Properties of minimum-flux coronae in dwarfs and giants
Using a method due to Hearn, we examine the properties of minimum-flux coronae in dwarfs and giants. If the fraction phi of the total stellar luminosity which is used to heat the corona is equal to the solar value phi/sub s/, then red dwarfs must have coronae that are cooler than the solar corona: in UV Ceti, for example, the coronal temperature is a factor 3 less than in the Sun. This is consistent with an independent estimate of coronal temperature in a flare star. If phi=phi/sub s/, main-sequence stars hotter than the Sun have coronae which are hotter than the solar corona. Soft X-rays from Sirius suggest that the coronal temperature in Sirius is indeed hotter than the Sun by a factor of about 40 percent. Giants show an even more marked decrease in coronal temperature at later spectral type than do the dwarfs. We suggest that the reason for the presence of O V emission in ..beta.. Gem and O VI emission in ..cap alpha.. Aur, and the absence of O V emission in ..cap alpha.. Boo and ..cap alpha.. Tau, is that the coronae in the latter two stars are cooler (rather than hotter, as McClintock et al. have suggested) than in the former two. Our results explain why it is more likely that mass loss has been detected in ..cap alpha.. Aur and ..cap alpha.. Boo, but not in ..cap alpha.. Tau or ..beta.. Gem. Using a simple flare model, we show that flares in both a dwarf star (UV Ceti) and a giant (..cap alpha.. Aur) were initiated not in the corona, but in the transition region. (AIP)
- Research Organization:
- Bartol Research Foundation of The Franklin Institute, Swarthmore, Pennsylvania 19081
- OSTI ID:
- 7332186
- Journal Information:
- Astrophys. J.; (United States), Vol. 209:1
- Country of Publication:
- United States
- Language:
- English
Similar Records
Radio continuum emission from winds, chromospheres, and coronae of cool giants and supergiants
Detection of soft X-rays from. cap alpha. Lyrae and eta Bootis with an imaging X-ray telescope
Related Subjects
GENERAL PHYSICS
DWARF STARS
RADIATION FLUX
GIANT STARS
MAIN SEQUENCE STARS
MASS TRANSFER
STAR MODELS
STELLAR ATMOSPHERES
STELLAR FLARES
STELLAR WINDS
X-RAY SPECTRA
ATMOSPHERES
MATHEMATICAL MODELS
SPECTRA
STARS
640102* - Astrophysics & Cosmology- Stars & Quasi-Stellar
Radio & X-Ray Sources