195 9ApJ. . .129. .2 8 7K 1 with theopenclusterpositionsgivenbyTrumpler (1930),Collinder(1931),andHaffner given bymodelatmospherecalculations,thoughinformation derivedfromrocketflights may alsoprovevaluable.Onesuchstar,SZCam, whichwasmentionedbyKuiper of cases.Themajoruncertainfactoristhatthe bolometric corrections;thesearebest of photoelectricandspectrographicobservations,absolute radiideterminedinanumber curate luminositiesforsomeofthesestarscouldnow bederivedand,byacombination B starsdependslargelyontheobservationsofasingleeclipsingbinary,wehavemade Miss UnderhillforherModelIII,whichissupposedtorepresentastarofspectral derive T=28300°K.Thisvalueisgratifyinglyclosetothe—28470°Kgivenby metric correctioncomputedbyMissUnderhill(1957)forastaroftypeB1.5V,we parallax, theabsolutedimensionsofprimarygivenbyStibbs(1948),andbolo- Keenan andMorganforthatspectraltype.IfweadoptthisstarBlaauw’s(1946) Kholopov 1958),leadtoaconsiderablyhighervalueofTthanthe21400°Kgivenby cluster photometryisavailable,andthespectraltype isnotknownontheMKsystem. search foreclipsingbinariesingalacticclustersandO-Bassociations.Presumably,ac- type B1.5V. adopted Kuiper’sscalewithonlyminormodifications.Indeed,furtherstudiesof¡j}Sco, be lowerthanthosecomputedbyKuiper.Ontheotherhand,KeenanandMorgan(1951) mean parallaxes,concludedthattheeffectivetemperaturesofearlyB-typestarsshould The result,however,wascriticizedbyKopalandTreuenfels(1951),who,fromstudiesof favorably withthatcomputedfromtheoryforastarofspectraltypeB3,viz.,18700°K. from thethenavailableluminosity,radius,andspectraltype(B3).Thisvaluecompared the primaryofwhichisnowclassifiedasB1.5V(Kukarkin,Parenago,Ephremov,and (1938) asbelongingtoNGC1502,hasbeenstudied byWesselink(1941);however,no based onamodelbyPannekoek(1936).Observationalconfirmationwasaffordedthe vational andtheoretical,theeffectivetemperaturescaleremainsfarfromdefinitely eclipsing binary¡jlSco,forwhichKuipercomputedaneffectivetemperatureof15800°K scale wasonecomputedbyKuiper(1938),which,forthestarsofearlyspectraltype, significantly fromthatfoundforthegroupofalleclipsingbinarieswithknownspectraltypesbrighter settled, particularlyamongthestarsofearlyspectraltype.Thefirstgenerallyaccepted I Car,Cru,XICyg,Per,andIISet.Theperiod-frequencyfunctionofthisgroupdoesnotdiffer brighter thanM—+1,withlogP^+1.4lyinginopticalcoincidencetheassociationsIAur, aie 577suchstarsinopticalcoincidencewithknownO-Bassociations.Ofthelatter,thereare105 e than M=+1andwithlogP^+1.4. e v v © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem The positionsofalleclipsingbinarieslistedbyKukarkin etal.(1958)werecompared In viewofthefactthatourknowledgeeffectivetemperaturescaleamong Though offundamentalimportanceinmanystellarastronomyproblems,bothobser- Twenty-six eclipsingbinariesarefoundtoliewithinthelimitsofgalacticclusters;inaddition,there ECLIPSING BINARIESINGALACTICCLUSTERS Goethe LinkObservatory,IndianaUniversity Yerkes Observatory,UniversityofChicago AND 0-BASSOCIATIONS Received November12,1958 Arlo U.Landolt Robert P.Kraet ABSTRACT AND 287 195 9ApJ. . .129. .2 8 7K are listedinTable1.Thefainteststarhas=14.0atmaximumlight.Inafew 288 NGC 7243 Pleiades clusters cover0.48percentofthetotalarea.Ifweassumethat1210eclipsingvari- well studied. cases clusterphotometryisalreadyavailable,but,onthewhole,grouphasnotbeen galactic