The core-wing anomaly of cool Ap stars^*

Abnormal Balmer Profiles

¹ Department of Astronomy, University of Michigan, David Dennison Building, Ann Arbor, Michigan 48109-1090, USA
² Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany e-mail: shubrig@aip.de
³ Institute of Astronomy, Russian Academy of Sciences, Pyatnitskaya 48, 109017 Moscow, Russia e-mail: ryabchik@inasan.rssi.ru
⁴ Institute for Astronomy, University of Vienna, Türkenschanzstrasse 17, 1180 Vienna Austria e-mail: mittermayer@astro.univie.ac.at
⁵ European Southern Observatory, Casilla 19001, Santiago 19, Chile e-mail: gmathys@eso.org
⁶ Uppsala Astronomical Observatory, Box 515, 751, 20 Uppsala, Sweden e-mail: piskunov@astro.uu.se

Corresponding author: C. R. Cowley, cowley@umich.edu

Received: 5 December 2000
Accepted: 15 December 2000

Abstract

The profiles of Hα in a number of cool Ap stars are anomalous. Broad wings, indicative of temperatures in the range 7000-8000 K end abruptly in narrow cores. The widths of these cores are compatible with those of dwarfs with temperatures of 6000 K or lower. This profile has been known for Przybylski's star, but it is seen in other cool Ap stars. The Hβ profile in several of these stars shows a similar core-wing anomaly (CWA). In Przybylski's star, the CWA is probably present at higher Balmer members. We are unable to account for these profiles within the context of LTE and normal dwarf atmospheres. We conclude that the atmospheres of these stars are not "normal". This is contrary to a notion that has long been held.