198Lapj. . .247. .1583 the Astrophysical Journal 247:158-172

198lApJ. . .247. .1583 © 1981.TheAmericanAstronomicalSociety.Allrightsreserved.PrintedinU.S.A. The AstrophysicalJournal247:158-172,1981July1 spheres istheOBsupergiantdomain.Inlastfewyears occurrence ofhydrodynamicactivityinstellaratmo- a vastliteraturehasmushroomedwhichexploresthe profiles ofmultiple-ionizedatomsintheultraviolet the presenceofaninfraredradiationexcessandline stellar windsandmasslossinthesestars,asinferredfrom Almost allstarsinthisdomainshowatleastintermittent spectra (e.g.,Cassinelli,Castor,andLamers1978). episodes ofHaemission,andfrequentlyareradialvelo- city variables(seeRosendahl1973a,b).Oneofthebest et al1979)forwhichnoHaemissionhasbeenreported studied earlyBsupergiantsispLeonis(Bllab;Parsons Astronomy, Inc.,undercontractAST 78-17292withtheNational until thispaper.Spectroscopicallystarisnotknown to exhibitradialvelocityvariations, rotationabove Science Foundation. 100 kms"Sorpeculiarchemical abundances.Underhill 1 The mostprominentregionintheH-Rdiagramfor OperatedbytheAssociationof UniversitiesforResearchin © American Astronomical Society • Provided by theNASA Astrophysics Data System -1 _ 1 ,U4552-74 absorptionlinesandintheHaprofileasincipientemission.Noradialvelocitychanges last threeyears.Variationsofafewpercentarepresentontimescales3hrorlessintheSim larger than1kmshavebeenobserved,butlarge,correlatedchangesfrequentlyoccurinthe The Haemissionappearsasafillinginofthelinecore,usuallywithin±200kmscenter,and the propertiesofstellarphotosphereandsubphotosphere,particularlyitstemperaturestructure. strengths andshapesofthesiliconlines.Thenaturethesevariationssuggestslargeglobalchangesin of days.ThestrengththisemissioniswellcorrelatedwiththemajorchangesinSimlines, seems toimplytheexpulsionandreturnofmattersurface,probablyinseveralhoursacouple early-type supergiants.Moreover,thecouplingofeventsinsubphotosphereandouteratmosphere suggesting anintimatelinkbetweensubphotosphericprocessesandtheouteratmosphereinthisstar. multimode nonradialpulsationsareresponsibleforthesespectralvariationsinpLeoandother provides supportfortheideathattheseoscillationsarerelatedtoheatingofcoronaearound luminous early-typestars. feature maywellberelatedtovelocitiesassociatedwithaHenconvectionzonejustbelowthe photosphere. Subject headings:stars:atmospheres—individualpulsation Seventy highqualityReticonspectrahavebeenobtainedofthestarRhoLeonis(Bllab)over There isnoevidenceforperiodicityinthedatathusfar,butthereareseveralindirectindicationsthat A constantdepressionisalsonotedintheredwingofSiill2/14552and4567linespLeo.This I. INTRODUCTION Department ofAstronomyandMcDonaldObservatory,UniversityTexasatAustin, Department ofAstronomyandMcDonaldObservatory,UniversityTexasatAustin, SPECTRAL VARIATIONSINRHOLEONIS(Bllab)FROM stars: supergiants—winds SUBPHOTOSPHERE TOOUTERATMOSPHERE and DepartmentofAstronomy,UniversityWisconsinatMadison Received 1980October10;accepted1981January7 1 and SacramentoPeakObservatory Myron A.Smith Dennis Ebbets ABSTRACT AND 158 nonradial pulsationdomainamongBstars,and,in and otherphotometricsystems.OurinterestinpLeo also astandardfortheHß(CrawfordandMander1966) example ofwhatthislineshouldlooklikeinanonerup- particular, todeterminewhetherperiodiclinewidthand stemmed fromadesiretoexploretheperipheriesof tive Bsupergiant.Beingbrightandwellplaced,pLeois asymmetry variationsofthetypeobservedin“53 (1961, 1966)usedtheHaprofileofthisstarasatextbook Persei variables”(Smith1978,1979a)occurinhigh proceeded, itsoonbecameapparentthatprofilemodula- luminosity starsaswell.Asourhighdispersionprogram tions ofthisprecisenaturewerenotevident.However,in the courseofstudyweobservederratic,andocca- paper wereportonthedetailed natureoftheSimline shapes ofthephotosphericSim224552-74triplet.This sionally enormous,rapidvariationsinthestrengthsand activity encouragedustomonitor Haaswell.Inthis variations andannouncethe presenceofweakinter- is thebestcasefor“quiescence ”inanearly-typesuper- mittent Haemissionatvariable velocities.BecausepLeo 198lApJ. . .247. .1583 1- _ - J -1 giant, itmaynowbeassumedthatmany,perhapsall,B degree. supergiant atmospheresshowHaemissiontoatleastthis infrared reemission(BarlowandCohen1977)ultra- typical outeratmosphericpropertiesforaBsupergiant. efficiency of40%accordingtoradiativedrivingtheory violet linestudies(Underhill1979;Morton1979)is Its mass-lossrateof7.9±0.7x10“Myr,from possible small,heated-by-shockinstabilities)ofpLeois velocity of1700±150kms/,andanormalmass-loss typical forBsupergiants.Italsohasawind hydrodynamics ofthestellarphotosphereandits relationship totheseouterlayers.Insodoing,wewill so normal,itwillbeespeciallyinterestingtoexaminethe substantial andrapidvariabilityinthephotospheric show thatthereisstrongobservationalevidenceof (Nerney 1980).Becausetheouteratmosphere(including properties, whichinturnarecausedbynonradialpulsa- are producedbyglobalmodulationsinatmospheric spectrum. Thereisreasontobelievethatthesechanges and supplementedthedataacquisition.Thissystemhasa operational atthecoudéfocusof82inchtelescope were alsomadeinbothsystemsattwicethereciprocal tions. Wewilldemonstratethatthereisalargereservoir of subphotosphericenergy(seealsoCannonandThomas similar speed,dispersion,bandpass,andresolutionatthe changes ina“coronal”wind,althoughseveralreports direct observationslinkingthisactivitytopropertiesor layers whereHaemissionisformed.Wedonothave ones. WiththeseparameterstheHaobservationswere dispersion (4Âmm)andresolution(0.1Â)oftheblue only 0.03Âbetweenpixels.ObservationsoftheHaline Tull, andKelton1978)onthe107inchtelescopeat program tosearchthespectra ofearly-typeBstarsfor obtained in15to20minutes.Tables1and2areobserving 4567, and4574tripletwithabandpassof50Â,sampling obtained mainlywiththecoudéReticondetector(Vogt, have beenmadeofvariationsultravioletlinesatlow line-profile variationsindicative oflow-order,single- logs foralltheseobservations. gram tofindsuchvariations, wedidnotundertaketo mode, nonradialoscillations. Failingearlyinthepro- blue-region observationtook50minutesandgavea interval of0.05A,andaresolution0.1Â.Atypical tions inthebluewerecenteredaroundSim>M4552, McDonald Observatory.Forty-six2.0Âmmobserva- p Leo. velocities, whicharereminiscentofwhatweobservein 0 observe thestarmanytimesover anightasonewouldfor 107 inchReticonsystembutoffersasamplingintervalof signal-to-noise (S/N)ratioof200to400. 