Variations in the intermediate wind region of the blue supergiant 55 Cygni

0577346 - ASÚ 2024 RIV FR eng J - Journal Article
Cidale, L.S. - Haucke, M. - Arias, M.L. - Kraus, Michaela - Castro, F. C. - Venero, R.O.J. - Mercanti, L. V. - Curé, M. - Granada, A.
Variations in the intermediate wind region of the blue supergiant 55 Cygni.
Astronomy & Astrophysics. Roč. 677, September (2023), č. článku A176. ISSN 0004-6361. E-ISSN 1432-0746
R&D Projects: GA ČR(CZ) GA20-00150S
EU Projects: European Commission(XE) 823734 - POEMS
Institutional support: RVO:67985815
Keywords : supergiants * stars * winds * outflows
OECD category: Astronomy (including astrophysics,space science)
Impact factor: 6.5, year: 2022
Method of publishing: Open access

We seek to enhance our understanding of the wind properties of B supergiants. To this end, we propose analysing their NIR spectra over different epochs to study wind variability and its connection with phenomena arising from regions close to the photosphere. We present the first sets of multi-epoch high-resolution K- and L-band spectra of 55 Cyg acquired with the Gemini Near-InfraRed Spectrograph (GNIRS). We measured line equivalent widths and modelled the Brα line to derive (unclumped) mass-loss rates. Synthetic line profiles were computed for a homogeneous spherical wind by solving the radiative transfer equations in the co-moving frame for a multi-level atom in non-local thermodynamic equilibrium (NLTE). We observe variations in the spectral lines originating in the upper photosphere and the wind. The perturbations, on average, have periods of ~13 and ~23 days, the latter is similar to that found previously from optical data (22.5 days). The NIR lines observed in 2013 are described with the same wind structure used to model a quasi-simultaneous observation in Hα. By contrast, from observations taken in 2015, we derived a higher mean mass-loss rate. Variations in the mass-loss rate are also detected within a few weeks. Interestingly, we find that the profile shape of the Hu14 line sets constraints on the mass loss. Moreover, we find the Mg II doublet in emission, which suggests a tenuous circumstellar gas ring or shell.
Permanent Link: https://hdl.handle.net/11104/0346972