P65	April 2001

¹ Institut d'Astrophysique et de Géophysique - Université de Liège, Avenue de Cointe 5, 4000 Liège, Belgium

^* Research Fellow FNRS, Belgium
^** Postdoctoral Researcher FNRS, Belgium

⁺ Based on observations collected at the Observatoire de Haute-Provence (France)

Abstract

     Since the beginning of the past century, the nature of HD108 has been a subject of intense debate. One after another, astronomers explored its variability and attributed it either to binarity, or to changes in the stellar wind of a single star. In this article, we analyse a 30 years long campaign of spectroscopic observations of this star with special emphasis on the last 15 years during which photographic plates have been replaced by CCD detectors. Our investigation of the radial velocities of HD108 yields no significant short- or long-term period and does not confirm the published periodicities either. Though the radial velocity of HD108 appears clearly variable, the variations cannot be explained by the orbital motion in a spectroscopic binary. However, our data reveal spectacular changes in the H I Balmer lines and some He I profiles over the years. These lines continuously evolved from P Cygni profiles to 'pure' absorption lines. A similar behaviour was already observed in the past, suggesting that these changes are recurrent. HD108 seems to share several characteristics of Oe stars and we discuss different hypotheses for the origin of the observed long-term variations. As we are now in a transition period, a continuous monitoring of HD108 should be considered for the next few years.