Chromospheric emission of solar-type stars with asteroseismic ages

TL;DR

This study measures chromospheric emission in old solar-type stars using asteroseismic ages, revealing that magnetic activity continues to decline beyond one gigayear and correlates well with age within spectral types.

Contribution

It provides new chromospheric activity data for old stars and shows that magnetic activity decreases with age without evidence of braking stalling, refining age-activity relations.

Findings

Magnetic activity declines with age in G and cooler F stars beyond 1 Gyr.

No evidence of magnetic braking stalling in old stars.

Chromospheric activity correlates with age within spectral types.

Abstract

Stellar magnetic activity decays over the main-sequence life of cool stars due to the stellar spin-down driven by magnetic braking. The evolution of chromospheric emission is well-studied for younger stars, but difficulties in determining the ages of older cool stars on the main sequence have complicated such studies for older stars in the past. Here we report on chromospheric Ca II H and K line measurements for 26 main-sequence cool stars with asteroseismic ages older than a gigayear and spectral types F and G. We find that for the G stars and the cooler F-type stars which still have convective envelopes the magnetic activity continues to decrease at stellar ages above one gigayear. Our magnetic activity measurements do not show evidence for a stalling of the magnetic braking mechanism, which has been reported for stellar rotation versus age for G and F type stars. We also find that the measured R'HK indicator value for the cool F stars in our sample is lower than predicted by common age-activity relations that are mainly calibrated on data from young stellar clusters. We conclude that, within individual spectral type bins, chromospheric magnetic activity correlates well with stellar age even for old stars.