1945Apj. . .102. .318S SIX-COLOR PHOTOMETRY of STARS III. THE

Home , 12 Lacertae, 14 Lacertae, HD 221525, Joel Stebbins, North Polar Sequence

1945ApJ. . .102. .318S giants inlowlatitudesarelikewiseaffected.Themostmarkedeffectofabsolutemagnitudeisnearspe< small dispersioninintrinsiccolor,butmanyarestronglyaffectedbyspacereddening.Adozenlate-tyx photoelectric cell,thethermocouple,etc.,orbyacombinationofsuchreceiverwit change ofcoloriscausedbyspectraltypeorspacereddening(Table11).Goo colors ofPCygniareanomalous,asisthespacereddeningTrapeziumclusterOrion(Fig: slightly affectedbyspacereddening.AdozenbrightstarsofthePleiadesseemnormalfortheirtype.Tl six spectralregionsfromX3530to10,300A(Tables2and3).Theearly-typestarsOB3sho trum K0,wherethecolorsofdwarfs,ordinarygiants,andsupergiantsarealldifferent{Fig.1). lected formeasurement.Exceptinspectrophotometrythespectralregionsaredetei 3 and4). has notbeendetermined. with anassumedtemperatureof5500°K.Onthisscalethevaluesare23,000°forOstars,11,000°A( filters suitableforthedesiredresult.Evenwithablack-bodyreceiverlikethermc mined bythecharacteristicsofreceiver,suchaseye,photographicplate,th multicolor, andspectrophotometry,dependinguponthenumberofspectralregionss€ by JohnS.Hall(Fig.5). agreement isfoundwiththeGreenwichgradientsandespeciallyresultsofspectrophotometr O stars,16,000°forA0,and6900°dGO(Table7).Adefinitivezeropointthetemperatureseal and 5950°fordGO.Analternativescale,with6700°spectrumdG2thesun,gives140,000°fc be easiertoobtainthanmeasuresfortheentirespectrum. Thephotocellgivesalinea on theonehand,andspectrophotometry,other. Obviously,measuresinsixspec be lookeduponasthenaturalapplicationofstellarphotometrytonarrowregionsc stars willneedalargetelescope.Infact,stellarspectroscopywithhighdispersionma dependent uponthetransmissionofatmosphereandopticalsysteminvolvec scale ofresponseoverawiderangeintensitiesand ofwavelengths;also,freedomfror wave length. energy available,itfollowsthatanythingapproachingmonochromaticphotometryc range ofwavelengths;andsincethesmallerspectrallesswillbetots When adispersingagentlikeprismorgratingisused,itpossibletoisolatesma couple, equallyreceptivetoallwavelengths,themeasuredresponsesradiationar of theNorthPolarSequencegiveratiosscalescolorindex.Thesedependuponwhethí tral regionsshouldgivemoreinformationthanmeasures inonlytwo,whiletheyshoul (Fig. 2).ThederivedrelativecolortemperaturesarebaseduponthemeanoftenstarsspectrumdG many difficultiesofphotographicphotometry.But, despitetheseadvantages,therer< . Thevariouskindsofstellarphotometrymaybeclassifiedasone-color,two-coloi 2 1 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem The observedcolorsofthestarsagreecloselywithablackbodyatsuitabletemperatur« The presentsix-colorphotometryofstarsliesbetween one-andtwo-colorphotometr} The bluestOandBstarsagreeverywellwitheachother,butthereisstillthepossibilitythatallai Colors havebeenobtainedfor238starsofallspectraltypesfromOtoMbymeasuringintensitiesi OnleaveatMassachusettsInstituteofTechnology. Comparisons ofthenewcolorswithInternationalandourpreviousphotoelectricC ResearchAssociateoftheMountWilsonObservatory,Carnegie InstitutionofWashington. * ContributionsfromtheMountWilsonObservatory,Carnegie InstitutionofWashington,No.712. III. THECOLORSOF238STARSDIFFERENTSPECTRALTYPES* Mount WilsonObservatoryandWashburn SIX-COLOR PHOTOMETRYOFSTARS 12 Joel StebbinsandA.E.Whiteord I. THEOBSERVATIONS Received June8,1945 ABSTRACT 318 SIX-COLOR PHOTOMETRY OF STARS 319

Lain the limitations of any method where spectral regions extending over a thousand or tore angstroms are integrated by the receiver into a single intensity. The effects of :rong absorption lines or bands are buried in the results. In this respect the present rork has the same drawback as ordinary photographic photometry; but even in spectro- hotometry, where measures are limited to the continuous spectrum between spectral nes, there is always the possibility of a veil over the surface of a star which will modify he ideal black-body radiation, even if such were emitted in the first place. It remains to •e seen what is the best method for deriving the color temperature of a star; up to the ♦resent there is much disagreement among the results from all methods. Our photometer with a photocell and six filters was devised primarily for measures of ixtragalactic nebulae; but for the observations to be significant, such nebulae must be eferred to standard stars of different spectral types. In the course of the work, so much TABLE 1 Observations of a Ursae Minoris, August 18,1944

Color

U B X(A)..,. 3530 4220 4880 5700 7190 10,300 1A (m-1) 2.83 2.37 2.05 1.75 1.39 0.97 0^530 0^292 0^180 0^136 0^58 0^30 Deflection, d 27.8 50.1 74.4 65.8 58.4 60.8 log¿ 1.444 1.700 1.872 1.818 1.766 1.784 0.4a sec z 0.382 0.210 0.130 0.098 0.042 0.022 log do 1.826 1.910 2.002 1.916 1.808 1.806 log (B, G, R)-log d0.. ■ 0.083 0.001 0.093 0.007 + 0.101 -f- 0.103 A mag 0.21 0.00 0.23 0.02 + 0.25 + 0.26 Reduction to standard. .06 .14 + .17 .01 - .16 - .07 Final color ;. .15 .14 .06 .03 + .09 + .19 Another set .18 .14 .06 .00 + .06 + .17 Mean. . . + 0^165 - 0m14 — 0^6 - 0^15 + 0^75 -b 0“18 Av. deviation. ± 0.015 ± 0.00 ± 0.00 ± 0.015 ± 0.015 ± 0.010 of interest was found in the measures of various stars that this secondary program of calibration has perhaps grown to outweigh in emphasis the original program on the nebulae. We found that measures of normal and reddened B-type stars3 gave a new determination of the law of space reddening by interstellar material, and other possibilities were opened up by the wide spectral range from 3530 A to 10,300 A. The observations used in the present paper were made at Mount Wilson during the five summers of 1940-1944. Some measures were made with the 100-inch reflector, but most of them with the 60-inch, which, besides having the advantage of reaching the pole, is, in general, more readily manipulated than the larger telescope. A description of the installation and the methods of observation and reduction is given in our paper on B stars,3 but a sample reduction is given here. In Table 1, giving data for a Ursae Minoris, the designations of the different quanti- ties under each color are mostly self-explanatory. The units used in Table 1 and throughout this paper are: angstroms for X, microns "1 for 1/X, and stellar magnitude for colors. In the next line below 1/X in Table 1, is given a, the extinction in magnitude at the zenith. The deflection d, in millimeters, is the mean of two deflections, taken forward 3 ML W. Contr., No. 680; Ap. /., 98, 20, 1943.

© American Astronomical Society • Provided by the NASA Astrophysics Data System 1945ApJ. . .102. .318S hm tra andcolorsarearrangedbytypes.TheOB stars previouslypublishedareincluded here, withadditions,corrections, andrevisions.Thelistofstarsincludes 75OtoB3 stars withdifferentdegrees ofspacereddening;94starsthemainsequence fromB5to M0; and69giantstars,mostly supergiants,fromF3toM7. gether withtherightascensionsanddeclinations andthegalacticco-ordinatesl are forindexpurposesonly;theyrefertothesections ofTable3wherethedefinitespec- referred tothepoleofLundtables,1240,+ 28?0(1900).ThespectrainTable2 320 JOELSTEBBINSANDA.E.WHITFORD is 0.16mag.inU—I,correspondingtoavariation inthespectrumfromcF7tocF8 between thetwosetsonsamenightisonlyfair; therearemanycasesofbetteragree- sume averageconditionsoverseveralnightsandbeonthelookoutforlargediscrepancies upon thespectraltypeofobservedstar;redderstar,longereffectivt been nearlyconstant.Whenachangeinthecellismixedupwithvariationat color variationofPolarisinthewell-knownperiod of3.96days.Theapproximaterange wave lengthandhencethesmallerextinction.Forthisreasonitisimpracticaltode- ment forotherstarsevenondifferentnights.We have inhandastudyofthelightand and toabouthalfthatamountfortheothercolors. For Polaris,inTable1,theagreemenl termine theextinctionthoroughlyandaccomplishanythingelse.Wesimplyhavetoas while thecorrectionsforextinctionvarywithairmassatdifferentzenithdis- mospheric extinction,thecorrectionsonaccountofcellaresameforallstars amounting tomorethan0.10mag.betweenadjacentcolors;butsince1941thecellhas rection inoneseasonwasdeterminedasfollows: A mag.,givesthefinalcolorreferredtomeanoftenstarsaveragespectrumdG6 of asingledeterminationtosomethinglike+0.02 mag.fortheultravioletandinfrarec correction foreachrun,oroccasionallyasinglenight.Forinstance,theinfraredcor- stant reductionstostandardfortheothercolors;butinfraredrequiresa“floating’ of theeffectivewavelengthat10,300A.Usually,forseveralnightswecanassumecon say severalhundredths,orevenatenth,ofmagnitude.Buttherearealsovariationsh The logdoisthensubtractedfrom1.909,thecorrespondingmeanofblue,green,andred tances. Moreover,inallstrictness,foreachfiltertheamountofextinctiondependí and backwardthroughthecolors.Forthisbrightstara3-mag.absorbingscreenove the infrared,causedpresumablybystrongwater-vaporbandspand4>oneithersid< enough thesame,butoccasionallyanincreasedextinctionwillappearinultraviolet- cell. Usually,inarunofseveralgoodnightsthecolorscontrolstarremainnearb The resultsofasecondsetobservations,madethesamenight,areinnextline,anc sensitivity. Tologdisadded0.4asecztoobtaindoforoutsidetheatmosphere the largemirrorwasused;also,ashuntongalvanometergivingone-thirdful ent seasons.Acontrolontheextinctionisgivenbymeasuresofapolarstar,usualb then themean.Theaveragedeviationinallcolorsfrommeanoftwosetsi NFS 4;thiscontrolalsotakescareofanyvariationinthecolorsensitivityphoto to obtainAlog;thenmag.=2.5Alog.Thereductionstandardcolor,appliedthi the resultsforsamestaratdifferentzenithdistancesonnightsandindiffer ± 0.009mag.,whichisnotparticularlygoodforsuccessivemeasuresonthesamenight © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem The useofameanextinctioncoefficientforeachcolorisjustifiedbytheaccordanceo The netresultoftheoutstandingerrorsis,forbrightstars,toraiseprobableerro] In Table2thestarsofpresentworkarelisted in theorderofHDnumber,to- Between thesummersof1940and1941therewererealchangesinphotocell 1944 July12-13+0^3 Aug. 21-.04 Aug. 17-20-.07 July 20-23-.03 Sept. 9-11+0.02 1945ApJ. . .102. .318S , 9270. ' 8890. 107192. 107113. 103483. 111812. 111395. 109358. 113865. 112570.' 112413. 118216. 115735. 114710. 114282. 113139.. 125162. 120933. 120315. 127762. 126327. 125351. 121409. 128165. , 432. 128998. 37128. 31964. 23408. 20902. 20123. 41074. 37742. 36486. 34759. 34085. 29139. 24912. 24504. 23862. 23753. 23630. 23441. 23432. 23302. 23288. 51802. 39801. 37022. 24760. 24398. 23850. 23480. 23324. 66368. 23338. 10307. 19356. 16901. 16397. 15830. 10516. 10204. 14662. 14633. 14622. 4727. 3651. 5394. 4406. 3765. 2905. 6920. 5914. 1064. 1337. 571. © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem hd Spec. gMO gM2 gM2 gM7 dKl dK5 gK5 dGO dK5 gK2 g KO dGO dGO dG5 dG3 dG6 gG3 gKl dGO dF2 cGO dF5 dF2 dF4 cG2 dF2 dF7 dF2 cF2 cF8 cF7 cF2 cF4 (BO) 07 08 AO A3 BO BO BO B5 B1 B8 08 BO A9 A5 B0 B0 B9 A1 A6 A8 B2 B7 B8 B8 B6 B9 B8 B9 B8 B7 B9 B5 B8 B7 B7 B7 AO A3 AO A5 AO AO B3 m . 041.3 12 46.8 12 43.9 12 14.4 12 13.9 13 30.3 13 1.5 12 56.5 12 51.4 14 28.1 14 13.8 14 12.6 13 43.6 13 14.0 13 4.5 12 52.6 12 29.0 11 49.9 14 35.1 14 30.2 13 50.1 13 47.4 13 7.2 14 19.7 6 53.7 4 54.8 4 30.2 3 52.5 0 5.1 Ob 38 5 31.1 5 14.7 3 47.8 3 43.3 3 42.5 3 39.9 0 50.7 0 44.3 0 12.5 5 57.9 5 49.8 5 26.9 3 48.8 3 41.5 3 40.4 3 40.1 3 40.0 3 9.1 3 1.7 2 27.7 2 16.9 2 16.6 0 55.6 0 35.3 0 34.2 0 27.3 0 9.8 7 58.0 5 35.7 5 30.4 5 9.7 3 51.1 3 43.2 3 39.3 3 39.2 3 39.0 3 38.9 3 17.2 2 37.6 2 32.6 2 16.7 1 35.7 1 26.1 1 22.6 1 4.6 1 34.7 1 37.4 R.A. 1900 SIX-COLOR PHOTOMETRYOFSTARS321 +42 21 +88 15 +87 12 +42 59 +41 43 +35 30 +31 35 +50 12 +29 34 +56 55 +38 52 +28 5 +25 23 +86 59 +88 56 + 723 +43 41 + 1618 +47 35 +23 51 +23 8 +23 48 +24 15 +24 4 +50 34 +40 34 +30 24 +40 57 +88 46 +88 29 +41 54 +47 2 +23 45 +23 39 +24 13 +24 10 +24 32 +23 48 +49 30 +54 55 +41 2 +50 11 +42 7 +42 47 +14 50 +41 33 +60 11 +40 32 +20 43 +62 23 +38 45 +49 49 +37 42 +28 23 +88 11 +46 44 +53 20 +35 58 +46 33 +34 56 -20 - 022 +39 43 +23 59 +43 52 +45 49 +39 39 +50 53 +45 31 +58° 36 - 116 - 527 +54 27 +54 13 - 819 -10 7 +26 11 Dec. 19.00 286.4 171.5 148.9 137.3 167.5 174.1 172.9 134.2 130.5 119.7 130.3 135.0 100.9 100.5 113.9 176.6 128.3 125.2 135.4 134.7 134.6 134.1 134.2 134.0 133.8 134.2 134.1 117.0 110.3 103.7 108.9 108.9 106.1 177.0 134.1 112.7 111.3 116.9 135.0 114.4 90.2 93.2 45.9 90.4 91.1 90.3 98.4 90.1 90.9 20.0 85.4 47.9 89.8 78.4 99.3 90.2 94.9 91.3 59.7 32.6 51.8 30.1 65.2 76.1 83.3 59.0 68.8 89.0 88.5 88.2 85.6 66.9 83.7 85 ?3 List ofStarsObserved 4.3 5.1 1.1 -+29.8 +28.4 +28.1 +11.7 + 4.2 +85.0 +60.9 +78.9 +88.5 +75.9 +29.7 +31.0 +68.6 + 2.4 +26.8 +65.1 +68.6 +64.0 +60.8 +65.0 +75.7 +66.9 +71.1 +87.3 +26.5 +56.3 +57.6 +74.1 +84.0 - 7.5 -15.1 -15.8 -17.9 -16.3 -18.8 -12.0 - 3.3 -21.9 -14.0 + 0.5 +67.8 -23.7 - 9.0 -15.5 -22.6 -22.2 -22.1 -22.1 -22.3 -22.0 -22.5 -15.4 -17.4 -17.5 -10.8 -18.7 -45.7 -22.0 -22.5 -22.6 - 4.8 -13.3 -25.7 - 4.5 -18.1 -20.2 - 1.8 -21.5 -22.3 - 5.0 -16.2 -22.3 -41.3 -10.9 -70.8 -16.1 - 3?1 TABLE 2 +472167. .. 183030.. . 183912.. . 180163.. . 178770.. . 174488.. . +35°3955 188439.. . 188209.. . 187642.. . 187076.. . 186994.. . 184915.. . 184279.. . 183914.. . 182917.. . 175865.. . 173648.. . 171871.. . 157056.. . 153344.. . 192947.. . 192640.. . 192281.. . 191201.. . 190919.. . 188892.. . 188252.. . 187138.. . 173649.. . 173638.. . 171779.. . 171635.. . 169454.. . 169034.. . 166205.. . 163506.. . 157910.. . 157779.. . 156729.. . 154345.. . 152601.. . 152391.. . 151288.. . 148783.. . 147394.. . 147379.. . 147365.. . 193443.. . 193370.. . 193322.. . 193183.. . 192876.. . 192422.. . 192107.. . 166926.. . 166734.. . 166620.. . 166182.. . 164514.. . 163770.. . 148478.. . 144206.. . 144205.. . 142373.. . 137422.. . 193514.. . 192639.. . 159181.. . 145328.. . 143807.. . 142143.. . 136064.. . 193237.. . 135722.. . 133208.. . 132813.. . HD gM6 gM5 dMO apee. gMl gM4 dMO gM2 gM6 gM6 gMl gM6 gM7 gM5 dKO dK2 gKO dG4 gK3 gK5 dG9 gKl gG5 gG2 gG9 gG8 cKl gG4 gG5 cG5 cG2 dF7 dF9 cA6 cF4 cF8 cF5 cF5 A9 Al A3 05 08 Al B2 AO 08 Al 07 BO B5 BO BO B2 B9 B5 BO A3 A2 B9 A9 08 09 BO B2 B2 Bl BO B2 B7 A1 Bl B2 BO Bl B2 B8 A1 hm 16 5.3 20 14.8 20 13.8 20 10.8 20 10.8 20 2.2 20 2.2 19 4.8 18 41.3 20 15.5 20 15.2 20 14.6 20 14.1 20 12.5 20 12.1 19 10.4 18 51.0 18 41.3 18 32.0 19 28.6 19 26.7 19 21.9 18 52.3 18 41.2 18 33.6 17 21.0 17 20.2 17 15.9 16 59.8 16 53.8 16 48.0 16 25.4 16 16.5 16 16.5 19 52.3 19 49.2 19 45.9 19 42.9 19 31.5 19 26.7 19 22.5 18 31.7 18 30.8 18 19.6 17 56.4 17 51.4 17 28.2 17 14.2 16 49.2 16 41.4 16-23.3 15 59.6 15 47.8 19 50.1 19 49.0 19 42.5 18 17.6 17 52.8 16 16.7 15 59.6 15 57.4 15 20.9 14560 19 43.3 15 49.2 15 13.5 15 11.5 14 58.2 R.A. 1900 4.5 4.4 9.0 6.9 8.1 3.6 7.8 6.3 9.7 +39 0 +43 49 +36 46 +37 30 +37 30 +37 2 +44 43 +27 45 +50 3 +38 58 +38 41 +51 2 +52 16 +56 58 +86 37 +26 4 +52-23 +37 14 +37 24 +47 12 +62 16 + 011 +33 41 +42 6 +67 29 +34 40 +35 26 +38 13 +47 41 +46 47 + 836 +88 41 +18 17 + 334 +27 45 +88 59 -10 14 +87 0 +38 27 +20 48 +37 16 +46 33 +39 57 +36 45 +46 19 +47 31 +37 57 +37 55 +36 30 +39 58 +35 24 +35 32 +47 34 -24 54 - 559 +30 7 +42 44 +48 47 +72 11 +67 44 +38 57 +40 25 +37 43 +37 3 +38 28 - 715 -14 2 -13 39 -10 46 -22 54 -26 13 +33 41 +40 47 - 119 +66° 2O' -12 49 -12 51 Dec. 1900 359.6 340.7 345.2 345.3 346.6 334.8 328.2 346.1 351.1 319.8 358.9 358.9 46.1 49.2 47.1 48.4 46.5 28.3 40.9 40.4 40.2 40.3 41.5 49.3 48.5 23.5 29.7 38.1 37.6 41.2 34.2 34.2 34.8 53.3 86.2 30.5 28.5 39.8 58.7 22.3 32.9 29.8 25.1 43.3 43.8 41.1 42.6 44.8 49.3 29.7 88.9 34.3 86.6 32.5 28.4 39.0 66.4 39.1 34.1 44.7 45.8 43.5 43.6 42.1 43.6 88.6 70.8 33.5 15.6 74.9 14.9 18.8 71°0 15.2 19.6 8.9 9.5 +23.0 + 3.5 + 3.5 +14.9 + 12.8 + 14 + 16 + 16 +18 +22 +24.4 +23.1 +28.5 +31.4 +31.6 + 5.1 +36.8 +36.8 +21.1 +24.6 +42.7 + 4.3 + 9.4 +27.6 + 9.3 +27.8 + 11.8 +16.9 + 5 +28.4 + 2.2 + 17.1 +25.3 +21.9 +32.5 +32.8 +38.6 + 13.7 +44.1 +39.2 +46 + 0 + 2 + 0.9 + 1.1 + 1.2 + 9.6 + 9.8 - 1.6 +44 +47 +46 +47 +49 +48.6 +40.8 + 1.0 + 0.3 + 0 + 0 + 0 + 1 -10.2 -14.7 - 9.0 - 2.2 - 1.7 +44.2 +57.2 +59.0 + 2 - 4.6 +46?4 -20.0 - 1.4 -26 -26 322 JOEL STEBBINS AND A. E. WHITFORD

