1958Apj. . .128 . .150S CEPHEIDS in GALACTIC CLUSTERS. I. CF CASS

1958ApJ. . .128 . .150S ms h 194 located withintheclusterareaasoutlinedby brightmemberstars,andthereis cepheid CFCasshasaperiodof487513days,anamplitudeAF=055mag,normalmeancolor 6664 (Arp1958),andwithNGC129(Arp,Sandage, andStephens1958),makeitalmost membership, thegeneralagreementofpositions ofCFCassinthecolor-magnitude papers willbewrittenbyArp,Irwin,Kraft,andSandage.Theaimoftheseriesisto is m—M=128±015Thedistance3630250parsecsinthedirection/83?5,b—0?8 period wasfound binary areprobablyBlVstarswithM~—36Fragmentarydatagivenforthestar,butno certain thatCEa,CEb,andCFCassbelongtoNGC 7790. diagram ofNGC7790,comparedwithM25and NGC6087(Irwin1958),with little questionofmembership.Althoughradial velocities arenotavailabletocheck Trumpler, incorrectbyaboutl30(Kraft1958). Thethreevariablesareactually is becausetherightascensionforNGC7790is, asquotedbyDreyer,Shapley,and Bergh (1957)failedtolistCFCassorCEas probable membersofNGC7790.This found. Afinaldiscussionofthecolorsandperiod-luminosityrelationwillbemade indices of(B—F)o=072±04,(U—B)4903,andmeanabsolutemagnitudesoíM is CFCass,whichanormalvariableofperiod4.87522days(ParenagoandKukarkin 6087 andM25. NGC 6664,and7790arereportedbyKraftinPaperII.Thedatafor6664 The resultsforNGC7790appearinthispaper.spectroscopicdata129, give thephotometricandspectroscopicdataforeachofatleasteightclusterswhich are givenbyArpinPaperIII.TwosubsequentpapersIrwinwillgivedataonNGC season fortherightascensionregionof0to6.Theindividualpaperswillappearin when alltheclusterdataareavailable.Thisshouldoccurafter1958-1959observing components AneweclipsingstarhasbeenfoundwhichmayalsobeamemberBothofthe This starisveryprobablyamemberofthegalacticclusterNGC7790.ThedoublecepheidsystemCE order inwhichtheyhavebeencompleted.Photometricmaterialisnowcompleteon contain cepheidssothatnormalcolorsandabsolutemagnitudesofthecanbe separation ofthestarsis2"atapositionangle266°.Thethirdcepheidincluster and 5.1275days(G.A.Starikova,quotedinRussianVariableStarCatalogue).The contains thethreecepheidsCECass,Cassa,andb.Thedoublestar 14.35 ±015,thereddeningisE(B—V)=05204,E{U—B)3803Thetruemodulus CF CassinNGC7790,EVSet6664,SNor6087,andUSgrM25. Cass aandCEbisalsoprobablyclustermember,butnophotometricdatawereobtainedforthe Cass aandbisunique.Eachcomponentofthepaircepheidwithperiods4.4462 °)- -2.50 ±0.15,andMy=-322015 v 0B © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Photometric datafor133starsinNGC7790aregivenTheapparentmodulusoftheclusterism—M= The recentsearchforcepheidsingalacticclustersbyKraft(1957)andvanden Light-curves inthreecolorshavebeenmeasuredphotoelectricallyfortheclassicalcepheidCFCass. In 1954,OlinEggencalledmyattentiontothegalacticclusterNGC7790,which This isthefirstofaseriespapersoncepheidvariablestarsingalacticclusters.The CEPHEIDS INGALACTICCLUSTERS.I.CFCASSNGC7790 Carnegie InstitutionofWashington,CaliforniaInstituteTechnology Mount WilsonandPalomarObservatories Received May5,1958 I. INTRODUCTION Allan Sandage ABSTRACT 150 1958ApJ. . .128 . .150S © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem

