Time-series Spectroscopy of Pulsating sdB Stars II: Velocity Analysis of PG1605+072

Abstract

We present the analysis of time-resolved spectroscopy of the pulsating sdB star PG1605+072. From our main observing run of 16 nights we have detected velocity variations at 5 frequencies that correspond to those found in photometry. Based on these data, there appears to be change in amplitude of the dominant modes over about a year. However, when we include extra observations to improve the frequency resolution, we find that some of the frequencies are split into two or three. Simulations suggest that the apparent amplitude variation can be at least partially explained by a series of very closely spaced frequencies around the two strongest modes. By combining observations taken over ~300 days we conclude that some of the closely spaced modes are caused by one mode whose amplitude is varying, however this frequency is still within ~1 microHz of an apparently stable frequency. Because of this kind of complexity and uncertainty we advise caution when trying to identify oscillation modes in this star.