TABLE 2—Continued

R.A. Dec. R.A. Dec. HD Spec. 1900 1900 HD Spec. 1900 1900 193536. B2 20h15m6 +46° O' 50 ?4 + 5°A 209339. BO 21h57m6 +62° 0' 72?1 + 5?; 194093. cF7 20 18.6 +39 56 45.8 + 1.1 209750. cGl 22 0.6 - 0 48 28.5 -43.: 194279. B2 20 19.7 +40 26 46.3 + 1.2 209772. gM5 22 0.9 +62 38 72.8 + 6.( 194335. B3 20 20.0 +37 10 43.8 - 0.8 209975. 09 22 2.1 +61 48 72.4 + 5.: 194839. BO 20 22.8 +41 3 47.2 + 0.9 210745. cK5 22 7.4 +57 42 70.7 + i.i 195295. cF4 20 25.3 +30 2 38.7 - 6.0 210839. 06 22 8.1 +58 56 71.5 + 2.Í 195592. BO 20 27.2 +43 59 50.0 + 2.3 211336. A6 22 11.4 +56 33 70.6 + o.: 195593. cF5 20 27.2 +36 36 44.2 - 2.3 212455. B3 22 19.3 +54 44 70.6 - 2.1 19632i. gK5 20 31.5 - 2 54 11.2 -25.9 212710. B9 22 21.3 +85 36 87.3 +24. ¿ 197345. A2 20 38.0 +44 55 51.9 + 1.4 213087. BO 22 23.9 +64 37 76.1 + 6.^ 197770. B2 20 40.7 +56 46 61.4 + 8.6 213306. cF4 22 25.4 +57 54 72.9 + 0.4 198084. dF9 20 42.9 +57 13 61.9 + 8.7 213310. gMO 22 25.4 +47 12 67.6 - 8.Í 198478. B2 20 45.5 +45 45 53.4 + 0.9 214168. B3 22 31.4 +39 7 64.5 -16.' 198781. B1 20 47.5 +63 40 67.3 +12.3 214665. gM4 22 34.7 +56 17 73.2 - l.< 198846. 09 20 48.1 +34-17 45.1 - 7.0 214680. 09 22 34.8 +38 32 64.8 -it.- 199081. B3 20 49.7 +44 0 52.6 0.8 214868. gK2 22 36.1 +43 45 67.6 -12.f 199216. B1 20 50.7 +49 9 56.6 2.3 214993. B1 22 37.0 +39 43 65.8 -16.' 199478. B8 20 52.4 +47 2 55.2 0.9 215766. AO 22 42.4 -14 35 20.1 -59.< 199579. 06 20 53.1 +44 33 53.4 0.9 216411. B1 22 47.6 +58 28 75.7 - 0.4 200120. B3 20 56.4 +47 8 55.7 0.4 216494. B9 22 48.2 -12 9 25.6 -59. Í 200857. B2 21 1.0 +54 51 61.8 5.2 217101. B2 22 53.1 +38 48 68.3 -18.Î 200905. cK5 21 1.3 +43 32 53.7 2.7 217476. cG3 22 55.9 +56 25 75.9 - 2./ 201601. cFl 21 5.5 + 9 44 28.1 -25.9 218173. B9 23 0.7 - 8 29 35.0 —59.5 201819. B1 21 7.0 +35 53 48.9 - 8.8 218342. B1 2.1 +62 41 79.0 + 2.Í 202751. dK6 21 12.9 - 0 15 20.0 -33.3 218356. cKO 2.2 +24 56 63.7 -32.1 203064. 08 21 14.8 +43 31 55.4 - 4.4 218376. B1 2.4 +58 53 77.7 - 0.Í 203280. A3 21 16.2 +62 10 68.5 + 8.9 218634. gM4 4.5 + 88 53.9 -47.1 203374. BO 21 16.7 +61 25 68.0 + 8.4 218639. AO 4.5 -15 3 25.4 -64.4 203938. B1 21 20.2 +46 44 58.3 - 2.7 218753. A9 5.5 +58 47 78.0 - l.C 204075. cG4 21 21.0 -22 51 354.9 -45.1 219659. AO 12.4 -12 16 33.1 -64.2 204172. BO 21 21.7 +36 14 51.3 -10.6 219833. AO 13.8 -12 43 32.9 -64.7 204867. cGl 21 26.3 - 6 1 16.3 -39.2 220020. AO 23 15.4 - 9 28 38.9 -62.8 205021. B1 21 27.4 +70 7 74.9 +14.0 221525. gFO 23 27.8 +86 45 88.9 +24.9 205139. B1 21 28.3 +60 1 68.1 + 6.4 222574. cGl 23 36.6 -18 22 30.1 -72.e 205196. BO 21 28.6 +57 4 66.2 + 4.1 222661. B9 23 37.5 -15 6 38.5 —70.6 206165. B2 21 35.2 +61 38 69.8 + 7.0 222847. B9 23 39.0 -18 50 30.0 -73.3 206773. BO 21 39.3 +57 17 67.4 + 3.4 222935. dK2 23 40.0 +29 0 74.6 -31.2 206778. cKO 21 39.3 + 9' 25 33.9 -32.5 223640. B9 23 46.2 -19 28 31.9 -75.C 206859. cG3 21 39.8 + 16 53 40.3 -27.4 224014. cGO 23 49.4 +56 57 83.1 - 4.4 206936. gM2 21 40.4 +58 19 68.2 + 4.1 224572. B2 23 53.9 +55 12 83.4 - 6.2 207198. 09 21 42.2 +61 59 70.7 + 6.9 225132. AO 23 58.6 -17 54 44.5 -76.1 207538. 09 21 44.6 +59 14 69.2 + 4.5 225212. cK5 23 59.4 -11 4 58.7 -70.6

In Table 3 the first column gives the HD number; an asterisk (*) indicates a note a the end of the table. The second column gives the name of the star, if it has one. In th column headed “Z,” an “i” denotes that the star is in E. P. Hubble’s4 zone of avoidanc of the extragalactic nebulae; “o” indicates that the star is out of the zone; and “?” tha it is near the border. The exact position may be found in Table 2. The magnitude m is always visual. If given to hundredths, it is the Harvard photo metric magnitude; if to tenths, it is usually a visual magnitude derived from photo electric measures, with Harvard magnitudes as a standard. A colon (:) designates i DM visual magnitude from the Henry Draper Catalogue. For a variable star either th maximum magnitude or the maximum and minimum are given. For a double star th magnitude of the measured component is marked with a dagger (f). The column heade< “M,” which begins with the F dwarfs, gives the visual absolute magnitude fror Mount Wilson5. The spectra in Table 3 are from different sources. The O to B5 stars were taken fror Plaskett and Pearce,6 supplemented by the lists of Be and cB stars of P. W. Merrill7 an< 4 Mt. W. Contr., No. 485, p. 34; Ap. 79, 41, 1934. 6 Mt. W. Contr., Nos. 244, 262, 511, 668; Ap. J., 56, 242, 1922; 57, 294, 1923; 81, 187, 1935; 96, 34^ 1942. * Pub. Dom. Ap. Obs., 5, 99, 1931. 1 Mt. W. Contr., Nos. 471, 512, 576, 682; Ap. J., 78, 87, 1933; 81, 351, 1935; 86, 274, 1937; 98, 15- 1943.

