The outer atmosphere of the M-type supergiant alpha Orionis: K I 7699 Åemission
Abstract
Spatially-resolved high-resolution long-slit spectra of Betelgeuse's circumstellar shell are described for a spectral window centered on the 7699 Å resonance line of neutral potassium. The K I emission from resonance fluorescent scattering of photospheric photons which is mapped out to 50 arcsec from the star is approximately spherically symmetric with a brightness decreasing as r-2.36 +/- 0.03, where r is the radial distance from the star. Our measurements together with the earlier theoretical interpretation by Rodgers & Glassgold suggest that the mass loss rate is about 2 x 10-6 M_sun y-1. The K I emission is far from homogeneous: intensity inhomogeneities are seen down to the seeing limit of about 1 arcsec and the velocity resolution of about 2 km s-1. There is clear evidence for a thin shell of 50 arcsec radius. This is identified with the weaker circumstellar absorption component known as S2. Estimates are made of the density of K atoms in this shell ( =~ 6 x 10-5 cm-3).
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- May 2002
- DOI:
- 10.1051/0004-6361:20020363
- arXiv:
- arXiv:astro-ph/0203209
- Bibcode:
- 2002A&A...386.1009P
- Keywords:
-
- stars: circumstellar matter;
- stars: individual: Betelgeuse;
- stars: supergiants;
- stars: winds;
- outflows;
- Astrophysics
- E-Print:
- 10 pages, 7 figures