Fig. 1.—The identification chart for stars in and near NGC 7790. The lettered stars are the photoelectric standards of Table 1. The numbered stars are the photographic stars of Table 2. The plate is a 1-minute exposure on Eastman 103a-D behind a Schott GG11 filter taken with the 1958ApJ. . .128 . .150S hms o Mount Wilson.ThephotometerusedhasbeendescribedbyWalker(1954).photo- are R.A.=235442,Dec.+61°10'(1960)forNGC7788and5626 was usedforthephotomultiplier.DeflectionswerereadfromaBrownstrip-chartre- electric filterswereCorning9863intheultraviolet,1mmofSchottBG12plus2 and thetrueapparentdistancemodulusforNGC7790. Dec. =+6100'(1960)forNGC7790.Thedata7790aregiveninthispaper. in 1952,andhegenerouslymadefindingchartsotherinformationavailabletome extinction coefficientsdeterminedfromtwoormorestarsofdifferentcolor corder andwerereducedintheusualwaytooutsideatmosphere,withnightly of SchottGG13intheblueand2mmGG11yellow.Anend-onEMI index. Iterationoftheextinctionvalueswasperformedbymethodconditioned photographic techniqueswasusedtoobtainthecolor-magnitudediagram,reddening, data for7788aregiveninafollowingpaper.Theusualcombinationofphotoelectricand in NGC7790.ThestarsareidentifiedFigure1. coefficients. on tennightsbetweenJuly13,1956,andOctober7,withthe60-inchtelescope and Morgan’spaper(1953).Atotalofonehundredtwenty-sixseparateobserva- 1954. good, withprobableerrorsinV,B—F,andU—Balllessthan+0.01mag.themean. The transformationfromtheinstrumentalmagnitudestoU,B,Vsystemwasvery visual wavelengthsweremeasuredbySandage. Thedispersionoftheresiduals NGC 7790withthe60-inchand200-inchtelescopes.Theplatefiltercombinations tions oftheseJohnsonstandardstarswasmadefromSeptember,1954,toOctober,1956. observations ofthirty-fourJohnsonstandardstakenfromTables3and5 no significantsystematicdifference.Ifeachoperator hasthesamepersonalerror,then Ross correctorlens. behind 2mmofSchottGG13fortheblue,andEastman103a-D below. due tothepersonalequationistherefore±0.019 mag.Thiserrorofmeasurementis were Eastman103a-Obehind2mmofSchottUG2fortheultraviolet, small enoughthatthefinalphotographicvaluesare accurateto±0.02mag.ascomputed ured byMissCynthiaStephenswiththeiris-diaphragm Eichnerphotometeratthe back throughthephotographic calibration-curves.Themeansaregiven in theright- about 1.5timeshigherthanwehavefoundinother similarinvestigations.Butitisstill Stephens minusSandageformeasurementsonthe sameplatewasa=0.039mag,with California InstituteofTechnology.Twoplates in eachoftheultraviolet,blue,and to 32inches.Theblueandvisualplatesweretakenwiththe200-inchthe/3.67 <7 (Stephens)=a(Sandage)0.028mag.Theprobable errorofasinglemeasurement GG11 forthevisual.Theultravioletplatesweretakenwith60-inchdiaphragmed © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem NGC 7790formsadoubleclusterwith7788.Thepositionsfortheseclusters Olin EggenknewoftheprobableconnectionthesethreevariableswithNGC7790 Three-color photoelectricobservationsweremadeinNGC7790ofthirty-threestars Table 1givestheF,B—V,andU—Bvaluesforthirty-threephotoelectricstars All dataweretransformedtotheJohnsonU,B,Vsystemwithcoefficientsfoundfrom Photographic platesinultraviolet,blue,andvisualwavelengthsweretakenof Two platesintheultravioletandthreeeach intheblueandvisualweremeas- The