Tony Lynas-Gray

Abstract:

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 ± 0.002 s and an amplitude dependent upon wavelength, with a value of 34.5 ± 1.6 mma 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 6 h to look for line profile variations. Models fits to the spectra give mean atmospheric values of T eff = 28 450 ± 700K and log g = 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 ± 1.1 kms-1. 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 ± 19090 pc, R = 0.19 ± 0.08 R⊙ and M = 0.39 ± 0.300.13M⊙, respectively, using the Baade-Wesselink method. © 2010 The Authors. Journal compilation © 2010 RAS.

Abstract:

A spectroscopic analysis of Sloan Digital Sky Survey (SDSS) J160043.6+074802.9, a binary system containing a pulsating subdwarf-O (sdO) star with a late-type companion, yields Teff = 70 000 ± 5000 K and log g = 5.25 ± 0.30, together with a most likely type of K3 V for the secondary star. We compare our results with atmospheric parameters derived by Fontaine et al. and in the context of existing evolution models for sdO stars. New and more extensive photometry is also presented which recovers most, but not all, frequencies found in an earlier paper. Therefore, it seems probable that some pulsation modes have variable amplitudes. A non-adiabatic pulsation analysis of uniform metallicity sdO models show those having log g > 5.3 to be more likely to be unstable and capable of driving pulsation in the observed frequency range. © 2009 RAS.

Abstract:

We report the discovery of oscillations in the hot subdwarf B (sdB) star JL 166 from time-series photometry using the Goodman Spectrograph on the 4.1 m Southern Astrophysical Research Telescope. Previous spectroscopic and photometric observations place the star near the hot end of the empirical sdB instability strip and imply the presence of a cool companion. Amplitude spectra of the stellar light curve reveal at least 10 independent pulsation modes with periods ranging from 97 to 178 s and amplitudes from 0.9 to 4 mma. We adopt atmospheric parameters of T eff= 34,350 K and log g = 5.75 from a model atmosphere analysis of our time-averaged, medium-resolution spectrum. © 2009. The American Astronomical Society.