1977) whichinfluencesmotionandtheenergybalanceof Except foritslackofstrongHaemission,pLeoexhibits In 1979January,aRL-1728HReticonsystembecame The highdispersionobservationsforthisstudywere Our programbeganasapartoflargerpatrol © American Astronomical Society • Provided by theNASA Astrophysics Data System a) DataAcquisition II. OBSERVATIONS SPECTRAL VARIATIONSINpLEO -1_ data. Theequivalentwidthsandfractionalwingdepths filling inofthelinecore.Theradialvelocity24552,42 which, exceptforonenight,ismanifestedatmostby worthy aspectofHawasthepresenceemission, are alsotabulated.ThespectralchangesofSimXXA561 km sonoursystem,isconstantwithin±1, equivalent widthsandlineshape,aswellaredwing unnecessary todetailtheiractivitytoo.Themostremark- and 4574aresosimilartothoseof24552thatitis red observationsoneverypossiblenighttoestablishthe a suspectedpulsator,butwemadeoneortwoblueand depressed by~2%relativetothebluewing.Thenote- able attributesoftheSimlinesarechangesin general characterofotherspectralvariationsthatdid near constancyofthefullwidthathalf-maximum contributors totheobservedphenomena.Likewise, ruling outbinarymembershipandradialpulsationas variations observedinpLeoarecertainlynotinstrumen- show up.Itisworthaddingthatthelargespectral tal, asthesamelinesobservedinothermain-sequenceB particularly concerningvariablevelocityfields. stars onthesamenightsshowednolinestrengthchanges. measured byplanimetry.Theprincipalerrorsinmeasure- versus thenightofobservation.Thesevalueswere (FWHM) of24552willexcludecertaininterpretations, particularly importantinthose24552observationsshow- ment areestimatedas±10mÂ,fromprobableuncer- exceeding ourerrorestimatesintheequivalentwidthdo tainties incontinuumplacement.Theseerrorsare ing strongwings.Thegeneraltrendoftheseresultsisthat extremely smallequivalentwidth,264mÂ,wasrecorded remains relativelyconstant,althoughsmallexceptions on perhapstwo-thirdsofthenightslinestrength occur. Occasionally,theequivalentwidthwillincreaseto a fewhours. slightly greatervalues,intherangeof460to480mÂ. on 1979February16,only2^hrafteranormalvalue. Many ofthesestrengthenhancementscomeaboutwithin different timesindicateperhapsa3hrtimescaleforfull mical recordfortheshort-termchangeofanyphoto- Parenthetically, wenotethatthisispossiblyanastrono- development oftheseevents.Onafewoccasionsin1978 spheric stellarabsorptionline.Severalsimilarepisodesat rates observedin1979,andagain suggestsafullampli- width withtime,e.g.,on1978 May14,issimilartothe lent widthobservedthenwerecorrespondinglysmaller time scale(20to30minutes),butthechangesinequiva- searches weremadeforspectralchangesonaultrashort than in1979.Infact,therateofchangeequivalent yet identified“recovery”phases oflinestrengthening. line weakeningepisodeshave beenobserved,wehavenot tude timescaleofabout3hr.Also, althoughseveralrapid Table 1providesanobservinglogoftheSim/14552 Figure 1showsaplotoftheequivalentwidthsof24552 Even moredramaticareepisodesoflineweakening.An b) DescriptionoftheSpectralVariations ii) EquivalentWidthChangesinÀ4552 i) General 159 198lApJ. . .247. .1583 Obsn. No. 1205 1191 1237 1231 1253 1209 1193 1184 900 924 849 925 901 875 826 800 798 772 722 731 728 723 721 © American Astronomical Society • Provided by theNASA Astrophysics Data System (1977/8/9) Observation reference profile,àW=W—W2o \ Emission(Â)=areaabovethe1.0levelindivideddata. Notes.— profile. (1) referenceprofile;(2)blueand/or redwingdepressedbelowreferenceprofile;(3)essentiallyidenticalto reference 1 1 12 Jan 11 Jan 14 May 19 Apr 11 Jan 10 Jan 09 Jan 13 May 20 Jan 12 Jan 09 Jan 14 May 13 May 21 Apr 20 Apr 19 Apr 18 Apr 01 Jan 01 Jan 12 May 31 Dec 31 Dec 31 Dec Date Notes toTable2.—FWHMÂ=full widthinangstromsathalfthetotaldepth;AfT(Â)=E.W.difference from 1447 1236 1232 1272 1207 1388 1372 1315 1312 1276 1456 1340 1289 1598 1576 1555 1400 451 626 625 684 652 370 700 U.T. Midpt. of Obsn. 11:58 13:08 10:47 13:06 11:22 11:26 12:35 11:16 13:21 11:50 10:18 11:57 13:14 4:14 3:34 5:35 5:00 5:37 2:07 2:35 5:03 5:20 2:54 (1979/80) Jan 12 Jan 21 Jan 21 Jan 12 Jan 11 May 17 May 16 Mar 19 Mar 19 Jan 22 May 19 Jan 7 Jan 5 Mar 17 Feb 16 May 11 Feb 15 Feb 14 Feb 13 Feb 13 May 26 May 25 May 24 May 11 Date E.W. 405 400 374 424 438 425 418 309 389 403 462 414 415 402 450 422 428 343 410 421 375 385 384 (mX) U.T. Midpt. of Obsn. 12:25 11:40 12:10 10:45 10:05 12:57 11:36 10:20 11:55 9:00 6:20 8:50 6:50 4:31 4:45 8:40 9:10 2:50 2:15 5:45 7:30 3:22 3:09 3:10 Observing LogforSchi24552 Mean Fract. Wing Depth Observing LogforHa .120 .078 .138 .055 .038 .149 .133 .123 .098 .105 .168 .113 .052 .060 .103 .103 .124 . 134 .136 .135 .100 .128 .157 TABLE 2 TABLE 1 W(Â) 1.20 1.42 1.24 1.46 1.43 1.52 1.43 1.39 1.30 1.48 1.18 1.49 1.36 1.06 1.27 0.83 1.08 0.92 1.08 1.34 1.47 .88 .97 .76 Obsn. No. 1399 1595 1553 1528 1520 1469 1451 1446 1404 1385 1378 1344 1511 1489 1423 1418 1389 1369 1337 1316 1292 1311 1275 HVUM ÂAW(Â)Emission(Â)Notes 4.96 4.48 4.57 4.38 4.67 4.52 5.45 5.25 4.77 4.77 5.45 4.91 4.62 5.01 5.16 4.96 4.67 5.35 5.25 4.30 4.23 4.38 5.37 5.36 (1977/8/9) 16 May 18 Apr 17 Apr 18 Mar 17 Mar 15 Feb 14 Feb 18 May 20 Apr 20 Apr 19 Apr 19 Mar 17 Mar 16 Feb 15 Feb 14 Feb 13 Feb 19 Mar 18 Mar 16 Feb 13 Feb 22 Jan 21 Jan Date .26 .02 .04 .28 .07 .06 .03 .22 .03 .16 .49 .58 .70 .10 .19 .03 .64 .55 .38 .40 .39 .13 U.T. Midpt. of Obsn. = 0 .16 .27 .23 .07 .04 .09 .15 5 0 .17 12:21 .37 .31 .16 .47 11:42 11:32 12:39 10:16 .30 .23 12:04 .35 .36 .37 .42 .17 .10 = 0 1:30 9:09 6:14 5:23 8:03 8:25 2:47 5:47 5:45 9:13 8:56 3:48 3:56 7:44 7:30 3:20 2:46 425 E.W. 372 435 298 441 482 445 421 408 417 333 370 381 428 427 428 435 480 423 348: 438 374 264 (mX) Mean Fract. Wing Depth .095 .114 .119 .088 .060 .088 .040 .140 .154 .131 .128 .124 ,137 .117 .129 .088 .030 .079 .085 .111 .006 .139 198lApJ. . .247. .1583 _ 1 changes arenotaccompaniedbyradialvelocityvaria- concomitant changesintheFWHMoflineareless strength changesduringafewhours.Werepeatthatthese tions abovethe±1kmsmeasurementerror.Any than 50mÁ,rulingoutincipientemissionasacauseof the Siinlinestrengthvariability. be calledthe“exponentialprofile.” Itwasquicklynoticed core andextendedwings,inthe followingthisshapewill valent widthatquiescentepochs exhibitsaratherpointed onset ofaroundedcorecorresponds tothedisappearance that atcertaintimestheprofile becomesU-shaped;the Fig. 1.—EquivalentwidthsofSimA4552inpLeoasafunctionobservingdata.Observationsmadeongivennightareconnectedbyline. Figure 2showsseveralexamplesofsubstantialline The 24552profilecorrespondingtothereferenceequi- © American Astronomical Society • Provided by theNASA Astrophysics Data System iii) A4552ShapeChanges SPECTRAL VARIATIONSINpLEO we measuredthedepthofblueandredwingsat ular criterionwaschosenasatrade-offbetweensensiti- of theextendedredwings.Toquantifywingstrength, continuum. Themeanoftheredandbluewingdepths depth. Thisparameterisreferredtoasthefractionalwing was measured,andtheresultnormalizedtocore vity totheasymmetryandplacementof depth inTable1. pointedness). Thiscorrelation illustratestheimpression valent widthandthisstrengthparameter(orthecore ± 1.38Âfromlinecenter(midpointbisector).Thispartic- evident duringthe“strongline ”episodesaswell. radial lineweakeningalsotend toproduceU-shaped one getsfromFigure2,thatthe “episodes”whichcause profiles. AsFigure3implies, thesesametrendsare Figure 3showsthatacorrelationexistsbetweenequi- 161 198lApJ. . .247. .1583 162 Leo, separatedbyafewhours.Notetheshapechangesaccompanying the strengthchanges.SolidlinesareFourier-smoothedresults. Fig. 4.—RepresentativeHainpLeo distributedoverseveralmonthsof1979and1980 same relation. Fig. 2.—PairsofweakandstrongA4552Reticonobservationsinp Fig. 3.