Browsing by Author "Puls, J."

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    The wind of rotating B supergiants - II. The δ-slow hydrodynamic regime
    (2024) Venero, R. O. J.; Cure, M.; Puls, J.; Cidale, L. S.; Haucke, M.; Araya, I.; Gormaz-Matamala, A.; Arcos, C.
    The theory of line-driven winds can explain many observed spectral features in early-type stars, though our understanding the winds of B supergiants remains incomplete. The hydrodynamic equations for slowly rotating stellar winds predict two regimes based on the line-force parameter delta: the fast and the delta -slow solution. In this paper, we aim to explore the capability of the latter to explain the observed properties of B supergiant winds. We calculate H alpha line profiles, the most sensitive wind diagnostics in the optical, for both fast and delta -slow wind models. We fit them to observed data from a well-studied sample of B supergiants, by adapting the line-force parameters (k, alpha, and delta) of the hydrodynamic model. Unexpectedly, the observed H alpha spectra can be reproduced by both hydrodynamic wind regimes with similar precision. We argue that this similarity results from the similar shape of the normalized velocity law produced by both regimes in the lower, H alpha -forming wind region. Our findings raise a dichotomy, because mass-loss rates and terminal velocities (v(infinity)) for each solution are quite different. The delta -slow solution predicts maximum values for v(infinity) that are systematically lower than those measured in the ultraviolet, whereas the v(infinity) values of the fast solution are closer, and probably more appropriate. However, our results also indicate that the delta -slow solution might better describe the dense winds of B hypergiants. Multiwavelength analyses and a larger sample of stars are needed to reach a definitive conclusion.
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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.