Physical properties of the pulsating hydrogen-deficient star LSS 3184 (BX Cir)

We report new determinations of the radius and mass of the pulsating helium-rich, hydrogen-deficient star LSS 3184 (BX Cir) using measurements of radial velocity and angular radius throughout its pulsation cycle. Measurements of radial velocity, and thus changes in stellar radius, were made using Anglo-Australian Telescope echelle spectra. Hubble Space Telescope ultraviolet spectra and ground-based BV photometry were used to find temperatures and fluxes throughout the pulsation cycle. The temperatures and fluxes were used to find the angular radius of the star (alpha). The alpha, Delta-alpha and Delta-radius values thus found were used to calculate the mean stellar radius <R_star> = 2.31 +/- 0.10 R_sun. If we use the previously determined logg = 3.35 +/- 0.1 for LSS 3184 and our radius estimate, we find its mass to be M_star = 0.42 +/- 0.12 M_sun.