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

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 perha ps iron (Rice & Wehlau 1990). The Ca II 866.2 nm line has allowed us to obt ain a detailed surface abundance map of calcium for epsilon UMa. The calciu m abundance map has been used to locate the position of the positive magnet ic pole on epsilon UMa at a longitude of 350.8 deg and a latitude of 25.8 d eg. Calcium is distributed in a ring along the magnetic equator, along whic h the abundance is [Ca/H] = -5, which is close to a normal population I val ue. This represents an enhancement with respect to other regions by a facto r of similar to 10(3). A secondary feature is present with [Ca/H] = -6.5. A chemically differentiated stellar wind is proposed as the main mechanism f or generating the surface abundance distribution of calcium.