Astron. Astrophys. 629, A62 (2019)

In a star, the ratio of elemental abundances of carbon to nitrogen depends on its evolution. Because the relative abundance of carbon to nitrogen in the stellar surface is related to the stellar mass, which for red giants is sensitive to the star’s age, it gives an estimate of stellar age — telling us more about the formation of a galaxy. However, ages of individual red giants are poorly constrained.

Giada Casali and colleagues have now reported an empirical relationship between the carbon-to-nitrogen abundance ratio in a star and its age for red giants observed with the Gaia-ESO and APOGEE spectroscopic surveys. The stars in the thin galactic disk were shown to typically be younger than those in the thick disk, confirming previous results. The data indicate that the disk evolved from the inside to the outside, and that the metal-rich stars in the inner thin disk formed at later stages of the galactic evolution. With the derived empirical formula, the age of red giants can be determined more precisely.