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Fastspectral variations ofOBA stars 7 1 A.F.Kholtygin1,S.Hubrig2,V.V.Dushin1,S.Fabrika3,A.Valeev3, 0 M.Schoeller4,A.E.Kostenkov1 2 1AstronomyDepartment, Saint-Petersburg StateUniversity, Russia; n a [email protected] J 2Leibniz-Institut fürAstrophysikPotsdam(AIP),Potsdam,Germany; 3 3Special Astrophysical observatory, NizhniiArhyz,Russia; ] R 4European Southern Observatory, Garching, Germany; S . h Abstract. Thepresentworkisstimulatedbytherecentdetectionofthemoderateline p profilevariationsofselectedlinesonatimescaleofminutesinFORS2spectraofthe - A0supergiantHD92207(Hubrigetal.2014).Recently,weinvestigatedthevariability o oflineprofilesofselectedOBA starswiththemulti-modefocalreducerSCORPIO at r t the6-meterBTAtelescope. WediscoveredregularvariationsofHandHelinesinthe s a spectra of the O-type star HD93521 (O9.5III)with periods 4-5 and 32-36 minutes. [ Thepossibleoriginofshorttime-scalespectralvariationsisdiscussed. 1 v 3 3 1. Introduction 7 0 0 Line profiles in spectra of OBA stars are varying on time scales from days to hours . (Kaper et al. 1997; Dushin et al. 2013). The variable bright A0 supergiant HD 92207 1 0 hasbeenmonitoredspectroscopically byKauferetal.(1997). Theauthorsrevealedthe 7 presenceofnon-radialpulsations(NRPs)inthisstarwithaperiodof27days. Theshort 1 time-scale line profile changes in the spectra of HD 92207 were detected by Hubrig : v etal.(2014), seealso(Hubrigetal.2015;Kholtygin etal.2015). Theauthorsdetected i the clearly visible LPVs belonging to different elements in individual subexposures X reaching upto3%inintensities andupto30km/sinradialvelocities. Suchshort-term r a periodicitywasnotknownbeforefornon-radially pulsatingsupergiantsanditsstudyis crucialformodelingthestellarevolution. Totestwhether short-periodic spectral variations arewidedispersed amongOBA stars, we investigated the variability of line profiles of selected OBA stars with the multi-mode focal reducer SCORPIO at the 6-meter BTA telescope. In this paper we present the results of our search for the fast LPVs in the spectra of the O-type star HD93521(O9.5III). 2. HD93521: lineprofilevariations ThespectralobservationsofthefastrotatingstarHD93521(Vsini = 390km/s,(Rauw etal.2008))werecarriedoutin2015Jan19–20withamulti-modefocalreducerSCOR- 1 2 Kholtyginetal. PIOmountedintheprimefocusofthe6-metertelescopeBTA.TheSCORPIOisusually usedforobservations ofstar-like andextendedobjects (Afanasiev&Moiseev2005)in integal light with a low spectral resolving power. Our observations were made width a slit width of 0.5” in the spectral range λλ4040 − 5850 with the 3s exposure. The spectralresolving powerofR∼ 2000andthesignaltonoiseratioS/N ∼ 2000. The total time of observations was T = 76 minutes. The number of obtained full spectrawas529,oneofthemappearedtobeabadquality,sothatfinally528SCORPIO spectra were used. The reduction of the SCORPIOspectra wasdone with the MIDAS package using the standard procedures. Allspectra werenormalized to the continuum levelusingtheapproach byKholtyginetal.(2006). Allanalyzed lines in the SCORPIOspectra appeared to be variable. In Fig. 1 we plottheLPVsforH andH lines. δ γ 1.0 1.0 x x u u l l F F d 0.9 d e e z z i i0.9 al Hd al Hg m m r r o o N0.8 N 0.8 4085 4090 4095 4100 4105 4110 4115 4330 4335 4340 4345 4350 Wavelength (Å) Wavelength (Å) Figure 1. The overplotted H and H line profiles in the SCORPIO spectra of δ γ HD93521. AsitclearlyseeninFig.2,thelineprofilesofHandHeIIlineschangeregularly. 3. HD93521: Fourierspectra Thefrequencies andperiods oftheLPVswerecalculated using theCLEANalgorithm (Roberts et al. 1987) with modification by Vityazev (1996). The Fourier spectra of LPVsforHandHeIIlinesarepresented inFig.3. In Fig. 3 one can separate three groups of the regular components in the Fourier spectra: ν = 0.21 − 0.26m−1 (P = 4 − 5min), ν = 0.028 − 0.030m−1 (P = 1 1 2 2 32−36min),andν ≈ 0.0092m−1 (P ≈ 108min). 