The optical continuum of solar and stellar flares

Abstract

A further development of the Kostyuk-Pikelner's model is presented. The response of the chromosphere heated by non-thermal electrons of the power-law energy spectrum has been studied on the basis of the numerical solution of the one-dimensional time-dependent equations of gravitational gas dynamics. The ionization and energy loss for the emissions in the Lyman and Balmer lines have been determined separately for the optically thin and thick La-line layers. Due to the initial heating, a higher-pressure region is formed. From this region, disturbances propagate upwards (a shock wave with a velocity of more than 1000 km s -1) and downwards. A temperature jump propagates downwards, and a shock is formed in front of the thermal wave. During a period of several seconds after the beginning of this process, the temperature jump intensifies the downward shock wave and the large radiative loss gives rise to the high density jump (02/0l -100). The numerical solution has been analyzed in detail for the case heating of the ionized and neutral plasma, and a value of this heating is close to the upper limit of the admissible values. In this case, the condensation located between the temperature jump and the shock wave front, may emit in the observed optical continuum.In their essential features, the gas dynamic processes during the flares in red dwarf atmospheres are the same as those in the solar atmosphere. However, the high atmospheric densities, smaller height scale in red dwarf atmospheres, and greater energy of this processes in stellar flares, give rise, in practice, to the regular generation of optical continuum. The photometric parameters of a source with n ~ 1015 cm -3, T-9000 K, and Az ~ 10 km are in a good agreement with observations.

Properties of Flares-Generated Seismic Waves on the Sun

“…This picture corresponds very well to the standard thick target model of solar flares (Svestka 1970) and the models of the hydrodynamic response (e.g. Kostiuk & Pikelner 1975;Livshits et al 1981;Fisher et al 1985;Kosovichev 1986). The soft X-ray image indicates this flare was rather compact.…”

“…In these models, a beam of high-energy is related to heating of the solar chromosphere, resulting in evaporation of the upper chromosphere and a strong compression of the lower chromosphere (e.g. Kostiuk & Pikelner 1975;Livshits et al 1981;Fisher et al 1985;Kosovichev 1986). This high-pressure compression produces a downward propagating shock wave (Kosovichev 1986) that hits the solar surface and causes sunquakes.…”

The Origin of Superflares on G-Type Dwarf Stars of Various Ages

“…As known, the first numerical modeling of this process was carried out by Kostyuk and Pikelner (1975). This approach was further developed by Livshits et al (1981) in the article entitled "The optical continuum of solar and stellar flares". The corresponding model of impulsive flares on red dwarf stars was developed by Katsova, Boiko, and Livshits (1997).…”

Physical Processes During Impulsive Solar and Stellar Flares

“…The first calculations of explosive evaporation in the atmosphere of red dwarfs were carried out by Livshits et al (1981) and Katsova et al (1981). Their main conclusion was that the low-temperature condensation formed in this process during large flares should emit in optical continuum.…”