2020AJ....160..217C

Stellar age cannot be directly measured, yet age determinations are fundamental to understanding the evolution of stars, planets, and galaxies. The work presented here builds upon the idea of a stellar-activity age. We utilized far-ultraviolet (FUV) photometry acquired by the Galaxy Evolution Explorer (GALEX) space telescope as an indicator of chromospheric activity to infer ages of late-F, G, and K type dwarf stars. We derived a purely empirical correlation between FUV magnitudes and stellar age in conjunction with (B - V) color. Our attention is restricted to Sun-like stars with color range 0.55≤ (B-V)≤ 0.71 and absolute magnitude range 4.3 <= M_V <= 5.3. The correlation is defined in terms of a FUV-excess parameter Q(FUV-B,B-V). We related stellar age, τ, to Q through the relation log_e(τ)=log_e(a)+bQ, where a and b are fit parameters and functions of (B - V). This correlation is functional up to 6 Gyr for FGK dwarfs. With such a correlation, one only needs Johnson (B - V) and FUV measurements to estimate the stellar age for Population I dwarf stars of solar-like temperature and metallicity. Such a calibration has utility in population studies of FGK dwarfs for further understanding of the chemical evolution of the Milky Way. As an illustration of one such application, we have constructed activity and FUV-age distributions for a sample of thin and thick disk stars, as distinguished by their chemical abundances. Considerable overlap is found between the activity distribution and age range of the two populations. We discuss the possibility that some high-[α/Fe] thick disk stars were formed as a result of the accretion of dwarf galaxies as recently as 4 Gyr ago.