The effects of inclination, gravity darkening and differential rotation on absorption profi

Mechanisms influencing absorption line profiles of fast rotating stars can be sorted into two groups; (i) intrinsic variations sensitive to temperature and pressure, and (ii) global effects common to all spectral lines. I present a detailed study on the la

Astronomy&Astrophysicsmanuscriptno.3947

(DOI:willbeinsertedbyhandlater)February2,2008

Thee ectsofinclination,gravitydarkeninganddi erential

rotationonabsorptionpro lesoffastrotators

A.Reiners1

arXiv:astro-ph/0306491v1 24 Jun 2003HamburgerSternwarte,Universit¨atHamburg,Gojenbergsweg112,21029Hamburg,Germanye-mail:areiners@hs.uni-hamburg.deacceptedbyA&AAbstract.Mechanismsin uencingabsorptionlinepro lesoffastrotatingstarscanbesortedintotwogroups;(i)intrinsicvariationssensitivetotemperatureandpressure,and(ii)globale ectscommontoallspectrallines.Ipresentadetailedstudyonthelattere ectsfocusingongravitydarkeningandinclinationforvariousrotationalvelocitiesandspectraltypes.Itisshownthatthelineshapesofrapidlyandrigidlyrotatingstarsmainlydependontheequatorialvelocityve,notontheprojectedrotationalvelocityvsiniwhichdeterminesthelineswidth.Thein uenceofgravitydarkeningandspectraltypeonthelinepro lesisshown.Theresultsdemonstratethepossibilityofdeterminingtheinclinationangleiofsinglefastrotators,andtheyshowthatconstraintsongravitydarkeningcanbedrawnforstellarsamples.Whilesigni cantlinepro ledeformationoccursinstarsrotatingas 1fastasve>~200kms,forslowerrotatorspro ledistortionsaremarginal.Inthesecasesspectralsignaturesinducedby,e.g.,di erentialrotationarenota ectedbygravitydarkeningandthemethodsapplicabletoslowrotatorscanbeappliedtothesefasterrotators,too1.IntroductionTheinformationcontainedinlinepro lesofrotatingstarshasbeenstudiedsincetherecognitionofspectralDopplerbroadeningitself.Themultitudeofdi erentmechanismsin uencinglinepro lespresentsaconfusingpictureforthepossibilityofdeterminingthem.Approximationsex-istforrotationallinebroadening,(linear)limbdarkening,di erentialrotation,turbulence,rotational atteningandgravitydarkening,etc..Whiledistinguishingtheseinter-actingmechanismsisadelicateissue,inthecaseofslow

rotators(vsini<50kms 1)rotational atteningand

gravitydarkeningcanbeneglected.UtilizingtheFourier

transformtechniqueGray(1973,1976)alsoshowedthat

turbulentvelocitiestosomeextentcanbedistinguished

fromrotation.

Infastrotatorsthesituationbecomesmorecomplex,

sincecentrifugalforcesdistortthesphericalshapeofthe

stellarsurfaceandthelinepro lesdependonthein-

clinationthestarisobservedunder.Beyondtheaddi-

tionaldegreeoffreedomthiswouldnotbeamajorprob-

lemiftemperature(andpressure)werenotconnected

togravity.Withdi erentregionsonthestellarsurface

havingsigni cantlydi erenttemperaturesandgaspres-

sures,linepro lesnolongercanbeapproximatedbycon-

volutionbetweenasingleintrinsiclinepro leandthe

rotationalbroadeningfunction.Forthisreason,theef-

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