Astronomy and Astrophysics – Astronomy
Scientific paper
Nov 1987
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1987aj.....94.1280d&link_type=abstract
Astronomical Journal (ISSN 0004-6256), vol. 94, Nov. 1987, p. 1280-1290.
Astronomy and Astrophysics
Astronomy
28
Continuous Spectra, Giant Stars, M Stars, Radio Emission, Brightness Temperature, Shock Waves, Stellar Flares, Stellar Winds, Supergiant Stars, Very Large Array (Vla)
Scientific paper
The authors present the results of a sensitive VLA continuum survey of 22 cool M and C type giants and supergiants, including nine carbon stars, one S type star, and 12 M stars. The purpose of the survey was to probe the physical properties of the partially ionized, expanding chromospheres of the coolest luminous stars. Of the 22 stars observed at 6 cm, none were detected directly, although extended emission was detected near NML Cyg and OH 26.5+0.6, and a point source was detected near AFGL 865. Of the three stars observed at 2 cm, R Aql (M6.5e-9e) was detected as a 0.54±0.17 mJy source, and a point source was detected 7arcsec from R Cas (M6e-9e) and may be physically associated with the star. These data imply small upper limits for the ionized-mass-loss rates and 2 - 6 cm spectral indices that are significantly steeper than the 0.6 value predicted by the "standard" stellar-wind model. The nondetection of ο Ceti (Mira) at both 2 and 6 cm, despite a previous 6 cm detection, supports the idea that the radio-continuum emission of these stars may be variable, perhaps due either to flares or to the passage of pulsation-generated shock waves through their outer atmospheres.
Drake Stephen Alan
Elitzur Moshe
Linsky Jeffrey L.
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