion; intheyfalse-colormap(Fig.3,top),asmooth co co av An apparentbridgeconnecting thenorthernTaurusfila- In summary,weuser=140pcfortheTaurus-Auriga The relationoftheopenclusterNGC1647toL1558(cloud The mostaccuratedistanceforanyobjectclearlyassoci- The onlyobjecttowardcloud10whosedistancehasbeen 0 b) AretheTaurusandIC348CloudsConnected! Vol. 63 198 7ApJS. . .63. .645U -1 12 in theareaofB5,IC348,andconnectingbridgemaybe photometric dataofStrom,andCarrasco(1974)is velocity alongthebridge.Infalse-colormapof Taurus cloudsandthatforIC348.Oursurvey,thefirstfully reason forconcludingthatthesecloudsareseparatehasbeen ble, therefore,thatasignificantamountofmoleculargasand upper limittothedistanceofnearestabsorbinglayerin only 240pc.Rydgren(1971)concludedfromphotometryof derived forIC348byFenkartandBinggeli(1979)fromthe IC 348,oPer,ispossiblymuchnearerthantheassociation,at significantly closerthan350pc.ThePerOB2membercloseto nected tothemoleculargasnearIC348. diagram (Fig.6c),theTauruscloudsappearsmoothlycon- Taurus filamentsandthePerOB2association. field starsintheregionofB5andPerOB2thatmost about 200pc(BorgmanandBlaauw1964),thedistance sampled, unbiasedCOmapofthisregion,confirmsthetenta- Baran 1985;OH:WouterlootandHabing1985).Themain bridge formsanextremelyelongatedstructurealongtheline projection, correspondingtoonly24and60pcatr=140 whether therearetwooverlappingcloudsoronecontinuous Cemicharo, Bachiller,andDuvert(1985)derive200pcasan absorption inthisregionoccurswithin200pcoftheSun. average velocity(Fig.3,top)aswellinthespace-velocity tive conclusionofBaran(1985)thatthereislittlechangein into Perseus,causingasignificantobscurationintheregion of connecting bridgewouldbemorelikelyifthedifferencein orientation ofthebridgemustbeunusual,unlessadopted object. Ifthecloudsareconnected,spatialstructureand extinction liesbetween150and200pc,i.e.,the the largestdarkpatcheswithoutforegroundstars.Itispossi- the largedifferencebetweendistancederivedfor line isnotopticallythin,experience showsthat,atleastif is notasingleobjectbutchancesuperpositionofseveral with IC348andNGC1333—andpossiblyPerOB2—are NGC 1333,whilethemoreactivemolecularcloudsassociated 200-240 pc. distance werenotsoextreme,e.g.,ifIC348atr= 2.5 kms,alongthebridgeissurprising(Fig.6c).A of sight,inwhichcasethesmallvariationvelocity,lessthan distances toIC348orNGC1333,both,arewrong.Wesee the regionofIC348andNGC1333onbasissize B5 aswellinthelargestdarkpatchesbetweenIC348 and clouds within200pcextendsthroughtheregionofbridge an apparentchangeinrfrom140to350pcover<10° No. 3,1987 clouds thathappentohavenearlyequalradialvelocities. molecular cloudsassociatedwithbrightnebulaeanddark 350 pc,respectively.Ifthischangeinrisreal,theconnecting clouds inPerseus,Taurus,and Auriga.AlthoughtheCO the massesofdarknebulae andassociatedmolecular complete andprobablythemostaccurateestimatestodate of separate andfartheraway(>300pc).Ifso,theIC348cloud averaged overatypicalcloud, theratioofintensities There issomeevidencetosuggestthatpartofthematerial This conclusion,however,failstoanswerthequestionof Alternatively, wemayconsiderthatapartoftheTaurus With theCOdatainhand,itispossibletomakemost © American Astronomical Society • Provided by theNASA Astrophysics Data System c) Masses CO SURVEYOFDARKNEBULAE 1213 -21 20 -12 4 -1 5 value isconsistentwithasimilaranalysisforlargesegments