Properties of minimum-flux coronae in dwarfs and giants

Details Properties of minimum-flux coronae in dwarfs and giants Properties of minimum-flux coronae in dwarfs and giants

Oct 1976

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1976apj...209..171m&link_type=abstract

Astrophysical Journal, vol. 209, Oct. 1, 1976, pt. 1, p. 171-178.

Astronomy and Astrophysics

Astrophysics

33

Coronas, Dwarf Stars, Giant Stars, Main Sequence Stars, Stellar Atmospheres, Stellar Luminosity, Energy Conversion Efficiency, Light Curve, Radiant Flux Density, Solar Flares, Stellar Spectra, Stellar Winds, X Ray Sources

Scientific paper

Hearn's (1975) minimum-flux corona model is applied to main-sequence and giant stars. In this model, the corona is assumed to have a strictly radial magnetic field and to adjust itself in such a way that for a given pressure at its base, the sum of radiative, conductive, and stellar-wind energy fluxes from it is a minimum. Numerical results for main-sequence stars of spectral type M6 V through O5 V are presented in terms of coronal temperatures and efficiency factors for converting thermal energy to mechanical energy. Similar results are given for the giant stars Alpha Aur, Beta Gem, Alpha Boo, and Alpha Tau. It is shown that: (1) coronae of red dwarfs must be up to three times cooler than the solar corona unless the efficiency of conversion increases by many orders of magnitude in later spectral types relative to the efficiency of the sun; (2) coronae of upper-main-sequence stars may be twice as hot as the solar corona; (3) the coronae of Beta Gem and Alpha Aur are hot enough to explain the presence of O V, O VI, Si III, and N V lines; (4) the coronae of Alpha Boo and Alpha Tau are so cool that insignificant O V emission is expected; and (5) line asymmetries due to stellar winds are most easily detectable in Alpha Boo and Alpha Aur because of the larger mass-loss rates per unit area in these stars.

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