magnitudesandcolors forthethirty-threephotoelectricstandards were read CEPHEIDS INGALACTICCLUSTERS151 2 ThePhotographicObservations 1. ThePhotoelectricObservations II. PHOTOMETRICDATA 152 ALLAN SANDAGE hand section of Table 1. The residuals of these values from the photoelectric values show no dependence on either V or B—V. Consequently, there is no magnitude or color equation between the photoelectric and the photographic results. Therefore, all data are on Johnson’s Z7, B, V system to within the accuracy of the measurements. Colors and magnitudes for one hundred additional stars were obtained by photographic interpolation from the two plates in the U and the three plates in the B and V. These stars are identified in Figure 1. The area around the cluster has been divided into three regions. Region 1 is a circle of 111" centered on star E. Region 2 is the annulus between circles of radii 111" and 161" centered on star E. Region 3 is the area outside regions 1 and 2. The adopted F, B—V, and V—B values for the hundred additional stars are given in Table 2. The distribution of the residuals of each measurement from

TABLE 1 Photometric Standards in NGC 7790

Photoelectric Data From Photographic Plates Star Region* B-V U-B B-V U-B A 11 08 +0 24 -0 59 38 11 08 +0 24 -0 63 B 12 16 +0 38 - 11 3 12 13 +0 41 -F 02 C 12 47 +0 55 + 21 7 12 50 +0 56 -F 18 L>t 12 59 +0 44 + 26 2 12 68 +0 31 E 12 79 +0 37 - 08 1 12 78 +0 36 - 07 F 12 82 + 1 98 1 12 82 +2 26 G 13 13 +0 55 + 26 1 13 02 +0 62 + 31 H 13 15 +0 49 + 29 2 13 13 +0 47 + 42 I 13 18 + 1 20 + 85 1 13 09 + 1 32 + 67 J 13 20 +0 53 + 31 3 13 30 +0 46 + 36 K 13 21 + 1 52 3 12 98 + 1 72 L. (13 25): +0 69 + -12 2 13 23 +0 72 + 08 M 13 32 +0 37 - 14 1 13 32 +0 38 N 13.48 +0 39 + 09 1 13 49 +0 46 00 O 13 54 +0 36 - 16 1 13 50 +0 36 P 13 60 +0 79 + 12 2 13 60 +0 80 -F 07 Q 13 72 +0 47 + 02 1 13 81 +0 42 - 07 R 14 16 +0 40 - 03 1 14 14 +0 35 - 05 S (14 32): (+0 46): - 29 2 14 24 +0 52 - 36 T 14 30 +0 68 1 14 11 +0 82 + 23 U 14 48 +0 56 + 34 1 14 52 +0 58 + 24 V. 14 51 +0 44 + 02 1 14 56 +0 44 00 w 14 55 + 1 44 3 14 55 + 1 52 X . 14.62 +0 42 + 06 2 14 62 +0 46 - 08 Y 14 72 + 1 35 3 14 68 + 1 34 Z 14 75 +0 48 07 1 14 75 +0 43 00 a 14 93 +0 73 1 14 89 +0 78 b 15 18 +0 48 0 06 1 15 08 +0 51 +0 08 c 15 29 +0 82 1 15 39 -F0 83 d 15 65 +0 91 3 15 72 +0 80 e 15 76 +0 51 1 15 76 +0 50 f 15 98 +0 80 1 15 94 +0 76 g 16 22 +0 83 1 16 14 +0 86

* Region 1 is a circle of radius 111" centered on star E Region 2 is the annulus between circles of radii 111" and 161" centered on star E Region 3 is everything outside regions 1 and 2 f Double star; p e measure includes companion

© American Astronomical Society • Provided by the NASA Astrophysics Data System 1958ApJ. . .128 . .150S 24 22 21 20 23 47 46 45 25 49 48 44 40 33 32 31 50 43 42 41 39 38 37 30 36 35 34 29 28 19 18 17 26 16 15 14 13 11 10 27 12 4 3 8 2 9 6 5 7 1 Star © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem * SeefootnotetoTable1fordescription ofregiondesignation 13 17 15 77 14 47 15 78 16 00 16 00 15 20 13 56 15 60 15 95 15 67 15 58 15 43 15 60 15 82 15 30 14 88 15 59 15 92 15 99 14 83 15 26 15 74 15 50 15 32 16 04 15 90 13 07 13 36 14 63 