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Astron. Astrophys. 319, 630-636 (1997)


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Abundance analysis of roAp stars

II. HD 203932 *

M. Gelbmann 1, F. Kupka 1, W.W. Weiss 1 and G. Mathys 2

1 Inst. of Astronomy, Univ. Vienna, Türkenschanzstr. 17, A-1180 Vienna, Austria (last_name@galileo.ast.univie.ac.at)
2 European Southern Observatory, Santiago, Chile

Received 3 May 1996 / Accepted 20 August 1996

Abstract

A new tool to simplify abundance analyses which is based on stand-alone programs has been applied to the rapidly oscillating Ap star HD 203932 (BI Mic, CD [FORMULA], SAO 212996; Ap(SrEu), [FORMULA] mag). The spectroscopically determined [FORMULA] = 7450 [FORMULA] 100 K and [FORMULA] = 4.3 [FORMULA] 0.15 put this star close to the ZAMS. Other fundamental atmospheric parameters are [FORMULA] [FORMULA] 0.6 km s-1 and the total abundance of all iron peak elements [M/H] = 0.0 [FORMULA] 0.1.

The fundamental parameters put HD 203932 in a region of the HR-diagram where convection starts becoming efficient and the standard mixing length theory models lead to severe problems in the determination of the atmospheric parameters. The difference between the upper limit for [FORMULA] obtained from several variants of the mixing length theory and the Canuto-Mazzitelli model indicates that the choice of a particular convection model can influence the determination of basic stellar parameters.

For the first time abundances were determined for HD 203932 showing a pattern for the 35 investigated elements which is similar to [FORMULA] Cir (Kupka et al. 1996, {1). Fe and Ni have about solar abundance, Cr and especially Co are clearly overabundant as well as rare earth elements. The most underabundant element is Sc, followed by C, N, and O, which is a common property of CP2 stars. The lack of a correlation in our data between individual line abundances and their effective Landé factors implies a mean magnetic field modulus not exceeding few kG.

Compared to the last homogeneous spectroscopic investigation of a large sample of chemically peculiar stars (21 cool Ap stars, Adelman 1973), our analysis is based on data with higher spectral resolution and signal-to-noise ratio. Even more important, we are using a much larger atomic line data base with more precise atomic parameters than available more than twenty years ago.

Key words: stars: abundances; atmospheres; chemically peculiar; magnetic fields; oscillations; HD 203932

* Based on observations obtained at the European Southern Observatory (La Silla, Chile)

Send offprint requests to: Michael Gelbmann

© European Southern Observatory (ESO) 1997

Online publication: July 3, 1998

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