Vol. 602
In section 7. Stellar structure and evolution

Kepler sheds new and unprecedented light on the variability of a blue supergiant: Gravity waves in the O9.5Iab star HD188209

by C. Aerts, S. Símon-Díaz, S. Bloemen, et al. A&A 602, A32

Space missions such as CoRoT and Kepler have had a tremendous impact on asteroseismological studies of low mass stars. Higher-mass stars (> 8 M_sun) and their evolved descendants have not been as amenable to similar scrutiny primarily because their oscillation periods are longer, leading to multi-periodic beating patterns with periods of several years, thus rendering observations unfeasible. For massive O and B supergiants, the situation is further complicated by the presence of other phenomena such as strong stellar winds. Although the saturation limit for the Kepler CCDs is ~11.5 mag., Aerts et al. were able to observe a 5.5 mag. O supergiant, HD188209, using a strategic placement of masks, thereby enabling a study of the target in scattered light over a time period of about four years. Extensive ground-based spectroscopy was also acquired. By combining these unique datasets, the authors were able to infer the presence of convectively driven internal gravity waves, making HD188209 the first case of a massive supergiant for which such variability has been observed.