WZ Cas – variability on multiple time-scales

¹ Institute for Astronomy (IfA), University of Vienna, Türkenschanzstrasse 17, 1180 Vienna, Austria e-mail: lebzelter@astro.univie.ac.at
² The Observatories, Madingley Road, Cambridge CB3 0HA, UK
³ National Optical Astronomy Observatory, PO Box 26732, Tucson, AZ 85726, USA

Received: 16 March 2005
Accepted: 23 May 2005

Abstract

We present results on our long-term velocity monitoring of the C-rich semi-regular variable WZ Cas with a Coravel instrument. Our findings are compared with light changes of the star. We suggest that the two main periods, 366 and 186 d, are due to radial pulsation. Furthermore, we find an interesting variation of the width and depth of the cross-correlation profile over a time-scale of at least 1000 d. Several possible explanations for this behaviour are discussed by comparison of time-scales and expected variability amplitudes. The influence of movements of large convective cells on the line profiles seems to be the most likely explanation of some of the observed phenomena.