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Session 32 - Stellar Astrophysics II.
Oral session, Monday, January 15
La Condesa, Hilton

[32.01] HST Direct Image of Betelgeuse

A. K. Dupree (Harvard-Smithsonian CfA), R. L. Gilliland (STScI)

A direct image of the surface of a star, Betelgeuse (Alpha Orionis; M2 Iab) has been obtained with the COSTAR-corrected Faint Object Camera (FOC) on the Hubble Space Telescope on 2-3 March 1995. Images in two ultraviolet bands centered at 2550Å\ and 2800Å\ show that \sim10 resolution elements on the stellar disk are achieved. The ultraviolet diameter of Betelgeuse is a factor of \sim2 larger than the optical diameter confirming the extended chromosphere in the supergiant star. A single bright unresolved spot is present in the southwest quadrant of the disk that dominates the total ultraviolet flux. This feature appears hotter than the surrounding chromosphere by at least 2000K. Such a major single feature is distinctly different from scattered smaller regions of activity typically found on the Sun, although the strong ultraviolet flux enhancement is characteristic of stellar magnetic activity. This inhomogeneity may be caused by a large scale convection cell or result from global pulsations and shock structures that heat the chromosphere. Comparisons with semi-empirical models will be presented.

Program listing for Monday