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Título: | A detailed non-LTE analysis of LB-1: Revised parameters and surface abundances |
Autor: | Simón-Díaz, S.; Maíz Apellániz, Jesús CSIC ORCID; Lennon, D. J.; González Hernández, Jonay I.; Allende Prieto, Carlos; Castro, N.; Dufton, P. L.; Herrero, A.; Toledo-Padrón, B.; Smartt, S. J.; de Burgos, A. | Fecha de publicación: | 2020 | Editor: | Springer Nature | Citación: | Astronomy and Astrophysics 634: L7 (2020) | Resumen: | Context. It has recently been proposed that LB-1 is a binary system at 4 kpc consisting of a B-type star of 8 M¿ and a massive stellar black hole (BH) of 70 M¿. This finding challenges our current theories of massive star evolution and formation of BHs at solar metallicity. Aims: Our objective is to derive the effective temperature, surface gravity, and chemical composition of the B-type component in order to determine its nature and evolutionary status and, indirectly, to constrain the mass of the BH. Methods: We use the non-LTE stellar atmosphere code FASTWIND to analyze new and archival high-resolution data. Results: We determine (Teff, log g) values of (14 000 ± 500 K, 3.50 ± 0.15 dex) that, combined with the Gaia parallax, imply a spectroscopic mass, from log g, of 3.2+2.1-1.9 M¿ and an evolutionary mass, assuming single star evolution, of 5.2+0.3-0.6 M¿. We determine an upper limit of 8 km s-1 for the projected rotational velocity and derive the surface abundances; we find the star to have a silicon abundance below solar, and to be significantly enhanced in nitrogen and iron and depleted in carbon and magnesium. Complementary evidence derived from a photometric extinction analysis and Gaia yields similar results for Teff and log g and a consistent distance around 2 kpc. Conclusions: We propose that the B-type star is a slightly evolved main sequence star of 3-5 M¿ with surface abundances reminiscent of diffusion in late B/A chemically peculiar stars with low rotational velocities. There is also evidence for CN-processed material in its atmosphere. These conclusions rely critically on the distance inferred from the Gaia parallax. The goodness of fit of the Gaia astrometry also favors a high-inclination orbit. If the orbit is edge-on and the B-type star has a mass of 3-5 M¿, the mass of the dark companion would be 4-5 M¿, which would be easier to explain with our current stellar evolutionary models. | Versión del editor: | http://dx.doi.org/10.1051/0004-6361/201937318 | URI: | http://hdl.handle.net/10261/233623 | DOI: | 10.1051/0004-6361/201937318 | Identificadores: | doi: 10.1051/0004-6361/201937318 issn: 1432-0746 |
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