© American Astronomical Society • Provided by the NASA Astrophysics Data System 1945ApJ. . .102. .318S 1 , 2905.. 207198. 210839. 209975. 207538. 204172.. 209339.. 198846*. 203374.. 206773.. . 192639. 193322. 199579. 203064. 213087.. . 193443. 192281. 205196.. 193514. L88209.. 1337.. 201819.. 205021*. 184915.. 186994*. 214993*. 192422*. +35°3955 191201.. . >14680.. 203938. 218376.. 166734*. 218342. 205139. 169034*. 194839.. 195592.. 216411. 190919. 198781.. 169454. 199216. 193237. 24912. 14633.. 37742.. 36486.. 37022*.. 37128.. 10516.. 24398. 5394*. © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem HD 68 Cyg 19 Cep 10 Lac 26 Cep 69 Cyg ŸCyg 12 Lac 7 Cas X Cep 0 Per Name pqyg £ Per ß Cep K Aql K Cas r Ori 5 Ori f Per e Ori 1 Cas Ori SIX-COLOR PHOTOMETRYOFSTARS323 4.05 4.91 5.19 5.17 5.06 5.51 6.12 5.97 7.1 7.3 2.48 7.03 5.82 6.01 4.24 4.19 2.05 2.25 7.4 7.47 7.02 5.04 5.84 7.29 8.8 6.48 7.3 4.93 5.18 8.6 7.45 7.15 7.10 6.64 5.66 6.98 7.3 7.12 7.36 1.75 6.40 3.32 4.88 2.91 7.46 7.30 6.38 7.16 7.13 5.52 6.84 7.10 cBOe cBOe cBOe cBO cBO cBOe cBO cBO cBl cBl cBl cBle cBle cBl cBl cBl (BO) 09 08nn 08s 09nn 08n 08 07f 09ss 09s 06nf 06 07n Spec. 08 09 05 08 09s BOne BOne BO BO BOne BOne BOne BO BOn BO BOe BO BO Bis Bln B1 Bln Bis Bleq Colors of238Stars +0.09 +0.09 -2.22 +0.66 -1.64 -2.18 -2.21 -1.74 -1.61 -2.04 -1.99 -2.13 -1.51 -1.64 -1.53 -1.88 -2.12 +0.03 -1.97 -2.04 -0.14 -0.77 -0.99 -1.33 -1.19 -1.39 -1.59 -1.88 -0.78 -1.30 -1.67 -0.72 -0.87 -1.11 -1.10 -1.57 -0.95 -1.12 -1.16 -1.23 -1.22 -1.31 -1.48 -1.64 -1.73 -1.77 -1.85 -1.93 -2.02 -1.96 -2.11 -2.26 -2.27 TABLE 3 U -1.04 -1.15 +0.63 + .40 + .13 + .34 - .86 -1.02 -1.10 -1.17 -1.07 -- .61 - .74 - .71 - .77 -0.83 -1.11 +0.28 -1.08 -1.17 - .12 - .37 - .53 - .55 - .63 - .91 - .87 -0.97 - .61 - .79 - .17 - .33 - .40 - .35 - .42 - .73 ■0.35 • .45 ■ .43 • .49 ■ .47 ■ .55 • .61 ■ .75 ■ .81 ■ .84 ■ .89 ■ .91 ■ .99 ■0.98 ■1.07 •1.16 ■1.7 B0 Stars B1 Stars O Stars +0.50 + .30 + .18 + .02 -0.53 + .38 - .36 - .50 - .51 - .18 - .23 - .25 - .30 - .33 - .45 - .44 - .55 - .47 -0.54 - .06 - .29 - .36 +0.30 - .35 - .42 - .48 - .17 - .15 - .07 - .12 - .17 - .33 - .03 - .08 - .03 - .29 -0.07 - .13 - .10 - .16 - .15. - .18 - .23 - .31 - .34 - .35 ■ .36 - .36 - .44 - .44 - .46 - .53 ■0.53 +0.01 - .03 -0.03 - .04 - .03 - .04 - .05 - .05 - .05 + .02 - .02 - .01 - .02 - .03 - .02 - .01 - .04 - .05 + .05 + .01 + .04 -0.05 +0.05 + .02 - .04 - .04 - .05 - .04 - .04 - .05 -0.07 - .03 - .07 - .03 - .05 - .05 + .02 + .03 - .04 - .05 - .05 - .01 - .01 - .03 +0.02 + .04 - .04 - .04 - .01 - .03 - .02 - .01 .00 + .40 + .48 + .51 +0.57 + .20 + .37 + .38 + .40 + .49 + .58 +0.05 + .15 + .12 + .18 + .18 + .24 + .35 + -21 + .39 + .49 + .54 + .56 + .61 +0.58 + .18 + .30 + .27 + .28 + .35 + .36 + .48 +0.61 + .07 + .18 + .38 + .37 + .47 + .52 + .53 + .08 + .06 + .08 + .20 + .31 + .38 - .43 - .04 + .06 -0.55 - .31 - .21 -0.31 - .01 •+ .25 + .91 +0..91 +1.09 +1.14 + .33 + .37 + .38 + .48 + .56 + .82 + .81 + .86 +1.14 + 1.33 + 1.38 +0.13 + .50 + .56 +1.16 +1.32 +1.33. +1.37 + .48 + .55 + .76 + .73 + .80 + .86 +0.92 +1.16 +1.27 +0.85 +1.36 + .10 + .43 + .52 + .60 + .78 +1.06 +1.21 + 1.24 + .15 + .16 + .22 -1.06 -0.80 - .62 - .12 + .75 -1.38 -0.76 - .08 -1.18 +1.46 +1.14 +0.75 +2.01 -1.09 -1.30 -1.72 -2.18 -2.20 -2.37 -2.43 -2.50 -2.52 +1.04 -1.57 -2.53 -0.47 -0.96 -1.07 -1.47 -1.50 -1.71 -1.75 -0.48 -0.60 -1.21 -1.48 -1.72 -2.03 -2.29 -2.31 -0.56 -0.64 -0.09 V-I Obs -0.48 -0.78 -0.80 -0.87 -0.97 -1.03 -1.17 -1.57 -1.62 -1.70 -1.80 -1.82 -2.08 -2.12 -2.21 -2.49 -2.55 0.00 1945ApJ. . .102. .318S 324 JOELSTEBBINSANDA.E.WHITFORD 200857. 200120.. 206165. 224572. 217101.. 166182.. 157056*. 188252.. 212455*. 214168.. 171871. 193536. 197770. 184279. 188439. 199081.. 120315.. 194279. 193183. 198478. 223640. 180163. 147394. 194335.. 216494. 218173.. 222661.. 222847. 144206. 212710.. 188892. 183914. 199478*. 157779*. 24760.. 23302. 34759. 23338. 24504. 23630. 23324. 23408. 23480. 23862. 23432. 23753. 34085. 23288. 23441. 23850. 19356*. 4727. 1064. © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem HD 102 Her 2 108 Aqr 106 Aqr 55 Cyg 57 Cyg 59 Cyg NPS 2 20 Tau 25 Tau 26 Tau 22 Cyg 27 Tau 23 Tau 19 Tau 28 Tau 22 Tau 21 Tau 18 Tau 74 Aqr 17 Tau co Aqr 16 Tau Name 9 Cep p Aur 9 Öpti ß Per ß Cyg,C 8 Lac,A 77 Lyr /SOri e Per r Her v And v Her Cas UMa Her 4.78 4.93 4.32 5.70 4.89 6.07 3.37 2.96 4.68 7.39 6.28 5.83 6.36. 6.78 6.15 4.46 3.91 8.0 4.86 5.68 7.05 7.12 4.37 4.42 5.12 7.16 4.87 4.64 5.32 3.80 4.02 4.25 5.63 5.34 3.81 1.91 5.76 4.14 4.62 0.34 6.85 5.38 2.3 5.18 5.43 5.85 5.89 5.36 2.96 5.51 5.76 5.26 6.46 cB2 cB2 cB2 cB2 cB2e cB2 cB3 cB8e cB8e B2 Spec. B2 B2 B2s B2se B2nn B2n B2s B2 B2s B3n B3ne B3ne B3 B3ne B5s B5s B7s B8n B7n B9sp B7n \ B5n B8nn B5s B8s B7n B9n B9 B9n B9 B9n B8nn B9n B9n B9ne B9s B6n B7ne B9n B7n B8n B9s B8n TABLE 3—Continued +0.20 -1.90 -1.75 -1.77 -1.92 -1.96 -2.12 -1.62 -1.92 -1.87 -1.79 -0.52 -0.88 -0.98 -1.08 -1.19 -0.87 -2.00 -1.94 -1.80 -1.65 -2.05 ■0.76 ■ .87 - .83 ■ ,90 ■0.93 -1.27 -1.55 -0.89 -1.24 -1.04 -1.13 -1.20 ■1.07 -1.20 ■1.25 ■1.30 -1.38 ■1.27 ■1.26 ■1.05 ■1.49 ■1.26 ■1.28 ■1.46 ■1.30 ■1.38 ■1.70 ■1.6 ■1.64 U 1.63 1.43 B5-B9 Stars +0.36 -1.11 -1.08 -1.14 - .85 -1.01 -1.07 -1.03 -1.02 -1.05 - .38 - .59 -0.99 - .25 - .43 - .53 -0.34- -1.00 -0.98 -1.03 -1.01 -1.07 -1.09 - .88 - .87 - .92 - .92 - .97 -0.96 -1..00 -0.97 - .98 -0.98 -0.98 -1.06 -1.07 - .89 - .96 - .93 - .94 - .92 - .95 - .92 - .96 -0.96 - .93 - .93 -0.47 -1.00 -1.06 -1.06 -1.11 -1.12 B2 Stars B3 Stars +0.34 + - .50 - .49 - .47 - .54 - .49 -0.53 - .37 - .45 - .44 - .43 - .50 -0.11 - .45 - .50 -0.52 - .41 -0.06 - .43 - .44 - .44 - .44 - .44 - .39 - .44 - .44 - .45 - .44 - .47 - .44 - .46 - .42 - .46 - .46 - .45 - .46 - .45 - .45 - .46 - .46 - .45 - .47 - .49 - .48 - .47 - .50 - .48 -0.50 .08 .20 .01 .12 .18 - .05 +0.03 - .05 - .05 - .06 - .04 - .05 - .05 -0.07 - .04 - .06 - .02 - .02 - .01 - .03 - .03 -0.03 - .02 - .04 - .05 - .06 -0.06 -0.01 • .02 - .03 - .06 - .06 - .04 - .03 - .05 - .05 - .06 - .06 - .06 - .05 - .04 - .05 - .05 - .03 - .05 - .05 - .05 - .04 - .05 - .06 - .06 - .05 - .05 - .05 - .05 - .05 - .06 -0.07 4 +0.07 + .50 + .55 + .46 + -47 + .49 + .42 + .48 + .50 + .25 + .42 + .46 + .54 + .51 + .60 + .54 +0.60 + .51 + .47 + -49 + .50 + .54 + .49 + .50 + .47 + .49 + .02 + .10 + .12 + .22 + .49 + .51 + .50 + .50 + .50 + .52 + .52 + .50 + .52 + .54 + .52 + .49 + .52 + .54 +0.14 + .43 + .55 +0.58 -0.37 + .55 +0.57 + .49 + .56 j ; ) +0.84 +1.17 + 1.21 +0.10 +1.04 +1.00 + .47 +1.11 +1.08 +1.24 +1.24 +0.98 +1.00 +1.02 +0.99 +1.00 + 1.09 + 1.04 +1.13 + .22 + .23 + .44 +1.12 +1.21 +1.33 +1.02 +1.03 +1.04 +1.06 + 1.08 +1.08 + 1.08 + 1.14 +1.01 +1.11 +1.16 + 1.22 +0.25 +1.06 + 1.20 +1.22 +1.16 + 1.22 +1.28, -0.92 - .02 .99 .85 .92 .94 .92 .96 .96 +1.28 -2.20 -2.26 -2.32 -0.44 -1.73 -1.81 -1.89 -1.91 -1.96 -1.97 -1.98 -1,99 -2.01 -2.02 -0.60 -1.06 -1.69 -2.12 -2.26 -2.32 -2.47 -1.84 -1.88 -1.88 -1.88 -1.94 -1.94 -1.96 -2.01 -2.02 -2.06 -2.06 -2.20 -0.66 -0.97 -2.11 -2.15 -1.94 -2.06 -2.11 -2.11 -2.12 -2.23 -2.29 -2.26 -0.23 -2.31 -0.71 -2.22 -2.40 -2.06 -2.33 V-I Ob 1945ApJ. . .102. .318S 215766. 219833. 220020. 218639. 219659. 225132. 203280.. 128998. 218753*. 211336*. 125162. 156729. 121409. 115735. 172167.. 143807.. 112413*. 103483. 187642.. 137422.. 113865.. 166205*. 164514*. 127762.. 173648*. 173649*. 166926*. 192640.. 197345.. 113139.. 147365.. 107113.. 107192'*' 198084. 136064. 118216.. 111812. 142373. 41074.. 66368.. 10204.. 14622.. 5914.. 6920. 432 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem HD HD -22°4510 31 Com 44 And 21 CVn 65 UMa 69 Her 86 UMa 69 Aqr 29 Cyg 39 Aux 78 UMa 2 CVn Name /3 Cas NFS 3s X Boo X Her NFS 2s 7 UMi 7 Boo a NFS 6 NFS 1 NFS 5 NFS 4 a Cep a Lyr 2 Cet f Lyr,B a Aql a Cyg Name 2 Cas f Lyr,A e Cep CrB t SIX-COLOR PHOTOMETRYOFSTARS 4.63 5.74 4.61 5.87 5.07 5.23 2.7f 5.3f 6.33 6.28' m Spec.M 4.26 4.80 4.62 2.60 4.98 4.44 4.23 3.00 4.29 5.86 0.89 3.14 0.14 4.91 2.90 6.46 5.52 5.70 5.13 4.89 5.90 5.54 6.43 5.87 7.01 6.36 7.12 6.23 5.65 7.8 5.54 5.63 6.44 7.28 1.33 cA2e F5 F9 F9 F4 F2 F2 cA6 F7 F7 F2 F2 AOn A0.5n AOn AOn AOn AO .5n A0.5n AOn AOn AOn AOn A0.5s A3n A3 A3p Ain - A1.5n Als A9n A9n A5n A9s A5 A3n Ain A2 Al A9s A6n A8n A6n A3n Als Spec. TABLE 3—Continued +2.3 +3.6 +3.1 +3.0 +2.7 +3.2 +3.0 +2.2 +2.8 +3.6 +0.96 -0.56 + .02 - .64 - .76 - .77 - .76 - .77 -0.88 -1.03 -0.98 -0.96 -1.00 -0.62 - .74 - .46 - .45 - .47 - .45 - .49 - .46 - .49 - .80 ■ .72 -0.81 -1.08 ■1.32 ■0.48 ■ .49 - .50 - .49 ■ .54 - .62 - .94 ■ .59 U -Q. 13 - .16 - .32 - .20 - .22 - .39 ■ .48 - .51 - .38 ■0.5 U A1-A3 Stars A5-A9 Stars +0.39 - .42 - .49 - .60 - .64 -0.76 - .37 - .48 - .53 - .64 F Dwarfs - .82 ■ .85 ■ .92 - .94 ■0.9 ■0.72 ■ .75 ■ .79 ■ .82 • .89 ■ .84 ■ .84 ■ .88 ■ .89 ■ .97 - .93 ■0.93 ■0.52 • .65 - .62 ■ .60 ■ .62 ■ .64 ■ .80 ■ .82 A0 Stars •0.07 - .12 ■ .18 • .20 ■ .20 • .38 ■ .36 ■ .49 ■ .47 ■0.53 V B +0.40 - .40 -0.35 - .38 - .40 - .40 - .45 -0.23 - .31 - .30 - .41 - .44 -0.48 - .37 - .41 - .41 - .43 - .44 -0.44 - .29 - .29 - .30 - .34 - .38 - .44 - .46 - .14 - .18 - .16 - .21 - .24 - .29 - .30 - .32 -0.36 B -0.02 - .07 - .05 - .04 - .07 - .14 - .13 - .20 - .20 -0.23 +0.06 - .04 - .03 - .02 - .02 - .02 - .02 -0.04 - .01 ■ .04 - .05 - .04 - .04 ■0.4 ■0.6 - .06 - .01 ■ .02 - .07 - .05 - .05 - .06 ■ .05 - .04 - .03 -0.06 ■0.2 - .01 - .04 - .04 - .01 - .03 ■ .02 - .03 .00 - .01 - .01 - .02 - .02 - .02 -0.01 0.00 .00 .00 .00 + .48 + .49 + .31 + .41 + .46 + .49 + .48 +0.52 +0.41 + -42 + .40 + .42 + .46 + .49 +0.50 +0.25 + .33 + .33 + .32 + .36 + .44 + -47 + .49 + .49 + -19 + .25 +0.40 + .33 + -14 + .27 + .32 + .32 + .34 + -19 -0.45 R +0.01 + .15 +0.24 + .06 + .04 + .07 + .08 + .15 + .¿2 + .22 R H- .91 + .62 + .89 + 1.00 +0.71 + .83 + .84 + .82 + .90 + .96 +0.95 +0.56 + .58 + .68 + .68 + .66 + .72 + .72 + .88 +0.93 + 1.13 + .82 + .95 +1.02 + 1.04 + .49 +0.80 + .34 + .25 + .44 + .54 + .63 + .68 + .69 -1.44 +0.06 + .10 + .15 + .22 + .24 + .34 + .50 +0.53 + .13 + .46 + 1.83 -0.86 -0.71 -0.73 -0.98 -1.07 -1.23 -1.33 -1.56 -1.32 V-I Obs - .42 - .70 -0.13 - .31 - .35 - .62 - .95 -0.97 -1.06 - .22 V-I Obs ■1.7 ■1.73 ■1.85 ■1.94 ■2.1 ■1.43 ■1.58 •1.61 ■1.6 ■1.7 •1.74 ■1.75 ■1.83 ■1.85 ■1.92 ■1.95 ■1.97 ■1.08 ■1.23 ■1.24 ■1.28 ■1.30 ■1.30 ■1.52 ■1.54 325 1945ApJ. . .102. .318S -31964*. 326 206859.. 209750. 224014*. 217476*. 204075*. 204867.. 213306*. 202751.. 109358. 201601.. 222574.. 222935. 187138*. 221525*. 114710. 153344. 111395. 192876.. 194093*. 171779.. 135722.. 192947. 159181. 133208. 173638*. 154345. 152391. 195593*. 193370*. 163506.. 128165.. 166620. 157910.. 151288*. 171635,. 195295.. 147379*. 20123*. 20902.. 10307. 15830. 16397. 16901.. 14662*. 4406. 9270. 3765. 3651. 8890*. 571. HD American Astronomical Society• Providedby theNASA Astrophysics DataSystem 1 104 Aqr 2 45 Dra 41 Cyg 44 Cyg 35 Cyg 22 And 89 Her 54 Psc 14 Ter a Cap a Cap T Cyg 7 Equ ß CVn ß Com NTS 4r ß Aqr Name ß Dra ß Boo p Cas NTS Is NTS 3 9 Peg a Aqr 7] Psc f Cap a Per ô Boo 5 Cep « Aur JOEL STEBBINSANDA.E.WHITFORD 4.85 4.52 4.32 4.32 5.48 5.29 5.42 4.55 8.26 3.54 4.If 3.19 3.63 3.72 4.2f 3.07 4.95 4.09 5.48 4.76 6.78 7.60 5.10 7.21 5.58 5.3f 5.5f 2.32 2.1 5.08 5.62 8.5: 6.40 8.9: 6.08 6.74 7.04 6.39 7.55 2.99 6.48 6.46 5.81 3.3 3.7 8.9: 8.2 7.37 7.52 6.30 1.90 m Spec. cGO cG3 cG2 cG3 cGl cG5 cG2 cG4 cGO cGl cGl cF7 cF4 cF5 cF8 cF5 cF4 cF2 cF8 cF7 cF2 cF4 cFl cF5 MO cF4 MO K0 K6 K5 K2 K2 Kl K5 GO GO GO GO G9 G4 G9 G4 G3 G5 G8 G5 G6 G3 G5 G2 FO TABLE 3—Continued +5.5 +4.7 +4.9 +4.0 +5.3 +4.4 +4.2 +4.1 +4.5 +0.4 +0.8 +6.8 +6.5 +5.9 +5.7 +5.2 -3.0 +0.3 +0.3 +0.4 +8.7 +6.7 +5.9 +0.3 +0.2 +8.7 -3.2 -1.4 -1.3 -2.2 -2.7 -1.3 -0.9 -2.5 -1.5 -0.2 -1.7 -2.1 -1.9 M -1.2 -1.9 -1.3 -0.5 -2.1 -1.7 -2.0 -2.2 -1.2 (+1.27) .+ .80 +0.96 +0.04 + .05 + 1.79 + .51 +0.05 + 1.53 +1.09 +0.77 + .37 - .24 + 1.32 +1.19 +1.03 + .94 + .80 + .62 + .75 + -74 + .66 + .36 - .05 - .07 - .20 - .25 - .48 -0.26 +0.56 +1.04 +0.67 + .40 + .50 + .38 + .28 + .11 + .78 + .73 + .55 + .57 + .12 + .09 + .02 - .05 - 07 - .42 -0.36 - .11 K andMDwarfs U G Dwarfs G Giants F Giants +0.86 +0.02 +0.06 + .67 + .57 + .62 + .46 + .23 + .20 + ■.49 + .50 + ..39 + .39 +0.18 + .90 + .57 + .34 + .18 - .01 - .08 - .14 - .21 -0.16 + .37 + .33 + .35 + .26 +0.98 + .35 - .02 - .05 - .14 + .33 + .26 + .24 + .17 +0.37 + ■17 - .05 - .33 - .01 - .09 - .17 - .45 - .51 -0.60 - .21 - .28 - .37 - .36 - .14 +0.43 + .29 + .10 +0.02 + .39 + .24 + .23 + .22 + -H + .04 + .04 + -21 + .16 + .16 + .15 + .15 + .08 +0.07 + .50 + -17 + .16 + .08 + .14 + .08 +0.27 + .01 - .14 +0.52 + .18 + .13 + .13 - .08 - .02 - .05 - .04 - .14 - .20 - .26 -0.27 - .11 - .17 - .02 - .01 - .01 • .05 - .02 - .04 - .08 •0.06 0.00 .00 + .01 + .04 +0.01 + .02 + .02 + .01 - .01 - .01 - .02 + .01 - .02 + .06 + .01 + .01 - .01 - .01 - .01 - .02 - .01 + .01 +0.06 -0.01 - .02 -0.02 - .01 - .04 + .01 + .04 - .01 - .05 - .01 - .01 -0.01 - .03 - .03 - .02 - .01 - .03 - .01 - .02 - .02 -0.05 - .01 0.00 0.00 .00 .00 .00 .00 .00 .00 + .15 + .06 + .05 + .09 +0.08 + .05 + .05 -0.02 + .04 + .05' + .06 + .09 + .13 + .14 + .22 + .30 +0.31 - .11 - .13 - .08 - .05 - .01 + -01 + .17 - .25 - .15 - .53 - .01 -0.59 -0.27 - .14 ■0.43 - .39 - .28 - .23 - .22 - .20 - .20 - .16 - .15 - .13 - .15 - .14 - .08 - .13 - .10 - .10 - .07 -0.05 R 0.00 .00 +0.02 + .04 + .16 + .10 + .24 + .05 + .06 + .10 +0.21 + .10 + .21 + .40 + -12 + .20 + .25 + .62 +0.57 - .41 - .28 - .20 -0.09 + .31 - .46 - .23 - .12 - .98 -0.69 - .35 - .07 - .16 - .01 -1.23 -0.87 - .90 - .59 - .46 - .41 - .40 - .31 - .28 - .23 - .25 - .25 - .21 - .25 - .24 - .11 - .19 - .10 ■0.9 .00 +1.73 + 1.57 + 1.08 +0.90 + .90 +1.16 + .77 + .65 + .62 + .58 + .56 + .50 +0.98 + .80 + .63 + .58 + .51 + .50 + .43 + .41 + .32 +0.15 + .43 + .27 +0.27 - .57 +2.21 +1.88 +0.52 + .06 + .02 - .24 - .30 -0.37 V-I Ob +1.06 - .02 - .06 - .11 - .12 - .31 - .15 - .20 - .21 - .49 - .62 - .67 -0.85 -1.13 -1.17 - .37 0.00 SIX-COLOR PHOTOMETRY OF STARS 327

