What is the real nature of HD108?

Since the beginning of the past century, the nature of HD108 has been a sub ject of intense debate. One after another, astronomers explored its variabi lity and attributed it either to binarity, or to changes in the stellar win d of a single star. In this article, we analyse a 30 year campaign of spect roscopic observations of this star with special emphasis on the last 15 yea rs during which photographic plates have been replaced by CCD detectors. Ou r investigation of the radial velocities of HD108 yields no significant sho rt- or long-term period and does not confirm the published periodicities ei ther. Though the radial velocity of HD108 appears clearly variable, the var iations 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 has already been observed in the past, suggesting that these changes are recurrent. HD1 08 seems to share several characteristics of Oe stars and we discuss differ ent hypotheses for the origin of the observed long-term variations. As we a re now in a transition period, a continuous monitoring of HD108 should be c onsidered for the next few years.