1954ApJ...120..316P 1 6 confirmed” (passagewritteninT948). spectrograms ofB. position anglenear180°,whichisperpendicular to theslitlength.Notraceofsucha strong lineinthespectraofstarsAandCasCVz i 4226couldbedetectedinanyofthe way. StarCismorethan4mag.fainterstar B intheblue,andnearly1"awaya and hasnumeroussharplinesinitsspectrum,distanceof82"placesitsafelyoutthe Hy) and15withthe100-inch(dispersion67A/mmatHy).Anumberof60-inch were obtainedatMountWilson,22withthe60-inchreflector(dispersion78A/mm have publishedobservationsofSiriusB,givingaredshift20km/sec.Althoughthe sibility thatlightfromeither40EriA(4.5mag.,Kl)orC(11.0M6)con- row cores(Kuiper1935;Babcock1948)standoutinenhancedcontrast.Thereisnopos- effort tofillinthewingsofverybroadhydrogenlines.Inthiswayrelativelynar- observations weremadebyDr.E.C.Yowell,whoseassistanceisgratefullyacknowl- binary systemBC. from observationsofA,whichhasapropermotionandparallaxincommonwiththe brightest knownwhitedwarf(9.5mag.).Thereisnodangerofcontaminationits for thewhitedwarf40EriB. reliable determination.Recently,however,lackofconfidencehasbeenexpressed(e.g., fractions ofthevaluesthemselves. spectrum fromthelightof40EriAorC,andradialvelocitysystemisknown of poorquality,Münch(1944)hasobtainedavelocitygivingredshift22+9km/sec agreement betweentheresultsoftwoexperiencedobserversseemstoindicatea well-known observationaldifficultiescausedbythelightofSiriusAareconsiderable, white-dwarf starsofknownmassismeageranduncertain.Adams(1925;Strömberg between observedandpredictedvaluesislessthanthesumoftheiruncertainties,whichareconsiderable km/sec predictedonthebasisofgeneralrelativityfrommassandradiusstar.Thedifference edged. Exposuretimesof1J-4hoursonbakedKodakIIa-0plateswereemployedinan Palomar Observatories. taminates thespectrumofwhitedwarf.AlthoughstarAis4mag.brighterinblue for awhitedwarf.Muchthemostfavorablecaseis40EriB.AfterSiriusB,it of theoreticaldifficulties(e.g.,Mestel1952).Onthebasistwospectrogramswithlines Einstein I960;GamowandCritchfield1949)inthevalidityofthisresult,partlybecause AX/X, of7X10~,correspondingtoavelocity21km/sec.Thisisbecomparedthevalue17 1926) onthebasisoffourspectrogramsandMoore(1928)3 1 © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem “TheshiftingofspectralUnestowardthered[predictedby generalrelativitytheory]...isnotyet Between December,1949,andJanuary,1953,37prismaticspectrogramsof40EriB It appearsdesirabletoobtainamorenearlydefinitivedeterminationoftheredshift The availableobservationalmaterialconcerningdisplacementsoflinesinspectra Measurement of42hydrogenlineson27spectrograms40EriBleadstoanobservedredshift, * Thisinvestigationwascarriedoutunderaco-operative arrangement withtheMountWilsonand RED SHIFTINTHESPECTRUMOF40ERIDANIB* Department ofAstronomy,UniversityCalifornia,LosAngeles Daniel M.Popper Received March12,1954 INTRODUCTION OBSERVATIONS ABSTRACT 316 1954ApJ...120..316P generally weakerexposuresatshorterwavelengths. grams. lines. measured line.Onlythehydrogenlines,Hô,Hy,andEß,couldbein spectrum of40EriB.Atthetimemeasurementeachlinewasassignedaweightac- best beevaluatedbyadoptingtheknownvelocity ofAandinvestigatingpossiblesys- ofthesystemBC,differentialvelocitieswith respectto40EriA,whichshowsa for byaccidentalerrorsofmeasurement.Thesmallnumbergoodlinesinthecase lines. Theadoptedresultsareobtainedfromsixteen60-inchandeleven100-inchspectro- The secondgroupofvalues,beingweightedmeansonlythebetterlines,isconsidered for eachofthetwosetsplates(60-inchand100-inch)aregiven40EriBinTable1. , HD36591(5.3mag.,B2)andrjLeo(3.6AO).Theselatterstarswerechosen taken of40EriA,and,startinginJanuary,1951,oneorboththestandardvelocity found whenthewavelengthsrecommendedby MountWilsonspectroscopydivision ferences ofvelocityamongthefifteenlinesmeasured inthespectrumof40EriAwere with thoseofHyandHß.Part,thoughapparently notall,ofthiseffectresultsfromthe results indicatethatthescatterofmeasureddisplacementscanbeadequatelyaccounted cording tothereliabilityofitsappearance.Meandisplacementsfordifferentlinesand Each spectrogramwasmeasuredtwice,andthemeandisplacementobtainedforeach to testforpossiblesystematicerrorsinvelocitiesobtainedfrommeasuresofhydrogen strong hydrogenlinesand well-determinedvelocitiesintheLicksystem, were usedfor were used.HenceIfeelthatanapparentdifference invelocitybetweenstarsAandBcan of 40EriA,however,arebadlyblendedonplates ofthedispersionused,sothatdirect common parallaxandpropermotion,shouldsuffice. Thehydrogenlinesinthespectrum the morereliableandisadopted.Theotherincludedtoshoweffectsofchoice differences ofvelocitycouldnotbeevaluated.Furthermore, appreciablesystematicdif- For thesharperlinesofstandardstars,meandifferenceis0.0011mm.These the purpose.Thecorrections tomeasuredvelocitiesindicatedbythemeasures ofthese tematic effectsinthemeasures ofB.SpectrogramsHD36591andtjLeo, whichhave the weightedmeandifferencebetweentwomeasuresofsameline,whichis0.0017mm. average, toadisplacementof0.0022mmontheplate.Thisvaluemaybecomparedwith 100-inch 60-inch © American Astronomical Society •Provided bytheNASA Astrophysics DataSystem The spectrogramsofallfourstarsweremeasuredwithamagnification14times. The probableerrorofthevelocityfromasinglelineunitweightcorresponds,on In additiontothespectrogramsof40EriB,oneachnightobservationaplatewas Since weareinterestedintheapparentvelocityof 40EriBrelativetothecenterof is aresultofthesmallnumberplatesonwhichthislineshowscorecomparable Tele- scope Measured DisplacementsofLinesinSpectrum40EriB Line m Hß By Hy HÔ Hß No. of Plates 22 21 13 16 11 8 Weights Sum of 10.6 3.1 4.6 8.4 5.6 7.4 All Lines 40 ERIDANIB (Km/Sec) TABLE 1 Displ. Mean -17 -12 -18 -26 -13 -22 (Km/Sec) P.e. of Mean Plates No. of 13 10 3 6 3 7 Weights Sum of 3.8 3.0 5.2 Better Lines 6.0 1.2 1.0 (Km/Sec) Displ. Mean •22 -25 •15 • 7 31 26 (Km/Sec) P.e. of Mean 317 318 DANIEL M. POPPER spectrograms are shown in Table 2. Only results from lines of reliable appearance are included. The systematic corrections are disappointingly large. In Table 3 we give the final results of the measurements, both corrected and uncorrected. The weights listed are those of the adopted displacements of Table 1 adjusted, for each telescope, for differences in linear displacement on the plate corresponding to 1 km/sec of velocity. Giving low weight to the uncorrected values, I finally adopt for the apparent velocity of 40 Eri B, —21 km/sec. A computation of the probable error of this result, when each of the 42 measured lines is treated as an independent determination, yields ±1.9 km/sec. Because of the differences between the results from the different hydrogen lines and

