Chromospheric activity of nearby Sun-like stars

Abstract

Context. The chromospheric emission in the cores of the Ca II H & 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 uses Gaia astrometric data to differentiate thin disc stars from thick disc stars. Measured distributions of R′HK chromospheric 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 the R′HK index 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.

Precise Masses and Orbits for Nine Radial-velocity Exoplanets

“…Pace (2013) and Gáspár et al (2016) have determined the age of the star to be between 4-5 Gyr, in agreement with our activity-based age of 4.436 +0.677 −0.576 Gyr. We adopt an activity index of R HK = −4.96 using S-indices from Arriagada (2011); Jenkins et al (2011); Pace (2013), consistent with the values published in many sources (Jenkins et al 2008(Jenkins et al , 2011Herrero et al 2012;Marmier et al 2013;Gondoin 2020). The spectroscopic mass of the star is between 0.96-1.03 M (Allende Prieto & Lambert 1999;Mortier et al 2013;Santos et al 2013;Mints & Hekker 2017;Goda & Matsuo 2019).…”

Doppler Constraints on Planetary Companions to Nearby Sun-like Stars: An Archival Radial Velocity Survey of Southern Targets for Proposed NASA Direct Imaging Missions

“…to -4.85(Gondoin 2020) -comparable to the active Sun. Analysis of the Mt.Wilson Ca II H & K survey data by Donahue et al (1996) detected seasonal rotation periods ranging from P rot = 35.4 to 37.8 d, with an average over 5 seasons of P rot = 36.4 d. Boro Saikia et al (2018) report a Ca II H & K activity cycle of P cyc = 7.19 ± 0.04 yr. GJ 688 is a SB1 with three published orbits listed in the SB9 catalog…”