Chromospheric activity of nearby Sun-like stars

Abstract

Context.The chromospheric emission in the cores of the Ca IIH & K lines of late-type dwarfs is a well known indicator of magnetic activity that decreases with increasing stellar age.Aims.I use this indicator to investigate the formation history of nearby G- and early K-type stars with origins at galactocentric distances similar to that of the region where the Sun was born.Methods.A parent sample of single main-sequence stars with near-solar metallicity and known magnetic activity levels is built from catalogues of stellar atmospheric parameters and chromospheric activity indices. A kinematical approach usesGaiaastrometric data to differentiate thin disc stars from thick disc stars. Measured distributions ofR′HKchromospheric activity indices are compared with Monte Carlo simulations based on an empirical model of chromospheric activity evolution.Results.The thin disc includes a significant fraction of Sun-like stars with intermediate activity levels (2 × 10−5≤R′HK≤ 6 × 10−5), while most early K- and G-type stars from the thick disc are inactive (R′HK< 2 × 10−5). The chromospheric activity distribution among nearby Sun-like dwarfs from the thin disc can be explained by a combination of an old (>6–7 Gyr) star formation event (or events) and a more recent (<3 Gyr) burst of star formation. Such an event is not required to account for theR′HKindex distributions of nearby thick disc stars.Conclusions.The distribution of magnetic activity among local G- and early K-type stars with a near-solar metallicity bears the imprint of an important star formation event that occurred ~1.9–2.6 Gyr ago in the thin disc of the Milky Way.