TABLE 2 Corrections

Correction To No. of Reduce to Lick P.e. Telescope Line Plates System (Km/Sec) (Km/Sec) Hb 11 -1.3 1.4 60-inch H 7 19 ±5.3 1.2 Hß 7 ±1.8 4.8 Hô 14 ±6.1 1.4 100-inch Hy 17 ±5.4 1.2 Hß 13 ±0.4 2.8

TABLE 3 Results of Measurements before and after Correction

Uncorrected Corrected Telescope Line Weight Displacement Displacement (Km/Sec) (Km/Sec)

Hb 1.2 7 - 8 60-inch. Hy 5.2 —- 26^1 — 26 (weighted 2D —21 (weighted Hß 2.2 — 31J mean) ■29J mean)

Hb 1.5 15 100-inch. Hy 6.0 -— 25^) — 22 (weighted ■20 > — 19 (weighted Hß 2.7 — 22J mean) ■22J mean)

because of the unexpectedly large systematic corrections, ±4 km/sec is considered as a more realistic estimate. After these reductions had been completed, Dr. J. L. Greenstein made available to me three plates of this exposed at Mount Palomar with a dispersion of 38 A/mm and one with a dispersion of 18 A/mm. Only Hy could be measured. The mean apparent velocity from these plates is —23 km/sec, while the rough value by Münch, quoted above, is — 20 km/sec. The inclusion of these values would not alter the adopted velocity. The of 40 Eri A in the Lick system is —42 km/sec, so that the apparent difference in velocity, B minus A, for a mean