  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. Both effects have been linked to stellar oscillations, but B
supergiants have not been systematically searched yet for the presence of
especially short-term variability caused by stellar pulsations. We have started
an observational campaign to investigate the line profile variability of
photospheric lines in a sample of Galactic B supergiants. These observations
aim to improve our understanding of the physical effects acting in the
atmospheres of evolved massive stars. We obtained four time-series of
high-quality optical spectra for the Galactic B supergiant HD 202850. The
spectral coverage of about 500 A around Halpha encompasses the Si II (6347 A,
6371 A), and the He I (6678 A) photospheric lines. The line profiles were
analysed by means of the moment method. 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. Since the star seems to fall outside the
currently known pulsational instability domains, the nature of the discovered
oscillation remains unclear.
