Rotation is always known as an important ingredient in stellar models. Studying the impacts of rotation on stellar structure and evolution is the goal of my thesis. PARSEC models is being widely used in the astronomical com munity over the last decade. Nevertheless, for the first time, the PARSEC rotating stellar tracks and isochrones are provided to the community, with a suitable range of masses and metallicities. Specifically, we consider the mod els from very low mass up to 14M⊙, and the metallicity ranges from 0.004 to 0.017. The PARSEC V2.0 code is used to perform the calculations, and the dedicated sites are created for delivering them to users. The concurrence between rotation and the convective core overshooting phenomenon has been carefully calibrated in previous works. In this project, I inherit this result and adopt the maximum value of core overshooting ef ficiency parameter λov,max = 0.4. A linear growth from zero of stars that do not develop a convective core to this maximum value where stars already have a fully convective core is adopted for stars with masses in the transition region. The shellular rotation is treated as a purely diffusive process under the assumption of Roche model. Seven initial rotation rates are considered from zero to the extremely close critical velocity (namely, ωi = 0 − 0.99). The mass loss process is now applied during the evolution of stars due to the enhancement caused by rotation, with the suitable adopted rates that depend on the mass range. In this project, the low-mass (0.8 ≳ M ≳ 2M⊙) and intermediate-mass (2 ≳ M ≳ 14M⊙) are the main targets of the analysis in this thesis. The effects of geometrical distortion and rotational mixing are clearly seen in the Hertzsprung-Russell diagram of our tracks. We have seen the rotating stars spend their time longer in the Main-Sequence phase with respect to their non-rotating counterparts. Also, the higher core mass they would have at the post-main-sequence phases. Especially in the case of intermediate-mass stars, where the CNO-cycles are the main channel of nuclear burning during the main-sequence, the enhancement (depletion) of surface nitrogen and helium (carbon and oxygen) are the most evidence of rotational mixing. Indeed, the faster stars rotate the more enhancement/de pletion. As a consequence, with our new models, we can reproduce very well the hook feature of the open cluster M67, as well as the “global” fitting. Furthermore, we also see a hint of at least two populations that harbour in the open cluster NGC 6633 to explain the extended main-sequence and the position of the three He-clump stars. Finally, this new collection of stellar tracks and corresponding isochrones are available online at the dedicated websites, and most suitably used for studies of young and intermediate-age open clusters.

Stellar Evolution with Rotation in PARSEC v2.0: Tracks and Isochrones for Low- and Intermediate-mass Stars / Nguyen, CHI THANH. - (2022 Dec 22).

Stellar Evolution with Rotation in PARSEC v2.0: Tracks and Isochrones for Low- and Intermediate-mass Stars

NGUYEN, CHI THANH
2022-12-22

Abstract

Rotation is always known as an important ingredient in stellar models. Studying the impacts of rotation on stellar structure and evolution is the goal of my thesis. PARSEC models is being widely used in the astronomical com munity over the last decade. Nevertheless, for the first time, the PARSEC rotating stellar tracks and isochrones are provided to the community, with a suitable range of masses and metallicities. Specifically, we consider the mod els from very low mass up to 14M⊙, and the metallicity ranges from 0.004 to 0.017. The PARSEC V2.0 code is used to perform the calculations, and the dedicated sites are created for delivering them to users. The concurrence between rotation and the convective core overshooting phenomenon has been carefully calibrated in previous works. In this project, I inherit this result and adopt the maximum value of core overshooting ef ficiency parameter λov,max = 0.4. A linear growth from zero of stars that do not develop a convective core to this maximum value where stars already have a fully convective core is adopted for stars with masses in the transition region. The shellular rotation is treated as a purely diffusive process under the assumption of Roche model. Seven initial rotation rates are considered from zero to the extremely close critical velocity (namely, ωi = 0 − 0.99). The mass loss process is now applied during the evolution of stars due to the enhancement caused by rotation, with the suitable adopted rates that depend on the mass range. In this project, the low-mass (0.8 ≳ M ≳ 2M⊙) and intermediate-mass (2 ≳ M ≳ 14M⊙) are the main targets of the analysis in this thesis. The effects of geometrical distortion and rotational mixing are clearly seen in the Hertzsprung-Russell diagram of our tracks. We have seen the rotating stars spend their time longer in the Main-Sequence phase with respect to their non-rotating counterparts. Also, the higher core mass they would have at the post-main-sequence phases. Especially in the case of intermediate-mass stars, where the CNO-cycles are the main channel of nuclear burning during the main-sequence, the enhancement (depletion) of surface nitrogen and helium (carbon and oxygen) are the most evidence of rotational mixing. Indeed, the faster stars rotate the more enhancement/de pletion. As a consequence, with our new models, we can reproduce very well the hook feature of the open cluster M67, as well as the “global” fitting. Furthermore, we also see a hint of at least two populations that harbour in the open cluster NGC 6633 to explain the extended main-sequence and the position of the three He-clump stars. Finally, this new collection of stellar tracks and corresponding isochrones are available online at the dedicated websites, and most suitably used for studies of young and intermediate-age open clusters.
Bressan, Alessandro
Girardi, Leo Alberto
Costa, Guglielmo
Nguyen, CHI THANH
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/20.500.11767/130690
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