Benefiting from the Gala 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 similar or equal to 1.2-1.6 Gyr and initial masses 2.1 greater than or similar to M-i/M-circle dot greater than or similar to 1.9), have unusually high core masses, M-c approximate to 0.67-0.7 M-circle dot. These results support the findings of a recent work (Mango 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-c data: the role of stellar winds in single-star evolution, and binary interactions through the blue straggler channel.

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

Marigo, P;Trabucchi, M;Addari, F;Girardi, L;Pastorelli, G;Dal Tio, P;Costa, G;Bressan, A
2022

Abstract

Benefiting from the Gala 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 similar or equal to 1.2-1.6 Gyr and initial masses 2.1 greater than or similar to M-i/M-circle dot greater than or similar to 1.9), have unusually high core masses, M-c approximate to 0.67-0.7 M-circle dot. These results support the findings of a recent work (Mango 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-c data: the role of stellar winds in single-star evolution, and binary interactions through the blue straggler channel.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11577/3420990
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