Search

We present the first results from the MultiSite Spectroscopic Telescope (MSST) observations of the sdBV star PG 1605+072. Pulsating sdB stars (V361 Hya stars) offer the chance to gain new insights into the formation and evolution of extreme Horizontal Branch stars using the tools of asteroseismology. PG 1605+072 is an outstanding object in its class, with the richest frequency spectrum, the longest periods, and the largest variations. The MSST campaign took place in 2002 May/June and we present here the massive data set, made up of 399 hr of photometry and 151 hr of spectroscopy. The overall aims of the project are to examine light/velocity amplitude ratios and phase differences, changes in equivalent width/line index, and λ-dependence of photometric amplitudes, and to use these properties for mode identification.

Velocity measurements of the G2 subgiant β Hyi with both UCLES and CORALIE show a clear excess of power centred at 1.0 mHz. In the UCLES data we find evidence for a short-lived, high-amplitude oscillation event. If confirmed as a feature of subgiants, such ‘starquakes’ would make it harder to measure accurate mode frequencies and perform asteroseismology.

We present analysis of rapid spectroscopy of PG 1605+072, a pulsating sdB star that is believed to have evolved off the extreme horizontal branch. Using a cross-correlation technique on five Balmer lines (Hβ to H8), we have been able to study the Doppler variations in this star over one year. Preliminary results for about 25% of the time-series were presented by O’Toole et al. (2000). We find evidence for amplitude variation between 1999 and 2000. We have also examined of equivalent widths of the Balmer lines looking for variation. Preliminary results are intriguing, with the amplitude of the equivalent width oscillations strongly dependent on wavelength.

We have obtained time-series spectra for the pulsating hot subdwarf (sdB) PG1605+072. Previous time-series photometry of this star has shown maximum amplitude variations of ∼0.1 mag and at least 50 periods. The pulsator has the largest amplitude and longest periods of all the pulsating sdBs (or EC 14026 stars) discovered so far, and appears to be unusual in its class. Preliminary results of a search for velocity variations are presented here. With these variations, along with equivalent width measurements, oscillation mode identification should be possible.