A Fresh Look at AGB stars in Galactic Open Clusters with Gaia: Impact on Stellar Models and the Initial-Final Mass Relation

• Published in: arXiv.org
• Main Authors: Marigo, Paola, Bossini, Diego, Trabucchi, Michele, Addari, Francesco, Girardi, Léo, Cummings, Jeffrey, Pastorelli, Giada, Piero Dal Tio, Costa, Guglielmo, Bressan, Alessandro
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 05.11.2021
• Subjects: Astronomical models; Asymptotic giant branch stars; Binary stars; Carbon stars; Cosmic dust; Luminosity; M stars; Metallicity; Open clusters; Physics - Astrophysics of Galaxies; Physics - Solar and Stellar Astrophysics; Radiative transfer; Red giant stars; S stars; Star clusters; Stellar evolution; Stellar models; Stellar winds
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2111.03527

Benefiting from the GAIA second and early third releases of photometric and astrometric data we examine the population of asymptotic giant branch (AGB) stars that appear in the fields of intermediate-age and young open star clusters. We identify 49 AGB star candidates, brighter than the tip of the red giant branch, with a good-to-high cluster membership probability. Among them we find 19 TP-AGB stars with known spectral type: 4 M stars, 3 MS/S stars and 12 C stars. By combining observations, stellar models, and radiative transfer calculations that include the effect of circumstellar dust, we characterize each star in terms of initial mass, luminosity, mass-loss rate, core mass, period and mode of pulsation. The information collected helps us shed light on the TP-AGB evolution at solar-like metallicity, placing constraints on the third dredge-up process, the initial masses of carbon stars, stellar winds, and the initial-final mass relation (IFMR). In particular, we find that two bright carbon stars, MSB 75 and BM IV 90, members of the clusters NGC 7789 and NGC 2660 (with similar ages of \(\simeq 1.2-1.6\) Gyr and initial masses \( 2.1 \ge M_{\rm i}/M_{\odot} \ge 1.9\)), have unusually high core masses, \(M_{\rm c} \approx 0.67-0.7\,M_{\odot}\). These results support the findings of a recent work (Marigo et al. 2020) that identified a kink in the IFMR, which interrupts its monotonic trend just at the same initial masses. Finally, we investigate two competing scenarios to explain the \(M_{\rm c}\) data: the role of stellar winds in single-star evolution, and binary interactions through the blue-straggler channel.