学术文献库

Large scale surveys open the possibility to investigate Galactic evolution both chemically and kinematically, however, reliable stellar ages remain a major challenge. Detailed chemical information provided by high-resolution spectroscopic surveys of the stars in clusters can be used as a means to calibrate recently developed chemical tools for age-dating field stars. Using data from the Open Cluster Abundances and Mapping (OCCAM) survey, based on the SDSS/APOGEE-2 survey, we derive a new empirical relationship between open cluster stellar ages and the carbon-to-nitrogen ([C/N]) abundance ratios for evolved stars, primarily those on the red giant branch. With this calibration, [C/N] can be used a chemical clock for evolved field stars to investigate the formation and evolution of different parts of our Galaxy. We explore how mixing effects at different stellar evolutionary phases, like the red clump, affect the derived calibration. We have established the [C/N]-age calibration for APOGEE DR17 giant star abundances to be $\log[Age({\rm yr})]_{\rm DR17} = 10.14 \, (\pm 0.08) + 2.23\,(\pm 0.19) \, {\rm [C/N]}$, usable for $8.62 \leq \log(Age[{\rm yr}]) \leq 9.82$, derived from a uniform sample of 49 clusters observed as part of APOGEE DR17 applicable primarily to metal-rich, thin and thick disk giant stars. This measured [C/N]-age APOGEE DR17 calibration is also shown to be consistent with astereoseismic ages derived from Kepler photometry.