The distribution of calcium on the surface of v epsilon Ursae Majoris: an abundance distribution Doppler image
Abstract
We present a surface abundance Doppler image of singly-ionized calcium for the Bp star epsilon 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 epsilon UMa. The calcium abundance map has been used to locate the position of the positive magnetic pole on epsilon 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 [Ca/H]=-5, which is close to a normal population I value. This represents an enhancement with respect to other regions by a factor of ~ 103. A secondary feature is present with [Ca/H]=-6.5. A chemically differentiated stellar wind is proposed as the main mechanism for generating the surface abundance distribution of calcium. Based on observations made at the Observatoire de Haute Provence (CNRS), and at the CFH Telescope, operated by the NRCC, the CNRS and the University of Hawaii. Tables 4-15 are available only in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr.(130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- December 2000
- Bibcode:
- 2000A&A...364..660H
- Keywords:
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- STARS: ABUNDANCES;
- STARS: CHEMICALLY PECULIAR;
- STARS: INDIVIDUAL: EPSILON UMA