Astron. Astrophys. 364, 660-664 (2000)

The distribution of calcium on the surface of Ursae Majoris: an abundance distribution Doppler image

D.E. Holmgren and J.B. Rice

Brandon University, Department of Physics & Astronomy, Brandon, Manitoba, R7A 6A9 Canada (holmgren,rice@brandonu.ca)

Received 19 July 2000 / Accepted 8 September 2000

Abstract

We present a surface abundance Doppler image of singly-ionized calcium for the Bp star UMa based on high signal-to-noise CCD spectra. This map shows striking similarities to that of oxygen (Rice et al. 1997) and perhaps iron (Rice & Wehlau 1990). The Ca II 866.2 nm line has allowed us to obtain a detailed surface abundance map of calcium for UMa. The calcium abundance map has been used to locate the position of the positive magnetic pole on UMa at a longitude of 350.8 deg and a latitude of 25.8 deg. Calcium is distributed in a ring along the magnetic equator, along which the abundance is , which is close to a normal population I value. This represents an enhancement with respect to other regions by a factor of . A secondary feature is present with . A chemically differentiated stellar wind is proposed as the main mechanism for generating the surface abundance distribution of calcium.

Key words: stars: abundances stars: chemically peculiar stars: individual: ffl UMa

Send offprint requests to: D.E. Holmgren

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Contents

• 1. Introduction
• 2. Observations and reductions
  • 2.1. Extraction of the Ca II 866.2 nm line
• 3. Doppler imaging
• 4. The Doppler image
  • 4.1. Location of the axis of symmetry
• 5. Interpretation of the Doppler image
• 6. Summary
• Acknowledgements
• References

© European Southern Observatory (ESO) 2000

Online publication: January 29, 2001
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