Luminosity recipes for Solar-type stars as a function of mass, rotation, metallicity and age

We present new comprehensive outputs for models that track luminosity evolution for low-mass stars from 0.5 to 1.2 M_SUN over a range of metallicities: Z = (0.006) 0.01 to 0.04. Our calculations use the MESA advanced, open-source 1D stellar evolution code (Paxton et al., 2019; Jermyn et al. 2023) to compute relevant parameters including bolometric luminosity, temperature (color), atmospheric convection, stellar abundances and gravitational settling effects. Output is compared with color-magnitude diagrams for a suite of stellar ages for benchmark stars and the Sun. Our new MESA mass-age-color-magnitude metallicity relationships are used as input for a model which describes the evolution of high energy X-ray and extreme ultraviolet (XUV), and Ly-α emission for F, G, K, and M dwarfs validated against young clusters (Johnstone et al., 2021; Scherf et al., 2024). We use a database of rotation rates for 30,000 F-G-K-M stars from the Kepler catalogue, filtered for those with surface gravitational acceleration g where log g < 3.5 to discard those off of the Main Sequence. At all ages, a star’s XUV evolution is determined not only by its mass and rotation rate, but also by its metallicity. As expected, we find that stars of solar mass and greater (F-G) are more XUV luminous than lower mass stars stars, and rapid rotators in these categories are more active in XUV than slow rotators. We also show that high metallicity stars have lower luminance owing to higher opacity but greater XUV output for a given mass and rotation. Our results underscore the requirement that comprehensive treatments of the atmospheric evolution of exoplanets (e.g. photochemistry) must account for stellar evolution as a function of rotation, mass and metallicity (Mojzsis et al., this meeting). Further, spectroscopic analyses of stars for devolatilization calculations of plausible exoplanet compositions (e.g. Spargaaren et al., 2023) may also need to correct for gravitational settling in certain circumstances. This model does not have enhancement in alpha elements (like, C and O), as we may expect from stars with that metallicity. We are in the process of producing a library of models with and without alpha enhancement for the metallicities affected. Interestingly, we find that the Sun is anomalous in the overall population by being both a (very) slow rotator (25 d) for a G star (mean 12.4 d) at moderate metallicity (Z=0.01-0.02) with particularly low activity.

 

Jermyn, A.S. et al. (2023) Modules for Experiments in Stellar Astrophysics (MESA): Time-dependent Convection, Energy Conservation, Automatic Differentiation, and Infrastructure. The Astrophysical Journal Supplement Series: 265 (1).

Paxton, B. et al. (2019) Modules for Experiments in Stellar Astrophysics (MESA): Pulsating Variable Stars, Rotation, Convective Boundaries, and Energy Conservation. The Astrophysical Journal Supplement Series: 243 (1).

Johnstone, C.P. et al. (2021) The active lives of stars: A complete description of the rotation and XUV evolution of F, G, K, and M dwarfs. Astronomy & Astrophysics: 649, A96.

Scherf, M., Lammer, H., and Spross, L. (2024) Eta-Earth Revisited II: Deriving a Maximum Number of Earth-Like Habitats in the Galactic Disk. Astrobiology: 24, e916

Spargaaren, R.J., Wang, H.S., Mojzsis, S.J., Ballmer, M.D., and Tackley, P.J. (2023) Plausible Constraints on the Range of Bulk Terrestrial Exoplanet Compositions in the Solar Neighborhood. The Astrophysical Journal: 948 (1).