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The distribution of oxygen on the surface of the Ap starθ Aur

An abundance Doppler image to compare withϵ UMa

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 starθ 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 starϵ UMa, where the oxygen displayed undepleted solar abundance in a band around the magnetic equator, forθ 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 forθ 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 ([CITE]). A striking asymmetry is apparent in the contrasting behaviour of the oxygen and chromium abundance pattern at the two magnetic poles.