Post first dredge-up [C/N] ratio as age indicator. Theoretical calibration

Salaris, MaurizioMaurizioSalarisPIETRINFERNI, AdrianoAdrianoPIETRINFERNIPIERSIMONI, Anna MarinaAnna MarinaPIERSIMONICASSISI, SantiSantiCASSISI2020-04-032020-04-0320150004-6361http://hdl.handle.net/20.500.12386/23802S.C. and A.M.P. warmly thank financial support by PRIN-INAF2014 (PI: S. Cassisi), and by Economy and Competitiveness Ministry of the Kingdom of Spain (grant AYA2013-42781-P). A.P. acknowledges financial support by PRIN-INAF2013 (PI: L. Bedin).We performed a detailed analysis of the use of [C/N] measured in red giant branch stars between the completion of the first dredge up and the red giant branch bump ([C/N] FDU) as age indicator. [C/N] FDU cannot give accurate ages for individual stars, but may provide a general chronology for the formation of composite populations and add constraints to analyses of red giants from surface gravity-effective temperature diagrams. We provide a theoretical calibration of [C/N] FDU in terms of total metallicity [M/H] and age, for ages greater than ~1 Gyr, which we tested against variations in the initial heavy element distribution (scaled-solar vs. α-enhanced), efficiency of overshooting from MS convective cores and from the convective envelopes, variations in the initial He abundance and in the mixing length parameter. Our calibration is compared with a small sample of available measurements of [C/N] FDU in star clusters and halo field stars, which at least qualitatively confirm the overall trend of the predicted [C/N] FDU with age and [M/H]. The use of [C/N] FDU-[M/H]-age relations obtained from independent sets of stellar evolution calculations cause age differences (for a given [C/N] FDU and [M/H] pair) up to ~2 Gyr. More accurate spectroscopic measurements of [C/N] FDU in star clusters with well-established ages and metallicities are required to better test theoretical calibrations of this age indicator.STAMPAenPost first dredge-up [C/N] ratio as age indicator. Theoretical calibrationArticle10.1051/0004-6361/2015269512-s2.0-84946554218000365072200133https://www.aanda.org/articles/aa/abs/2015/11/aa26951-15/aa26951-15.html2015A&A...583A..87SFIS/05 - ASTRONOMIA E ASTROFISICA