Parent Stars of Extrasolar Planets. VIII. Chemical Abundances for 18 Elements in 31 Stars

Mon.Not.R.Astron.Soc.000,1–7(??)Printed5February2008(MNLATEXstylefilev2.2)

ParentStarsofExtrasolarPlanets.VIII.ChemicalAbundancesfor18Elementsin31StarsGuillermoGonzalez1󰀁,ChrisLaws21IowaStateUniversity,DepartmentofPhysicsandAstronomy,Ames,IA500112DepartmentofAstronomy,UniversityofWashington,Box351580,Seattle,WA98195

Accepted??.Received??;inoriginalform??

ABSTRACT

Wepresenttheresultsofdetailedspectroscopicabundanceanalysesfor18elements

in31nearbystarswithplanets.Theresultingabundancesarecombinedwithother

similarstudiesofnearbystarswithplanetsandcomparedtoasampleofnearbystars

withoutdetectedplanets.Wefindsomeevidenceforabundancedifferencesbetween

thesetwosamplesforAl,SiandTi.Someofourresultsareinconflictwitharecent

studyofstarswithplanetsintheSPOCSdatabase.Weencouragecontinuedstudyof

theabundancepatternsofstarswithplanetstoresolvethesediscrepancies.

1INTRODUCTION

Thepresentstudycontinuesourseriesonthechemicalabun-

dancesofnearbystarswithplanets(SWPs);forasummary

ofpreviouspapersintheseries,seeLawsetal.(2003).To

date,theonlywell-establishedchemicalabundanceanomaly

amongSWPsisthedependenceoftheincidenceofgiant

planetsonthehoststar’smetallicity(Fischer&Valenti

2005;Santosetal.2005).

Lessconclusivehasbeenevidencefordifferencesinthe

chemicalabundancepatternsbetweenSWPsandstarswith-

outknownplanets.Severalrecentstudieshavepresentedthe

resultsofextensiveabundanceanalysesofSWPs(Bondet

al.(2006);Ecuvillonetal.(2006);Gillietal.(2006);Gon-

zalezetal.(2001);Luck&Heiter(2006);Robinsonetal.

(2006);Takeda&Honda(2005)),buttheresultsofthese

studiesarenotentirelyconsistentwitheachother.Forex-

ample,Robinsonetal.(2006)reportedstatisticallysignif-

icantdifferencesbetweenSWPsandacomparisonsample

forSi/FeandNi/Feabundanceratios.Otherstudieshave

reported,instead,differencesforLi,Na,MgandAl.

TheobservedcompositionaldifferencesbetweenSWPs

andcomparisonstarshavebeendiscussedwithinthecontext

ofthreeclassesofexplanation(Gonzalez2006b):primor-

dial,orbitalperiodbiasandself-enrichment.Theprimor-

dialexplanationbestaccountsforthedata,buttheother

twoexplanationscannotyetbeeliminated.Discoveryof

additionalabundanceanomaliesamongSWPswouldhelp

ustestthesethreeexplanationsmorecriticallyandallow

ustodeterminetheirrelativecontributions.Theresultsof

thesetests,inturn,willallowustosettighterconstraints

onplanetformationmodels.Forexample,Ida&Lin(2005)

havereproducedtheobservedmetallicitydependenceofgi-

antplanetincidenceassumingthecoreinstabilityaccretion

modelofplanetformation.

Inthepresentworkweemploythestellaratmospheric

parameterspresentedinLawsetal.(2003)for31SWPsto

determine[el/H]valuesfor18elements:Li,C,N,O,Na,Mg,Al,Si,S,Ca,Sc,Ti,Cr,Mn,Ni,Cu,ZnandEu.Since

mostoftheseelementshavebeenstudiedinSWPsbyoth-

ers,wecancompareourresultstopublisheddatatocheck

forconsistency.Moreimportantly,sincethelistsofSWPs

includedinthepublishedspectroscopicstudieshaveconsid-

erableoverlapwitheachotherandwiththepresentwork,

wecanproduceanew,improveddatabaseofSWPabun-

dancesbycorrectingforsystematicabundancedifferences.

Wecandothesameforpublisheddataoncomparisonstars.

Inthisway,weprovidemoresensitivetestsoftheclaimed

abundancedifferencesbetweenSWPsandcontrolsamples.

2ABUNDANCEANALYSISANDRESULTS

2.1SampleandAnalysis

Wefocusonthe31SWPsexaminedinLawsetal.(2003)

(here,wearenowincludingHD202206amongsttheSWP

sampleforcomparisonpurposesinthispaper).Wemeasured

equivalentwidths(EWs)foratomiclinesofC,N,O,Na,Mg,

Al,Si,S,Ca,Sc,Ti,Cr,Ni,ZnandEu.Wethenusedthese

EWsvaluesandthevaluesofTeff,logg,ξt,and[Fe/H]for

eachstargiveninLawsetal.(2003)andtheKurucz(1993)

LTEplane-parallelmodelatmospheresasinputtotheline

analysiscodeMOOG(Sneden(1973),updatedversion)to

determinetheelementalabundances.Thisisthesamecode

wehaveusedinourpreviouspapersinthisseries.

Detailsofourmethodofanalysis,includingdetermina-

tionoftheuncertaintiesoftheatmosphericparametersand

abundances,aredescribedinGonzalez(1998)andGonza-

lez&Vanture(1998).Inbrief,foreachstarwedetermined

thefourbasicatmosphericparametersandtheiruncertain-

tiesfromthemeasuredFeIandFeIIEWsandassuming

excitationandionizationequilibrium.Wethenpropagated

theseuncertaintiesinourcalculationoftheuncertainties

oftheabundancesoftheotherelements.Theexceptionsto

thisprocedurewereabundancesdeterminedfromspectrumarXiv:0704.2220v1 [astro-ph] 17 Apr 20072G.Gonzalez1.0

0.9

0.8

0.7

0.6

0.5

0.4Relative Intensity

60146013601260116010600960086007Wavelength (Å)Mn IFe IFe INi I

b)1.0

0.9

0.8

0.7

0.6

0.5

0.4Relative Intensity

5786578557845783578257815780Wavelength (Å)Cu ICr I

Cr IFe ICr I

Fe I

a)

Figure1.SamplesynthesesofthespectralregionsinHD82943

containingtheCuI(panela)andMnI(panelb)absorptionlines

usedinthepresentwork.Theobservedspectraareshownas

solidcurves,andthesynthesesareshownasdottedcurves.Three