—TheequivalentwidthofA4552 vs.themeanfractionalwingdepth(±1.38Âfromlinecenter).Both 1978and1979dataexhibitthe © American Astronomical Society • Provided by theNASA Astrophysics Data System Fractional WingDepth Fig. 3. SMITH ANDEBBETS 1 _ 1 1 _ changes oftenbeingevidentontimescalesasshorta Both theshapeandstrengtharevariable,with line whichoftenshowsanirregularasymmetricprofile. few hours.Wewillarguethatmost,ifnotall,ofthis distorting ofthephotosphericprofile. activity iscausedbyincipientemissionfillinginand Table 2listssomerelevantmeasurements.Theonly profile whichwasfoundtooccurmorethanonceisthat 19 nightsin1979and1980.Thisfeatureisanabsorption represented byobservation1207.Duringthe17mpnths width, andwasalwaysrecordedonnightswhentheSim four nights.Itissymmetrical,hasamaximumequivalent of monitoringHathistypeprofilewasobservedon lines appearedtobeundisturbed.Thevariabilityofthe reference. other observationsisdiscussedwiththisprofileasthe central depth.Between±200kms~oflinecenter,all the otherprofilesareshallower.Onafewoccasions,e.g., center, indicativeofsuperposedemission.Usually, however, thewingsofdisturbedprofilesmatchthose region isratherbroad—neverlessthan200kmsor of thereferencelineprecisely.Inallcases,disturbed greater than300kms~intotalwidth.About50%ofthe essentially symmetrical.Ontheothersixnights time (nineoutof16cases),thedisturbancewascentered 1232 and1289,anactualreversalwaspresentnearline at zerovelocity,sothattheprofileisshallowbutstill disturbance wasdisplacedbyupto150kms\withred Our Haobservationsconsistof24spectraobtainedon Figure 4showsseveralexamplesoftheHaprofile. This referenceprofilehasthemaximumobserved -400 -2000 200 400 iv) HaProfileVariations Fig. 4. km/sec Vol. 247 No. 1, 1981 SPECTRAL VARIATIONS IN p LEO 163 and blueshifts occurring with equal frequency. On time The extremes in this measured intensity differences at scales of hours, the disturbance was never observed to the wings are 0 and 3.4%. Although it is our impression change in velocity. However, over the four nights, 1979 that the spectrophotometric errors in the data do not February 13-16, an initially symmetrical profile ordinarily permit this large a range, we do not have developed a disturbance near +100 km s~1, which sub- confidence that the variations are real. In fact, the ex- sequently shifted to about —100 km s_ 1 in the blue wing. tremes in this asymmetry parameter occurred for a pair of In two cases the blue wing of the disturbed profile was observations made on an inactive night when no other actually depressed below the reference level (a trait also profile changes were present. Moreover, when the line shared by Si m near the same time). When divided by the wings were remeasured at ± 1.0 Â in these two profiles, reference profile, these disturbances have the appearance no asymmetry difference resulted. There is no relation- of a weak P Cygni feature. The time scales for the ship between the asymmetry parameter and any of the development of these features is a few hours. The observa- other “episodic” parameters: equivalent width, wing tions suggested that similar weak emission might be strength, and Ha emission. Therefore, in § Hie the de- responsible for the filling in and distortion of the pressed wing, or “ red asymmetry,” will be treated as a profile at other times. To investigate this possibility, quasi-static phenomenon. Several observations in the Ha we divided each of the observations by the reference spectral region also show evidence for l%-2% asymme- profile, and displayed the results on the same scale as tries in the red wing of the C n 226587-82 doublet. the original data (Figs. 5 and 6). Having assured ourselves that transient disturbances in. ANALYSIS were presently in both Si m and Ha, we made a deliberate effort to obtain as many nearly simultaneous observa- a) Static Atmosphere Velocities tions of the two lines as possible. We believe that the Si m Because accurate rotational velocities are often useful lines are formed in the photosphere and that their in the evaluation of winds in these stars, it was decided to variability indicates that disturbances of some kind occur apply a Fourier velocity dissection analysis on the 24552 in rather deep layers of the atmosphere. On the other profile. Observation 1520 was selected to represent p Leo hand, the core of Ha is formed higher up and would probe in its quiescent state because of the high signal to noise in the unstable conditions in a different region. A correla- this spectrum and because of its detailed agreement in tion in the activity of these lines would therefore imply a shape with several other observations of similar quality. coupling of the properties of different regions, either as The asymmetry at ±1.38 Â in this observation, almost separate responses to a common perturbation or as the exactly equal to the mean asymmetry for all observations, propagation of a disturbance from one region to the was ignored in this particular analysis. Our technique other. We had 13 sets of data in which the Si m and Ha proceeded along the lines described by Smith and profiles were obtained within an hour of each other. The Karp (1978). measured equivalent widths of these lines form the basis The non-LTE line profile computations of Kamp for the correlation which is shown in Figure 7. (1976) were used for the analysis of the intrinsic profile. We have plotted the equivalent width of À5442 versus His work shows that even if departures from LTE are the departure of Ha from its reference value. Since Ha included in the line formation, a microturbulence of always weakened during active episodes, we interpret the >15kms_1 is necessary to match the reference anomaly as Ha emission, the magnitude of which is in the quiescent-phase equivalent width, 420 mÂ. (As a compar- abscissa. Si m usually weakened as well, but on two ison, van Helden 1972 obtained a micro turbulence of occasions its absorption strength increased during epi- 24 km s“1 in his LTE analysis of a similar type super- sodes. Therefore, we have folded the equivalent widths giant, o2CMa [B3 la].) Following Smith and Karp, we around the reference value of420 mÂ, so that the ordinate computed a 24552 profile with equivalent width of represents departures of M552 Â from its reference value. 420 mÂ and ^ = 15 km s~1 with our ABUND program. We consider the outcome to be an important result of This computation was made using the (20,000, 3.0) refer- our story : not only are the active episodes well correlated ence atmosphere of Kurucz, Peytremann, and Avrett in time, but the magnitudes of the disturbances are related (1974; hereafter “ KPA ”) and with a departure coefficient in an almost linear way. We conclude that when disrup- in the line source function which forced the line’s core to tions occur in the atmosphere of p Leo, they affect a wide the residual intensity (43%) that Kamp had computed in range of heights simultaneously. his non-LTE model. Thus, we incorporate an “ excitation temperature ” to simulate the full departures from LTE v) The Red Asymmetry in X4552 and a “microturbulence” to mimic the differential mo- A comparison of the blue and red wing depth at 1.38 Â tions responsible for the enhanced line strength. A second shows that the red wing is depressed by 12 + 0.7% computer program, BROADEN, explicitly integrates the (continuum units) relative to the blue wing. This trans- line broadening effects of rotation and MRT, the radial- lates to + 50 mÂ in the bisector function at a residual tangential macroturbulence (Gray 1976), over a 5000 intensity of 97%. The asymmetry is also consistently element stellar disk model. The velocity dissection was present in the 24567 line. Spectral line lists show no simplified by the presence of a sidelobe in the data indication of a blend at the measured position of this transform because the rotational sidelobe amplitude can depressed wing in either line. be matched to the observational signature at 1 cy Â-1.