intensity overvelocityandthetwomapdimensions,S,is With ameanatomicweightperHatomof1.36,weobtain of theGalacticplane(Lebrunetal1983;Bloemen part ofthesky.Sincethisanalysishasnotyetbeenperformed fairly constant(Solomon,Sanders,andScoville1979;Stark, COand(whichismuchmorenearlyopticallythin) region oflocalcloudsatdistancestypically500pc.This for theOrion-MonocerosregionbyBloemenetal(1984),a cm (Kkms)derivedfromColumbiaCOsurveydata rently availablemeasurementsarebasedonacorrelation Penzias, andBeckman1983).TheintegraloftheCOline where risthedistancetocloudinpcandSunitsof for oursurvey,weusetheratioAr(H)/tT=2.6x10 1986), andagreestowithinafactorof2withresultsfrom analysis ofCO,HI,andtheCOSBy-raysurveyoveralarge termination oftheaverageY(H)/JFratio.Thebestcur- Calibrating *Scointermsofmassrequiresobservationalde- therefore approximatelyproportionaltothecloudmass. ing virialequilibriumbetweenthegravitationalpotentialand K kmsdeg. in oursurvey,whiletheneardarkcloudsTaurus and which becomes where GisthegravitationalconstantandRcloudradius, Auriga coverthelargestareaandprovidemostof CO integration boundariesthatfollowtheminimalfinesthrough where risthedistanceinpcandAcloudareasquare sight, wesimplyusedthevirialformulaforahomogeneous sity structureoftheclouds,particularlyalongline sources ofpressure.Lackingadequateknowledgetheden- the kineticenergyinabsenceofmagneticfieldsorother clouds, accountforthelargestcontributionstoCOmass Table 1andFigure4.Forcloudsnotwellseparated,we use mean velocity(v)andFWHMAvoftheaveragespectrum, sphere andaMaxwellianvelocitydistribution: each amassofabout5X10 M, orabout50%ofthemass flux. Thetotalmolecularcloudmassinthesurveyamounts to degrees; Av=0.94Ai;(inunitsofkms)istheFWHM the largestobjectsinOrionand Monoceros(Maddalenaetal. almost 2xl0M.TheIC 348 andNGC1499cloudshave the valleysandsaddlepointsbetweenpeaks. adopted distance,accordingtothedefinitionofclouds in the COlineobtainedbyaveragingallobservedspectrawithin 1986). Otherestimatesofthese massesexist:fortheIC348 the angulararea,integratedCOintensity*Sco>and the the cloud. co W/A ratios(Bloemenetal.1984;Maddalenaetal1986). 2co 2co 0 eq Q cov For comparisonwecalculatedthevirialmass,M,assum- Distant objects,inparticulartheIC348andNGC1499 For selectedclouds,Table2fiststhemassessoderived, vir 21/ M/ =209.6r(Ay)tan(^/w),(3) vilQ 2 M/ =l.lïXl^rS(1) 2 C0QC09 M^ =5R^v)A%G\nl),(2) 655 198 7ApJS. . .63. .645U 4 4 =z21- 4 4 4 4 4 656 NGC 1333andIC348takeintoaccountonlyabout50% Wouterloot andHabing(1985),assumingr=300pc,derivea The onlyextensiveindependentmolecular-linemapof the molecular cloudsinthesky;becausetheyaresoclose,how- mass of4X10MfromanOHsurvey.Giventhedifferent of theareawherewedetectCO.ForNGC1499cloud, r =330pc,obtains1.2XlOMfromCO.Theseestimates cloud, Sancisietal.(1974),assumingr=300pc,derive1.6X Assuming thatN(¥Í2)/^v0.94X10cmmag'(Bohlin, low-resolution AmapofMcCuskey(1938,1939),which A roughestimateofthecloudmassispossiblealsofrom the Taurus-Auriga cloudsistheOHsurveybyWouterloot and (clouds 21and24-33),areinangularsizethemostextensive sonably well;theuncertaintyindistanceprobablycon- sampling andcoverageofthemaps,thesevaluesagreerea- 10 Mqfromopticalextinction,andSargent(1979),assuming our cloud27,theagreementisasgoodcouldbeexpected. of 1.5XlOMq.Sincetheirmapdoesnotcompletelycover Habing (1985),who,foradistanceof110pc,estimatemass ever, theirtotalCOmassismodest,onlyabout3.5X10M. tributes thelargestuncertaintyinmass. are basedondatalimitedtotheregioncloseandbetween compared with2.6XlOMq fromCO. 