The mass of the white dwarf in GW Libra

We report a mass and rotational broadening (v sin i) for the pulsating white dwarf (WD) component of the WZ Sge type Dwarf Nova GW Lib based on high-resolution Very Large Telescope spectroscopy that resolves the Mg II 4481 angstrom absorption feature. Its gravitational redshift combined with WD mass-radius models provides us with a direct measurement of the WD mass of M-1 = 0.84 +/- 0.02 M-circle dot. The line is clearly resolved and if associated with rotational broadening gives v sin i = 87.0 +/- 3.4 km s(-1), equivalent to a spin period of 97 +/- 12 s