Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1992
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992aas...181.5113h&link_type=abstract
American Astronomical Society, 181st AAS Meeting, #51.13; Bulletin of the American Astronomical Society, Vol. 24, p.1207
Astronomy and Astrophysics
Astronomy
Scientific paper
We have detected [O\I.] 63 \mm. and [Si\II.] 35 \mm. emission from alpha Orionis (Betelgeuse), an oxygen rich, M2 Iab supergiant. This is the first reported detection of far-infrared fine-structure emission from the expanding atmosphere of a star. The [O\I.] line flux is 2.2 +/- 0.2 times 10(-18) W cm(-2) and the [Si\II.] line flux is 0.9 +/- 0.4 times 10(-18) W cm(-2) . The associated narrow-band continuum flux is 140 +/- 40 Jy at 63 \mm. and 720 +/- 30 Jy at 35 \mm.. For a late type star, alpha Ori's envelope is unusually devoid of dust and molecules. Glassgold and Huggins (1986, ApJ, 306, 605) summarized the observational data and developed a model for alpha Ori's ionization structure, concluding that its envelope is principally atomic. Rodgers and Glassgold (RG; 1991, ApJ, 382, 606) computed the thermal structure and found that [O\I.] 63 \mm. is the dominant coolant over a significant portion of the inner envelope ( ~ 10 - 40 R_*). Their predicted fluxes for the [O\I.] and [Si\II.] lines are in good agreement with our measurements when a realistic velocity field is employed. Our observations are consistent with RG's choice of distance (200 pc), hydrogen mass loss rate (4 times 10(-6) M\sun. yr(-1) , and chemical abundances (x_O = 6.3times 10(-4) and xSi = 3.8 times 10(-5) ). The RG calculation predicts that the temperature drops sharply from ~ 1700 K at 10 R_* to ~ less 100 K at 40 R_* as a result of this fine-structure cooling, suggesting that these lines arise in a particularly interesting region of the envelope where molecules and dust are expected to form.
Glassgold Alfred E.
Haas Michael R.
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