27 is150squaredegrees,weobtain(1.8-2.2)XlOM , as 27, theTauruscloud,do M andM^agreeto50%. and 27ageneraldistributionsimilartoourCOmap. shows anaverageextinctionof=1.0-1.2maginclouds 24 CO andvirialmassesformost oftheclouds.Onlyincloud Savage, andDrake1978)thattheareaofclouds24 and Q 0 v 0 0 co The largedarknebulaeinTaurusandAurigaat140pc An importantresultofoursurvey isthedifferencebetween © American Astronomical Society • Provided by theNASA Astrophysics Data System 23 21 26 25 24 12 10 velocity fluctuations(clumping).Cloud34wasonlypartially(~50%)mapped. 29 28 27 14-20 (total) 11 34 32 33 2-6 (total). 9 7 1 8 Total Note.—Distances inparenthesesareuncertain.Virialmassesshownbracketsforcloudswithlarge Cloud x (km s) + 10.0 <"> -3.3 + 4.6 + 1.0 + 1.3 + 5.3 + 9.4 -1.6 + 3.7 -4.2 + 4.2 + 6.5 + 1.4 + 5.5 + 4.3 + 5.7 + 8.4 + 8.6 UNGERECHTS ANDTHADDEUS -1 (km s) 4.5 4.3 4.3 4.4 6.4 2.1 4.0 4.1 2.6 3.3 3.4 7.4 2.7 2.4 2.4 3.1 8.3 3.2 Ay 2 (deg) (KkmsMeg 128 374 Area Cloud Masses 41.8 20.9 34.6 15.2 20.5 14.1 35.8 13.3 18.6 0.8 4.7 6.4 2.6 2.5 3.1 3.0 1.8 5.9 1.9 TABLE 2 higher N(R)/Wratiooranycloudstructureimplyinga by afactorof4-6thanassumed,butthecloudswouldthen M /MforthesubstructuresofTauruscloud(27a-27j) M typicallybyafactorof4-6;theaverageratio Elsewhere, e.g.,inclouds8,10,and12,M^.ishigherthan lower Mforthesameobservedvelocitydispersionwould have tobeunrealisticallyfarfromtheGalacticplane,e.g., M andwouldberesolvedifthedistancesweregreater cloud 27(B18andHeilesCloud2).Thediscrepancybetween Murphy andMyers(1985)from8'observationsofpart possibility thattheseobjectsarebound.Inanycase,themore most ofthecloudsarenonspherical,wecannotruleout the range (see,e.g.,thediscussioninBloemenetal.1984),and more than300pcinthecaseofNGC1499.Alternatively,a also isapproximately4,consistentwithvaluesderivedby broad andmultiplelines,e.g.,nearNGC1333 distant cloudsaredynamicallymuchmoreactivethan the decrease M^/Mqq.SinceavalueofN(ñ)/Wabout pected invirialequilibrium by aboutafactorof10(Blitz, dark cloudsinTaurusandAuriga,asindicatedbyrather twice ashighweusediswithinthegenerallyaccepted for thesmallestindividualclouds,whicharemorenearly Magnani, andMundy1984; Keto andMyers1986;DeVries, observed COvelocitydispersion exceedsthedispersionex- clouds seenbyIRASathigh Galacticlatitudes,forwhichthe are listedinTable2.Theysimilartothesmallnearby spherical; withabout20suchobjectsinoursurvey,onlya few and 12aswellas,althoughmoreirregularly,withinclouds 10 and 34. 1499, andbysystematicvariationsinvelocityalongclouds 8 1co virco co vir virco 2co The ratioofAftoMisevenlarger,typically10-30, virco 1736 263 668 235 119 110 27.6 12.9 30.0 19.3 11.3 31.2 68.3 38.3 18.6 51.5 2.2 5.0 5.1 3.1 8.4 Distance (125) (350) (350) (125) (140) (350) (140) (140) (500) (140) (pc) 140 350 350 350 125 140 140 140 140 140 4 (10 Mq)M) 0 18.7 M 0.05 0.08 0.04 0.02 0.40 0.66 0.58 0.27 4.96 0.01 0.05 0.01 0.13 0.06 0.17 0.03 0.34 2.98 2.26 5.55 r 19.2 30.1 [0.98] [3.1] [1.2] [2.3] 0.7 0.16 0.31 0.30 0.59 0.29 3.4 3.4 3.25 1.3 1.3 7.5 Vol. 63 198 7ApJS. . .63. .645U -1 -1 o km s,probablycausedbytheoverlappingandblendingof £ Per,NGC1499,LkHa101,and1579.Thedistanceto