  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.

Astrophysics