15 78 15 74 16 10 16 06 15 36 15 81 15 30 15 68 15 74 16 07 15 95 16 02 14 63 14 88 12 60 14 48 15 20 13 66 15 64 15 61 Magnitudes andColorsfor100StarsinNearNGC7790 0 51 0 55 0 72 0 50 0 49 0 59 0 60 0 53 0 66 0 55 0 70 0 88 0 53 0 42 0 47 B—V 0 75 0 64 0 26 0 77 0 73 0 16 0 72 0 48 1 66 1 20 1 24 0 45 0 58 0 70 0 54 0 43 1 69 1 54 0 80 0 85 0 77 0 88 0 32 0 91 0 60 0 40 0 48 0 54 1 70 1 11 1 63 1 00 1 09 Determined fromPhotographicPlates + 08 +0 15 - 01 - 08 - 08 U-B 0 00 Region* TABLE 2 100 67 66 65 56 55 54 53 52 51 64 63 62 61 60 59 58 57 69 68 81 80 73 72 70 82 74 71 77 95 93 92 91 90 89 88 87 86 85 84 83 79 78 76 75 97 96 94 99 98 Star 15 67 15 72 15 65 15 99 15 82 16 00 15 77 16 15 13 69 14 84 13 32 14 67 15 48 14 19 15 90 15 80 15 34 13 06 15 64 14 82 14 38 16 00 15 64 13 14 45 15 12 15 59 15 98 16 05 14 40 15 70 15 18 14 97 15 83 15 77 14 25 14 89 13 68 14 02 16 13 12 67 15 30 15 63 14 81 15 16 15 39 15 04 14 36 13 34 14 36 B-v 0 51 0 73 0 51 0 98 0 58 0 58 0 44 0 50 0 34 0 46 0 53 0 27 0 34 0 73 0 51 0 50 0 39 0 41 0 52 0 54 0 49 0 33 0 40 0 52 0 46 0 50 0 55 0 52 0 85 0 91 0 84 0 54 0 45 0 48 1 60 0 33 0 45 0 51 0 72 0 65 0 37 0 45 0 72 0 88 1 41 0 48 0 40 0 29 1 46 1 66 + 10 + 02 + 18 - 03 - 13 + 25 + 03 - 14 - 04 -0 04 - 19 - .21 + 03 - 11 - 12 -0 08 U-B Region* 1958ApJ. . .128 . .150S tabulated valuesofTables1and2. Fig 2.—Thedistributionoftheresidualsindividual magnitudemeasurementsfromthe © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem 1958ApJ. . .128 . .150S 95 40 § 99 O A E D The positionofasinglecomponenttheneweclipsingbinaryisshownbycross. m —M=1435.ThepositionofCFCassisshown.atmeanlightshownbyacircle 7790 Theage-zeromainsequenceisdrawn,assumingE{B—V)=052andanapparentmodulusof A well-populatedmainsequenceisevident.Manyredstarspopulatethediagramfainter than F=14.Thesearelikelytobefieldstarsnotphysicallyconnectedwiththecluster. therefore, be±0.014mag.forV,±0.013B,and±0.015U. these distributionsgiveprobableerrorsof±0.024mag.forV,±0.023B,and the tabulatedmagnitudesofTables1and2isshowninFigure2.Thedispersions ±0.021 mag.forl/.TheprobableerrorofthetabulatedvaluesinTables1and2should, Mean Star © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem * FromKraft,PaperIIofpresentseries § StarNo40wasomittedfromthe mean values J FromthepresentU,B,Vmeasures t Foundfromnormalcolor-spectral-type lelationofJohnsonandMorganinApJ,117,313,1953 Fig. 3—Thecolor-magnitudediagramforallstarsinregions1and2centeredonstarENGC The color-magnitudediagramforstarsinsideregions1and2isshowninFigure3. B7 IV: B5 IV B8IV B9 IV B5 IV: B9 III B2 III-IV Sp Type* iWV(Sp) III. THECOLOR-MAGNITUDEDIAGRAMFORNGC7790 2 1 8 1 7 1 0 CEPHEIDS INGALACTICCLUSTERS155 Stars withSpectralTypesinNGC7790 Observed 13 34 12 67 13 07 13 54 12 79 11 08 12 59 V 14 74 15 14 14 89 14 77 14 54 14 99 14 59 14 28 m—M TABLE 3 Observed ±0 40 ± 33 ± 26 ± 36 ± 37 ± 44 ±0 24 B-V (B-V)o, sp -0 0 24 09 05 05 16 13 16 E(B— F)t Sp Type 0 49 0 53 0 48 49 41 35 49 53 Three-color (B-V)ot Double - 13 -0 10 - 08 - 15 - 13 -0 27 E(B-V) Three- 0 50 0 50 0 51 color 46 34 51 50 1958ApJ. . .128 . .150S and Morgan’snormalrelationisshownbutshiftedbyE(B—F)=052E(UB)38CF is shownbyacross Cass