limited bypoororconflictinginformationaboutdistancesto ing ofthestructurecloudsalonglinesightare clouds inthesoutheastareincludedbyMagnani,Blitz,and Mundy (1985)inthelistofhighGalacticlatitudeclouds,but, L1457, L1458(cloud1)showsanextremelylargeUnewidth,7 Heithausen, andThaddeus1986).ThegroupL1453,L1454, NGC 1499cloudatnegativevelocitiesextendingfromAuriga as expected,wefindseveralsimilarobjects,e.g.,clouds11, several clumpsorcloudsatdifferentvelocities.Somesmall Auriga darkcloudsbutiswellseparatedinvelocity.TheIC (b =—25°to¿>-35°). distances (350pc)aretheIC348cloudandelongated dark cloudsinTaurusandAuriga.Majoratlarger grees) showsCOemission,mostlyfromthenearby(140pc) 16-20, and33,muchclosertotheGalacticplane. cloud, atadistanceof350pc(250-800pc),overlapsthe (conservatively withintherange100-200pc).TheNGC1499 clusters, particularlyNGC1333,oPer,IC348,PerOB2, also detectseveralsmallcloudsfarofftheGalacticplane along NGC1579totheCalifornianebula(NGC1499).We associated Hnregions,reflectionnebulae,stars,andstar 348 cloud,withanadopteddistanceof350pc,appears the Taurus-Aurigacloudsisfairlywellestablishedat140pc integration timeateachgridpointwithinthe0?5x0?5effectivebeamisamultipleofbasicsignal-reference cycle.The baselines overarestrictedspectralrange,wefoundthatthe subtractionofacurvedbaselinecauseserrorsintheintensitiesno used inthepresentsurvey;durationofcyclewasmaintainedcloseto1sandadjustedautomatically, sothatthe frequency switching,butissubtractedoutbypositionswitching.Frequencyswitchingoveranintervalofeither8 or 6MHzwas from themesosphere,atrestinlaboratoryframeofreferencealthoughgenerallynotLSR,alsoappears during consisting ofasingleastronomicalemissionlineatanLSRvelocitybetween-15and+15kms;telluric emissionline be attributedtothedifference inangularresolution.Wedonotresolvethepeculiar velocitystructurearoundNGC1333, reference phaseofthefrequency-switchingcycleyieldsnegativeimagesbothastronomicalandtelluric lines(Fig.7, more than5%. top). Third-orfifth-orderpolynomialbaselineswerefittedtothechannelswithoutastronomicalCOlinesand removed(Fig. full spectralrange,whichistherangeusedforbaseline fit.Fromacomparisonofresultsfordifferentbaselineordersorlinear 7, middle),andthespectrathenfolded(Fig.bottom)to increasethesignal-to-noiseratio.Thelinesaremuchnarrowerthan attributed toacollisionbetween cloudsbyLoren(1976),orthesmallregionofabipolar high-velocityflowinL1455(B204),about I southofNGC1333(Snell andEdwards1981;Goldsmithetal.1984). 1333 andIC348.OurCOintensities arelowerthanSargent’s(1979)byafactorofthe order of3,adifferencewhichcanprobably No. 3,1987 2. Theaccuracyofourmassestimatesandunderstand- 1. Nearly50%ofthetotalareasurveyed(750squarede- The 115GHzCOspectrumtowardthedarknebulaeinPerseus,Taurus,andAurigaisgenerallysimple,atmost locations Molecular cloud8,locatedin thevicinityofPerseusOB2association,containsatleast tworegionsofstarformation,NGC © American Astronomical Society • Provided by theNASA Astrophysics Data System V. SUMMARY COMMENTS ONINDIVIDUALCLOUDS CO SURVEYOFDARKNEBULAE DATA REDUCTION I. THEIC348CLOUD APPENDIX A APPENDIX B -1 4 4 jects aremoreturbulent,owingtoassociatedstarformation, high Galacticlatitude. resemble thesmallmolecularcloudsobservedbyIRASat M havethelargestratioofvirialtoCOmass:10-30.They are apparentlynotgravitationallyboundandinthisrespect