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Issue A&A
Volume 424, Number 1, September II 2004
Page(s) 237 - 244
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20035639



A&A 424, 237-244 (2004)
DOI: 10.1051/0004-6361:20035639

The distribution of oxygen on the surface of the Ap star $\theta$ Aur

An abundance Doppler image to compare with $\epsilon$ UMa
J. B. Rice1, D. E. Holmgren2 and D. A. Bohlender3

1  Department of Physics and Astronomy, Brandon University, Brandon, MB, R7A 6A9 Canada
    e-mail: rice@brandonu.ca
2  SMART Technologies Inc., Bay 8, 1460-26th Street NE, Calgary, AB T2A 7W6, Canada
    e-mail: DavidHolmgren@smarttech.com
3  Herzberg Institute of Astrophysics, National Research Council of Canada, 5071 West Saanich Road, Victoria, BC, V9E 2E7, Canada
    e-mail: david.bohlender@nrc-cnrc.gc.ca

(Received 6 November 2003 / Accepted 23 May 2004)

Abstract
We present a Doppler Image of the oxygen abundance distribution over the surface of the star $\theta$ Aur. The symmetry of the oxygen distribution appears to be consistent with the magnetic field observations such that the oxygen is highly depleted at the magnetic poles. In contrast to the star $\epsilon$ UMa, where the oxygen displayed undepleted solar abundance in a band around the magnetic equator, for $\theta$ Aur the instances of more normal solar levels of abundance occur in bands midway between the magnetic poles and the magnetic equator. The oxygen abundance at the magnetic equator is only mildly depleted for $\theta$ Aur. It is suggested that the oxygen abundance distribution is consistent with a global field that has a strong quadrupolar component. A detailed comparison is made between the oxygen abundance distribution and that of the distribution of chromium as mapped by Hatzes (1991a). A striking asymmetry is apparent in the contrasting behaviour of the oxygen and chromium abundance pattern at the two magnetic poles.


Key words: stars: chemically peculiar

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© ESO 2004

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