3.5 hour periodic variability of WR66 (HD 134877, WN8): the first example of non-radial pulsations among Wolf-Rayet stars?

Extract

We report a first result from an extensive observing campaign for the WN8 star WR66 (HD 134877). We obtained 219 photometric observations of WR66 in a standard broadband V-filter during 61 nights, distributed in a T = 83^d interval. Details of observations and data reduction can be found in Antokhin et al. (1994). The power spectra of WR66-C1, WR66-C2 and C2-C1 are shown in Fig.1. Both the WR66-C1 and WR66-C2 spectra clearly show high frequency components. The overall structure of the peaks is evidently determined by 1-day aliasing. The highest peak in both spectra has frequency v₁ = 6.828 d⁻¹ (period P = 3^h.51). Inspection of the power spectra shows that C1 is a low-amplitude variable, but luckily at low frequencies only. We conclude that WR66 is significantly variable with a period of 3^h.5. A phase plot of the data (WR-C2 and C2-C1) with this frequency is shown in Fig.2. Plausible scenarios which could potentially account for the observed variability are: (i) non-radial pulsations (NRP); (ii) rotational light-modulation by spots or (magnetic) loops at the stellar surface; (iii) spiral-in system (WR+c), like the massive X-ray binary Cyg X-3 (van Kerkwijk 1993).