DETECTION OF O-I AND SI-II FAR-INFRARED FINE-STRUCTURE EMISSION FROM ALPHA-ORIONIS

We have detected [O I] 63 mum and [Si II] 35 mum emission from the oxy gen-rich, M2 Iab supergiant, alpha Orionis (Betelgeuse). The [O I] lin e flux is 2.4 +/- 0.2 x 10(-18) W cm-2, and the [Si II] line flux is 0 .9 +/- 0.4 x 10(-18) W cm-2. These fluxes are consistent with the ther mal model of Rodgers & Glassgold, which indicates that the emission ar ises in dense, warm gas in alpha Ori's inner envelope and implies that nearly all of the available O and Si is in atomic form. This is the f irst reported detection of far-infrared, fine-structure emission from the inner or transition region of a circumstellar envelope, where mole cules and dust are expected to form.