isplottedThepositionatmeanlightindicatedbyacircle.oftheeclipsingbinary with m—M=12.80.Theposition ofCFCassatmeanlightisshownbyacircle. The positionof main sequenceofFig.3and correctedbyE(B—F)=0.52.Theage-zeromainsequence isdrawn a singlecomponentoftheeclipsing binaryisshownbyacross. U —B,BVvalueswereindividually corrected.StarsfainterthanFo=135were taken fromthe © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Fig 4—TheU—B,BVdiagram.OnlystarswithphotoelectricvaluesareplottedJohnson Fig. 5.—Thecolor-magnitudediagramforNGC7790corrected tozeroreddening.Allstarswith 2 46810121416 B-V 1958ApJ. . .128 . .150S E{U—B) =0.38,and1.56.Theabsolutemagnitudes atmaximum,minimum,and values willbediscussedinthefinalpaperofpresent series. mean lightfollowfromthetruemodulusofm—M —12.80.Thesignificanceofthese E(B—V) =0.52andE{U—B)0.38.Inthefollowinganalysis—is Morgan’s normalcolors,givesE(B—V)=0.49±0.024(p.e.)fromthespectraldata. These arereportedanddiscussedinKraft’spaperthepresentseries(1958).Table3 determined spectraltypesontheMKsystemforsevenstarsinfieldofNGC7790. Russian Cataloguegivesan improvedperiodof4.87513daysforCFCass. with otherphotometricparameters,aregivenin Table 5.Theunreddenedparameters age-zero mainsequencetoFigure5. NGC 7790ism-M=±14.350.15. main sequenceofFigure3.ThefitwasmadeforstarsfainterthanF=15,sothatthe This epochatmaximum light combinedwiththeepochofJD2428651.57 quoted inthe quoted inthistablefollowfromthereddening correctionsofE(B—V)=0.52, etry, andthisvaluewasconvertedbacktomagnitudes. Thesemeanvalues,together bands werechangedintointensityunits.Theaverage intensitywasfoundbyplanim- interior. Tofindthemeanvalues,light-curves foreachofthethreewave-length Catalogue. Thisperiodfitsthepresentobservations.Figure6showslight-andcolor- JD 2435688.931withanassumedperiodof4.87522days,astabulatedintheRussian assumed toholdforallclusterstars. which hasbothB—VandU—Bavailable.Areddeninglineofslope0.73wasassumed. estimate. IndividualE(B—V)valueswerefoundforeverystarofTables1and2 The truemodulusoftheclusterism—M=12.80+0.15,asdeterminedbyfitting from themainsequenceofFigure3butwereshiftedbyE{B—V)=0.52,Av1.56. slope 0.73.Figure5showstheresultingdiagram.StarsfainterthanF=15wereadded B—V andU—Bvalues.Eachstarwascorrectedindividuallyalongareddeninglineof evolution ofthebrighterstarswouldnotinfluenceresult.Theapparentmodulus The solidcurveisJohnson’snormalrelationformain-sequencestarsshiftedby 0.49 +0.024(p.e.).Thereisnoevidencefordifferentialreddeningacrossthecluster. regions 1and2wereassumedtobeclustermembers.ThemeanE(B—V)forthese Twenty-four starswithunambiguousvaluesofE(B—V)between0.40and0.65in star overlongtimeintervals.Thisgivestherateofenergyproductioninstellar are giveninTable4.Thephaseswerecomputedfromanarbitraryepochatheliocentric curves fromthedataofTable4.CFCassisacepheidEggentypeA. spectral types.ThemeasuredcolorsfromTables1and2,togetherwithJohnson of thepresentpapergivesdataandcomputationreddeningfrom twenty-four starsis0.522±0.040(p.e.),whichingoodagreementwithE(B—V)= (Johnson andHiltner1956;Sandage1957),shiftedbyE(B—V)=0.52,totheobserved © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem The