BAFFLES: Bayesian Ages for Field Lower-mass Stars

Age is a fundamental parameter of stars, yet in many cases, ages of individual stars are presented without robust estimates of the uncertainty. We have developed a Bayesian framework, BAFFLES, to produce the age posterior for a star from its calcium emission strength (log( ${R}_{{HK}}^{{\prime} }$ )) or lithium abundance (Li EW) and B - V color. We empirically determine the likelihood functions for calcium and lithium as functions of age from literature measurements of stars in benchmark clusters with well-determined ages. We use a uniform prior on age, which reflects a uniform star formation rate. The age posteriors we derive for several test cases are consistent with literature ages found from other methods. BAFFLES represents a robust method to determine the age posterior probability distribution for any field star with 0.45 ≤ B - V ≤ 0.9 and a measurement of ${R}_{{HK}}^{{\prime} }$ and/or 0.35 ≤ B - V ≤ 1.9 and measured Li EW. We compile colors, ${R}_{{HK}}^{{\prime} }$ , and Li EW from over 2630 nearby field stars from the literature, and present the derived BAFFLES age posterior for each star.