Browsing by Author "Gormaz-Matamala, A. C."

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    Evolution of massive stars with new hydrodynamic wind models
    (2022) Gormaz-Matamala, A. C.; Cure, M.; Meynet, G.; Cuadra, J.; Groh, J. H.; Murphy, L. J.
    Context. Mass loss through radiatively line-driven winds is central to our understanding of the evolution of massive stars in both single and multiple systems. This mass loss plays a key role in modulating massive star evolution at different metallicities, especially in the case of very massive stars (M* >= 25 M-circle dot).
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    Evolution of rotating massive stars adopting a newer, self-consistent wind prescription at Small Magellanic Cloud metallicity
    (2024) Gormaz-Matamala, A. C.; Cuadra, J.; Ekstrom, S.; Meynet, G.; Cure, M.; Belczynski, K.
    Aims. We aim to measure the impact of our mass-loss recipe in the evolution of massive stars at the metallicity of the Small Magellanic Cloud (SMC). Methods. We used the Geneva-evolution code (GENEC) to run evolutionary tracks for stellar masses ranging from 20 to 85 M-circle dot at SMC metallicity (Z(SMC) = 0.002). We upgraded the recipe for stellar winds by replacing Vink's formula with our self-consistent m-CAK prescription, which reduces the value of the mass-loss rate, (M) over dot, by a factor of between two and six depending on the mass range. Results. The impact of our new [weaker] winds is wide, and it can be divided between direct and indirect impact. For the most massive models (60 and 85 M-circle dot) with (M) over dot greater than or similar to 2 x 10(-7) M-circle dot yr(-1), the impact is direct because lower mass loss make stars remove less envelope, and therefore they remain more massive and less chemically enriched at their surface at the end of their main sequence (MS) phase. For the less massive models (20 and 25 M-circle dot) with (M) over dot less than or similar to 2 x 10(-8) M-circle dot yr(-1), the impact is indirect because lower mass loss means the stars keep high rotational velocities for a longer period of time, thus extending the H-core burning lifetime and subsequently reaching the end of the MS with higher surface enrichment. In either case, given that the conditions at the end of the H-core burning change, the stars will lose more mass during their He-core burning stages anyway. For the case of M-zams = 20-40 M-circle dot, our models predict stars will evolve through the Hertzsprung gap, from O-type supergiants to blue supergiants (BSGs), and finally red supergiants (RSGs), with larger mass fractions of helium compared to old evolution models. New models also sets the minimal initial mass required for a single star to become a Wolf-Rayet (WR) at metallicity Z = 0.002 at M-zams = 85 M-circle dot. Conclusions. These results reinforce the importance of upgrading mass-loss prescriptions in evolution models, in particular for the earlier stages of stellar lifetime, even for Z << Z(circle dot). New values for (M) over dot need to be complemented with upgrades in additional features such as convective-core overshooting and distribution of rotational velocities, besides more detailed spectroscopical observations from projects such as XShootU, in order to provide a robust framework for the study of massive stars at low-metallicity environments.
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    Evolution of rotating massive stars with new hydrodynamic wind models
    (2023) Gormaz-Matamala, A. C.; Cuadra, J.; Meynet, G.; Cure, M.
    Context. Mass loss due to radiatively line-driven winds is central to our understanding of the evolution of massive stars in both single and multiple systems. This mass loss plays a key role in modulating the stellar evolution at different metallicities, particularly in the case of massive stars with M-* >= 25 M-circle dot.
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    X-Shooting ULLYSES: Massive stars at low metallicity IV. Spectral analysis methods and exemplary results for O stars
    (2024) Sander, A. A. C.; Bouret, J. -C.; Bernini-Peron, M.; Puls, J.; Backs, F.; Berlanas, S. R.; Bestenlehner, J. M.; Brands, S. A.; Herrero, A.; Martins, F.; Maryeva, O.; Pauli, D.; Ramachandran, V.; Crowther, P. A.; Gomez-Gonzalez, V. M. A.; Gormaz-Matamala, A. C.; Hamann, W. -R.; Hillier, D. J.; Kuiper, R.; Larkin, C. J. K.; Lefever, R. R.; Mehner, A.; Najarro, F.; Oskinova, L. M.; Schoesser, E. C.; Shenar, T.; Todt, H.; ud-Doula, A.; Vink, J. S.
    Context. The spectral analysis of hot, massive stars is a fundamental astrophysical method of determining their intrinsic properties and feedback. With their inherent, radiation-driven winds, the quantitative spectroscopy for hot, massive stars requires detailed numerical modeling of the atmosphere and an iterative treatment in order to obtain the best solution within a given framework. Aims. We present an overview of different techniques for the quantitative spectroscopy of hot stars employed within the X-Shooting ULLYSES collaboration, ranging from grid-based approaches to tailored spectral fits. By performing a blind test for selected targets, we gain an overview of the similarities and differences between the resulting stellar and wind parameters. Our study is not a systematic benchmark between different codes or methods; our aim is to provide an overview of the parameter spread caused by different approaches. Methods. For three different stars from the XShooting ULLYSES sample (SMC O5 star AzV 377, LMC O7 star Sk -69 degrees 50, and LMC O9 star Sk-66 degrees 171), we employ different stellar atmosphere codes (CMFGEN, Fastwind, PoWR) and different strategies to determine their best-fitting model solutions. For our analyses, UV and optical spectroscopy are used to derive the stellar and wind properties with some methods relying purely on optical data for comparison. To determine the overall spectral energy distribution, we further employ additional photometry from the literature. Results. The effective temperatures found for each of the three different sample stars agree within 3 kK, while the differences in log g can be up to 0.2 dex. Luminosity differences of up to 0.1 dex result from different reddening assumptions, which seem to be systematically larger for the methods employing a genetic algorithm. All sample stars are found to be enriched in nitrogen. The terminal wind velocities are surprisingly similar and do not strictly follow the u infinity-Teff relation. Conclusions. We find reasonable agreement in terms of the derived stellar and wind parameters between the different methods. Tailored fitting methods tend to be able to minimize or avoid discrepancies obtained with coarser or increasingly automatized treatments. The inclusion of UV spectral data is essential for the determination of realistic wind parameters. For one target (Sk -69 degrees 50), we find clear indications of an evolved status.