3 3 The third component P > T . In this case, we can not decide whether this 3 full component is real. However as it was shown by Kholtygin et al. (2007) even in this casesuch notvery reliable component can beclose totherealharmonic oftheFourier spectraifitsperiodonlyslightly exceedthefulllengthofthetimeseries. Rauw et al. (2008) detected two regular components of HeI and H LPVs in the α spectra of HD 93521 with periods of 1.75 and 2.89h. The authors identified these Fastmicrovariations 3 0.025 0.03 0.02 70 70 70 0.02 0.015 0.02 60 0.015 ) 60 60 s 0.01 e 0.01 s) 50 ut 50 0.01 s) 50 e e 0.005 ut 0.005 n ut n i 40 n mi 40 0 m 0 mi 40 0 ( ( ( me 30 -0.005 e 30 me 30 Ti m −0.01 Ti -0.005 -0.01 i 20 20 T 20 -0.01 -0.015 −0.02 10 10 10 -0.015 -0.02 0 −0.03 0 -0.025 −800−400 0 400 800 0 -0.02 -800 -400 0 400 800 -800 -400 0 400 800 Velocity (km/s) Velocity (km/s) Velocity (km/s) Figure 2. The dynamical spectra of H , H and HeIIλ4686Å line profiles for β γ HD93521. 0.5 4 0.5 3 0.5 0.6 3.5 2.5 0.5 0.4 0.4 0.4 3 ) ) 1 1 -(m 0.3 2.5 -1m)0.3 2 -(m0.3 0.4 y y ( y nc 2 nc 1.5 nc 0.3 a a a qu 0.2 1.5 equ0.2 qu0.2 re Fr 1 re 0.2 F F 1 0.1 0.1 0.1 0.5 0.1 0.5 0.0 0 0.0 0 0.0 0 -800 -400 0 400 800 -800 -400 0 400 800 -800 -400 0 400 800 Velocity (km/s) Velocity (km/s) Velocity (km/s) Figure3. TheCleanedFourierspectraforH ,H andHeIIλ4686Ålineprofiles β γ inspectraHD93521. components as NRP l = 8 ± 1 and l = 4 ± 1 modes, respectively. Importantly, the shortestperiodP=1.75h(105min)isveryclosetoourcomponent P . Wesuggestthat 3 our components P and P also can be assigned to NRP modes l ∼ 25 and l ∼ 180, 1 2 accordingly. 4 Kholtyginetal. 4. Discussionandconclusion ThemassiveOBAstarsareconsideredastypeIIsupernovaprogenitors. Acarefulstudy oftheirvariabilityprovidesimportantdiagnosticmeansforinternalandexternal(atmo- spheric)structure. Ourrecentsearch(Hubrigetal.2014)formagneticfieldsinselected OBAstarsusingFOcalReducerlowdispersion Spectrographs FORS1andFORS2in spectropolarimetric moderevealed thepresence ofstrong line profilevariations (LPV) inspectra ofmagneticOBAstars. Simple estimations by Kholtygin et al. (2015) show that the LPVs of such an amplitude as was detected for HD 92207 can be connected with the huge spots with diameter about of40R⊙ orwiththelargeprominences withthemeansizeabout afew solar radia. Regular LPVs in spectra of HD93521 are variable on the time scales of 4-5and 32-36minutescanbeconnected withthehighmodeofNPPs. Theconnection oftheseLPVswithpossible magneticfieldofthesturisunderquestion. ThenumberofourspectrapolyrimetricobservationsofHF92207withtheminutes time resolution (Hubrig et al. 2014) is too small to find the regular component in the LPVsof this star. Therefore we can not exclude the possibility that LPVsin the spec- trumofHD92207arealsoassociatedwithhighmodesofnon-radialpulsationslikethe 5-minutesolaroscillations (see,e.g. Marmolino&Severino(1989)). Acknowledgments. The research was supported by the Russian Scientific Foun- dation(grantN14-50-00043) inobservations withtheBTAtelescope, AFK,VVDand AEKacknowledgeRFBRforasupportbygrant16-02-00604 Aintheiranylysisofthe lineprofilevariations inspectraofHD93521. References Afanasiev,V.L.,&Moiseev,A.V.2005,AstronomyLetters,31,194.astro-ph/0502095 Dushin,V.V.,Kholtygin,A.F.,Chuntonov,G.A.,&Kudryavtsev,D.O.2013,Astrophysical Bulletin,68,184 Hubrig,S.,Kholtygin,A.F.,Schöller,M.,Anderson,R.I.,Saesen,S.,González,J.F.,Ilyin,I., &Briquet,M.2015,AstronomischeNachrichten,336,168.1502.00227 Hubrig,S.,Schöller,M.,&Kholtygin,A.F.2014,MNRAS,440,1779.1403.2219 Kaper,L.,Henrichs,H.F.,Fullerton,A.W.,Ando,H.,Bjorkman,K.S.,Gies,D.R.,Hirata,R., Kambe,E.,McDavid,D.,&Nichols,J.S.1997,A&A,327,281 Kaufer,A.,Stahl, O., Wolf, B., Fullerton,A.W., Gaeng,T.,Gummersbach,C.A., Jankovics, I.,Kovacs,J.,Mandel,H.,Peitz,J.,Rivinius,T.,&Szeifert,T.1997,A&A,320,273 Kholtygin, A. F., Burlakova, T. E., Fabrika, S. N., Valyavin, G. G., & Yushkin, M. V. 2006, AstronomyReports,50,887.astro-ph/0612183 Kholtygin,A. F., Hubrig,S., &Schöller,M. 2015,in PhysicsandEvolutionofMagneticand RelatedStars,editedbyY.Y.Balega,I.I.Romanyuk,&D.O.Kudryavtsev,vol.494of AstronomicalSocietyofthePacificConferenceSeries,239 Kholtygin,A.F.,Shneiwais,A.B.,Burlakova,T.E.,&Milanova,Y.V.2007,Astrophysics,50, 225 Marmolino,C.,&Severino,G.1989,Mem.SAI,60,181 Rauw,G.,DeBecker,M.,vanWinckel,H.,Aerts,C.,Eenens,P.,Lefever,K.,Vandenbussche, B.,Linder,N.,Nazé,Y.,&Gosset,E.2008,A&A,487,659.0806.3640 Roberts,D.H.,Lehar,J.,&Dreher,J.W.1987,AJ,93,968 Vityazev,V.V.1996,AstronomicalandAstrophysicalTransactions,11,159