effectsofabsorptionandreddeningwerenextremovedfromallstarswhichhad The reddeningoftheclusterstarswasfoundbytwoindependentmethods.Krafthas The presentobservationsgive: The B—V=f(U—B)methodofJohnsonandMorgan(1953)givesanindependent The apparentmodulusoftheclusterwasfoundbyfittingage-zeromainsequence Twenty-nine separatephotoelectricobservationswereobtainedofCFCass.Thedata The physicallyinterestingquantityforCFCassisthemeanenergyradiatedby Figure 4showstheindividualU—B,B—VvaluesforallphotoelectricstarsinTable1. Epoch F(max.)=Helio.JD2435671.76±0.05, Epoch F(min.)=Helio. JD 2435670.39±0.03. CEPHEIDS INGALACTICCLUSTERS157 IV. THEVARIABLESTARS 1. TheCepheids 1958ApJ. . .128 . .150S © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem 1128 876 1129 803 1128 898 1135 620 1130 933 1130 915 1130 644 1130 638 669 825 668 936 669 962 670 828 670 966 688 863 687 867 687 768 691 973 690 855 689 973 689 811 688 964 687 965 691 779 690 974 690 870 754 773 752 967 752 739 752 723 * PhasecomputedfromepochathelioJD2435668931 Helio JD 2435+ Fig 6—Thelight-andcolor-curves ofCFCass Photometric DataforCFCass 94 343 94 705 94 533 94 348 94 762 94 706 95 727 94 765 17 237 17 608 17 17 Phase* 0 211 0 183 0 001 0 417 4 4 4 521 0 389 088 904 884 864 497 283 316 687 500 726 109 191 187 TABLE 4 PHASE 11 20 11 22 11 34 11 31 11 25 11 10 11 06 11 13 11 39 11 29 11 10 10 87 10 91 11 39 11 32 11 34 11 32 10 99 10 92 10 90 10 84 10 87 11 32 10 93 11 32 11 00 10 95 10 94 11 01 1 260 1 188 1 240 1 332 1 302 1 126 1 322 1 324 1 297 1 320 1 268 1 253 1 350 1 342 1 360 1 160 1 060 1 090 1 088 1 070 1 338 1 326 1 133 1 030 1 277 1 178 1 134 1 161 1 156 B—V 0 957 0 785 U-B 954 907 922 900 960 983 922 930 903 820 930 970 690 697 965 662 680 865 750 768 686 702 817 758 772 734 1958ApJ. . .128 . .150S f(U—B) relationofJohnsonandMorgan(1953). Theunreddenedmagnitudeandcolor B— V=0.28,andU—B=—0.63.Ifweassumeequalcomponentsofthesamespectral membership inNGC7790.Spectroscopicandphotometric observationsshouldbemade gan andKeenan1951).Thepredictedpositionof eachcomponentinthecolor-magni- for eachstararepredictedtobeF=9.22,(B—V) =—0.29,(lf—B)o—1.04ifthe equation L— tude diagramisshowninFigures3and5asacross. components areequal.Thepredictedspectraltype isaboutBl.Finally,ifm—M= indicate thatE(B—V)=0.57,E(U—B)0.42, asdeterminedfromtheB—V= a totaleclipseoftwosimilarcomponents. that weknowthedistance, thenthisstarcanprovideacalibrationpointfor theeffective to determinetheperiodandeclipsecharacteristics ofthebinary.Ifitreallyturnsout type, thenVforeachstaris10.93withthecolors unchanged.Thecolordatafurther is atleast0.50mag.andmaybeaslarge0.75mag.,whichsuggeststhepossibilityof temperature scalebecause LandRwillbeknown.ThenTfollowsfrom itsdefining plates wereobtainedtogetcompletecoverageofthelight-andcolor-curves. spectral class.Table6givestheobservationswhichareavailable.Thedepthofeclipse The starisundoubtedlyaneclipsingbinarywithbothcomponentsofaboutthesame hours. Duringthistimethecolorsremainedconstantwithinerrorsofobservation. ard forseveralnights.ButduringobservationsonAugust2/3,1956,andOctober7/8, 60-inch telescope.Thecomponentswereadequatelyseparatedonplatestakenwiththe not beseparatelymeasuredwitheitherthephotoelectricequipmentorplatesat 12.80, asforNGC7790,thenM=—3.6,which is quitenormalforaBlVstar(Mor- is showninFigures3,4,and5.Thecepheidfollowsawell-definedloopeachdiagram. 