equator,asdo23ofthestarslistedinTable1.Withinthisband,open NGC 7790 NGC 7380 NGC 7209 NGC 6871 IC 4756.. Tr 31.... ables brighterthan14.0pgatmaximumlightwhich liewithinthisbandaredistributed Tr24.... fact thatwefind23inclustersindicatesthe relationship isaphysicaloneinmost NGC 6416 NGC 5316 NGC 4103 Tr 18 NGC 1502 (1957). Atotalof26starswasfoundtoliewithinthelimitsopenclusters,andthese NGC 3766 IC 2602.. TrlO NGC 2632 NGC 2437 cases. at random,wewouldpredictthat6shouldlieaccidentally withintheclusters.Thus NGC 3532 Coma. ... C 213.... O-B associations,thedimensionsandpositions of whichhavebeensummarizedby Schmidt (1958).Weshallmakenoattempttolist eventhebrightestoftheseobjects. star whetheritsdistance is compatiblewiththatgivenbySchmidtforthe association. So fewspectraltypesareavailablethatitisseldom possibletodetermineforaparticular whether agivenstarbelongs tooneortheother,ifeither. In afewcases,twoassociations mayoverlapsothatitisnotpossibleto determine © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem The greatmajorityofopenclusterslieswithinabandwidth16°centeredonthe * 1NotedbyKuiper(1938);studiedWesselink(1941);noclusterphotometry. We havefound,aswell,that577eclipsingbinaries areinopticalcoincidencewiththe 3. AcoirectedpositionforNGC7790hasbeengivenbyKraft(1958). 2. Starisclosetotheedgeofcluster. Cluster TZ Lac V453 Cyg V447 Cyg V789 Sgr V588 Sco BU Ser V496 Sco V589 Sco V619 Cen DH Cep AI Cm IX Cen QX Cas CN Lac SS Lac BE Cen EN Car DU Car DX Vel BX Vel SZ Cam AH Tau RW Com GV Car RY Cnc GIPup Star ROBERT P.KRAFTANDARLOU.LANDOLT Eclipsing BinariesinGalacticClusters EA EA E EW EA EA EA EA EA EA E E EB EA EA EA EA EA EA EA EA EA EA EA EB EW Type (Max.) 13.5 10.2 13.2 12.5 11.8 11.9 11.1 14.0 12.6 10; 4 13.6 10.2 13.8 10.1 13.1 13.9 12.8 12.5 11.2 12.4 w pg 9.2 8.9 7.0 8.3 8.5 8.9 (Min.) 15.3 12.5 11.0 15.2 14.6 15.0 15.5 16.5? 10.7 10.6 15.1 12.9 10.5 14.5 13.0 12.3 13.8 14 11.9 13.8 Wpg TABLE 1 9.4 9.4 7.3 9.95 9.0: 8.6 Period 16.45 14.42 (days) 0.333 4.29 4.97 2.70 3.89 0.637 0.237 9.09 3.69 2.40 2.21 5.10 2.19 2.61 1.09 2.11 2.88 1.12 1.34 1.53 1.84 1.42 A5 F5 A0 BOn OB B7 B B2 B1 III 06+06 B7 Glp G3 G2+G2 Spec- trum Johnson (1952) Johnson and Johnson and Koelbloed (un- Becker and Sandage (1958) published) Knuckles (1955) Knuckles (1955) Stock (1954) Photometry Cluster marks* Re- 195 9ApJ. . .129. .2 8 7K frequency functions(logPS 1.4)ofthestarswithin1000pcandassociation “mem- is concerned. constitutes arandomsampleofeclipsingbinariesbrighter thanM=+1withlogP^ certainly within1000pcofthesun,iffrequency functionoftheluminosityclasses sumed thatthosedidnotweredwarfs.Themajority ofthese158starsarealmost one componentoftypeO,B,orA,manydidnot haveluminosityclasses,butweas- distances givenbySchmidt(1958).Theseassociations wereselectedonthebasisof certainly greaterthan1000pc;oftheremaining158stars,allwhichcontainedatleast The fulllinereferstotheassociationfields. A2 V,andwithwg^+10.ThiseliminatesvirtuallyallstarsoftheWUrsaeMajoris so astoincludeonlystarsmoreluminousthanthosecorrespondingspectraltype coincidence withtheassociationsareactuallyassociationmembers;(2)groupof limiting magnitude.Wemakethreeassumptions:(1)theeclipsingbinariesinoptical numbers ofstarsandfreedom fromoverlappingwithotherassociations. The period- counted intheassociationsIAur,Car,XICyg, ICru,Per,andIISet,usingthe among theearly-typestars(cf.TrumplerandWeaver 