| 1. |
- Marigo, Paola, et al.
(författare)
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Carbon star formation as seen through the non-monotonic initial-final mass relation
- 2020
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Ingår i: Nature Astronomy. - : NATURE RESEARCH. - 2397-3366. ; 4:11, s. 1102-
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Tidskriftsartikel (refereegranskat)abstract
- The initial-final mass relation (IFMR) links the birth mass of a star to the mass of the compact remnant left at its death. While the relevance of the IFMR across astrophysics is universally acknowledged, not all of its fine details have yet been resolved. A new analysis of a few carbon-oxygen white dwarfs in old open clusters of the Milky Way led us to identify a kink in the IFMR, located over a range of initial masses, 1.65 less than or similar to M-i/M-circle dot less than or similar to 2.10. The kink's peak in white dwarf mass of about 0.70-0.75 M(circle dot)is produced by stars withM(i) approximate to 1.8-1.9 M-circle dot, corresponding to ages of about 1.8-1.7 Gyr. Interestingly, this peak coincides with the initial mass limit between low-mass stars that develop a degenerate helium core after central hydrogen exhaustion, and intermediate-mass stars that avoid electron degeneracy. We interpret the IFMR kink as the signature of carbon star formation in the Milky Way. This finding is critical to constraining the evolution and chemical enrichment of low-mass stars, and their impact on the spectrophotometric properties of galaxies. An analysis of the relation between a star's initial mass and its final mass (as a white dwarf) reveals a kink in the initial mass range 1.65-2.10 M-circle dot. This kink appears to correspond to the minimum mass required for carbon star formation in the Milky Way at solar metallicity.
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| 2. |
- Pastorelli, Giada, et al.
(författare)
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Constraining the thermally pulsing asymptotic giant branch phase with resolved stellar populations in the Large Magellanic Cloud
- 2020
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 498:3, s. 3283-3301
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Tidskriftsartikel (refereegranskat)abstract
- Reliable models of the thermally pulsing asymptotic giant branch (TP-AGB) phase are of critical importance across astrophysics, including our interpretation of the spectral energy distribution of galaxies, cosmic dust production, and enrichment of the interstellar medium. With the aim of improving sets of stellar isochrones that include a detailed description of the TP-AGB phase, we extend our recent calibration of the AGB population in the Small Magellanic Cloud (SMC) to the more metal-rich Large Magellanic Cloud (LMC). We model the LMC stellar populations with the TRILEGAL code, using the spatially resolved star formation history derived from the VISTA survey. We characterize the efficiency of the third dredge-up by matching the star counts and the K-s-band luminosity functions of the AGB stars identified in the LMC. In line with previous findings, we confirm that, compared to the SMC, the third dredge-up in AGB stars of the LMC is somewhat less efficient, as a consequence of the higher metallicity. The predicted range of initial mass of C-rich stars is between M-i approximate to 1.7 and 3 M-circle dot at Z(i) = 0.008. We show how the inclusion of new opacity data in the carbon star spectra will improve the performance of our models. We discuss the predicted lifetimes, integrated luminosities, and mass-loss rate distributions of the calibrated models. The results of our calibration are included in updated stellar isochrones publicly available.
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| 3. |
- Pastorelli, Giada, et al.
(författare)
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Constraining the thermally pulsing asymptotic giant branch phase with resolved stellar populations in the Small Magellanic Cloud
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 485:4, s. 5666-5692
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Tidskriftsartikel (refereegranskat)abstract
- The thermally pulsing asymptotic giant branch (TP-AGB) experienced by low-and intermediate-mass stars is one of the most uncertain phases of stellar evolution and the models need to be calibrated with the aid of observations. To this purpose, we couple high-quality observations of resolved stars in the Small Magellanic Cloud (SMC) with detailed stellar population synthesis simulations computed with the TRILEGAL code. The strength of our approach relies on the detailed spatially resolved star formation history of the SMC, derived from the deep near-infrared photometry of the VISTA survey of the Magellanic Clouds, as well as on the capability to quickly and accurately explore a wide variety of parameters and effects with the COLIBRI code for the TP-AGB evolution. Adopting a well-characterized set of observations - star counts and luminosity functions - we set up a calibration cycle along which we iteratively change a few key parameters of the TP-AGB models until we eventually reach a good fit to the observations. Our work leads to identify two best-fitting models that mainly differ in the efficiencies of the third dredge-up and mass-loss in TP-AGB stars with initial masses larger than about 3 M-circle dot. On the basis of these calibrated models, we provide a full characterization of the TP-AGB stellar population in the SMC in terms of stellar parameters (initial masses, C/O ratios, carbon excess, mass-loss rates). Extensive tables of isochrones including these improved models are publicly available.
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| 4. |
- Pawlak, Michał, et al.
(författare)
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Investigating the long secondary period phenomenon with the ASAS-SN and Gaia data
- 2024
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Ingår i: Astronomy and Astrophysics. - 0004-6361. ; 682
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Tidskriftsartikel (refereegranskat)abstract
- Aims. The aim of this work is to create a complete list of sources exhibiting a long secondary period (LSP) in the ASAS-SN catalog of variable stars, and analyze the properties of this sample compared to other long period variables without an LSP. Methods. We used the period-amplitude diagram to identify the 55 572 stars showing an LSP, corresponding to 27% of the pulsating red giants in the catalog. We used astrometric data from Gaia DR3 and spectroscopic data provided by the APOGEE, GALAH, and RAVE surveys to investigate the statistical properties of the sample. Results. We find that stars displaying an LSP have a spatial distribution that is more dispersed than that of the non-LSP giants, suggesting that they belong to an older population. Spectroscopically derived ages seem to confirm this. The stars with an LSP also appear to be different in terms of the C/O ratio from their non-LSP counterparts.
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