Betelgeuse: Giant convection cells

Spectroscopic observations of the M supergiant star Betelgeuse were taken at the Elginfield Observatory over 17 months in the 1999-2000 observing seasons in order to search for giant convection cells. Although the photospheric spectral lines show some temporal variations, mainly in their depths (consistent with a previously study), the Doppler shift distribution inferred from them is remarkably stable. The spectral lines show characteristic macroturbulence dispersion similar to 15 km s(-1) and cover a full span of +/-50-60 km s(-1). The widths of the lines show occasional as well as longer term changes of a few percent but no evidence for giant convection cells. These spectroscopic observations are more consistent with a classical picture of nonthermal photospheric velocities in which large numbers of convection cells appear on the stellar disk at all times.