Stellar ages

(G. Casali, E. Franciosini, L. Magrini, S. Randich, G. Sacco)

Stellar ages are important ingredients of Galactic Astronomy, since they allow us to trace back the star formation history and to investigate the Galactic structure in previous epochs. However, they are among the most elusive stellar properties. The most common method to derive stellar ages is the isochrone fitting technique, very effective for star clusters (Randich et al., 2018), in particular when combined with the Gaia satellite data, but less reliable for field stars.

In our group, we are investigating the use of chemical abundance ratios, the so-called chemical clocks, to measure stellar ages. These ratios, calibrated on stars with well-known ages (such as open clusters or solar-twin stars), are allowing us to derive ages of large sample of stars through empirical relationships.

So far, we have calibrated relationships between the [C/N] abundance ratio in giant stars and age using Galactic open clusters observed by the Gaia-ESO and APOGEE surveys (Casali et al. 2019), and between slow neutron-capture (as, e.g. Yttrium) over alpha (e.g. Mg) abundance ratios vs the age of solar-twin stars (Casali et al. 2020). Both these relationships have been successfully applied to the Milky Way field stars allowing us to detect differences in age between the thin and thick disc populations.

The new spectroscopic surveys and instruments in which we are involved (e.g., WEAVE, MOONS, MSE, MAVIS) will allow us to extend the use of these relationships and to find new ones to larger sample of Galactic populations.

Figure 1: Relation between [C/N] and age in open clusters observed by Gaia-ESO and APOGEE surveys (from Casali et al. 2019).