Improved Age Estimation for Solar-Type Dwarfs Using Activity-Rotation Diagnostics

TL;DR

This paper presents improved methods for estimating the ages of solar-type dwarf stars by refining activity-rotation diagnostics, leading to more accurate age determinations between 0.6 and 4.5 billion years.

Contribution

The authors develop new activity-age calibrations based on chromospheric activity and rotation, enhancing age estimation accuracy for F7-K2 dwarfs compared to previous models.

Findings

New activity-age calibration with ~0.2 dex precision

Color-dependent effects improve age estimates

X-ray activity provides comparable age and rotation information

Abstract

While the strong anti-correlation between chromospheric activity and age has led to the common use of the Ca II H & K emission index (R'_HK = L_HK/L_bol) as an empirical age estimator for solar type dwarfs, existing activity-age relations produce implausible ages at both high and low activity levels. We have compiled R'_HK data from the literature for young stellar clusters, richly populating for the first time the young end of the activity-age relation. Combining the cluster activity data with modern cluster age estimates, and analyzing the color-dependence of the chromospheric activity age index, we derive an improved activity-age calibration for F7-K2 dwarfs (0.5 < B-V < 0.9 mag). We also present a more fundamentally motivated activity-age calibration that relies on conversion of R'_HK values through the Rossby number to rotation periods, and then makes use of improved gyrochronology relations. We demonstrate that our new activity-age calibration has typical age precision of ~0.2 dex for normal solar-type dwarfs aged between the Hyades and the Sun (~0.6-4.5 Gyr). Inferring ages through activity-rotation-age relations accounts for some color-dependent effects, and systematically improves the age estimates (albeit only slightly). We demonstrate that coronal activity as measured through the fractional X-ray luminosity (R_X = L_X/L_bol) has nearly the same age- and rotation-inferring capability as chromospheric activity measured through R'_HK. As a first application of our calibrations, we provide new activity-derived age estimates for the nearest 100 solar-type field dwarfs (d < 15 pc).