200-inch telescopediaphragmedto100incheswith9seconds’exposure,butnotenough 0 0 1956, thestardecreasedinluminosityfromaboutV=10.17toF10.657 e v © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem More workonthisstarisbadlyneeded.Radialvelocities shouldbeobtainedtocheck Table 6showsthatthemagnitudesforsystemoutofeclipseareaboutV=10.18, The starmarked“variable”inFigure1wasusedasasecondaryphotoelectricstand- No completedatawereobtainedforCECassaandbbecausethecomponentscould The positionofCFCassinthecolor-magnitudediagramandcolor-color Mi Mvi (U-B)ot (B-F)ot Fof ..• V Bo U-B B-V 0 * EpochV(Max)=243567176+487522w t E(B—V)052,E(U—B)=38,Ay156assumed t (tn—M)o=1280assumed CEPHEIDS INGALACTICCLUSTERS159 Photometeric ParametersforCFCass* -3 -3 10 84 Max 0 29 0 51 9 28 0 67 1 03 2. ANewEclipsingBinary 01 52 TABLE 5 -2 14 -2 97 11 39 Min 0 58 0 83 9 83 0 96 1 35 -2 -3 11 14 Mean 0 49 0 72 9 58 0 87 1 24 22 50 Amplitude 0 87 0 55 29 32 55 32 55 29 160 ALLAN SANDAGE

I should like to express thanks to Dr. Olin Eggen, who called my attention to this unique cluster and its cepheids. It is also a real pleasure to thank Miss Cynthia Stephens for her efficient and knowledgeable help in the measurement and reduction of the plates and for many other detailed tasks connected with this paper. She has been a real asset.

TABLE 6 Colors and Magnitudes for Variable Star in Field of NGC 7790

Helio JD 2435+ B—V U-B 687 885 10 19 0 28 0 65 687 978 10 19 26 • 62 688 772 10 24 26 62 688 814 10 32 28 ■ 62 688 844 10 38 28 62 688 966 10 63 26 .62 689 817 10 20 26 62 689 919 10 22 26 ■ 64 689 965 10 22 26 .64 690 880 10 17 29 • 63 690 970 10 21 26 64 691 790 10 20 23 ■ 58 691 868 10 19 27 63 691 922 10 20 27 63 691 964 10 22 27 64 752 740 10 22 754 648 10 17 28 • 59 754 701 10 17 29 - 59 754 877 10 35 28 - 62 754 962 10 55 28 • 58 754 994 10 67 0 26 •0 59

Added August 25> 1958,—Mr. Andrew Young has called my attention to the fact that the suspected eclipsing binary is not a new discovery. It was first found by G. E. Erlek- sova of the Stalinabad Astronomical Observatory of the Tadzhik Academy of Sciences and was published in the Astronomical Circular (U.S.S.R.),No. 155, p. 15,1954. The spectral class is quoted in the Eighth Supplement to the Russian Variable Star Catalogue as B2. The star has been named QX Cas. No period was given.

REFERENCES Arp, H. C. 1958, Ap. J , 128, 166. Arp, H. C , Sandage, A. R., and Stephens, C 1958, in preparation Bergh, S. van den. 1957, Ap. /., 126, 325. Irwin, J. B. 1958, in preparation. Johnson, H. L , and Hiltner, W. A. 1956, Ap /., 123, 267. Johnson, H L., and Morgan, W. W. 1953, Ap. /., 117, 313. Kraft, R. P. 1957, Ap J, 126, 225. . 1958, ibid , 128, 161. Morgan, W. W., and Keenan, P. C. 1951, Astrophysics, ed. J. A. Hynek, chap. 1, p. 23. Parenago, P. P., and Kukarkin, B V. 1940, Variable Stars, 5, 331. Sandage, A. R 1957, Ap. J., 125, 437. Starikova, G. A. 1948, quoted in Russian Variable Star Catalogue, p. 396. Walker, M. F. 1954, Pub. A.S.P., 66, 71.