Spectroscopy of the post-common envelope binary HW Virginis

• Published in: Monthly notices of the Royal Astronomical Society 1999-06, Vol.305 (4), p.820-828
• Main Authors: Wood, Janet H., Saffer, R.
• Format: Article
• Language: English
• Subjects: binaries: eclipsing; stars: individual: HW Vir; subdwarfs
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1046/j.1365-8711.1999.02501.x

We present optical spectroscopy of the post-common envelope binary HW Vir covering λ = 3704 – 8667 Å. We use the low-resolution blue spectra to determine the atmospheric parameters of the sdB primary star and the medium resolution Hα observations to measure its radial velocity. We find K1= 82.3 ± 4.0 km s−1 and γ = 2.9 ± 3.1 km s−1. The effective temperature, gravity and helium abundance of the sdB star are Te= 28488 ± 208 K, log g = 5.63 ± 0.03 and N(He)/N(H) = 0.0066 ± 0.0004. These characteristics are typical of a classical sdB star, as is our derived mass of M1 = 0.48 ± 0.09 M⊙. We find the distance to HW Vir is 171 ± 19 pc. The predicted value of the projected orbital velocity of the secondary star is 284 ± 21 km s−1. Using previously published photometric light curves of HW Vir we corrected our spectra to absolute fluxes and extracted the spectrum of the secondary star. This spectrum shows Hα absorption lines at phases close to the maximum of the reflection effect, with a measured radial velocity semi-amplitude of 275±15 km s−1. We attribute these lines to irradiation of the face of the secondary star closest to the sdB star.