Detection of a 1.59 h period in the B supergiant star HD 202850

Photospheric lines of B-type supergiants show variability in their profile shapes. In addition, their widths are much wider than can be accounted for purely by stellar rotation. This excess broadening is often referred to as macroturbulence. The authors have started an observational campaign to investigate the line profile variability of photospheric lines in a sample of Galactic B supergiants. They obtained four time-series of high-quality optical spectra for the Galactic B supergiant HD202850. The spectral coverage of about 500 Aa around H alpha encompasses the Si II lambda lambda 6347, 6371, and the He I lambda 6678 photospheric lines. The time-series of the photospheric Si II and He I lines display a simultaneous, periodic variability in their profile shapes. Proper analysis revealed a period of 1.59 h in all three lines. This period is found to be stable with time over the observed span of 19 months. This period is much shorter than the rotation period of the star and might be ascribed to stellar oscillations.