TABLE 3—Continued

HD Name Spec, M U V-I Obs

K Giants

145328.. CrB 4.94 K1 + 1.3 +1.02 +0.43 +0.19 0.00 ■0.19 ■0.34 +0.77 112570.. 6.22 K0 + 1.8 +0.84 + .43 + .18 - .01 - .18 - .36 +0.79 125351.. 5.If Kl +0.4 + 1.36 + .57 + .24 - .02 - .22 ■ .41 +0.98 152601.. 23 Oph 5.35 K3 +0.2 + 1.25 + .52 + .20 - .01 ■ .18 - .49 + 1.01 183912*. ß Cyg, AB 3.8f (KO) -0.7 +0.90 + .57 + .31 - .01 • .30 ■ .61 + 1.18 163770.. 0 Her 3.99 cKl -1.3 +2.04 + .87 + .35 - .02 ■ .32 ■ .63 +1.50 218356.. 56 Peg 4.98 cKO -1.6 +1.76 + . 87 + .39 .00 ■ .39 • .76 + 1.63 214868*. 11 Lac 4.64 K2 -0.1 +1.91 +0.88 + +1 - .02 ■ .38 ■ .81 +1.69 114282*. NFS 3r 7.57 K2 +2.44 +1.09 + .48 - .02 ■ .46 • .91 +2.00 206778.. e Peg 2.54 cKO -2.3 +2.51 +1.17 + .49 - .01 ■ .47 ■ .90 +2.07 210745*. f Cep 3.62 cK5 -2.3 +2.58 + 1.16 + .49 - .02 ■ .47 •0.92 +2.08 192107.. 66 Aql 5.64 K5 -0.1 +1.98 + 1.03 + .51 .00 ■ .52 ■1.08 +2.11 225212*. 3 Get 5.5f cK5 -2.7 + 1.26 + .54 - .01 ■ .53 •1.04 +2.30 29139.. a Tau 1.06 K5 0.0 +2.63 +1.20 + .54 + .02 ■ .56 ■1.18 +2.38 200905.. £ Cyg 4.2f cK5 -2.0 +2.76 + 1.28 + .57 + .01 ■ .58 ■1.15 +2.43 196321 70 Aql 5.22 K5 -0.4 +2.61 +1.25 +0.53 +0.01 ■0.53 ■1.23 +2.48

M Giants

51802.. NPS Ir 5.3 MO ■0.1 + 1.28 +0.63 +0.03 -0.66 -1.42 +2.70 213310.. 5 Lac 4.6 MO -2.3 + 1.33 + .66 + .02 - .69 -1.42 +2.75 187076*. ô Sge 3.8 M2 ■1.2 +1.09 + .62 + .09 - .71 -1.71 +2.80 183030.. NPS 2r 6.6 Ml ■0.3 + 1.41 + .70 + .07 - .77 -1.76 +3.17 120933.. 5.0 M2 -0.5 +1.51 + .69 + .10 - .79 -1.85 +3.36 39801. a Ori 0.1-1.2 M2 -4.1 +1.60 + .77 + .04 - .81 -1.78 +3.38 148478. a Sco 1.5t Ml -3.7 + 1.55 + .84 + .04 - .87 -1.99 +3.54 209772. 18 Cep 5.5 M5 0.0 +1.34 + .79 + .12 - .91 -2.22 +3.56 132813. 4.9 M5 -0.3 +1.37 + .85 + .12 - .97 -2.31 +3.68 214665. 5.5 M4 -0.4 +1.43 + .81 + .13 -0.94 -2.25 +3.68 218634.. 57 Peg 5.4 M4 -1.1 +1.33 +,.87 + ,15 -1.01 -2.42 +3.75 175588.. Ô2 Lyr 4.5 M4 -1.6 +1.46 +0.84 + .11 -0.95 ■2.30 +3.76 175865.. RLyr 4.0- M5 -1.1 +1.48 +1.02 + .15 -1.18 -2.844 +4.32 .5 206936*. n Cep 4.0- M2 -4.5 +1.18 - .01 -1.18 -2.474 .8 178770.. 7.6 M6 -0.9 +1.13 + AÏ -1.25 -3.07 148783. g Her 4.4- M6 -1.0 + 1.29 + .11 -1.40 -3.255 .6 144205. X Her 5.8-7.2 M6 -1.1 +1.47 + .05 -1.52 -3.60 182917. CHCyg 6.4- M6 -1.4 + 1.54 + .01 -1.55 -3.787 .4 142143. ST Her 7.0- M7 ' •0.7 + 1.93 - .14 -1.78 -4.198 .2 126327. RX Boo 7.0- M7-8e -0.6 +2.27 -0.42 -1.85 -4.589 .2