© American Astronomical Society • Provided by the NASA Astrophysics Data System 198lApJ. . .247. .1583 for 82inchdata).The“PCygni”featureinthe1312,1315,and1340 observationsisanartifactofasmallmisalignmentintheprofiles water features. telluric features;thePCygnifeatureinobservation1276isauthentic.“T” markersindicateposition(forJanuary)andrelativestrengthsoftelluric p 5—ResultsofthedivisionHadatabya“quiescentepoch” observation (observation1207for107inchdata,and1271 IG © American Astronomical Society • Provided by theNASA Astrophysics Data System 164 198lApJ. . .247. .1583 © American Astronomical Society • Provided by theNASA Astrophysics Data System vo d 198lApJ. . .247. .1583 -1 -1 1 _1 166 frequency domainswithVsini=50±1kms, M =48+2kms"^Arepetitionofthefittingwitha to epochsof24552enhancement. Ha, expressedincontinuumunits.Crossesparenthesiscorrespond Figure 8showsthebestfitinbothwavelengthand model profilehaving^=7kmsledtoarotational value only2kms"larger.Despitethisapparentpreci- M as±10and±5kms,respectively,withthe principal errorsourcesarisingfromajudgmentofwhich sion, weestimatetheactual,externalerrorsonVsiniand phase ”observationandfromthe“velocitydistribution observation bestrepresentsthereference“quiescent R of theassumed“macroturbulence.” tangential macroturbulence.Notethe slightlydepressedredwing,(b)(right)Fig.8hshowsthesamecomparison intheFourierdomain. rt can takeplaceonlyifthereisachangeintheratioofline to continuousopacities,thetemperaturestructure,or rt R (mÂ) q X4552 Fig. 7.—Theequivalentwidthof24552vs.the 36 E.W. Fig. 8.—(a)(left)AComparisonof aquiescent-epoch24552observationwithcomputedprofileincorporating effectsofrotationandradial- In agivenatmospherechangeinspectrallinestrength © American Astronomical Society • Provided by theNASA Astrophysics Data System 340 300 420 400 280 320 260 380 b) EquivalentWidthChanges 100 200300 Hex EmissionE.W. SMITH ANDEBBETS -1 both. Wedonotconsidermicroturbulenceinthefollow- cannot easilyexplaintheprofile’sbecomingmoreexpo- ing discussionbecausetheobservedvariationswould is aboutanorderofmagnitudeshorterthanthedecay motions overmostofthestellardisk.Also,thistimescale require asudden(<2hr)reductionbyseveralkmsof nentially shapedbecausethelatterimpliesincreasein of aBsupergiant.Finally,decreaseinmicroturbulence time scaleofhomogeneousturbulenceintheatmosphere changes arerequiredtoreducethereference420mÀ macroturbulence. p Leo(Kamp1978;seealsoBahúnasandButler1980) perturbed ourreferenceKPAatmospherestoseewhat and themoderateexcitationof24552line,silicon variations asisthecontinuousopacity.Therefore,we line opacityisonlyone-thirdassensitivetotemperature easiest waytoeffectthischangeisbyimposinguniform equivalent widthto300mÂ.Ourresultsshowedthatthe in onlythelowerorupperatmospherictemperatures would havetobe2or3timeslargerandbetray hydrogen intheatmosphere.This,turn,increases temperature dropthroughtheatmosphereof1000K.A themselves asspectraltypechangesofoneortwo be formedatashallowerandcoolerstrata,closertothe continuous opacitymarkedly,forcingthecontinuumto temperature dropcausesapartialrecombinationof While wehavenotyetincludedeffectsofgeometrical changing theSimlinestrengthsistoinvokeaminimum subtypes. AspLeohasneverbeenreportedtobea region ofcoreformation.Theresultisashallowerand inhomogeneities ordynamicsinourmodeling,itappears temperature perturbation,butoftheentireatmosphere. spectral typevariable,itseemsthatthemostlikelywayof weaker 24552line. with aglobalchangeinthetemperaturestructureof that thelinestrengthchangesmostlikelyareassociated Because ofthedominanceSiminatmosphere Further experimentswithmodelsshowedthatchanges Vol. 247 No. 1, 1981 SPECTRAL VARIATIONS IN p LEO 167 atmosphere, with changes in the low to subphotospheric is asymmetric, and the equivalent width is smaller. These regions contributing most heavily. signatures are interpreted as being caused by emission in the central 4-6 Â of the profile. On at least two occasions, c) Line Shape Changes an actual emission reversal was observed. An important conclusion that emerges from the quasi- This emission cannot be attributed to a static condition static profile analysis in § Ilia is that the macroturbulence in the atmosphere, e.g., changes in thermodynamics, since is so high, at least twice the sound speed, as to raise the disturbance in general is neither symmetrical nor serious doubts that the “exponential component” of the stationary, and also because Ha is not sensitive to line broadening is caused by radial-tangential macrotur- temperature among early B supergiants. We interpret the bulent motions at all, or by any other matter motion. An fact that the disturbance moves in wavelength as a alternative possibility is that it arises from noncoherent Doppler shift. This implies that velocities up to electron scattering in the line formation process, ±150 km s-1 can be present. Since the photospheric especially as this is a major source of continuous opacity Si in lines are observed to be constant in radial velocity, in the atmospheres of early-type stars. Note that in fitting we conclude that it is the disturbance rather than the the Ha profile of p Leo to his non-LTE models, Mihalas photospheric profile which moves. (1972) found it necessary to incorporate additional There are several types of moving disturbances which “ macroturbulent ” broadening over and above the rota- can be considered. If a large active region or prominence tional estimate available to him. However, his radiative were present, a weak emission line might appear. The transfer of the line did not include effects of electron velocity would vary slowly as the feature rotated across scattering. the disk and over the limb. This is unlikely to be the case A check of our (20,000 K, 3.0) shows that through the for p Leo, as both the time scale and velocity are wrong. line formation region 40% to 50% of the continuous The projected rotation velocity of p Leo is only 50 km opacity is contributed by electron scattering, and the s_1, so the rotation period would be 3 or 4 weeks. The remainder comes from hydrogen ionization. Because disturbances are observed at radial velocities at least 4 both sources contribute about equally to the opacity, one times greater than this, and vary on a time scale of days. sees that the ratio of /cel scat /Khydrogen is doubly sensitive to Another possibility is that there is material in Keplerian temperature. This sensitivity suggests that the line shape motion around the star, perhaps in an equatorial disk, as may depend on this opacity ratio as well. Munch (1948) envisioned for Be stars. Although this possibility is not and others have shown that electron scattering creates excluded by the observations, there is no other reason for profiles with pointed cores and extended wings. However, expecting such a disk to be present. Most Be stars are rapid this mechanism still does not appreciably affect the rotators (V sin