NEUTRAL CARBON IN THE CIRCUMSTELLAR ENVELOPE OF ALPHA-ORIONIS

We report the detection of emission in the 609 mum P-3(1) --> P-3(0) f ine-structure line of neutral atomic carbon in the circumstellar envel ope of alpha Ori, using the 10.4 m telescope of the Caltech Submillime ter Observatory. The C I line is centered at a radial velocity of + 3 km s-1 with an intensity of 200 mK, and a width of 30 km s-1 character istic of the expanding circumstellar envelope. The observations show t hat C I is an important component of the circumstellar gas. The number of C I atoms in the envelope exceeds the number of CO molecules by a factor of almost-equal-to 5, and the C I column density is large enoug h that significant absorption of the stellar and chromospheric spectru m can be expected at wavelengths shorter than the C I ionization edge at 1100 angstrom. The mass-loss rate determined from our observations using the photospheric carbon abundance and assuming full recombinatio n of carbon in the transition region is 2 x 10(-6) M, yr-1. This is in good agreement with the value determined from H I 21 cm observations and confirms that C I is a major carrier of carbon between the chromos phere and the outer envelope.