NOTES TO TABLE 3 HD 5394 Magnitude and color variable 8890 Polaris, variable, colors at maximum 14662 Reddened 19356 Algol at maximum; colors change during eclipse 20123 Probably reddened 31964 Eclipsing variable, definitely reddened 37022 Four stars of Trapezium; combined color assumed equivalent to B0. 107192 Keenan calls this star an ordinary giant 112413 Variable, period 5.5 days; no large change in color noted 114282 Spectrum from Keenan; color of a supergiant 147379 Ultraviolet too faint to measure 151288 Ultraviolet too faint to measure 157779 Both components 164514 Strongly reddened. In Trifid nebula; see Scares and Hubble, Mt. W. Contr., No. 187, pp. 10 and 15; Ap. J., 52, pp. 17 and 22, 1920. Spectrum cA6 from Adams and Joy, unpublished 166205 Standard star 166926 Standard star 169034 Variously classified, B0-B3; most strongly reddened star 173638 Reddened 173648-9 The brighter A9 component is definitely bluer than the fainter A3 component 183912 Spectrum and color composite 186994 Spectrum from HD only 187076 HD spectrum, Ma + A0; color also composite , 187138 Spectrum from Keenan; ordinary giant. Ultraviolet poor but definitely weak 192422 Measures discordant 193370 Reddened 194093 Possibly not reddened

NOTES TO TABLE 3—Continued 195593 Strongly reddened 198846 Eclipsing variable; weak ultraviolet could be caused by a red companion 199478 Reddened '204075 Measures discordant 205021 Not tested for change of color in light-period of 4.6 hours 206936 Must be reddened ' 210745 If spectrum is as early as cKl, this star could be reddened 211336 Comparison star for 5 Cephei; used also as secondary standard for color 212455 Strongly reddened / 213306 Variable, colors at ma.yirmim; see J. Stebbins, Mt. W. Contr., No. 704; Ap. J., 101, 47, 1945 214868 Possibly reddened; see 12 Lacertae under Bl stars 214993 No detectable change of color in light-period of 4.6 hours 217476 Reddened 218753 Weak ultraviolet has been confirmed 221525 Spectrum from Keenan 224014 Reddened 225212 Ultraviolet doubtful of J. O’Keefe.8 From B6 to M the classification is usually by Adams and Joy and others,5 with additions of unpublished spectra kindly secured for us by Mr. A. H. Joy. The spectra for the North Polar Sequence are from P. C. Keenan.9 Exceptions are marked in the notes. The six colors írom U to I are on the uniform system in magnitudes referred to the mean of blue, green, and red for each star; a plus sign (+) indicates that the color is rel- atively fainter than the mean. Because of the variability of the ultraviolet with the hydrogen absorption the difference V — I in the next to last column serves better than U — I as the over-all index for color in all spectral types, and the stars in each group are arranged according to that differeiice. The last column gives the number of observations, averaging about two per star; but about two-fifths of the stars have only one observation each. II. COLORS BY SPECTRAL TYPES In addition to the notes on individual stars in Table 3, we may consider each spectral type as a group. From the way the colors run down eàch column of the table, a discordant or peculiar star can be picked out, though too much should not be inferred from one observation alone. It is always possible, owing to variable extinction, that the ultraviolet or infrared should be off as much as 0.10 mag., but such cases must be rare for the mean of two or more observations. We note that the first, or bluest, star in the entire list is an O star, while the last, or reddest, star has the latest spectrum, M7-8. Among the early-type stars from O to B3 we have found almost no clear-cut case oi two stars with identical spectra but with different intrinsic colors. Even the slight variation in the three B0 stars in the Belt of Orion may be caused by differential absorption the whole region of Orion is full of nebulosity. The color of P Cygni stands out among the Bl stars, but the spectrum of this star is anomalous. Otherwise the O’s and B’s, being nearly all in the zone of avoidance, simply show different degrees of space reddening which was the basis on which they were selected in the first place. For types B5 and later, the dispersion in color for a given spectrum becomes more ap- parent, although it is still possible that the dispersion may be as much in the spectra classification as in the color. About a dozen star$ from B9 to M, practically all supergiants within the zone, are obviously reddened ; but the difficulty in selecting proper nonreddened comparison stars prevents a study of the law of absorption comparable witi that of the B stars. : ^ v- O stars.—Ovly the first two stars in this group are outside the zone, and these appar ently have normal colors; the others show various amounts of reddening which mask an) progressive change in intrinsic color from 05 to 09. The smooth run of the colors dowr the list indicates that there are no large errors in the observations. B0 stars.—Almost the only nonreddened B0 star in the summer sky is y Cassiopeiae 8 Ap. 94, 353, 1941. *Ap. 91, 113, 1940.

