Oxygen 6156a€“8 ?… Triplet in Chemically Peculiar Stars of t he Upper Main Sequence: Do HgMn Stars Show an Oxygen Anomaly?

摘要

Anextensivespectrum-fittinganalysisinthe??a??6150?…regionwasperformedforfortylate-BandAchemicallypeculiar(HgMn,Ap,Am,weak-lined)andnormalstarsoftheuppermainsequence,inordertoquantitativelyestablishtheabundanceofoxygenfromtheOI6156-8tripletandtostudyitsbehavior/anomalyforeachpeculiaritygroup,wherespecialattentionwaspaidtoHgMn-typestars.MagneticApvariables(SiorSrCrEutype)generallyshowaremarkablylargeoxygendepletion(bya??a?’1.6dextoa??a?’0.4dexrelativetothesolarabundance),andclassicalAmstarsalsoshowaclearunderabundance(bya??a?’0.6dexontheaverage).Incontrast,theoxygenabundanceinHgMnstars,exhibitingonlyamilddeficiencyrelativetotheSuntypicallybya??0.3a?’0.4dex,isnotmarkedlydifferentfromthetendencyofnormalstars,alsoshowingasubsolarabundance([O/H]a??a?’0.2).Inviewoftherecentobservationalimplicationthatthepresentsolaroxygenabundanceisenrichedbya??0.2a?’0.3dexrelativetotheinterstellargas(fromwhichyoungstarsareformed),andthusunsuitableforthecomparisonstandard,weconcludedthattheextentoftheaverageO-deficiencyinHgMnstarsisappreciablyreduceddowntoonlya??0.1a?’0.2dex(i.e.,notmuchdifferentfromtheinitialcomposition),whichcontrastswiththeirwell-knowndrasticallylargeN-depletion.Yet,ascanbeseenfromthedelicateandtightOvs.Feanticorrelation,thismarginaldeficiencyshouldbereal,andthussomephysicalprocesssimultaneouslyproducingO-depletion/Fe-enrichmentmusthaveactuallyworkedintheatmosphereofHgMnstars.