i > 200 km s"x) of nearly main-sequence FWHM of the line, which is also in agreement with Si m luminosity, p Leo is a fairly slowly rotating star of high line observations. Other sources of variable atmospheric luminosity. One could suppose ad hoc that p Leo is seen “ turbulence ” can only cause exponentially shaped at an unfavorable inclination angle, so that the projected profiles by appreciably broadening the FWHM of the line rotation velocity is low. However, the type of variable Ha and conflicting with these observations. This point emission at small velocities reported here has been ob- appears to rule out conventional “ macroturbulence ” as served in several other sharp-lined B- and A-type super- the cause of variable line shapes. Consequently, it may giants (Rosendhal 1973a, b). It cannot be claimed that all well be that the line shape changes occur as part of the of these stars are rapid rotators seen pole-on. We con- same recombination process responsible for the weaken- clude that emission from a Keplerian disk is physically ing of À4552. This would explain the shape-strength possible but unlikely to be related to the activity observed correlation of Figure 2. in the supergiants. Our present profile modeling scheme is not equipped The third possibility, which we favor, is that there are to handle the effects of noncoherent electron scattering in frequent eruptive events during which material rises from the formation of the line transfer problem. However, Auer the photosphere and either returns to the surface or and Mihalas (1968, see their Fig. 6) show that with escapes in the stellar wind. We have noted previously, and reasonable parameters a profile resembling the quiescent- shown in Figure 7, that the Ha events are well correlated phase exponential profile in our Figure 8a can be both in time and strength with the disturbances of the simulated without an appeal to a supersonic photospheric Si in lines. Furthermore, about half the macroturbulence. time the emission component has a significant Doppler shift. Taken at face value, this implies that we see both d) The Ha Emission rising and falling material with about equal probability. An important conclusion of this paper is the interpreta- This leads us to believe that a substantial fraction of tion of the Ha variability as being caused by the inter- the Ha emitting material never rises to great heights mittent presence of material moving up and down in the above the surface and never accelerates above the escape atmosphere of p Leo. Briefly the argument is as follows. velocity. It seems that most of the ejected material returns On a few occasions (four out of 19 nights) the Ha line to the surface of the star. appears symmetrically in absorption, with the strength The return of this material seems to be an inevitable and profile that would be expected from a quiescent feature of any interpretation of our data. Otherwise, the B-type supergiant. On most other nights, the inner profile Ha emitting material must join the radiatively driven

© American Astronomical Society • Provided by the NASA Astrophysics Data System 198lApJ. . .247. .1583 -1 -1 1 1 45 flow regiononatimescaleofseveralhours(Wegnerand wind andaccelerateto10001500kmsthroughthe during 24hr.Inaddition,theobservationofredshifted and 17)onlyverysmallchangesinemissioncanbeseen 168 emission linkedwithvisiblediskeventsmakesthereturn Snow 1978).However,atsomeepochs(e.g.,1979May16 of thematerialallmorenecessary.Onotherside extended atmosphericflow.Consideringtheoccasional ejection episodesarenotfeltasguststhroughoutan the sameargument,itisalmostinconceivablethatHa emission features(at—200kms;cf.V^540 moderate edgevelocityexhibitedbyafewofourHa few hundredkms";Abbott1980),escapethestarwith accelerated tothecriticalvelocity(takenusuallybea s “),onecanassumethatafractionofthematerialwillbe escaping materialmayhavebeenacceleratedmorethan the quasi-steadyflow,andbecomevisibleasasmaller variation nearthehighvelocityedgeofcoronallines.This the bulkofmatterleavingphotosphereeitherin initial ejectionprocessorbyradiationpressureduringits general picture.Fluctuations,mainlyatthelowvelocity edges ofcoronalNvandSiivlines,havealreadybeen transit. reported inpLeo(Snow1977)andseveralotherOB Lamers, Stalio,andKondo1978),sometimesovertime esc bility supporttheviewthatagreatdealofintermittent supergiants (Yorketal1911\SnowandHayes1978; been observed(e.g.,aCam;deJagereíal1979), scales ofhours.While/ng/rvelocityvariationshavealso photospheric changes.Aspectrumofejectiontimescales pulsation cycle.TheHaejectionmayevenprecedethe upon theejectionenergyandnot,say,onlengthofa most variationsinchromospheric/coronallinesareseen at lowvelocities(e.g.,WegnerandSnow1978;Hutchings emission peaksatlowvelocities.Longerlivedeventsare the data.Shorterlivedepisodesprovidegood lasting fromabout10tosseemsberequired profiles fromnighttonight.Theseenergeticevents implied fromthepersistenceofcertainDoppler-shifted regions ofHaemission.Asimilarviewtoourshasbeen activity occursclosetothestellarsurfaceandnear cannot betoofrequent,orelsethecorrelationinFigure8 advanced byWegnerandSnow(1978)fromobservations would notbeasgooditis. Si m-Hacorrelationandexplainthepreponderanceof of short-termoptical/UVspectralvariationsin(Puppis 1979). Altogether,theobservationsofcoronallinevaria- conditions underwhichthematerialmoves. about detailsoftheHaejectionmechanismand (04 If). are formedeitherbyanincreaseinthesourcefunctionof but itcannotalwayscausethe observedDoppler-shifted a linewithheightorbyviewing materialabovethestellar emission. Theshort-livednature oftheejectionsuggests limb. Inafewcases,thelatter explanationcouldapply, that thematerialrises1to10 R(0.03to0.3R*)above ö Recent coronallinevariationsseemtobearoutthis Note thatthetimescaleofHaemissionwilldepend Turning fromthisbasicoutline,severalquestionsarise 1) WhatcausestheHaemission?Stellaremissionlines © American Astronomical Society • Provided by theNASA Astrophysics Data System SMITH ANDEBBETS 1 blueshifted absorptioncomponentinHatobeobserved. 