1953)isthesameamongbinaries 200 starsremaining,weeliminatedthosewhichhadlogP>1.4anddistances binaries downtoacertainapparentmagnitudelimit.Wehavechosenthelattergroup eclipsing binarieshavingspectraltypesconstitutesarandomsampleofall However, itisofinteresttocomparetheperiod-frequencyfunctioninassociationfields bers” arecomparedinFigure 1.Achi-squaredtest,runonthehypothesis that thetwo as amongsinglestars.Weshallthereforefurtherassume that(3)thisgroupof158stars with thatofalleclipsingbinarieshavingspectraltypesandwhicharebrighterthansome regions (cf.Plaut1953).Thusnothingcanbesaidregardingtheratioofnumber type; theseobjectsareclosetotheplatelimitinmostofassociationfields.From ingly spottybecausesurveyshavebeenmadetofaintmagnitudesonlyincertainlimited eclipsing binariestoallstarsinassociation,ascomparedwithnon-association,fields. + 1.4andlyingwithin1000pcofthesun,atleastso farastheperiod-frequencyfunction v P © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem One hundredandfiveeclipsingbinariesdowntothis absolutemagnitudelimitwere The distributionofeclipsingbinariesasafunctiongalacticco-ordinatesisexceed- Fig. 1.—Theperiod-frequencyfunctionofeclipsingbinariesinassociationandnon-associationfields. ECLIPSING BINARIES 289 195 9ApJ. . .129. .2 8 7K Underhill, A.1957,Pub.Dom.Ap.Obs.Victoria,10,357. Trumpier, R.J.,andWeaver,H.F,1953,StatisticalAstronomy(BerkeleyLosAngeles:University Wesselink, A.J.1941,LeidenAnn.,Vol.17,No.3. Trumpier, R.J.1930,LickObs.Bull.,14,170. Stibbs, D.W.N.1948,M.N.,108,398. Schmidt, K.H.1958,Astr.Nach.,284,76. Plaut, L.1953,Pub.KapteynAstr.Lab.Groningen,No.55,p.43. Sandage, A.R.1958,Ap.J.,128,150. Pannekoek, A.1936,Ap.J.,84,484. Kukarkin, B.,Parenago,P.,Ephremov,Y.,andKholopov,P.1958,GeneralCatalogueofVariableStars, Kuiper, G.P.1938,Ap.J.,88,429. Kopal, Z.,andTreuenfels,C.1951,HarvardCirc.,No.457. Johnson, H.L.,andKnuckles,C.F.1955,Ap.J.,122,219. Kraft, R.P.1958,Ap.J.,128,161. Kholopov, P.N.1958,PeremmennyeZvezdy,11,325. Keenan, P.C.,andMorgan,W.1951,inAstrophysics,ed.J.A.Hynek(NewYork:McGraw-Hill binaries doesnotdifferfromthatofeclipsinginthe“vicinity”sun.If conclusions, butitappearsthattheperiod-frequencyfunctionofassociationeclipsing 290 Johnson, H.L.1952,Ap.J.,116,640. Haiïner, H.1957,Zs.f.Ap.,43,89. Collinder, P.1931,LundAnn.,No.2. Blaauw, A.1946,Pub.KapteynAsir.Lab.Groningen,No.52. Becker, W.,andStock,J.1954,Zs,f.Ap.,34,1. Kholopov’s discussionincludesneithersomestarsgivenmourtablenoranyremarkson listed inourTable1.However,wehavedecidedtoproceedwithpublication,since zero agetostandardmainsequence. these starsdonotchangetheirperiodsappreciablyinthetimetakentoevolvefrom age mainsequencethanbinariesofthegeneralfield,wemaytentativelyconcludethat true, onlyonceintwentytimes. distributions donotdiffersignificantly,suggestedthatwewouldrejectthehypothesis,if Kholopov (1958)whichcontainsalistofmanytheeclipsingbinariesandclusters the associationbinarieswerethoughttorepresentapopulationofstarsnearerzero- the eclipsingbinariesinopticalcoincidencewithO-Bassociations. © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem of CaliforniaPress),p.393. Yol. 1(Moscow:AkademiiaNaukS.S.S.R.). Book Co.),p.20. Because ofthegreatuncertaintystatistics,itisdangeroustodrawanydefinite Just asthispaperwasabouttobesentthepress,wereceivedanarticlebyP.N. ROBERT P.KRAFTANDARLOU.LANDOLT REFERENCES