We present a study of optical spectra of the Wolf--Rayet star AzV 336a (= SMC WR7) in the Small Magellanic Cloud. Our study is based on data obtained at several Observatories between 1988 and 2001. We find SMC WR7 to be a double lined WN+O6 spectroscopic binary with an orbital period of 19.56 days. The radial velocities of the He absorption lines of the O6 component and the strong He{\sc ii} emission at λ4686\AA of the WN component describe antiphased orbital motions. However, they show a small phase shift of ∼ 1 day. We discuss possible explanations for this phase shift. The amplitude of the radial velocity variations of He {\sc ii} emission is twice that of the absorption lines. The binary components have fairly high minimum masses, ∼ 18 \modot and 34 \modot for the WN and O6 components, respectively.
@article{arxiv.astro-ph/0202203,
title = {The Massive Wolf-Rayet Binary SMC WR7},
author = {V. S. Niemela and P. Massey and G. Testor and S. Gimenez Benitez},
journal= {arXiv preprint arXiv:astro-ph/0202203},
year = {2009}
}