4 fraction ofthevisibledisk,onecanexpectasubstantial the photosphere.Ifitisindeedejectedfromalarge observed intheHaejectionevents.Moreover,anymaterial projected abovethelimbwillnotbeappreciablyDoppler However, withoneexception,blueshiftedabsorptionisnot Doppler-shifted emissionthatcoincidewithaphoto- not always(orevenfrequently)occurbyprojectionover spheric disturbance(observations1388,1340,and1553). in sourcefunctionwithheightoccursbecausethema- the stellarlimb,butratherthatmatterhasentereda shifted, contradictingourfrequentobservationsof upper photosphere.Onemightspeculatethattheincrease region inwhichtheHasourcefunctionexceedsthatof Such behaviorsuggestsstronglythattheemissiondoes terial hasmovedintoanopticallythinenvironmentinthe become collisionallycoupledtoamoderatelyheated radiation, or(lesslikely)thatthesourcefunctionhas Lyman continuum,whereitisexcitedbyEUVcoronal postcoronal temperaturerise. interrupted floworofalargechangeinionization conditions astheejectedmaterialtransistscorona. that donotaffectthepassageofthismoreglobally Perhaps the“corona”actuallyconsistsofdensehotspots distributed material. from? Thecoincidenceintimeofphotospheric24552 process isresponsibleforboth.Ifso,theirenergetics activity andHaemissionindicatesthatacommon equated thechangeinthermalenergyperatmospheric particle, 1000K(§Illfr),tothepotentialenergythat might alsoberelated.Toseeifthisisreasonable,wehave upward motionfromanunspecifiedcouplingprocess.We photospheric massbecausethecoreofSim24552 assume thatthisfractionisontheorderof1% some fractionoftheatmosphereacquiresduringits finds anorderofmagnitudeagreementinsurrendered line, formedatthe5%masslevel,doesnotparticipatein and gainedenergiesifthegasrisesat~100kms~for the emissionorradialvelocitychangesofHaline.One probably issufficientenergyinthesubphotosphereto expecting envelopepulsationsinpLeo,sothatthere observations suggeststhatthematerialresponsiblefor the tossedmaterial?OurinterpretationofHaemission magnitude agreementinbetweentheinferredatmo- account forthemoreenergeticepisodes.Thisorderof of theHacomponentsreported hereandbyRosendhalin to roughlythecoronaldistance(<0.1R*).Thevelocities Ha emissionisprobablytossedabovethestellarsurface material areshiftedwellbeyond theintrinsiclinewidth, the radiativelydrivenwind.Still, becausethelinesinthis other Bsupergiantsarewellbelow theescapevelocitiesof “ tossedblobs”supportstheexpectationthatexpul- one canexpectthatthematerial shouldpickupaddi- spheric cooling(§lllb)andthepotentialenergyofour than acoincidenceintime. sion andphotosphericphenomenaarelinkedbymore 10 s.Asshownin§IV,therearestrongargumentsfor It remainstobeaddedthatthereisnoevidenceofan 2) Wheredoesthekineticenergyofejectioncome 3) Whydoesradiationpressurenotpermanentlyeject Vol. 247 198lApJ. . .247. .1583 No. 1,1981 tional radiativeaccelerationtoescapethestar.Indeed,p does thematerialreturn?Themostplausibleansweris Leo alreadyliesjustwithinthedomainwhichAbbott (1979) hascalculatedforself-initiatingwinds.Why,then, that theionizationofmatterisalteredbyexpul- comes lessionizedanditsspectrumshowsmoreabsorp- radiative accelerationmightoccurifthematerialbe- sion process.Purelyasaspeculation,reductioninthe contrary tothemorefortunatecaseinconventional tion linesredwardofthestellarfluxmaximum.Thisis models inwhichthemostfavorablelinesforradiative acceleration arebluewardof912Â(e.g.,Lamersand Morton 1976). in ¿4552showthatadepressedredwingisvirtually different ininterpretationfromanyofthespectralvaria- always present(§Ilf).Thisposesaproblemsignificantly consider whethertheasymmetrymightbeaphotospheric however, thattheobservedasymmetryinatypicalphoto- manifestation ofthewind.Aquickinvestigationshows, tions discussedabove.Thefirstapproachmightbeto determined fromUVcoronallinesorinfraredreemission. spheric lineismuchtoolargetoexplainthemass-lossrate instead asashiftofthelinecorerelativetowings,this For example,iftheasymmetryat±1.38Âisinterpreted connected withthemasslossinthisstarobservedby metry isinthewrongsenseand40timestoolargetobe shift is—6kms"LComputationsshowthatthisasym- Barlow andCohen(1977). line asymmetryistocouplearadialvelocityfieldwith changes inthermodynamicparameterstheatmo- understanding theblueasymmetriesobservedinmany sphere. Historically,mostattentionhasbeenpaidto field consistingofrisingandfallingcolumnsweightedby thought toarisefromaconvective-granulationvelocity strong solarlines.Theseasymmetriesaretraditionally be capableofexplainingtheredasymmetriesthatGray their temperaturedifference.Thesamemechanismmay umns ratherthantheascendingonesinline Arcturus atmosphereemphasizesthedescendingcol- the changeindominantionizationstates (1980) hasobservedinneutrallinesofArcturusbecause formation. The Graymechanismcannotbeusedinthiscase,because similar problem:blueasymmetriesforiSeo(B0.2V; To attempttoresolvetheiScoLeoasymmetrysign difference, wehaveconsideredanumberofmodelsin Smith andKarp1978)redasymmetriesforpLeo. which temperatureandvelocityvariationsarecoupled, but mostofthemleadtophysicalcontradictionsorare Si inisthedominantionstageforbothBOandB1stars. believe themostpromisingapproach ofunderstanding incapable ofproducingthesize oftheasymmetries.We position Henionizationzone relativetothephotosphere the asymmetriesistocallattention tothesensitivityof to T.Thiszonecanbeexpected tosetupaconvective eff The intensitymeasurements±1.38Âfromlinecenter The mostpromisingwayofcreatingaquasi-permanent In thecontextofBstars,wearenowconfrontedwitha © American Astronomical Society • Provided by theNASA Astrophysics Data System e) ThePersistentRedAsymmetry SPECTRAL VARIATIONSINpLEO -1 -1 granular-flow patternashydrogenionizationdoesinthe The KPAmodelatmospheresshowthattheionization zone movesfromroughlyone-halfapressurescaleheight Sun andproducelineasymmetriesincertaincases. tion mayappeardifferentlyinthetwostars,anddifferent below T=IiniScotoagreaterdepth(over2 “ radial-flowvelocitylaw’’responsibleforthelineforma- no morethanaconjecture. line formationwilllieclosetothesourceofgranules’ asymmetries mayresult.However,webelievethistobe coincide withthedecelerationoftheseelements.Then acceleration, whereasinpLeothedepthofformationwill scale heights)inpLeo.Therefore,tScothedepthof spectral variationsiswiththesimplerecognitionthat rapid, globalatmosphericchangesinvolvinglarge Rosseland amounts ofenergyareinvolved.Figure3showsthatthe shape andstrengthchangesofthesiliconlinesfollow This factimpliesthatthechangesdevelopfullyover same trajectoryonhourlytimescalesaslongerones. of shorterones.Thispointrulesoutavarietymodels month “trends”arenotaresultofincompletesampling several hoursandthatanynight-to-nightormonth-to- for thespectralvariations,example,modulations associated withtherotationperiodofpLeo.Theglob- bance acrossthedisk.If,forexample,adisturbance alness requiredofthemechanismplacesconstraintson the propagationvelocity(orphasevelocity)ofdistur- appears ata“sourcepoint”onthediskandpropagates across thediskinafewhours,velocityofseveral photosphere andbecomesvisiblesimultaneouslyoverthe disturbance actuallyemergescoherentlyfromthesub- thousand kmsisrequired.Thiscouldmeanthatthe nonradial pulsationsarepresent.Inthisconnection,note disk. Alternatively,thislargevelocitycouldmeanthat indeed acharacteristicofnonradialoscillationsin that phasevelocitiesofseveralthousandkmsare B-type star(e.g.,Osaki1971).Ineithercase,oneseesthat pulsation. the mostlikelysponsorofglobalphenomenaisa pulsations causespectralvariationseitherbythe displacement oftheatmosphereorbyupwardpropagat- density environment.InpLeonistheconsistentlackof ing shockwavesgeneratedbynonlinearitiesinalow- pulsations (singlemode,orotherwise).Also,intheleft radial velocityvariationsautomaticallyrulesout and middleregionsoftheH-Rdiagramradialpulsations frequency (e.g.,ßCepheistars,classicalCepheids).The tend