Activity of the sun in the age of 1–2 Gyr

Abstract

We discuss basic properties of the solar activity in the modern epoch and the further development of ideas about estimate the age of stars by the level of activity (gyrochronology). From comparison of properties of solar activity and processes on other G stars we have determined activity levels of the chromosphere and corona of the young Sun in its age of 1–2 Gyr. So, activity of the Sun in such an age is closest to the processes in the G stars, HD 152391 (V2292 Oph) and HD 1835 (BE Cet) with the rotational periods of 11 and 8 days correspondingly. The total spot area is of 2–3 orders of magnitude higher than the current value at the maximum of the solar cycle, the activity levels of the chromosphere and the corona are quite high and similar to the Hyades, but it did not reach the saturation level. We have analyzed new measurements of longitudinal magnetic fields and distribution of the toroidal and poloidal fields on the G main sequence stars. The mean value of the longitudinal fields for active G stars is of one order of magnitudes stronger than the mean daily magnetic field of the Sun as a star, for instance those during the 21th cycle maximum. Besides, the detection of large-scale toroidal magnetic field in such stars is important. Taking into account the activity levels and magnetic fields, we analyzed data on superflares on G stars registered with the Kepler mission. We have defined the upper limit of energy of flares that can occur in the magnetic fields of active G stars.