Letter to the Editor

The calcium isotopic anomaly in magnetic CP stars^*

¹ Department of Astronomy, University of Michigan, Ann Arbor, MI 48109-1090, USA e-mail: cowley@umich.edu
² European Southern Observatory, Casilla 19001, Santiago 19, Chile e-mail: shubrig@eso.org

Received: 20 December 2004
Accepted: 26 January 2005

Abstract

Chemically peculiar stars in the magnetic sequence can show the same isotopic anomaly in calcium previously discovered for mercury-manganese stars in the non-magnetic sequence. In extreme cases, the dominant isotope is the exotic ⁴⁸Ca. Measurements of lines arising from 3d-4p transitions reveal the anomaly by showing shifts up to 0.2 Å for the extreme cases – too large to be measurement errors. We report measurements of miscellaneous objects, including two metal-poor stars, two apparently normal F-stars, an Am-star, and the N-star U Ant. Demonstrable anomalies are apparent only for the Ap stars. The largest shifts are found in rapidly oscillating Ap stars and in one weakly magnetic Ap star, HD 133792. We note the possible relevance of these shifts for the GAIA mission.