Astronomy Astrophysics The enigmatic WR46: A binary or a pulsator in disguise? I. The photometry

Abstract. We discuss the observational history of the Wolf-Rayet object WR 46 (WN3p), including a re-investigation of the original discovery plates from early this century. We nd that the reported presence of N iii lines is a mis-interpretation of N v lines and conclude that the object did not change its spectral type since the rst recording one century ago. We performed photometric monitoring in the period 1986{1999, and conrm that the object shows cyclical variability on a time scale of hours. The shape of the light curves varies from purely sinusoidal to irregular, and from an amplitude of nearly 0:m1 to constancy. In addition, night-to-night variability of the mean brightness causes folded light curves to display a large scatter. We investigate the frequency behaviour of the photometric data. From the periodograms of our two large data sets, in 1989 and in 1991, we identify frequencies of signicantly dierent values 7.08 cd−1 and 7.34 cd−1, respectively. Moreover, the 1989 data show strong evidence for an additional frequency fx = 4:34 cd −1. The periodograms of our eight smaller data sets show more ambiguous behaviour. We discuss whether these latter data show evidence for multi-frequency behaviour, or whether they can be reconciled with a single clock with a changing clock-rate. As pointed out by van Genderen et al. (1991), if the data are folded using twice the single-wave period, the light curves appear ellipsoidal with unequal minima. Although the dierence in depth of the minima is hardly signicant, it does occur in both larg