Monitoring mass motions of Betelgeuse's photosphere using robotic telescopes .

We started monitoring Betelgeuse using STELLA/SES, the STELLA echelle spectrograph fed by a robotic 1.2 m telescope on Tenerife, and the automatic photometric telescope (APT) T7 in Arizona in fall 2008. In this first observing season, we have collected 67 high resolution spectra from 390 to 900 nm at a resolution of 50,000 and a S/N between 100 and 300, and a comparable number of photometric observations in the Hα filter. In this presentation, we report on the initial findings based on this first data set: Radial velocities, effective temperature (along with surface gravity and metallicity) are automatically computed by the STELLA/SES data reduction & analysis pipeline. We compare these global measurements and the photometric brightness with velocities and temperature indicators derived from individual spectral lines, to bring these values in line with recently published observations. Furthermore we compute synthetic line profiles from state-of-theart 3D stellar convection models, and compare the line-profiles, their shapes and positions to our observations. The final aim of the observing program is to find out if the spectral line variations can be explained using these non-magnetic convection models.