bridge about200pclongconnectstheTaurusandIC348 km s)invelocity. needs tobereviseddownwardabout200pc;or(3)thatin M (assumingadistanceof350pc).Themuchmoreex- molecular cloudmassinoursurvey,eachwithabout5X10 clouds; or(2)thatthedistancetoIC348andNGC1333 smoothly connectedtotheTaurusclouds,implying(1)thata separated (by100-200pc)inspacebutareveryclose(<2 the regionnearIC348twolayersofclumpycloudsarewell equal tothatderivedfromtheCOluminosity,butfor 10M. tended butnearerTaurus-Aurigacloudscontainabout3.5X derived fromtheirCOluminosity,indicatingthattheseob- IC 348andNGC1499cloudsis4-6timeshigherthanthat or havelarge-scalevelocitygradients. 0 manuscript. H.U.wassupportedbytheAlexandervon editorial assistance,andE.Michaudforhelpwithtypingthe Humboldt FoundationthroughaFeodor-LynenFellowship. the telescope,P.Myersforhelpfulcomments,E.Sarot 0 g 5. About20small,isolatedcloudswithmassesoforder100 4. ThevirialmassforthenearbyTauruscloudsisabout 3. TheIC348andNGC1499cloudscontainmostofthe We thankE.S.PalmerandT.M.Dameformaintaining 657 S 658 UNGERECHTS AND THADDEUS Vol. 63 00 KO CHANNEL NUMBER 0 128 256 ^0 ft r- O'!oo

LSR RADIAL VELOCITY (km s-1) Fig. 7.—A typical spectrum from the survey, obtained at peak 27f near TMC-1: (top) the unprocessed raw spectrum; the crosshatched bars indicate the region fit with a third-order baseline; (middle) the spectrum after baseline subtraction; (bottom) the spectrum flipped and folded to enhance the signal-to-noise ratio.

Several regions in the IC 348 cloud show double peaks, broad lines, or line wings, mainly on the ridge but also in the weak southwest, indicating that the cloud is clumped and turbulent. Only one region, north of NGC 1333, shows line peaks sufficiently separated to suggest the definition of another cloud, cloud 9, which appears as an arc northeast of NGC 1333 in the Wco map (Fig. 1). In our survey the line at the NGC 1333 position is very broad and shows a wing extending down to 0 km s-1 (Fig. 6c), including contributions from the possibly colliding clouds and from cloud 9.

© American Astronomical Society • Provided by the NASA Astrophysics Data System 198 7ApJS. . .63. .645U -1 1 _1 hm-1 hm-1 m -1 1 -1 -1 -1 -1 _1 -1 -1 m -1 -1 -1 peaks andasymmetriclinesatseveralpositions,suggestingadistinctobjectwithmajorpeak,12d,-2.7kms.Peak12eis by SchneiderandElmegreen(1979).Westnorthwestofpeak24a,atÔ=30°-33°,thereareblendeddouble lines,which, km s“,somewhatlowerthanthoseoftheTaurusclouds.ThevelocitiessomecompactdarkcloudsinAurigaare knownfrom velocity ofthesecoresisknownfromobservationsmanymolecules,includingHCNandNH,mosttheCO emissionis observations ofNHandothermoleculesthattracehighdensities,e.g.,forL1517(BensonMyers1983;Myers, Linke,and . (1976). OursurveyshowsthattheNGC1579cloudismerelyalocalmaximuminlargecomplexextendsasfar 101 (Herbig1956);themolecularcloudinthisregionwaspartiallymappedCOwithhighangularresolutionbyKnappetal at thepositionofNGC1579(S222),areflectionnebulaandcompactHnregionexcitedbyluminousemission-linestarLkHa find broadlines,singleandmultiple,atvelocitiesfrom—8to+4kmsinaregionthatextendstheHnfrontnear survey. ItsionizationfronthasapparentlyreachedthedarkcloudL1449tonorthwest(ElmegreenandElmegreen1978).We The northwesternpartoftheTauruscloudsisdominatedbyabroad,strongmaximum,27c,closetoL1495(B7) andIC359. 