Stars: From Collapse to Collapse
In 2016 the leading center of Russian ground-based observational astronomy, the Special Astrophysical Observatory of the Russian Academy of Sciences, celebrated its 50th anniversary. As part of the anniversary celebration, the Observatory organized a conference to discuss a broad range of topics related to the astrophysics of stars and star systems, which brought together the leading experts from Russia, the Russian Commonwealth, and our foreign colleagues. The main idea of the meeting is reflected in its name: the life of a star from its birth (molecular cloud collapse) to death (supernova core collapse). The result of the conference is the present volume containing the latest achievements of the Russian astronomical community in stellar astrophysics, obtained both with domestic instruments and as part of international cooperation. This volume presents recent results of the studies of star-forming regions and the interstellar medium, stellar atmospheres and magnetism, activity of stars, multiple stellar systems and exoplanets, and stars after the nuclear burning stage. Methods and instruments of present-day stellar astrophysics are also discussed.
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 of 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.