The enigmatic WR46: A binary or a pulsator in disguise

III. Interpretation

¹ Leiden Observatory, Postbus 9513, 2300 RA Leiden, The Netherlands
² Space Research Organization Netherlands, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands

Corresponding author: A. M. van Genderen, genderen@strw.leidenuniv.nl

Received: 1 September 2000
Accepted: 5 November 2001

Abstract

Photometric and spectroscopic monitoring campaigns of WR 46 (WN3p), as presented in Veen et al. (2002a,b; hereafter Papers I and II, respectively), yield the following results. The light- and colour variations reveal a dominant single-wave period of d in 1989, and d in 1991. Because of a small difference in the minima, this periodicity may be a double-wave phenomenon (P_dw). The line fluxes vary in concert with the magnitudes. The significant difference of the periods can be either due to the occurence of two distinct periods, or due to a gradual change of the periodicity. A gradual brightening of the system of 012 appeared to accompany the period change. In addition, the light variations in 1989 show strong evidence for an additional period d. Generally, the radial velocities show a cyclic variability on a time scale of the photometric double-wave. However, often they do not vary at all. The observed variability confirms the Population I WR nature of the light source, as noted independently by Marchenko et al. (2000). In the present paper, we first show how the photometric double-wave variability can be interpreted as a rotating ellipsoidal density distribution in the stellar wind. Subsequently, we discuss what mechanisms could drive such a configuration. First, stellar rotation of a single star is discarded as a likely cause. Second, the obvious interpretation of the double-wave photometry, i.e., a close binary system, is investigated. However unlikely, we discuss how the observed period change might be reconciled within a model of a strongly interacting binary. Third, an interpretation of a non-radial multi-mode pulsator is investigated. The observed period change and the multi-frequency behaviour do support this interpretation. We propose that the pulsational mode and may mimic a “binary” light- and radial-velocity curve. However, the phasing of the radial velocity and the light curve may be inconsistent. The possibility and is also discussed. Finally, we suggest how the enigma of the variability of WR 46 may be solved.