© American Astronomical Society • Provided by the NASA Astrophysics Data System 1945ApJ. . .102. .318S 1 a10 1 bluest oftheirclass.Thesethreeand6OrionisarediscussedinSectionIV.Thecolors known tobevariableinlightandcolor;butweseemhavecaughtthisstarthenor- violet isextrabrightinthetwocstars,ßOrionisandHD199478.Thelatterobviously slightly reddened.Thelaststar,aneighth-magnitudesupergiantinlatitude—2°,was HD 169034.Althoughthespectrumofthisvariableisweakinshorterwavelengths, 4.5 mag.ontheV—Iscale,orpossibly1.5mag.,International.Dr.R.Minkowski called ourattentiontothevariable,RYScuti,aboutonedegreedistantinskyfrom cur incasesofoneobservation. in September^1943,andagain1944;and,asexpected,theyturnedouttobeamongthe mal, orbluest,phase.Thethreestars5,e,andfOrioniswereobservedjustbeforedawn A’s the.ultravioletisusuallyfainterthantheviolet;but,astobeexpected,ultra- sure tobefoundreddened. stars discussedinthepresentpaperculminatenorthofzenith,andonlyafewwere Lacertae towardthegalacticequator. 73 BStars”astheonlystarwelloutsidezonewithcolorexcesslargeE\= reddening ofHD216200=14Lacertae,whichstoodoutlikeamistakeamongour This evidenceforaslightabsorptioninLacertaispossibledelayedconfirmationofthe a traceofreddening;andnear-by§Lacertae,spectrumB3,islikewisepossiblycolored. RY Scuti,arethemoststronglyreddenedstarswehavefoundinentiresky. it isprobablyanearlyB.WecomparedthesetwostarsdifferentiallywiththeCifilters ing. AswegofromB5tolatertypes,thehydrogenabsorptionincreases,untilin could possiblyalsobenearlynormal.ThefirstB3starlooksnormal,andtheotherslook enough tousmisstheabsorption;and0Ophiuchi,observedonlyonceatalowaltitude, measured intheheavilyobscuredsouthernregionnearl=345°. tween thelastB1starandoneprecedingismerelyamatterofselection;most sidered inthenotestoTable3.Thoughwelloutofthe,zone,12Lacertaeappearshave than HD169034—^practicallythesame.Thethreestars,166734,169034,and on onenightandfoundRYScutitobeof10.0visualmagnitude0.01mag.redder, of theBO’sdonotrunassmoothlythoseO’s,butdiscordancesusuallyoc- ficient ofspaceabsorptionfromonlyadozenstars. V —Iarewellcorrelated,buttherangeindistance isnotenoughtodetermineacoef- reddened. A9’s showalargedispersion.Theanomalousultraviolet magnitudeof2Cassiopeiaewas wire screen,fitinwellenoughwiththefainterstars ofthesametype,whileaCygniwith tempt todetectspacereddeningtowardthepolesofgalaxy.ThevaluesCiand the earlier-typestarsofsameapparentmagnitudes,showlittleevidenceredden- +0.12 mag.SincethenwehavefoundE=+0.13forHD215227,whichis3°from14 no caseofstrongreddeninginthisgroup. that ofanumbertheBstars. observed twice.ThecolorexcessofHD164514,about 3mag.inV—I,isexceededby a 3-mag.screenhastheusualstrongultravioletintensity ofacstar.Thereisapparently 1 11 10 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem B5-B9 stars.—Mostofthesestarsareoutsidethezoneand,beingnearertousthan B1 stars.—Thetwosimilarshort-periodvariables,ßCepheiand12Lacertae,arecon- B2-B3 stars.—Thefirststar,ePersei,thoughinthecriticalzone,seemstobenear The discordantcaseofPCygniisdiscussedinSectionIV.jumpthecolorsbe- The lasttwoBO’sstandoutinanylistofcolors,HD169034havingacolorexcess A0 stars.—AllbutoneofthesewereobservedpreviouslywiththeCifiltersinanat- A1-A3 stars.—Thebrightstars,aLyraeandaAquilae, measuredthrougha6-mag. A5-A9 stars.—Thecolorsprogressinawaywith advancingspectraltype,butthe F, G,K,andMdwarfs.—Thesestarsmaybediscussed together;theyweretaken Stebbins,Huffer,andWhitford, Mt.W.Contr.,No.650;Ap.J.,94,215,1941. StebbinsandHuffer,Pub.Washburn Obs.,15,237,1934. SIX-COJrOR PHOTOMETRYOFSTARS329 1945ApJ. . .102. .318S 12 13 persion ofthecolorswithinspectraltypes.TheG’sandK’sscarcelyoverlap,nordp 330 JOELSTEBBINSANDA.E.WHITFORD less than3,orr<40parsecs.Theprogressionofthecolorsisfairlyuniformdown and theyfitinataboutG2thenextgroup,givingasgoodevidencewehaveofdis- list, butthereissomeoverlappingofthegroups.ThefirstF’sarebluerthanlastnon- measured. the K’sandM’s.TheultravioletintensitiesoftwofaintMstars"weretooweaktobe reddened A’s.ThelastthreeF’s,whichaverageF6,areredderthantheF9’sbeforethem; mostly withthe100-inchtelescopeforcomparisonnebulae.Thereislittlechance ly reddened. but thelastfourstarsareallreddened. The colorsrunprettysmoothlyfromstartostar;eventhevariables,bCepheiandNFS all supergiants,owingtothewell-knowngapforordinarygiantsinRusselldiagram. differences betweenordinarygiantsandsupergiants.TheF’sinthelistarepractically that reddeningmaybedetectedinanybrightdwarf,themodulusm—Mbeingusually dence ofabsorptionnearthisstar.ThelasttwoGgiants,bothinthezone,areundoubted- change ofthecolorswithadvancingspectraltype.Thereseemstobeanabsolute-magni- the samespectrumandcolor;but9Pegasiisoutsideth£zone,therelittleotherevi- ficiently tested.Wemightaswellcallthemallvariable,particularlyHD178770,with tween thesupergiantsanddwarfs.ThiseffectisshowninFigure1. tude effectintheearlyK’s.SixgiantswithMfainterthan0.0havecolorsmidwaybe- its latespectrum,M6.Theultravioletinaredstarisusuallytooweaktomeasure;to- been foundwiththephotocelltobeeithervariableorsuspicious,leavingthreenotsuf- values forthelastsevenstarsarealsoomitted;infact,violetbecomesuncertain intense astheultravioletwearetryingtomeasure.Becauseofalesserleak,violet infraréd radiationthroughtheultravioletfiltermaybecomefiftyoronehundredtimesas ward theendoflistultravioletbecomes10or12mag.fainterthaninfrared. If merefaintnesswereall,theultravioletcouldbemeasured,butleakofstrong all theMstars. Is =Polaris,fitinwell.ReddeningseemstobeginateAurigae;yCygnimaybenormal; later inthelist. sorption whenhenotedthecolor.Withmodulusw—lf=8.5,r=500parsecs,b star, althoughitstillshouldnotlookasredtotheeyegHerculisandotherstars assumption thatalltheothersaremoreorlessreddened. LaterthanB5,starsinthezone “garnet star”byWilliamHerschel,whowasprobablynotthinkingofinterstellarab- four starstoatype,thetwohighestandlowest valuesareused;andafterA6allre- that areclearlyreddenedordoubtfulomitted. From B6toA6,iftherearemorethan type. Fortheearlystars,OtoB5,twobluest starsareusedforeachtype,onthe liable starsareplotted.Thescaleofabscissaeisdoubled fortheM’swithoutanattempt +4?1, ¡iCepheiundoubtedlyshowsspacereddeningandis,indeed,adoublyred about G5andextendstoK3.Itwillrequireseveral timesasmanystarsintheregion done forthespectra.Thedifferencebetweenordinary giantsandsupergiantsbeginsat to differentiatebetweenthescalesfordwarfsand giantsintheintervalK5-M0,asis effect satisfactorily. G5-M0 ashavebeenusedinthisinvestigation to establishthisabsolute-magnitude 13 12 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem F giants.—Inthegiantswecanexpectreddeningofstarsinlowlatitude,andperhaps G giants.—ThereddeningmightbeginatHD20123wereitnotfor9Pegasiwithabout K giants.—Anyslightreddeningofthebrightstarsinzoneishiddenrapid M giants.—Ofthetwentystarsinlist,eightarerecognizedvariables,ninehave No spacereddeningintheMgiantsisevidentuntilwegetto¡iCephei,called All types.—InFigure1thevaluesofV—IfromTable 3areplottedagainstspectral AdamsetaL,Mt.W.Contr., No.511,p.7;Ap.81,193,1935. StebbinsandHuffer,Pub.Washburn Obs.,15,147,1930. 1945ApJ. . .102. .318S 1475 3 < thanhalftheshiftofwavelengthinaphotographic magnitude. plate, theshiftofwavelengthwithspectraltype—for instance,intheviolet—isless atmosphere fordifferentspectraltypes,andtheopticalsystemoftelescope.Ourcol- ors havethesamecharacteristicasthoseofanyothersystemnotdealingwithmono- extinction foreachstar;evenwiththeMountWilson sky,therearenight-to-nightvaria- ured; butsincethefilterstakeinsmallerspectralranges thantheordinaryphotographic chromatic radiation;theeffectivewavelengthdepends uponthecolorofstarmeas- effective wavelengths^ofF.H.Scaresorthe“isophotallengthsA.Brill, if desired,applymeancorrectionsforeachstarlater. Thesensitivity-curveofthecell two aluminummirrorsaretheonlyadditionaleffects intheopticalsystem. seems besttogoaheadusingthesameextinctionfor allstarsasafirstapproximationand, tions whichexceedthedifferentialeffectsbetween starsonthesamenight.Hence,it which takeintoaccounttheenergy-curvesofstars,differentialextinction referred toasourceofuniformenergythroughoutthespectrum.Theyarenot“mean was determinedthroughtheregularwindowof photometer,sothatreflectionsfrom of thepresentmethod. agreeing withmanyothers,weconsideragainthelimitations,aswelladvantages, at differenttemperatures;butsinceweareprettysuretogetatemperaturescaledis- 15 14 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Veröjf.d.U.Sternw.Berlin-Babelsberg, 7,PartV,5,1929. Whatever maybetheshortcomingsoffiltersinisolating spectralregions,thephoto- As mentionedbefore,itisimpracticaltomakeacomplete correctionforatmospheric Mt.W.Contr,,No.685,p. 28; Ap.98,329,1943. The wavelengthsforthedifferentcolorsareeffectivemeanscellandfilters With sixcolorswecancomparetheenergy-curvesofstarswiththoseablackbody SIX-COLOR PHOTOMETRYOFSTARS331 HI. COLORTEMPERATURES 1945ApJ. . .102. .318S photometry, whereclearspacesofcontinuousspectrum aremeasured,therecanalway be anundetectedveilofgeneralabsorptionoverthe surfaceofastar,andwecomebac black-body radiationcanbereferredtoanyapproximatecurve. giving thebestfitwithobservedenergy-curveofstaroverspectralregion 332 side ouratmosphere. color temperaturesimplydescribestheover-alldistribution oftheenergyasreceivedoui affected bytheabsorptionlinesandbandsintheir spectra,justascolorindicesinth cally, itturnsoutthatagoodfitservesaswellthebestone,sincedeviationsfror six pointsbythecorrespondingblack-bodycurve,whichisnearlyastraightline.Practi concerned.” Inthepresentcase,whenintensitiesinsixcolorsareplottedmagni provement ofthezeropoint canbereadilyintroducedlater.Thecolorsofthese starsai arbitrary standardsforcolorandtemperature. For convenienceofreferenceforth International andotherphotographicsystemsare likewiseaffected.Eveninspectre tudes against1/X,thattemperatureisselectedwhichgivesthebestrepresentationofth of intensity.Thevariationsensitivityavailableintheinstallationatanytimeisdis magnitudes isapparentlylinearandessentiallycorrectforallcolorsovertheentirerang cell willalwaysrepeataccuratelythesameresponseforradiation.Thescaleo nebulae, tenstarsoftypesdGOtodK2wereselected; theaveragespectrumisdG( to thequestionofwhatpartastarwemeanwhen wespeakofitstemperature.Th which isassumedtocorrespond toacolortemperatureof5500°K.Anychange orin The extremerangehasnotbeenneeded;but,forinstance,thedifferenceininfrare< tribu tedasfollows: scale runsoffasmuch0.10mag.fromproportionalityofresponsetoenergyreceived between aOrionis,spectrumM2,andHD14633,08,isabout10mag.,an< in Table4.Althoughmarked asstandards,theyarenotbettermeasuredthan othersc neither herenorelsewhereinotherstarsandcolorsdoourtestsindicatethatth 154345. 152391. 153344. 166620. 111395. 15830. 10307. 16397. 1 ? 3651. 4406. © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem The energy-curvesandresultingtemperaturesfor the starsherestudiedare,ofcoursí The “colortemperature’ofastarmaybedefinedas“thetemperatureblackbod; Since allourmeasuresweredifferentialbetweenstars orgroupsofstars,webeganwit Mean. hd 6.40 6.08 6.78 6.74 6.7 6.39 7.04 5.10 7.60 7.55 7.21 Low tohighresistanceincircuit2 Wire screens6 Galvanometer scale,deflectionsfrom10to400mm4 Galvanometer shunts,from1/1to1/1005 Spec. dKl dKO dG4 dG6 dK2 dG9 dG3 dG5 dG6 dGO dGO < Total !.17 JOEL STEBBINSANDA.E.WHITFORD +5.9 +5.5 +4.7 +4.0 +5.9 +5.2 +5.0 +4.9 +5.3 +4.4 +4.1 M +0.05 +0.51 + .36 + .04 + .05 -Ó.05 - .07 - .24 - .20 -0.48 0.00 U Standard Stars TABLE 4 + .20 + .06 +0.23 + .02 -0.02 • .14 0.00 0.01 0.21 .05 .08 +0.10 + .04 + .02 -0.02 -0.08 -0.01 - .01 - .05 - .02 0.00 B .00 +0.02 + .01 + .01 +0.02 +0.01 - .01 - .05 - .02 0.00 0.00 .00 +0.09 + .05 + .06 + .05 -0.01 ■0.13 ■ .05 ■ .02 0.00 0.00 R .00 Mag. +0.05 + .06 +0.10 + .02 + .04 + .10 - .12 -0.20 - .09 0.00 0.00 I + .32 +0.43 + .15 -0.02 -0.06 - .11 -0.31 - .12 - .24 V-I 0.00 .00 1945ApJ. . .102. .318S polar staritselfcanserveasastandard.Onanynightthecolorsofeachobservedare several goodcomparisonsofapolarstarwiththetenstandardstarsareobtained, the list;reallystandardstarsareintermediateones,NPS4and1.After then referredtotheoriginalstandardsbywayofpolarstars,thuscontrollingpossible changes inthephotocellorextinction. from Planck’sformula, 100,000° where theconstantciandunitsofenergycanceloutinratiotwovalues E, andwhereXistakenincentimeters,Tdegreesabsolute,cj=1.435cmde- grees. ForT=theratioofenergiesfortwowavelengths,XiandX2,becomes ?or eachtemperaturethecolorswerereferredin magnitude tothemeanofblue, rreen, andredthentothecorrespondingcolors forT=5500°.Thecompletetableis 30.000. 20.000. 50.000. ibout fivetimesasextensiveTable5.Therelative temperatureofanystarmaybe lerived byacomparisonofitscolorswiththose the table.Inanticipationofsub- 15.000. 10,000. 12.000. equent discussion,thetemperaturesonthisscale are denotedbyTi. olors fromTable5.Foreachtypethefirstlinegives theobservedcolors,andsecond ne thedifferencesfrom black-bodycolorsatthestatedtemperature,taken inthe snse, ObservedminusComputed. Onlythosestarsclearlyfreefromspace reddening rere used,thusomittingall high-luminositystarsinthezoneofabsorption. Ofcourse. © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem In Table5theblack-bodycolorsforsixwavelengthsconcernedwerecomputed 8000. 9000. 4000. 6000. 6500. 3000. 3500 4500. 5000. 7000. 5500. 2000. 2500. In Table6themeancolorsofstarsgroupedbytypes arecomparedwithblack-body +0.30 +2.57 + 1.16 -1.58 -2.04 -2.24 -2.50 -2.59 +5.45 +1.77 +0.69 -1.16 -1.34 -1.82 -2.40 +3.71 -0.26 -0.47 -0.64 -0.93 0.00 U SIX-COLOR PHOTOMETRYOFSTARS333 + .18 +3.15^ + 1.50 +0.67 + .39 -1.16 -1.42 +2.16 + 1.02 -0.90 -1.04 -1.28 -1.36 -1.47 - .66 - .76 - .27 - .38 - .54 - .15 .00 Black-Body Colors Ex + .33 - .56 - .62 - .69 -0.71 £1 + 1.57 +0.74 + .51 + .19 + .09 - .32 - .44 - .50 - .66 + 1.07 - J8 - .26 - .37 £2 - .07 - .13 TABLE 5 gCt/XT— I’ 5 .00 Ci/X x r X| + .01 - .03 - .04 - .04 -0.04 +0.11 + .05 + .03 + .02 - .02 - .03 - .03 - .04 + .07 + .01 - .01 - .02 - .02 - .01 .00 .00 + .73 + .46 + .59 + .65 + .70 +0.75 + -19 + .28 + -34 + .39 + .53 + .08 + .14 - .35 - .09 -1.67 -0.79 - .54 - .21 -1.14 R .00 + +0.99 + 1.13 + 1.27 + 1.40 + 1.55 +Í.61 + + + + 1.49 + + -1.17 -0.76 - .45 - .20 -3.70 -2.51 -1.73 .41 .59 .73 .83 .16 .30 .00 + 1.43 +0.84 +0.38 -2.43 -2.97 +4.67 +3.23 +2.19 -0.79 -1.13 -1.39 -1.89 -2.17 -2.68 -2.85 -3.08 +6.85 -0.57 -1.60 -0.31 v-l 0.00 1945ApJ. . .102. .318S c F3. as superfluous.Forconvenience, thetemperaturehasbeentakenfrom the valuec V —Iineachcase,giving agreementofthecurvesforpointsV and Iinth gM6. 3100. gMl. 4900. /C gK5. cGl. 4550. dK5. standards ofanyprecisesystemstellarcolorswillhavetobebaseduponstarsclosetc 334 2130. 3750. cKl. 6900. 3590. 3450. dMO. dKl. dG6. dF2. 5150. 5500. dGO... A0.... 21,000. 23,OOO o there isstilltheprobabilityofasmallreddeningtowardgalacticpoles,andfina] 5950.. B5.... BO.... the sun,iftheycanbefound. 7300. 11,300. 16,000. Spectrum © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem In Figure2thecomparisons inTable6areshowngraphically,omittingseveral type and T\ +0.75 +2.19 +0.35 +0.17 +0.81 +0.72 +0.50 +0.31 +0.10 +0.31 +0.64 -0.11 -0.24 +0.23 -0.42 -0.86 -1.65 -0.13 -2.20 -0.14 -2.26 0.00 U .00 .00 Colors andTemperaturesofStarsbySpectralTypes JOEL STEBBINSANDA.E.WHITFORD + 1.18 +1.38 +0.12 +0.16 +1.00 +0.05 +0.27 +0.09 +0.46 +0.03 +0.94 +0.15 -0.01 -0.03 -0.39 +0.05 -0.01 -0.02 -0.16 -0.03 +0.05 -0.47 -0.01 -0.87 -1.07 -1.13 -1.16 0.00 .00 .00 + 1.36 +0.67 + .53 + .01 -0.06 + .02 + .43 + .12 + -14 + .04 + .51 + .05 -0.01 + .01 + .02 - .01 - .18 - .04 + .04 + .05 - .01 +0.06 - .05 - .19 - .42 - .48 - .52 -0.53 .00 .00 .00 .00 TABLE 6 +0.07 + .01 + .06 -0.03 + .05 + .03 + .04 - .02 + .02 + -01 + .01 - .04 - .04 - .01 - .01 - .02 - .01 - .01 - .01 - .02 - .03 - .05 - .01 - .02 - .05 - .01 - .04 -0.01 -0.04 .00 .00 .00 +0.08 + .03 -1.43 + .03 + .19 + -01 + .02 -0.73 - .53 - .41 - .11 + .06 + .21 + .03 + .47 + .54 - .06 - .56 - .18 + .57 - .01 - .07 - .01 +0.58 - .01 - .03 - .01 -0.04 0.00 .00 .00 .00 +0.10 +0.06 -0.08 -3.42 +0.16 +0.36 +0.08 -0.01 -1.61 -1.12 -0.80 +0.04 -0.18 -0.03 -0.01 -1.10 +0.12 +0.43 +0.93 -0.34 + 1.17 +0.05 + 1.34 +0.04 +1.36 -0.10 -0.02 -0.04 -0.01 0.00 .00 .00 +2.99 +0.02 +2.30 +1.80 +0.45 +2.04 +0.01 +0.80 -0.01 +0.25 -0.75 +0.01 +0.01 -0.01 -0.28 -0.90 -1.80 -2.24 -2.47 -2.52 V-I 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 .00 .00 Stars 10 2 4 4 2 3 5 3 2 2 SIX-COLOR PHOTOMETRY OF STARS 335 graph. In the main sequence the radiation of the ultraviolet is strong in BO; it decreases from B5 to AO, owing to hydrogen absorption, and is back to normal at dGO. In the giants the ultraviolet is weak from hydrogen absorption in cF3, blit in the G and K giants

the weak ultraviolet simply conforms to the general curve of the deviations from a straight line. This curve of the deviations, suggested in the dwarf K’s but conspicuous in the giant G’s and K’s, is apparently not present in the dwarf or giant M’s, which, despite

the strong spectrum bands, give very good over-all agreement with black-body radiation. The measures of color index in the diagram range from U — I = —3.54 for BO to B — I = +4.78 for gM6, or more than 8 mag. The zero point of our temperature scale must remain preliminary until we have actual- ly determined it from a standard terrestrial source. It should not be too difficult to turn the 60-inch telescope toward a standard lamp placed on one of the towers at Mount Wil- son and to measure the colors with the optical system used for the stars. We hope to make this calibration in due time; but until that is done, almost any zero point will suf- fice. The zero point of the temperatures in Tables 5 and 6 was taken from Russell, Dugan, and Stewart,16 using Ti = 5500° for dG6. Their scale is based upon 6000° for the sun, with spectrum dGO and color index +0.57 on the Harvard photographic-visual scale. 17 However, if we follow G. P. Kuiper and use color temperature r2 = 6700° and spec- TABLE 7 Mean Color Temperatures of Spectral Types

V-I 2T 72 Spectrum* Main Giants Main Main Sequence Sequence Giants Sequence Giants O.. -2^52 23,000c 140,000° + B0. -2.47 21,000 85.000 + B5. -2.24 16,000 34.000 A0. -1.76 11,000 16.000 A5. -1.30 8700 11,200 F0. -0.92 7300 9000 F5. -0.52 6400 7600 GO. -0.28 +0^30 5950 5100° 6900 5780° G5. -0.05 +1.00 5570 4360 6420 4830 K0. +0.16 +1.68 5280 3830 6020 4180 K5. +0.80 +2.30 4550 3440 5080 3730 MO +2.04 +2.86 3590 3160 3900 3400 M5 +4.00 2710 2880

* From O to B5 the classification can be taken as from Victoria;8 from A0 to M5, as from Mount Wilson.5 trum dG2 for the sun, our value for spectrum A0 is raised from Th = 11,000° to r2 = 16,000°, which many would prefer. Also, 11,200° for A5 on the new scale agrees with the 18 value 11,000° adopted by F. H. Scares. But our measures of V — I will then give T2 = 85,000° for B0 stars and 140,000° for O stars, while if we use U — I for the index, the value —3.62 for O stars exceeds —3.56 for T2 = oo. In Table 7 the mean values of V — I for the spectral types are taken from the curves in Figure 2. As before, the temperatures under Ti are based on dG6 = 5500°, while under T2 they are on dG2 = 6700°. On either system a difference of a few hundredths of a magnitude in V — I makes a large difference in the hottest stars; or, putting it the other way, if we could fix the upper end of the scale, the lower temperatures would be well established. For instance, a variation of 1000° in Ti at 25,000° corresponds in V — I to less than 50° at Tx = 6000°. Now that the relative temperature scales are established, we consider again the pos- u Astronomy, p. 753, New York, 1927. 17 ^488, 461, 1938. 18 ( Mt, W. Contr., No. 685, p. 27; ^p. /., 98, 328, 1943.

