2010MNRAS.403..324B

We report the discovery of a large-amplitude oscillation in the hot subdwarf B star CS 1246 and present multicolour photometry and time-resolved spectroscopy supporting this discovery. We used the 0.41-m Panchromatic Robotic Optical Monitoring and Polarimetry Telescopes array to acquire data in the u', g', r' and i' filters simultaneously over three consecutive nights in 2009 April. These data reveal a single oscillation mode with a period of 371.707±0.002s and an amplitude dependent upon wavelength, with a value of 34.5±1.6mma in the u' filter. We detected no additional frequencies in any of the light curves. Subsequently, we used the 4.1-m SOAR telescope to acquire a time-series of 248 low-resolution spectra spanning 6h to look for line profile variations. Models fits to the spectra give mean atmospheric values of T_eff= 28450±700K and logg = 5.46 ± 0.11 undergoing variations with semi-amplitudes of 507±55K and 0.034 ± 0.009, respectively. We also detect a radial velocity oscillation with an amplitude of 8.8±1.1km/s. The relationship between the angular and physical radii variations shows that the oscillation is consistent with a radial mode. Under the assumption of a radial pulsation, we compute the stellar distance, radius and mass as d = 460±¹⁹⁰₉₀pc, R = 0.19±0.08R_☉ and M = 0.39±^0.30_0.13M_☉, respectively, using the Baade-Wesselink method.