Argon Abundances in the Solar Neighborhood: Non-LTE Analysis of Orion Association B-type Stars - AstrophysicsReport as inadecuate




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Abstract: Argon abundances have been derived for a sample of B main-sequence stars inthe Orion association. The abundance calculations are based on NLTE metalline-blanketed model atmospheres calculated with the NLTE code TLUSTY and anupdated and complete argon model atom. We derive an average argon abundance forthis young population of AAr = 6.66 +- 0.06. While our result is in excellentagreement with a recent analysis of the Orion nebula, it is significantlyhigher than the currently recommended solar value which is based on abundancemeasurements in the solar corona. Moreover, the derived argon abundances in theOrion B stars agree very well with a measurement from a solar impulsive flareduring which unmodified solar photospheric material was brought to flareconditions. We therefore argue that the argon abundances obtained independentlyfor both the Orion B stars and the Orion nebula are representative of the diskabundance value in the solar neighborhood. The lower coronal abundance mayreflect a depletion related to the FIP effect. We propose a new reference valuefor the abundance of argon in the solar neighborhood, AAr = 6.63 +- 0.10,corresponding to Ar-O = 0.009.



Author: Thierry Lanz U Maryland, Katia Cunha NOAO, Jon Holtzman New Mexico State U, Ivan Hubeny U Arizona

Source: https://arxiv.org/



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