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Photospheric lines of B-type supergiants show variability in their profileshapes. In addition, their widths are much wider than can be accounted forpurely by stellar rotation. This excess broadening is often referred to asmacroturbulence. Both effects have been linked to stellar oscillations, but Bsupergiants have not been systematically searched yet for the presence ofespecially short-term variability caused by stellar pulsations. We have startedan observational campaign to investigate the line profile variability ofphotospheric lines in a sample of Galactic B supergiants. These observationsaim to improve our understanding of the physical effects acting in theatmospheres of evolved massive stars. We obtained four time-series ofhigh-quality optical spectra for the Galactic B supergiant HD 202850. Thespectral 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 wereanalysed by means of the moment method. The time-series of the photospheric SiII and He I lines display a simultaneous, periodic variability in their profileshapes. Proper analysis revealed a period of 1.59 h in all three lines. Thisperiod 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 beascribed to stellar oscillations. Since the star seems to fall outside thecurrently known pulsational instability domains, the nature of the discoveredoscillation remains unclear.

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