We study the nature of the [TiII] and [NiII] emission from the so-called strontium filament found in the ejecta of eta Carinae. To this purpose we employ multilevel models of the TiII and NiII systems which are used to investigate the physical condition of
Mon.Not.R.Astron.Soc.000,()Printed5February2008
A(MNLTEXstyle lev1.4)
[Tiii]and[Niii]emissionfromthestrontium lamentof
ηCarinae
M.A.Bautista1,H.Hartman2,T.R.Gull3,N.Smith4,K.Lodders5
deF´ sica,IVIC,P.O.Box21827,Caracas1020A,VenezuelaObservatory,LundUniversity,Box43,SE-22100Lund,Sweden
3Code667,NASAGoddardSpaceFlightCenter,GreenbeltMD,USA
4CenterforAstrophysicsandSpaceAstronomy,UniversityofColorado,389UCB,Boulder,CO80309,USA
5PlanetaryChemistryLaboratory,Dept.ofEarthandPlanetarySciences,WashingtonUniversity,St.Louis,MO63130,USA
2Lund1Centro
arXiv:astro-ph/0606275v1 12 Jun 2006
ABSTRACT
Westudythenatureofthe[Tiii]and[Niii]emissionfromtheso-calledstrontium lamentfoundintheejectaofηCarinae.Tothispurposeweemploymultilevelmod-elsoftheTiiiandNiiisystemswhichareusedtoinvestigatethephysicalconditionofthe lamentandtheexcitationmechanismsoftheobservedlines.FortheTiiiion,forwhichnoatomicdatawaspreviouslyavailable,wecarryoutabinitiocalcu-lationsofradiativetransitionratesandelectronimpactexcitationratecoe cients.Itisfoundthattheobservedspectrumisconsistentwiththelinesbeingexcitedinamostlyneutralregionwithanelectrondensityoftheorderof107cm 3andatemper-aturearound6000K.Inanalyzingthreeobservationswithdi erentslitorientationsrecordedbetweenMarch2000andNovember2001we ndlineratiosthatchangeamongvariousobservations,inawayconsistentwithchangesofuptoanorderofmagnitudeinthestrengthofthecontinuumradiation eld.Thesechangesresultfromdi erentsamplingsoftheextended lament,duetothedi erentslitorientationsusedforeachobservation,andyieldcluesonthespatialextentandopticaldepthofthe lament.TheobservedemissionindicatesalargeTi/Niabundanceratiorelativetosolarabundances.ItissuggestedthattheobservedhighTi/Niratioingasiscausedbydust-gasfractionationprocessesanddoesnotre ecttheabsoluteTi/NiratiointheejectaofηCarinae.WestudythecondensationchemistryofTi,NiandFewithinthe lamentandsuggestthattheobservedgasphaseoverabundanceofTiislikelytheresultofselectivephoto-evaporationofTi-bearinggrains.Somemechanismsforsuchascenarioareproposed.
Keywords:atomicdata–atomicprocesses–line:formation–stars:abundances–stars:EtaCarinae
1INTRODUCTION
ηCarinaeisthemostluminousstarinourpartoftheGalaxyandindeedisoneofthemostmysteriousknowntous(Davidson&Humphreys1997).Itissurroundedbycom-plexejectacreatedinseveraloutburstsofthestarandanoutgoingmassivewindwithperiodiceventsevery5.54years(Damineli1996).Thelargestmassejectionoccurredduringtheso-calledGreatEruptionobservedinthe1840s–whichthestarsurvived.Inthatevent,ηCarinaereleasedabout1049.6ergsofkineticenergycontainedinmorethan10M⊙ofmaterial(Smithetal.2003),whichhassinceexpandedtoformthebipolarHomunculusnebulaweseetoday(Gaviola1950;Smith&Gehrz1998;Morseetal.2001).Despitethehotandveryluminouscentralstar,thecircumstellarneb-ulaiscoolenoughtoproducearemarkablyrichemission
cRAS
spectrumoflinesfromneutralandlowionizationspecies
likeFe+andNi+(Davidsonetal.2001;Zethson2001;Zeth-sonetal.2001),line-of-sightabsorptionfromseveralneutralandsinglyionizedatoms(Gulletal.2005),andevenemis-sionfromH2andverycooldust(Smith2002a;Smithetal.2003).Inadditiontobeingdenseandcool,theejectaofηCarinaearenitrogenrich,representingashesoftheCNOcycle(Davidsonetal.1982,1986;Smith&Morse2004;Verneretal.2005).Itisthehighdensity,low-excitation,andCNOabundancesoftheejectathatmaketheHomunculusauniquelaboratoryamongcircumstellarnebulae,havingaprofounde ectontheresultsdiscussedinthispaper.InFebruary1999aseriesofSTISobservationsofηCari-naewasmadeofaregionabout1.5”northwestofthestar(Zethsonetal.2001).Thespectrumfromthisregionwassigni cantlydi erentfromthenebularemissionspectra
Cleaning up Eta Carinae Detection of Ammonia in the Homunculus We report ...We also detect ammonia emission from the so-called “strontium ?lament” ...
Cleaning up Eta Carinae Detection of Ammonia in the Homunculus We report ...We also detect ammonia emission from the so-called “strontium ?lament” ...
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