The activity of the solar atmosphere and solar-type stars at 11-year and quasi-biennial timescales

Observations of a time series of solar activity indices are compared with new simultaneous observations of the flux variations of the photospheric and chromospheric emissions of 33 stars during the HK project that were conducted over the past 20 years. In addition to the known cyclic chromospheric emissions of stars in the 11-year time scale, which was discovered at the Mount Wilson Observatory and Stanford University, we found a recurrence that is similar to the quasi-biennial variations of solar radiation fluxes. The results of calculations of the of radiation flux variation periods of stars at the quasi-biennial scale are given.