tobehighlycoherentandaredominatedbyasingle erratic natureoftheobservedspectralvariationsrulesout this sortofregularity. stars ofthisparttheH-R diagram,aswellthe The bestplacetostartinaphysicalanalysisofpLeo’s Let usconsiderfirsttheradialoscillations.Radial The presenceofmultiperiodic nonradialpulsationsin IV. ANINTERPRETATION:MULTIMODE a) GeneralConsiderations NONRADIAL PULSATIONS? b) NonradialPulsations 169 198lApJ. . .247. .1583 _1 be placedonanonradialpulsationmechanismrightaway implausibility ofothersuggestions,leadsustoconsider of thespectrallinesinpLeo.Theonerestrictionthatmust this mechansimasthecauseofremarkablebehavior well-defined spectralvariationsduetoasinglemode 170 is thatthevariabilitycannotbesinglyperiodic: We proposethatthespectralactivityreportedherein each havingavelocityamplitudeoffewkms.We tively, ifalargenumberofmodes(>100)werepresent, (Osaki 1971)werenotdetectedinthisstudy.Alterna- phase, thethermodynamicparametersassociatedwith interferences causetoomanycancellationsatmostpoints arises fromtheinteractionofseveralnonradialmodes, spectral changesofanykindwouldbeseldomobserved. each waveaddconstructivelyandcauserapidchangesin across thediskforspectralchangestobeobserved. suggest thatundernormalcircumstancesdestructive be estimatedfortheseoscillationsfromthe~3hrtime and strengthofthelines)overasignificantfraction the structureofatmosphere(andhenceinshape However, wheneverafewdominantmodescomeinto visible disk.Atypicalperiodofhalfaday,orlonger,can ulated byenvisioningapairofquadrupole(/=2) required foreventstofullydevelop. serve toreproducethepLeoobservationscanbeform- results whenthetroughoftwoopposingwavesmeets retrograde (m=2)sense.Imaginethesituationthat sectorial modestravelingintheprograde(m=—2)and and atemperaturedropinthephotosphere.However, at thesubstellarpoint.Thereoneobservesararefaction from theverticalpulsationalvelocities,radialvelocity will remainzero.At71%oftheprojecteddistanceoutto since thethermodynamicvariationsrun90°outofphase the limb,temperatureandvelocityvariationsof undistorted byDopplershifts,withitslinestrength compression ofthewavecontributesonlyasmallamount the limbradialvelocitiesareagainnearzero,and two wavesnowopposeoneanotherandcancelout.Near to theintegratedlight.Therefore,netresultisaline above demonstrateshowreadilyspectralanomaliescan multimode variationstothisgeneralidea.Thisexample the innertwo-thirdsofsurface.Therearemany changed becauseofthetemperaturechangeover will addinsuchawayastoproducevelocityvariations.) come aboutwithoutnecessarilybetrayingthemselvesin changes andmaywellbecausedmorebyatmospheric Luminosity variationswillaccompanythespectral the radialvelocitydata.(Certainothernonradialmodes atmosphere exhibitsatemperaturerise,correspondingto temperature variationsthanbydisk-geometryeffects. uous opacity,andthereforeon theshapeandstrengthof is truebecauseadditionalhydrogenionizationinthe variations inthe24552parameterswillbeobserved.This the passageofalargecompressionwave,onlysmall emplify amirrorsymmetry withthelineweakening equivalent widthexcursions ofthislineprobablyex- already ionizedgaswillhave littleeffectonthecontin- the siliconlines.In§libitwas suggestedthatseveralhigh A simpleexampleofhownonradialoscillationsmight An additionalfacetofthismodelisthatwhenthe © American Astronomical Society • Provided by theNASA Astrophysics Data System SMITH ANDEBBETS d equal frequencies.Inthesamevein,itisconceivablethat episodes. Thisobservationfitssquarelyintothepresent believing thatnonradialoscillationsareimportantinB context because“troughs”andcrestsmustoccurwith because itliesjustabovethenonradialpulsationdomain rarefaction phaseandejectedmaterialarepresentatthe the zero-velocityHaemissionobservedwhen24552is occupied bythe53PerseiandßCepheivariableclasses. supergiants. RhoLeoniswasputinourinitialsurvey the diskandcommencesejectionevent. limbs, whilethecompressionwavereachescenterof strong correspondstoanonradialgeometryinwhichthe line widthsinaCam(09.5la),whicharestrongly in aB3IIstar,iCMa(Smith1979a).Also,recent In fact,lineprofilevariationshavebeenalreadyobserved paper, Ebbets(1981)findschangesinasymmetryand overtone g-modeswithshortlifetimes.Theaverage period observedinthesestarsis~12hr,closetothe pulsating 53Perseistars.Thestarsarepartic- reminescent ofprofilechangesinthenonradially ularly interestinginthattheyseemtopulsatehigh been observedonafewoccasionsinsomeofthesestars mean valuesuggestedforpLeo.Atleasttwomodeshave differences inscaleheights,theionizationstructuresof at typeBl,thespectralofpLeo.Therefore,exceptfor Cephei starsoccurinthecenterofthisinstabilitydomain (Smith 1979h).Itisalsoimportanttonotethattheß oscillations inBstarsaredriventheoutermostregion current picture(Smith1980)suggeststhatthenonradial these variablesisquitesimilartothatinpLeo.One ence cannotbemaintainedexceptinthepresenceofa of thestellarenvelopeandaresounstablethatacoher- oscillations inthelatter.Also,massofpLeo resonant radialmode.Becauseofthesimilarionization tually coincideswiththemassof10Lac(09V,22M; supergiants, thereisgoodreasontosuspectnonradial structure oftheenvelopesthesepulsatorsandearlyB nonradial pulsationsextendtohighermassstarsornot.) Snow andMorton1976),whichalsoexhibitsnonradial (23 M;SnowandMorton1976;Underhill1979)vir- pulsations (Smith1978).(Itisnotyetknownwhether Altogether, the,circumstancesseemrightfornonradial example ofDeneb(A2la),forwhichLucy(1975)has oscillations inastarwithpLeo’sparameters. modes withperiodsbetween7and100.Inourviewhis demonstrated theprobableexistenceofasmany16 data reductiontechniquesaresufficientlygoodtogivehis claim ahighweight,despitetheimpliedcomplexity.In picture suggestedabovefor temperaturevariationin negative spikes.Thisbehavior isreminiscentofthe “jitter” andoccasionallarge-amplitudepositive indeed showstheusualpresenceofsmallamplitude addition, anexaminationoftheradialvelocitydata 0 p Leo. 0 comes fromphotometricwork, whichshowsperiodicities There areafewadditionalcircumstantialreasonsfor A secondreasonfavoringnonradialoscillationsisthe A thirdreasonforsuspecting nonradialoscillations c) OtherArguments Vol. 247 198lApJ. . .247. .1583 1 No. 1,1981 among OBAFsupergiants(MaederandRufener1972; dominant periodsobservedinthevariabilityofsuper- recent reviewofthiswork,Ebbets(1980)pointsoutthat our observations. g-value. IfthislawisextrapolatedtopLeo,aperiodof proceeds toearliertypes,thedominantperiodsbecome giants arehighlysignificantamonglatertypes,butasone modes, apicturesimilartoourdescriptionofpLeo. decrease insignificanceoftheseperiodsearlysuper- less significantandshorter.Mostauthorsbelievethe Sterken 1977;Burki,Maeder,andRufener1978).Ina giants arisesfromthecompetitionofseveraldominant a period-luminositylowwiththeappropriatepulsation Ebbets showedthatthedominantperiodsofthesestarsfit analysis ofpLeoareasfollows: of bothlineweakening(factor2)andstrengthening strong linesarisingfromadominantionizationstate ~ 10hrispredicted,closetothevaluesuggestedfrom occasionally occur,perhapswithequalfrequency velocity andwithverylittlechangeintheFWHM. (Si m)occuratapparentlyerraticintervals.