MEASUREMENT AT 11-MICRON WAVELENGTHS OF THE DIAMETERS OF ALPHA-ORIONIS AND ALPHA-SCORPII, AND CHANGES IN EFFECTIVE TEMPERATURE OF ALPHA-ORIONIS AND VERY RECENT DUST EMISSION

The angular diameters of the stellar disks of a Ori and a Sco have bee n determined to be 56.6 +/- 1 and 44.4 +/- 2 mas, respectively, at 11 mu m using long-baseline interferometry. These values are about 10% la rger than the most reliable diameters determined at visible wavelength s, and are consistent with predictions of significant visible limb dar kening, but only minor infrared limb darkening. Variations in temperat ure and luminosity of alpha Ori during 1989-1995 have been studied by a combination of interferometry, optical photometry, and spectrophotom etry. This shows that observed variations in rn, are primarily due to temperature changes. A recent episode of dust formation at about 0 ''. 1 from the star has been detected; it is probably the result of a disc rete mass-loss event of modest size.