Two-site Photometry and Spectroscopy of the Rapidly Pulsating sdB Star EC 22221-3152

Abstract

We present follow-up photometry and spectroscopy of the rapidly pulsating subdwarf B star EC 22221-3152. Using the SAAO 1.0-m telescope and the 0.4-m Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes (PROMPT) at the Cerro Tololo Inter-American Observatory (CTIO), we monitored the star photometrically for one week. By combining data from both telescopes, we were able to resolve 18 significant periodicities in the light curve. Seven of these signals consist of combination frequencies, a first harmonic, and possible rotational splittings that would be indicative of an 8.2-d rotation period. The remaining 11 periodicities appear to represent independent oscillation modes, including three not originally detected in the discovery work. Time series spectroscopy obtained with the Goodman spectrograph on the 4.1-m SOAR telescope reveals possible velocity variations corresponding to two of the observed pulsation modes. From atmospheric model fits to the spectra, we derive K, log g = 5.86 ± 0.15, and log N(He)/N(H) = −1.4 ± 0.3 and confirm the star's status as one of the hottest sdBVr stars currently known.