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

Abstract

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 (Delta R_star ), 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 R 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 log g = 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. Based on observations obtained with the NASA/ESA Hubble Space Telescope, which is operated by STScI for the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. Based on observations obtained at the Anglo-Australian Telescope, Coonabarabran, NSW, Australia