The First Far Ultraviolet Image of Alpha Orionis (Betelgeuse, HD 39801)

We have successfully recorded the first far ultraviolet (FUV) image of the supergiant star Alpha Orionis (Betelgeuse, HD 39801) using the Hubble Space Telescope Imaging Spectrograph (STIS) in the camera mode with the narrow band Lyman Alpha filter. The image shows an atmosphere that is both larger in extent and more structured than that observed earlier at near ultraviolet (NUV) wavelengths around 2500 Å and 2800 Å (Gilliland and Dupree, 1996). The measured mean FWHM in the FUV bandpass of 145 Å is 148 +/- 6 mas, and the measured mean diameter to the 10% intensity level is 260 +/- 12 mas. Two unresolved but clearly separated hotspots are seen in the image. The structure shows significant differences from the 1995 NUV images, but some similarities to the more recent NRAO radio image (Lim et al., 1998). This work was supported in part by NASA grant NAG5-3378 to the Catholic University of America.