© American Astronomical Society • Provided by the NASA Astrophysics Data System SIX-COLOR PHOTOMETRY OF STARS 337 sible systematic errors introduced by neglecting the shift of the effective wave lengths of the filters with the colors of the stars. First, as a sample, the mean wave lengths for the violet and infrared filters were computed for sources of 20,000° and 5000°, instead of for uniform energy throughout the spectrum. The change in 1/X for 20,000° is from 2.37 to 2.40 for the violet and from 0.97 to 1.00 for the infrared. Similar small changes hold for 5000°. The net differential effect turns out to be less than 0.01 mag. in V — I between 20,000° and 5000° in Th in Table 7. The effect of atmospheric extinction, treated in the same way, is to give only a slightly longer wave length for the violet filter—a change of 1/X from 2.37 to 2.36—while the change in the infrared is negligible. The net result is that the computed Ti is raised from 20,000° to 20,500° for an observed value of V — I for a star in the zenith. The two reflections from the aluminum mirrors of the telescope have even less effect on the effective wave lengths than does the atmospheric extinction; so we conclude that there is no need of modifying the temperature scales at present. When the zero point is fixed and we are able to present absolute temperatures, further refinements can be dis- cussed in detail. The representation of the observed colors by black-body curves is practically inde- pendent of the adopted zero point for temperature. For each value of Th in Table 7 or Figure 2 there is a corresponding value of which will give the same computed colors, usually within less than 0.01 mag. The use of six colors has shown that the stars radiate so nearly like black bodies that the conventional color index from two colors gives a very good measure of the relative color temperature of a star. The determination of the effective temperature, which requires a knowledge of both the diameter and the total radiant energy of a stair, is another matter. We are forced to leave our color temperatures without a definitive zero point. For the present we prefer the system Ti to that of r2 in Table 7, perhaps because Ti does not give such extremely high values as r2; but either choice will have to be changed. IV. SPECIAL GROUPS OP STARS The bluest stars.—The bluest O and early B stars may be compared with each other without the complication of the many absorption lines or bands of the later types. In Figure 3 are shown the deviations for some individual stars from black-body colors at Ti = 23,000°, the necessary data being in Tables 3 and 5. The two O stars are almost certainly more than 500 parsecs distant, and in galactic latitude —17° their colors could be affected by an absorbing layer near the plane of the galaxy. Likewise the differences in the three Orion stars may be caused by space reddening; all three of their spectra show the interstellar K line of calcium. As we go along the Belt eastward from b Orionis, we get nearer to the Orion nebula, where the Trapezium is strongly reddened, although the measured order of color is 5, f, e, not 5, €, f, according to their positions. In terms of V — I we have e — ô = +0.15; and for the Trapezium, 01 — ô = +1.22. With faint nebulosity over all the constellation we may assume that the differential absorption in the distance of 1?4 between ô and e could amount to one- eighth of that in the 5° between 5 and the Trapezium. It is a strange coincidence that b Orionis, the first star with an observed interstellar spectrum line, should turn out to be the blqest B0 star we have measured. Therefore, in the O’s and BO’s we are suspicious of space reddening in the bluest stars in the whole sky. At present there seems to be no possibility of telling whether the small differences at the top of the color scale axe caused by such reddening or by intrinsic differences in the stars themselves. The two stars ß Cephei and e Persei stand out as the bluest of spectrum B1 and B2, respectively, but both are in the zone of avoidance. Their distances, probably less than 200 parsecs, are small for much absorption. The curves for these two stars are practically

