The distribution of calcium on the surface of Ursae Majoris: an abundance distribution Doppler image
D.E. Holmgren and
Received 19 July 2000 / Accepted 8 September 2000
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
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© European Southern Observatory (ESO) 2000
Online publication: January 29, 2001