Estimating the Ages of FGK Dwarf Stars through the Use of GALEX FUV Magnitudes

Abstract

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 and absolute magnitude range 4.3 ≤ M V ≤ 5.3. The correlation is defined in terms of a FUV-excess parameter . We related stellar age, τ, to Q through the relation , 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.

Age-velocity relations with GALEX $FUV$-determined ages of Sun-like, solar neighborhood stars

“…Development of our new age-calibration comes from an F UV -based analysis similar to that of Crandall et al (2020) in which stellar age data from four catalogs were combined to produce a set of calibration stars. Each of these catalogs, Ballering et al (2013), Isaacson and Fischer (2010) Isaacson and Fischer (2010) were derived via log R HK and calibrations from Mamajek and Hillenbrand (2008).…”

“…2.1 against the Q values for each star. Following Crandall et al (2020), the fitting function that we use is a linear equation involving the natural logarithm of the stellar age τ , which is taken to be in units of Gyr throughout this paper. The basic age-calibration equation that we empirically adopt is thus the Equation (1) given above.…”

“…In Crandall et al (2020) the stellar activity-age relationship is the basis of a calibration between stellar age and far-ultraviolet (F UV ) brightness which can be added to the toolbox of other age-dating techniques. Therein F UV magnitude observations from the Galaxy Evolution Explorer telescope (GALEX) are shown to be tracers of chromospheric activity (see e.g.…”

“…Smith and Redenbaugh 2010) and hence age (Findeisen et al 2011). Crandall et al (2020) derived an F UV -age calibration through which ages may be determined without introducing errors associated with model-based methodologies, such as isochrone fitting.…”

“…The F UV -age relationship in Crandall et al (2020) is calibrated in a combined GALEX F UV and Johnson B and V color space. In Sect.…”