24a, B26-B28(L1517,L1519)areveryclosetotheeasternrimofmolecularcloud,asnotedpreviouslyfrom POSSprints compact, withdiameters<5',andquiteopaque.Thisregionisfilledmolecularclouds2124,atvelocities from3to6 358, 37°to4841°.Southeastofpeak12c,thevelocityincreasesbykmsover2°,andspectrashowclosedouble No. 3,1987 without anyvisiblecondensations,whilethedarkcloudnear peak27ihasagooddealofopticalfinestructureon5'-10'scale. our maps,probablybecauseitistoonarrow,containedinthegeneralCOridgealongB7(27c),L1521(27b),and L1528(27f). toward thewesternborderofcloud,near43,33°,separateintotwoclearcomponentsatand7kms. CO component,suggestingthatthedarkcondensationsareembeddedinAurigaclouds.Locatedabout12 eastofpeak Benson 1983;Gaida,Ungerechts,andWinnewisser1984).Thesevelocitiesgenerallyagreewellwiththatofthepositive-velocity connected tocloud17byemissionbelowourdetectionlimit. km s,extendingsouthwest tocloud32,whichshowsonlyextremelyweakopticalextinction. Thenarrow-lineclouds32and33 molecules. EastofHeilesCloud2,thedarkcloudsL1538 (withpeak27g)andL1537,L153927h)extendover2° naturally wonderswhetherotherapparentlysimilarpeaks inthesurroundingmolecularcloudsaresimilarlyrichcomplex nebula IC2087.TheembeddeddensecoreTMC-1isnot conspicuous inoursurvey,owingtothelowangularresolution,andone region allcomponentsblendintoonelineat6kms“. or secondarypeakat6kms,and27ethereisonly asingle,rathernarrowlinecloseto6kms.Northofthistransition the northernborderofTaurus,andcloud26havelowervelocities. at thesamevelocity:i?=5-8kms.WedesignatedveryextendedCOcloudinthisvelocityrangeas27; cloud25,at and TMC-2(see,e.g.,Myers,Ho,Benson1979;Myers1983;Gaida,Ungerechts,Winnewisser 1984).The 15-17 appearconnectedtoeachotherandpeak12c(L1459),buttheyareallwellseparatedinvelocity;cloud18maybe the POSSprintsshowonlysomediffusebrightnebulosity,LBN713,714(Lynds1965).Inprojectiononsky,clouds connected. Southeastofpeak 28theaveragevelocityremainshigh,-10kms,so thiscloudiswelldistinguishedfromthe unstructured darkcloudL1559. at 7-8kms(peak27d)weakens,andadifferentlineshows upnear4kms;farthereast,thecomponenthasawing Halfway betweenpeaks27dand27e,nearB212B215, isapeculiartransitionbetweendifferentvelocitycomponents:theline spectra atsomepositionsinthevalleyhaveclosedoublepeaks,indicatingthatfilamentsmaybeseparatedvelocity byabout eastern halfofthesouthern filament(peak27e).About1?5westofpeak27j,anarrow bridgeofemissionappearsatu=5 Beyond peak27i,COemissionatvelocitiesnear7kms continues foranother18,reachingalastpeak,27j,closetothediffuse, 1 kms. than 8Kkms,correspondstotheregionwithlowopticalextinctionbetweennorthernandsouthern filaments. The South ofpeak27cawell-definedvalleyintheCOdistribution,whereWdropsbelow2Kkmsbeforerising again tomore are rathercloseinvelocityto thecentralTaurusclouds,soweincludetheminthiscategory. 53 3 av av co The CalifornianebulaNGC1499(orS220),withalengthofover5°,istheonlybright,extendedHnregioninareaour North oftheNGC1499complexareseveralsmallclouds(14-20),allbutoneatnegativevelocities.Inregioncloud14 The northernopticalTaurusfilament(B213,B216-B218),veryprominentonthephotographsbutnotclearlyoutstanding in The Tauruscloudsinthecenterofoursurveycontainfilamentarydarkwithembeddeddensecores,such asTMC-1 The southerndarkfilamentincludespeak27d,closetoL1501andB208,27e,nearTMC-2B18(Kutner’s cloud). 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