Radio continuum emission from winds, chromospheres, and coronae of cool giants and supergiants
In this paper we present the results of a sensitive VLA radio continuum survey at 6 cm of 39 of the nearest, single cool giants and supergiants with spectral types in the range G0--M5. We discuss our findings in the context of the various mechanisms that might be producing radio emission in these cool stars. We have definitely detected four K and M giants ( Her, Boo, rho Per, and Gem) and probably detected a fifth ( US UMi) at flux levels of 0.1--1.0 mJy. We believe that in all five of these cases the radio emission is thermal emission from cool stellar winds. We have made additional 2 cm observations of several stars, including the four stars definitely detected at 6 cm. We have derived spectral indices for Boo, Her, and rho Per of 0.80, 0.84, and 0.95, respectively, that are close to the 0.6 value predicted by standard stellar wind models in the optically thick regime. An additional cool giant ( Tau) was detected only at 2 cm, implying a spectral index of > or =0.87. None of the coronal or hybrid-chromosphere giants observed were detected in this study, with the exception of Aur, a 0.2 mJy radio source at 6 cm, which is in fact a widely separated, long-period (P/sub orb/approx.104/sup d/) RS CVn system containing two cool giant stars. In this case, we believe that the 6 cm radio emission is optically thin, thermal emission from the corona(e) of one or both of the components, since the radio-emission measure is consistent with that of the observed x-ray emission.
- Research Organization:
- Joint Institute for Laboratory Astrophysics, University of Colorado and National Bureau of Standards, Boulder, Colorado 80309
- OSTI ID:
- 6176070
- Journal Information:
- Astron. J.; (United States), Vol. 91:3
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GENERAL PHYSICS
GIANT STARS
RADIOWAVE RADIATION
STELLAR CHROMOSPHERES
STELLAR CORONAE
STELLAR WINDS
SUPERGIANT STARS
COSMIC RADIO SOURCES
RADIATION FLUX
STAR MODELS
THERMAL RADIATION
ATMOSPHERES
ELECTROMAGNETIC RADIATION
MATHEMATICAL MODELS
RADIATIONS
STARS
STELLAR ACTIVITY
STELLAR ATMOSPHERES
640102* - Astrophysics & Cosmology- Stars & Quasi-Stellar
Radio & X-Ray Sources