WR 7a: a V Sagittae or a qWR star?

The star WR 7a, also known as SPH 2, has a spectrum that resembles that of V Sagittae stars although no OVI emission has been reported. The Temporal Variance Spectrum - TVS - analysis of our data shows weak but strongly variable emission of OVI lines which is below the noise level in the intensity spectrum.

Contrary to what is seen in V Sagittae stars, optical photometric monitoring shows very little, if any, flickering. We found evidence of periodic variability. The most likely photometric period is P_phot= 0.227(+/-14) d, while radial velocities suggest a period of P_spec= 0.204(+/-13) d. One-day aliases of these periods can not be ruled out. We call attention to similarities with HD 45166 and DI Cru (= WR 46), where multiple periods are present. They may be associated to the binary motion or to non-radial oscillations.

In contrast to a previous conclusion by Pereira et al., we show that WR 7a contains hydrogen. The spectrum of the primary star seems to be detectable as the NV 4604Åabsorption line is visible. If so, it means that the wind is optically thin in the continuum and that it is likely to be a helium main sequence star.

Given the similarity to HD 45166, we suggests that WR 7a may be a qWR - quasi Wolf-Rayet - star. Its classification is WN4h/CE in the Smith, Shara & Moffat three-dimensional classification system.