arXiv subjects

Andrei Sadovski

Publications and source records attributed to Andrei Sadovski.

3 recordsLinked to original sources

arXiv2017

Cosmic Rays near Proxima Centauri b

Cosmic rays are an important factor of space weather determining radiation conditions near the Earth and it seems to be essential to clarify radiation conditions near extrasolar planets too. Last year a terrestrial planet candidate was discovered in an orbit around Proxima Centauri. Here we present our estimates on parameters of stellar wind of the Parker model, possible fluxes and fluencies of galactic and stellar cosmic rays based on the available data of the Proxima Centauri activity and its magnetic field. We found that galactic cosmic rays will be practically absent near Proxima~b up to energies of 1~TeV due to the modulation by the stellar wind. Stellar cosmic rays may be accelerated in Proxima Centauri events, which are able to permanently maintain density of stellar cosmic rays in the astrosphere comparable to low energy cosmic ray density in the heliosphere. Maximal proton intensities in extreme Proxima events should be by 3--4 orders more than in solar events.

astro-ph.SR↗

arXiv2017

Stellar Cosmic Rays in a Habitable Zone

According to recent observations relative number of flare stars does not change very much from cool dwarfs to hot A stars. Flare energies are strongly correlated with stellar luminosity and radius. Whence it follows that the typical magnetic field associated with a flare is several tens gauss and the typical flare loop length-scales are parts of the stellar radius. Flares on O--B stars were not observed, but they are possible, since strong magnetic fields are detected on O--B stars. Therefore stars of O--M spectral classes are potential sources of cosmic rays. Energy estimates of a magnetic field strength in a tube in photospheres of O--M stars are performed. Basing on their values possible flare energies and numbers of accelerated protons are estimated. The values obtained for the Sun correspond to observations by order of magnitude that justify estimates for other stars. Values of magnetic field strength in a tube differ less than five times for O and M flares (700 and 3500~G), but corresponding flare energies and numbers of accelerated protons for O stars are greater by five orders. Contrary fluencies of stellar protons appear to be five orders less.

astro-ph.SR↗

arXiv2004

The effects of induced scattering of Alfven waves for the solar wind acceleratio

The analysis of energy balance of coronal holes gives that to accelerate the fast solar wind streams the energy flux of the order of 800 erg/cm$^2$ s is needed. Axford and McKenzie suggested that the energy source, necessary to accelerate fast solar wind, is in the regions of strong magnetic field that define the boundaries of chromospheric supergranules. If the magnetic field is not strictly unipolar in these regions, the necessary energy is released in the processes of impulsive reconnection events. For the plasma parameters appropriate for the coronal base such processes of impulsive reconnection are accompanied by the generation of Alfven and fast magnetosonic waves with the period of the order of 1 s. On the basis of kinetic equation the model for the evolution of Alfven waves in solar wind is suggested. The induced scattering of these waves by plasma ions is considered as the dominant mechanism of dissipation of Alfven waves. The description of the evolution of the wave spectra in the process in the processes of their propagation till the distance of 187 solar radii was found.

physics.plasm-ph↗