Properties and nature of Be stars ^*,**

26. Long-term and orbital changes of ζ Tauri

¹ Hvar Observatory, Faculty of Geodesy, University of Zagreb, 10000 Zagreb, Croatia e-mail: rdomagoj@geof.hr
² Astronomical Institute of the Charles University, Faculty of Mathematics and Physics, V Holešovičkách 2, 180 00 Praha 8, Czech Republic
³ Mathematical Institute, University of Bayreuth, 95447 Bayreuth, Germany
⁴ Ritter Observatory, MS 113, Department of Physics and Astronomy, University of Toledo, OH 43606, USA
⁵ Center for High Angular Resolution Astronomy, Department of Physics and Astronomy, Georgia State University, PO Box 4106, Atlanta, GA 30302-4106, USA
⁶ Department of Physics and Astronomy, George Mason University, Fairfax, Virginia 22030, USA
⁷ Astronomical Institute of the Academy of Sciences, 251 65 Ondřejov, Czech Republic
⁸ Department of Astronomy, University of Virginia, PO Box 400325, Charlottesville, VA 22904-4325, USA
⁹ Physics & Astronomy Department, University of Victoria, PO Box 3055 STN CSC, Victoria, BC, V8W 3P6, Canada

Received: 4 July 2008
Accepted: 24 August 2009

Abstract

Context. One way to understand the still mysterious Be phenomenon is to study the time variations of particular Be stars with a long observational history. ζ Tau is one obvious candidate.

Aims. Using our rich series of spectral and photometric observations and a critical compilation of available radial velocities, spectrophotometry of Hα, and  photometry, we characterize the pattern of time variations of ζ Tau over about a century. Our goal is to find the true timescales of its variability and confront them with the existing models related to various aspects of the Be phenomenon.

Methods. Spectral reductions were carried out using the IRAF and SPEFO programs. The HEC22 program was used for both photometric reductions and transformations to . Orbital solutions were derived with the latest publicly available version of the program FOTEL, period analyses employed both the PDM and Fourier techniques – programs HEC27 and PERIOD04.

Results. We derived a new orbital ephemeris  HJD (2447025.6±1.8) + (132987 ±0050) . The analysis of long-term spectral and light variations shows a clear correlation between the RV and changes, and a very complex behaviour of the light changes. The character of the orbital light and changes varies from season to season.