Thermal X-rays from stellar flares - Reevaluation of scaling from solar flares

Abstract

view Abstract Citations (39) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Thermal X-rays from stellar flares: reevaluation of scaling from solar flares. Mullan, D. J. Abstract A simple method of estimating the ratio of thermal X-ray luminosity to optical luminosity in stellar flares is presented which is valid at times close to and following peak flare luminosity. It is proposed that at such times, the X-ray and optical luminosities are, respectively, the energy radiated by the plasma and the energy conducted out of the plasma. If the conductive energy directed downward toward the photosphere and lower chromosphere is regarded as the energy source for optical flares, then the luminosity ratio is equal to the ratio of conductive to radiative cooling times in the hot flare plasma. A self-consistent model for red-dwarf flares is discussed in which the decay time of the optical light curve is controlled by the time scale for thermal conduction from the hot flare plasma. The condition that the two times must be approximately equal leads to estimates of electron densities in flares, provided the flare temperatures are known; it is argued that stellar flare temperatures are 1 to 4 times higher than the mean temperature of solar flares. Numerical results are given for the luminosity ratio in flares of seven UV Ceti stars. It is concluded that if the solar luminosity ratio is used in attempting to predict thermal X-ray fluxes from stellar flares, the predicted X-ray flux accompanying an optical flare of given amplitude will provide only an upper limit on the actual thermal X-ray flux. Publication: The Astrophysical Journal Pub Date: July 1976 DOI: 10.1086/154492 Bibcode: 1976ApJ...207..289M Keywords: Energy Dissipation; High Temperature Plasmas; Light Curve; Solar Flares; Solar X-Rays; Stellar Flares; Stellar Luminosity; Convective Heat Transfer; Dwarf Stars; Numerical Analysis; Radiant Cooling; Stellar Models; Stellar Radiation; Stellar Temperature; X Ray Astronomy; Space Radiation full text sources ADS |