The nature of the Cygnus extreme B supergiant 2MASS J20395358+4222505

• Published in: Monthly notices of the Royal Astronomical Society Vol. 511; no. 3; pp. 3113 - 3124
• Main Authors: Herrero, A, Berlanas, S R, Gil de Paz, A, Comerón, F, Puls, J, Ramírez Alegría, S, Garcia, M, Lennon, D J, Najarro, F, Simón-Díaz, S, Urbaneja, M A, Gallego, J, Carrasco, E, Iglesias, J, Cedazo, R, García Vargas, M L, Castillo-Morales, Á, Pascual, S, Cardiel, N, Pérez-Calpena, A, Gómez-Alvarez, P, Martínez-Delgado, I
• Format: Journal Article
• Language: English
• Published: 22.02.2022
• DOI: 10.1093/mnras/stab3660
• ISSN: 0035-8711

ABSTRACT 2MASS J20395358+4222505  is an obscured early B supergiant near the massive OB star association Cygnus OB2. Despite its bright infrared magnitude (Ks = 5.82) it has remained largely ignored because of its dim optical magnitude (B = 16.63, V = 13.68). In a previous paper, we classified it as a highly reddened, potentially extremely luminous, early B-type supergiant. We obtained its spectrum in the U, B and R spectral bands during commissioning observations with the instrument MEGARA at the Gran Telescopio CANARIAS. It displays a particularly strong Hα emission for its spectral type, B1 Ia. The star seems to be in an intermediate phase between supergiant and hypergiant, a group that it will probably join in the near (astronomical) future. We observe a radial velocity difference between individual observations and determine the stellar parameters, obtaining Teff = 24 000 K and log gc = 2.88 ± 0.15. The rotational velocity found is large for a B supergiant, $v$ sin i = 110 ± 25 $\rm km\, s^{-1}$. The abundance pattern is consistent with solar, with a mild C  underabundance (based on a single line). Assuming that J20395358+4222505  is at the distance of Cyg OB2, we derive the radius from infrared photometry, finding R = 41.2 ± 4.0 R⊙, log(L/L⊙) = 5.71 ± 0.04 and a spectroscopic mass of 46.5 ± 15.0 M⊙. The clumped mass-loss rate (clumping factor 10) is very high for the spectral type, $\dot{M}$ = 2.4 × 10−6 M⊙ a−1. The high rotational velocity and mass-loss rate place the star at the hot side of the bi-stability jump. Together with the nearly solar CNO abundance pattern, they may also point to evolution in a binary system, J20395358+4222505  being the initial secondary.