The pulsating hydrogen-deficient star LSS 3184 (BX Cir)

We present extensive photometry and spectroscopy of the extremely hydrogen- deficient star, LSS 3184, recently discovered to be a rapid variable (perio d similar to 0.1066 d) strikingly similar to V652 Her. Over 95 h of photome try confirms the reported variability, which is of rather low amplitude (De lta V similar to 0.03 mag), defines the light curve with greater precision and establishes a much more accurate ephemeris (period similar to 0.106 578 4 d) to form a basis for detecting period change. Attention is drawn to th e usefulness of a period-finding technique that fits harmonic components to the photometric observations. Spectroscopy shows a peak-to-peak variation in radial velocity of about 30 km s(-1), which, when combined with the phot ometric observations, confirms the pulsational nature of the variability an d strongly indicates that the pulsations are radial in nature.