© American Astronomical Society • Provided by the NASA Astrophysics Data System 1945ApJ. . .102. .318S 20 viously measuredamongthe1332BstarsgiveEi =+0.01+0.006(p.e.),onascale with respecttoanyother. no greatsignificanceisgiventothesesmallfigures; butsincethescaleofV—Iisabout about halfthatofInternational.Withtheever-present possibilityofsystematicerrors, find: averagespectrumB7.9,V—I=—2.04,as againstB7.7,V—I=—1.99for Even inthiscloselyrelatedclusterofstarsthereseems tobeadispersionofeachproperty ing properties:magnitude,spectrum,color,andhydrogenabsorptionintheultraviolet. the PleiadesinV—Ibecomes+0.07,or£=+0.02. Similarly,thesixPleiadespre- twelvé Pleiades.Allowing0.02forthedifferencein averagespectrum,thecolorexcessof we donotseemtogetinthebrightstars.Forfifteen otherB5-B9starsinTable3we stars; buttheprogressionofthesequantitiesisnotuniformdownscalebrightness. The hydrogenabsorptionandthecolorindex,V—I,arebothgreaterforfainter referred to7\=13,000°.ThespectraarefromthelatestunpublishedresultsofAdams 338 JOELSTEBBINSANDA.E.WHITFORD Pleiades starsbypairsfromblack-bodycolorsatTV=13,000°.EachpairisidentifiedtheFlamsteed and Joy.Wehavefoundnoclear-cutcaseofcorrelationbetweenanytwothefollow- some ofthemhavebeenobservedonlyonce,theyaregroupedinpairsFigure3and son forthedifferenceisnotclear. the same;and,takentogether,theybothdifferfromothersinFigure3,butrea- numbers inTaurus. int 20 19 19 Stebbins,Buffer,andWhitford, Mt.W.Contr.,No.621,p.10;Ap.J91,29,1940. © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem MLW.Ann.Kept.,1943-1944, p.8. Scares hasfoundageneralcolorexcessE-ofat least +0.10forthePleiades,which Fig. 3.—{a)Deviationsofblueststarsfromblack-bodycolorsatTi=23,000°K.(b) The Pleiades.—WehavemeasuresofadozenbrightstarsthePleiades;butsince int 1945ApJ. . .102. .318S 1 body at5500°.Pendinganabsolutecalibrationofthescale,wecanuseanystarorgroup shown arenotfromanidealblackbody;theythedifferentialdeviationsasys- reasons forthedisagreementarenotclear. three timestheInternationalscale,wecouldscarcelymissacolorexcessof0.30mag.The 1 tem wherethemeanoftenstandardstarsaveragespectrumG6istakenasablack green by0.02mag.each;thesameimprovementwouldalsoholdformain-sequence of starsforthestandard.Ifweignoredultraviolet,couldmakerunfour type totype.Afterall,itisstillremarkablehowcloselywecanrepresentthestarswith colors, violettored,smootherbyraisingthebluepoints0.02mag.andlowering stars fromOtodGoinTable6andFigure2.Buttheinfraredwouldstillrunoff gion, inlatitude+0?4,theremustbeconsiderablespacereddeningaddedtotheintrinsic might beexpectedtodeviateincolorfromanormalBstar.Intheheavilyobscuredre- their complicatedspectrabysimpleblackbodies. color ofthestar;andbestwecandoistoestimatethisselectiveabsorptionfrom P Cyg—NormalB1 Mean Deviations from True colors,PCyg. Observed colors, 0?3 distantfromPCygni. near-by stars.Twosuchstars,HD193183and193443,are,respectively,0?2 Normal B1 lines; thesedeviationsarealsoshowninFigure4. Ordinarily, thebrightlinesinaspec- and thethirdlinemean.SubtractingmeanfromobservedcolorsofPCygniin of thetablegivesdeviationsPCygnifromanormalstarwithsameabsorption the meanofbOrionis,B0;ßCephei,Bl;andePersei,B2.ItseemsbestnottoreferP the nextline,wehave“true”colorsofPCygni.ThenormalB1infollowinglineis our filters,butinPCygnithecurveofdeviations showingextrastrengthintheul- trum seemtohavelittleeffectupontheover-alldistribution ofenergymeasuredthrough Any otherguessforthespacereddeningwillgivea similar curveforthecolorsofthisstar. Cygni tothevariableßCepheialone,onlyapparentlynormalBlstar.Thelastline traviolet andtheinfraredcanpresumablybetraced inparttoanomaliesthespectrum. lous backgroundwerefrom1to2percentofthe intensifiesofthevariouscolors.The measured togetherthroughadiaphragmof41"diameter; thecorrectionsfornebu- lines itisseenthatthedeviationsof0Orionisfrom the1/Alawaremorethandouble three starsoftheBeltinprocedurefollowedfor reddenedstars.Fromthelasttwo average spectrumofthegroupmaybetakenasB0. InTable9isthecomparisonwith comparison ismadewith the Beltstarsorwithanyotherstandards,result wouldbe with thenebulaweshould notexpectanomalouscolorintheTrapezium;but whetherthe corresponding deviations of reddenedBstars.(SeealsoFig.4.)Exceptforthe connection ' TheTrapeziumclusteroftheOrionnebula.—The fourcomponentsof0Orioniswere P Cyg normal colors... © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Another mattertoconsiderinbothsidesofFigure3isthatthedeviationsthere P Cygni.—Thiswell-knownstarwithitspeculiarspectrumandmanybrightlines In Table8thefirsttwolinesgiveamountofspaceabsorptionfo:thesestars, /193443 \193183 193237 hd SIX-COLOR PHOTOMETRYOFSTARS339 cB2 Spec. 09 Bleq + 1.14 + 1.19 + 1.24 -2.29 -1.10 -0.13 -2.16 U Colors ofPCygni TABLE 8 +0.71 + .74 + .76 +0.01 -1.15 -1.14 -0.40 +0.40 + .45 + +2 +0.03 - .53 - .50 - .08 +0.02 + .04 + .05 +0.04 + .02 - .06 - .02 + .52 + .60 + .06 -0.43 - .46 - .50 -0.08 + 1.35 + 1.23 +0.16 -1.07 -1.03 -1.11 -0.12 +2.17 +2.26 +2.35 -3.51 -3.52 -0.01 -1.26 U-I 1945ApJ. . .102. .318S 22 portunity inthewholeconstellationofOrionforwork ondifferentialcolorsofearly-type scale ofcoloristhroughthirteenbrightstarsthe NorthPolarSequence.InT^ble10 stars, bothintheapparentlyclearspacesand variousnebulosities. a largerclusterbecausetheopticalpropertiesof absorbinginterstellarmaterialare these starsarelistedintheorderofV—I.Thefifth columngivesCtbyF.H.Scares; modified togivegreatertransparencyintheTrapezium region.Thereisplentyofop- tal line). open circlesaredeviationsfromnormallawofspacereddening{brokenline)and1/X{horizon- we findadditionalevidencefortheirsuggestionthattheTrapeziumstarsstandoutfrom 340 JOELSTEBBINSANDA.E.WHITFÔRD deviations fromthegenerallawofreddeningarequalitativelysameastheirs.Also, absorption intheTrapeziumregionisdifferentfromthatofreddenedstarsgeneral.Our age lawofspacereddening. in the same.Thisisonlyclear-cutcasewehavefoundofhwidedifferencefromaver- 21 22 1 21 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Mt.W.Contr.,Nos.571,572; Ap.86,119,123,1937. ■ Mt.W.Contr.,No.701,p. 2; 101,16,1945. The NorthPolarSequence.—Theonlydirectconnection wehavewiththeInternational Fig. 4.—PCygni:opencirclesaredeviationsfromcolorsofanormalBlstar{brokenline).0Orionis: These resultsconfirmtheconclusionof-BaadeandMinkowskithatselective 1 1 1 0—Mean Mean, b,e,Ori.... 0 Ori Difference, 0Ori.... Difference, Bstars.. 1/X law U-I=1.00 +0.41 +0.41 +0.53 -2.17 -1.64 Colors oftheTrapeziumCluster 0.00 0.00 u +0.06 + .13 + .16 + .29 +0.38 -1.12 -0.74 r TABLE 9 +0.09 + .18 + .17 + .22 - .01 - .51 -0.29 B +0.08 +' .22 + .05 + .06 +0.02 - .17 - .04 +0.05 + .14 + .56 +0.27 - .36 - .29 - .22 R + 1.32 -0.59 +0.56' -0.59 -0.76 0.00 0.00 ■I +1.00 +1.00 + 1.29 -3.49 -2.20 U-I 1945ApJ. . .102. .318S 3 23 12 probably variableinbothlightandcolor.Wehave measuresoffourotherNPSstars; the sixth,CiofphotoelectricsystemforBstars,previouslyunpublished.Theother value inthetable.The52ÂstarsgiveCmt/Ci= 1.90 +0.10(p.e.).Thesestars,which space reddening. 0 andBstars;column(6)thecorrespondingratiocomputedfromderivedlawof of declination+80°isbyScares.Column(5)givesanobservedratiofrom69reddened to thedifferencebetweenl/X’sofCi.Thevalueincolumn(4)from52Astarsnorth The singlevalueincolumn(3)istheratioofdifferencebetween1/X’sVandI columns areself-explanatory. them now.Therespectivevaluesincolumn(2)werederivedfromthedataofTable10., Cint, andCi,arethebrightpolarBtars,which difficulttoobservebyphotography; sion inspacereddening;buttheygivethesameresult aseveryothertestwehavemade, and fromthetotalofseventeenwegetCint/Ci= 1.44+0.01(p.e.),whichisnearthe and, moreover,twooftheredstarswhichcarrymuch weight,NPSland2,are what weactuallyhave.Theonlystarsobservedin commoninthethreesystems,V—I, 221525. 212710. namely, thattheratioof alongbase-linecolorscaletotheCiisgreater forspace range fromB8toA4,areaffectedbÿhydrogenabsorption andhaveonlyasmalldisper- 183030. 187138. 107113. 107192. 166926. 166205. 114282. 51802. 66368. 23 8890. 5914. © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem In Table11theratiosofdifferentscalescolorarebroughttogetheraswehave Table 11,withhalftheentriesblank,indicatesmore whatweshouldliketogetthan MLW.Contr.,No.684,p. 12; Ap.98,272,1943. hd (V-I)/C (v-p/G. Cint/Cl tot (i) NFS 4 3r 4r 3 2r 3s 6 5 2s 2 Ir Is 1 4.44 6.55 5.26 8.26 2.12 6.33 6.28 5.86 6.48 5.62 5.38 7.57 7.01 SIX-COLOR PHOTOMETRYOFSTARS341 13 NFSStars gMl gMO gK2 gG9 Spec. dF4 dF2 dFO cF7 A3p A2 A3 A5 B9 Colors oftheNorthPolarSequence Obs. 2.7 3.9 (2) 1.5 + 1.57 + 1.02 +0.49 + +1.41 + + +1.53 + + + + -0.11 Cint Ratios ofColorScales .14 .23 .18 .06 .03 .15 .03 + + + + +0 +0 + + + + +1 -0 1A Law Comp. Cl 4.9 (3) TABLE 10 TABLE 11 08 07 04 08 99 08 30 03 01 98 67 13 15 +2.44 +1.40 +0.16 - .51 - .49 - .62 -0.90 - .48 - .36 - .49 - .72 52 AStars +1.09 +1.41 +0.46 +1.28 - .59 - .60 - .49 - .76 -0.92 - .14 - .36 - .65 - .85 Obs. (4) 1.9 +0 + + + -0 B 40 06 44 48 20 31 36 27 29 63 22 70 13 69 OandB Stars +0.07 + .03 - .02 - .04 - .01 - .04 - .04 -0.06 - .02 - .02 - .05 - .02 - .02 Obs. 6.5 (5) + .30 + .33 + .40 +0.49 + .08 + .15 + .22 + .33 + .46 - .46 - .20 -0.77 - .66 Reddening Comp. Law 6.4 (6) + . + , + . + ■ + , + • +0 + , + ■ -1 -0 -1 +3.17 +2.00 +0.77 +2.70 -1,15 -1.23 -1.28 -1.84 -0.30 -0.70 -0.95 -1.56 -1.73 V-I 1945ApJ. . .102. .318S -1 25 26 -1 24 matic aberration.(2)Thediameteroftheextrafocal imageoftheMadisonrefractorfor usually 2.34—1.58=0.76/¿;thisisslightlylessthanourdifferencebetweenvioletand and refertospectralregionsapparentlyfreefromabsorptionlines.Theirrangeof1/Xis gradients. Thegradientsweredeterminedphotographicallywithaspectrophotometer several considerations:(1)TheCiscaleoftherefractor atMadisonagreeswithin1per through aholetoosmalltoletthelight!That suchwasnotthecaseisshownby focal diaphragmsthatcutoutpartoftheshorter wavelengthscanbediscarded.It good ;therearenooutstandingdiscordances,either fornormalorreddenedstars. portunity offered.Obviously,anysuchlistastheforegoingcanscarcelyservestand- cent withthescaleofreflectorsatMountWilson, wherethereisnoquestionofchro- would, indeed/beextraordinaryiffortenyearswe hadkeptontryingtomeasurestars reddened starshasbeendiscussedbyAtkinson,Hunter, andMartin.Theirsuggestion reduced toourscaleandcompared,starbystar,with ourcolors,theagreementisvery simply tocommentononeortwoothersystems. some interrelations,thoughwhereonlytwosenesarecompared,itmaybedifficultto significance. Nevertheless,wehaveenoughstarsincommonwithotherliststoderive in andoutoftheMilkyWay,obscuredunobscuredregions.Weprobablywasted count ofundeterminedspacereddening,thecolorssuchstarsarenotparticular some timeinmeasuringthelate-typegiantstarslowgalacticlatitude,since,onac- ers; andafewvariablestarslike8Cephei,Polaris,ßtobeobservedasop- fitted intotheforegoingprograms;first-magnitudestarslikeVega,Betelgeuse,andoth- that theresultsofElveyatYerkesandourselves Madisonmayhavebeenvitiatedby the meanofgreenandred,whichgives2.37—1.57=O.SOai.Whengradientsare trace thecausesfordiscrepancies.Itißourpurposeherenottogivedetailedstudiesbut ard. Thestarsrangefromthezeromagnitudetoninth;theyarealloversky— scaleds about3timesthescaleforspacereddening. main sequence;F-Msupergiantsforfurthercalibration;ordinarygiantsasconvenient; as standardsfornebulae;0-B3starsspacereddening;B5-A9tofilloutthe ously, ourstarswere,inpart,selectedsomewhatthefollowingfashion:F-Mdwarfs details ofthespectrumstar.Thepresentsituationinstellarcolorimetryisthat dependent colorindicesofvariouswavelengths,nottomentiontheclassificationand ferent colorindices,whichmaybecomparedwitheachotheraswellstillin- systems ofotherobservers.Assomeonehasputit,thesixcolorsastargivefifteendif- we letthefiguresinTable11standuntilhavemoresix-colorobservationsofInter- from theinvestigationsofScares,butInternationalphotographicmagnitudesare the brighteststarsofNorthPolarSequence;otherspecialgroupsasthey there isnoextendedlistofstarsforintercomparisonsbyeverybody.Asmentionedprevi- reddened Bstars.InthemeantimeweshallnotgofarwrongifassumethatV—I national starsanduntilsomeonehasmanagedtogetInternationalcolorsofstrongly affected byhydrogenabsorptionintheultraviolet,whichmustbeconsidered.Hence, reddening thanfordifferencesofspectraltype.Thesameeffectin(V—I)/Cicolumns columns (3)and(6). 342 JOELSTEBBINSANDA.E.WHITFORD (2) and(5)followssimplyfromthecurveofdeviations1/Xlaw,asshownin # 25 24 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem M.N.,100,189,1940. 100, 196^1940. Mt.W.Contr.,No.685;Ap. 98,302,1943. The apparentdiscrepancyingradientsandourprevious colorsCibetweennormaland Greenwich gradients.—Wehaveaboutforty-fivestarsincommonwiththe The possibilitiesareendlessforthecomparisonofforegoingresultswithcolor We havenotattemptedtocomputetheoreticalratioswithCi;thesecouldbederived nt V. COMPARISONWITHOTHERCOLORSYSTEMS 1945ApJ. . .102. .318S 28 star ontheMountWilsonclassification,whichisbetweenourTi=11,000°andr follow closelythe1/Xlaw;changesofreddeningdeviatefromthatlaw. of ourvioletandbluetothesameinfrared.Unlessperformanceaphotocellisan be fewcasesofmarkeddisagreement. blunder onourpart,butsimplyaconfirmationofthelawspacereddeningand come byusinganegativelensforthewindowofbox,thusexpandingallimagesupto small violetimageactuallyhitthewireanodeofphotocell.Thedifficultywasover- back; andtherewasatremendousguidingerror,dependinguponwhetherornotthe aberrations evenifwehadwantedto,owingtqthescaleofthingsatfocus40- filter. computed for4000A,becauseoflongerwavelengths,upto4500transmittedbythe ance wasmadeatYerkes:5-mmimagewith8-mmdiaphragm.(3)Measureswereusually effect showninthediscussionofTable11presentpaper.Changesspectraltype if desired,nearthecircleofleastconfusionforwavelengthsconcerned.Wecoulddo eyepiece infrontofthefocus,diaphragmcouldbeplacednotatvisualfocusbut, focus ataconvenientplaceinfrontofthecell-boxvioletwassome10cmfarther of curiosity.(5)Thesimplestcheckistolookatabrightstarthroughvioletfilter. field. Suchtestsareamatterofroutineforanyobserverendowedwiththeslightesttrace pared themgraphicallywithhismeasures.Thereareeighteenstarsincommon,allof ultraviolet. WehavethereforereferredourcolorstothemeanoftenAO’sandthencom- illusion, weoughttogetverygoodagreementbetweenhiscolorsandours. isolate spectralregionsabout485Ainextentfrom4560to10,300A,orthemean Hall onsixty-sevenbrightstarswithaphotocellattheSproulandAmherstobserva- gence fromastraightlinethatwefoundinotherK giants.Withourtotaloffiveregions inch objective.Whenthephotometerwasfirstinstalled,wefoundthatwithvisual The haloaroundSiriusappears,totheeye,beconsiderablysmallerthan2mm alternate measuresweremadewiththediaphragmsforacheckonskycorrection. the sameatMadison,butwedidnothaveto. made withthesmallerdiaphragminmoonlightandlargeradarksky.Occasionally, dence ofsystematicdifferencebetweentheseries. Thereareadozenother.starswhich in theinfrared,wherebothserieshavelessweight. Theonlystarwithevenmoderate in Figure5.Noattemptwasmadetopickoutthebest cases.Theworstdivergencecomes 4000 Ais2.0mm;thediametersofdiaphragmsusedwere2.7and4.0mm.S'milarclear- 16,000°; butwhenthecolorsarecompareddifferentiallyfromstartostar,thereseem (4) Testswereoftenmadeforguidingerrorbymeasuringastarmdifferentpartsofthe against histhirteen,ourmeasuresnaturallylooka littlesmoother;butthereisevi- third magnitudeorbrighter;andsixofthesefrom theSprouldataareshownassamples tories. Bymeansofagratingoverthetelescopeobjectiveandslitsatfocus,hecould give aboutthesamegoodagreement;and,alltold, thecomparisonisquitesatisfactory. reddening isfPersei,andweagreeonthatone.The starePegasishowsthesamediver- 1 or2cmonthesurfaceofcell.AlsoinYerkesinstrument,withaseconddiagonal different two-colorsystemsofotherobservers,whether photoelectricorphotographic. 2 the sameeffect. 29 27 24 28 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Spectrophotometry byJohnS.Hall.—Theworkmostnearlylikeoursisthat Other colorindices.—AfterthecomparisonwithHall thereislittlepointingoingover No; whattheGreenwichobserversunearthedwas,notalong-continuedridiculous There issuchathingasoverprovingcase;butatYerkeswecouldnotignorethe The revisedzeropointoftheGreenwichgradientsgivesabout12,700°foranA0 Halks measuresarereferredtothemeanofA0stars,sincehewasnotbotheredby InprivatecorrespondenceDr. Y.Öhman,oftheStockholmObservatory,statesthathe hasfound 27 J,Stebbins,Ap.74,289,1931. ™Ap. /.,94,71,1941. SIX-COLOR PHOTOMETRYOFSTARS343 1945ApJ. . .102. .318S (open circles). © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem Fig. S.—Comparisonoffivecolors,violettoinfrared(solid circles), withobservationsofJohnS.Hal 1945ApJ. . .102. .318S 30 the reductions,anunseenpassingcloudinsky,orasystematicvariationofex- avoidance. Wearenotatallsurethatwehavethepurecolorsofasingleearly-typestar. errors. may oftenbebettertobunchseveralstarsofthesamecolorminimizeaccidental found. WenotethatevenAltair,atameasureddistanceof5parsecs,istooredforspec- should benearlyasmuchfordistantstars.PerhapsacriticalcaseisSpica(magnitude, able amountofreddening.Evenatthegalacticpoles,whereE.P.Hubble’sfigureis Orion atlatitude—17°caneasilytraverseenoughinterstellarmaterialtogiveadetect- tinction mayremainundetectedtotheend.Webelievethatsuchcasesarerare,butit sion andimprovement.WhenMr.Joykindlyhelpedtofilloutthelistbygettingnew neous. Evenwhentheycomefromthesamesource,aresubjecttocontinuedrevi- 0.25 mag.forthephotographicabsorption,selectiveabsorptiononourU—Iscale If thesunisimmersedinanabsorbinglayer,opticalpathof,say,500parsecsto curately classifiedfromtheircolors,butthereisnoprospectofthisdevelopment.Al- spectra forus,wefoundinsomecasesthatcouldhaveestimatedthespeptraltype trum A1;butinthiscase,atleast,wecanfeelsurethatthecolorsareuncontaminated. always possiblethatanerrorinreadingthegalvanometer,undiscoveredmistake our pointofviewitwouldbeapleasantsurpriseifthespectrastarscouldac- Although themeasuresareself-checkingbymannerinwhichtheyweretaken,itis îme purposeoranother,wégive,attheriskofrepetition,afewcommentswords though thespectramaybesimplefunctionsofmasses,densities,andtemperatures and eventheapproximateabsolutemagnitudenearlywellenoughfromourcolors.From the stars,individualdifferencesinspectraarenotimaginary;itmaybe,however, 1.21; spectrum,B2;latitude,+50°),whichmayturnouttobeasblueastarcan Caution. near-by stars.Fordistantstarsthecolorsarevitiatedbyspacereddening. may aidconsiderablyindeterminingbothspectraltypesandabsolutemagnitudesof that theinformationderivedfromcolors,addedtolineratios,etc., A goodtemperatureforanyoneofourstarswill fix alltherestofthem.Whenweget cannot dodgethefactthatzeropointoftemperature scaleisnotwelldetermined. sible, fordifferenttemperatures.Thereisnouseof dQing ahalfwayjobinthisdetermina- around todeterminingthezeropointbycomparison withaterrestrialsourcelikestand- tions asallothercolortemperaturesofstars.Differentially theymaybeallright,butwe ard lamp,weshouldplantousenotfewerthanthree suchlamps—allcalibrated,ifpos- tion. Inthemeantimefieldisopentoanyone else, asithasbeenforhalfacentury, retical considerations. though thereissomethingtobesaidforfixingthe topofthetemperaturescalebytheo- stars, butlittlewouldcome outofthateffort.Neithershouldweexpectmuch fromaddi- In undertakingfurtherwork wecouldcompletethemeasuresofinsufficiently observed it least,wearecontenttoletthesixcolorsstandforthemselves. ¡nough. Suchcomparisonsareusuallymadeforadefinitepurpose;andthepresent, Cach timewfegetanewsetofcolorswecannotundertaketocomparethemwithevery- hing thathasgonebefore;eventhecheckingwithourownpreviousworkistroublesome © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem In thehopethatresultsofpresentinvestigationmaybevaluetoothersfor First, toomuchweightshouldnotbegiventóanystarwithonlyoneobservation. Next, bewareofthecolorshigh-luminositystarsinlowlatitudeorzone The spectraandabsolutemagnitudesquotedthroughoutthispaperarenothomoge- The relativecolortemperatureswehavegivenare tobetakenwiththesamereserva- The photometryinsixcolorshasnaturallyraised moreproblemsthanithassolved. 30 Mt.W.Contr.,No.485,p. 44; Ap.70,51,1934. SIX-COLOR PHOTOMETRYOFSTARS345 VI. CONCLUDINGREMARKS 1945ApJ. . .102. .318S of theCaliforniaInstituteTechnologyandfromAlumniResearchFundtl University ofWisconsin. puted colorsofthecompaniondonotfitanormalstar.Presumablywewerepushingt] original problemofthecolorsextragalacticnebulae. observations alittletoofar,anditislegitimatetosuppresstheresultsforpreser disks intheeclipsingsystemshouldgivecolorsandspectraltypeofcompanio bination ofthecolorsatmaximumandminimumwithdimensionsappare almost exactlyatminimum,whennaturallythestarwasredderthannormal.Thecoi We havecarriedthroughthecalculations,butwedonotbelieveresults;coi on eachoffourgoodnightsshouldbesufficient.Quitebyaccident,weoncecaughtAlg ation ofthisstar,itseemsbesttodothemoveragaininanotheryear—anhourort\ lem. Thepossibilitiesinvariablestarsareendless.Besidesthelight-curvesfor8Cephe already published,wehavethesixlight-curvesforPolaris;butbecauseofsmallva effect indwarfs,giants,andsupergiantsaroundspectrumKOpresentsanattractivepro tional starsoftypesalreadywellrepresentedinthesequence.Theabsolute-magnitu 346 JOELSTEBBINSANDA.E.WHITFORD 31 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem J.Stebbins,Mt.W.Contr.,No.704;Ap.101,47,1945. This investigationhasbeensupportedinpartbygrantsfromtheObservatoryCoun< Thus thereareopportunitiesformany-diversions,butweexpectsoontoreturnt]