“Episodes” change inshapetowardamoreU-shapedprofile (Fig. 1).Thesechangesoccurwithoutvariationsinradial manner onshortandlongtimescales.Thisfactsuggests (Figs. 2,3). likely reflectsimultaneousglobalchangesoveran that allthevariationsoccurrapidly.Thesechangesmost The energyrequirementsforchangesintheatmospheric appreciable fractionofthediskstar. decreases of~1000Koccurringthroughoutthephoto- appear tobemostconvenientlyexplainedbytemperature recombination ofhydrogen,whichinturn,causesa sphere. Thedropintemperaturecancauseapartial reduction inelectronscattering(U-shapedprofiles)and an increaseinthecontinuousopacity(Simweakening). subphotosphere cancontainthenecessaryenergytocause with thepresenceofweakHaemission.WhenSimis the globalvariationsinatmosphericstructure. temperature ofthisorderarelargeenoughthatonlythe abnormally strong,theHaemissionisparticularlystrong and isseenatzerovelocity,probablyprojectedabovethe +100 kms“rangesuggeststhatasmallfraction(~1%) limb. .1980,privatecommunication. Abbott, D.C.1979,IAUSymposium83,MassLossandEvolutionof Abt, H.A.,andBiggs,E.S.1972,Bibliography ofStellarRadialVelocities Auer, L.H.,andMihalas,D.1968, Ap. J.,153,923. The conclusionsemergingfromourspectroscopic 2. Thelineweakeningisinvariablyaccompaniedbya 1. Rapid,extremechangesintheequivalentwidthof 3. Thechangesjustdescribedoccurinthesame O-Type Stars,ed.P.S.ContiandC. W.H.deLoore(Dordrecht: 4. BoththeU-shapedprofilesandlineweakening Reidel), p.237. (New York:Latham). 6. Therandomlowvelocitiesinthe—100to 5. TheepisodesofSimweakeningcorrelatedverywell © American Astronomical Society • Provided by theNASA Astrophysics Data System V. SUMMARYANDDESIDERATA SPECTRAL VARIATIONSINpLEO REFERENCES photospheric dynamicscausethisejectionofmatter. radius andreturnsseveralhoursoradaylater.The of thephotosphereistossedupafractionstellar coincidence intimingandenergeticssuggeststhatthe ejection eventsseemtoberelatedultravioletobserva- “ coronal”resonancelines,especiallyatlowvelocities. above activityisinitiatedbymultimodenonradialoscilla- tions ofmassfluxvariations(Snow1977)observedin for most“erratic”variationsofspectrallineshapesand tions. Itissuggestedthatthesepulsationsareresponsible by monitoringbothHaandSimoverentirenights.We tions inothersupergiants.Theoscillationsmayalso strengths, fortheHaemission,andluminosityvaria- “ coronal”)windobservedinallluminousOandBstars supply theheatingtermforhigh-ionization(so-called an Haejectioneventthroughtocompletion,preferably presentation becauseoftheincompletesamplingin ejection asoneoftheleastwell-definedaspectsour regard ourdiscussionofthe“ballistics”Ha (Snow andMorton1976). behavior ofSiivvU4089and4116n/Ü4128-32 observations. Itwouldalsobeusefultodocumentthe during theseepisodes,asacomparisonoflinestrengths from twominorityionswouldprovideasensitivemeas- ure ofchangesinatmosphericstructure. nonlinear relationshipbetweenpulsationamplitudeand variations havebeenreportedforpLeo.Further,the means arenotgood.Asnotedinthisandpreviousstudies equivalent widthwouldmarseriouslyanyquantitative (Abt andBiggs1972),nosignificantradialvelocity perhaps alongthelinesofLucy’speriodogramanalysis from ananalysisofextensivephotometricobservations, time-series analysis.Greaterprogresswillprobablycome subtype, or~0.02maginboththeseindices.Itisclear work predictsoccasionalvariationsofhalfaspectral also searchfortemperaturechanges(0[u—b],(5c).Our Paddock’s radialvelocities.Suchobservationsshould phenomena inOBsupergiants. with Drs.DavidAbbott,LawrenceCram,AlanKarp, giants cangreatlyincreaseourunderstandingofa that aconcentratedphotometricattackonfewsuper- referee. mechanism responsiblefortime-dependent,atmospheric acknowledge usefulsuggestionsfromananonymous Michael Marlborough,andDimitriMihalas.Wewishto Bahúnas, S.L.,andButler,E.1980,Ap.J.(Letters),235,L45. Cassinelli, J.P.,Castor,I.,andFarmers, H.J.1978,Pub.A.S.P.,90, Burki, G.,Maeder,A.,andRufener, F.1978,Astr.Ap.,65,363. Barlow, M.,andCohen,M.1977,Ap. J.,213,737. Cannon, C.J.,andThomas,R.N.1977, Ap.J.,211,910. Crawford, D.L.,andMander,J.1966, A.J.,71,114. 2 7. Althoughwehavenotdemonstratedit,theHa 8. Avarietyofindirectargumentssuggeststhatallthe Future spectroscopicstudieswoulddowelltofollow The prospectsforfindingperiodicitiesbyspectroscopic 496. It isourpleasuretoacknowledgehelpfuldiscussions 171 172 SMITH AND EBBETS de Jager, C, Lamers, H. J., Macchetto, F., and Snow, T. P. 1979, Astr. Parsons, S. G., Wray, J. D., Henize, K. G., and Benedict, G. F. 1973a, Ap., 79, L28. Ap. J., 187, 523. Ebbets, D. 1980, IAU Colloquium No. 51, Stellar Atmospheric . 1973b, Ap. J., 187, 898. Turbulence, ed. D. F. Gray (Dordrecht: Reidel), in press. . 1978, Ap. J., 224, 927. . 1981, Ap. J., in press. -. 1919a, Tucson Conference on Nonradial Pulsations in the Sun Gray, D. F. 1976, The Observation and Analysis of Stellar Photospheres and Stars, ed. H. Hill and R. Kippenhahn (New York: Springer- (New York: Wiley), p. 423. Verlag), in press. . 1980, Ap. J., 235, 508. —. 1979b, Proc. 17 th I AU General Assembly (Dordrecht: Reidel), Hutchings, J. B. 1979, IAU Symposium 83, Mass Loss and Evolution of in press. O-Type Stars, ed. P. S. Conti and C. W. H. de Loore (Dordrecht: . 1980, Ap. J., 240, 149. Reidel), p. 231. Smith, M. A., and Karp, A. H. 1978, ¿p. J., 219, 522. Kamp, L. 1976, NASA TR R-455. Snow, T. P. 1911, Ap. J., 217, 760. . 1978, Ap. J. Suppl, 36, 143. Snow, T. P., and Hayes, D. P. 1978, Ap. J., 217, 760. Kurucz, R. L., Peytremann, E., and Avrett, E. A. 1974, Smithsonian Ap. Snow, T. P., and Morton, D. C. 1976, Ap. J. Suppl, 37, 429. Obs. Spec. Kept. Sterken, C. 1977, Astr. Ap., 57, 361. Lamers, H. J., and Morton, D. C. 1976, Ap. J. Suppl, 32, 715. Stothers, R. 1977, private communication. Lamers, H. J., Stalio, R., and Kondo, Y. 1978, Ap. J., 223, 207. Underhill, A. B. 1961, Nuovo Cimiento, 22, 69. Lucy, J. B. 1976, Ap. J., 206, 499. . 1966, The Early-Type Stars (New York: Gordon and Breach), Maeder, A., and Rufener, F. 1972, Astr. Ap., 20, 437. p. 216. . 1972, Ap. J., 176, 139. . 1979, Ap. J., 234, 528. Morton, D. C. 1979, M.N.R.A.S., 189, 51. van Helden, R. 1972, Astr. Ap., 21, 209. Munch, G. 1948, Ap. J., 108, 116. Vogt, S. S., Tull, R. G., and Kelton, P. 1978, Appl. Optics, 17, 574. Nerney, S. 1980, Ap. J., 242, 723. Wegner, G. A., and Snow, T. P. Jr. 1978, Ap. J., 226, 425. Osaki, Y. 1971, Pub. Astr. Soc. Japan, 23, 485. York, D. G., Vidal-Madjar, A., Laurent, C, and Bennet, R. 1977, Ap. J., Parsons, S. G., Wray, J. D., Henize, K. G., and Benedict, G. F. 1979,1A U 213, 461. Symposium 83, Mass Loss and Evolution of O-Type Stars, ed. P. S. Conti and C. W. H. de Loore (Dordrecht: Reidel), p. 95.

Myron A. Smith: Sacramento Peak Observatory, Sunspot, NM 88349 Dennis Ebbets: Department of Astronomy, University of Wisconsin, Madison, WI 53706