Excess chromospheric emissions within deep photospheric lines are effective proxies of stellar magnetism for FGK stars. This emission decays with stellar age and is a potential determinant of this important stellar quantity. We report absolutely calibrated H𝛼 chromospheric fluxes for 511 solar-type stars in a wide interval of precisely determined masses, [Fe/H], ages, and evolution states from high S/N, moderately high-resolution spectra. The comparison of H𝛼 and H+K chromospheric fluxes reveals a metallicity bias (absent from H𝛼) affecting Ca II H+K fluxes thereby metal-rich stars with deep line profiles mimic low chromospheric flux levels, and vice versa for metal-poor stars. This bias blurs the age-activity relation, precluding age determinations for old, inactive stars unless mass and [Fe/H] are calibrated into the relation. The H+K lines being the most widely studied tool to quantify magnetic activity in FGK stars, care should be exercised in its use whenever wide ranges of mass and [Fe/H] are involved. The H𝛼 age-activity-mass-metallicity calibration appears to be in line with the theoretical expectation that (other parameters being equal) more massive stars possess narrower convective zones and are less active than less massive stars, while more metal-rich stars have deeper convective zones and appear more active than metal-poorer stars. If regarded statistically in tandem with other age diagnostics, H𝛼 chromospheric fluxes may be suitable to constrain ages for FGK stars with acceptable precision.

Files: table3.dat Atmospheric parameters collected from the literature and the final values used in this paper for the sample stars. -- table4.dat Bolometric correction and magnitude, luminosity, radius, mass and age for the sample stars. -- table5.dat Final total and purely chromospheric fluxes for the sample stars. -- table10.dat Chromospheric ages for the sample stars

Peer reviewed