Volume 621, January 2019
|Number of page(s)||15|
|Section||Stellar structure and evolution|
|Published online||03 January 2019|
Impact of binary interaction on the evolution of blue supergiants
The flux-weighted gravity luminosity relationship and extragalactic distance determinations
School of Physics, Trinity College Dublin, The University of Dublin, Dublin, Ireland
2 Geneva Observatory, University of Geneva, Chemin des Maillettes 51, 1290 Sauverny, Switzerland
3 Institute for Astronomy, Univeristy of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
4 University Observatory Munich, Scheinerstr. 1, 81679 Munich, Germany
5 Department of Physics, Private Bag 92019, University of Auckland, New Zealand
6 Department of Physics and Astronomy, Seoul National University, Gwanak-ro 1, Gwanak-gu, Seoul 08826, Korea
Accepted: 26 September 2018
A large fraction of massive stars evolve in interacting binary systems, which dramatically modifies the outcome of stellar evolution. We investigated the properties of blue supergiants in binary systems and whether they are suitable for extragalactic distance determinations using the flux-weighted gravity luminosity relationship (FGLR). This is a relationship between the absolute bolometric magnitude Mbol and the spectroscopically determined flux-weighted gravity gF = g/T4eff, where g is the surface gravity and Teff is the effective temperature. We computed a grid of binary stellar evolution models with MESA and use the v2.1 BPASS models to examine whether they are compatible with the relatively small scatter shown by the observed relationship. Our models have initial primary masses of 9–30 M⊙, initial orbital periods of 10–2511 days, mass ratio q = 0.9, and metallicity Z = 0.02. We find that the majority of primary stars that produce blue supergiant stages are consistent with the observed FGLR, with a small offset towards brighter bolometric magnitudes. In between 1%–24% of cases, binary evolution may produce blue supergiants after a mass transfer episode, that lie below the observed FGLR. A very small number of such stars have been found in extragalactic FGLR studies, suggesting that they may have evolved through binary interaction. Some models with shorter periods could resemble blue hypergiants and luminous blue variables. We used CMFGEN radiative transfer models to investigate the effects of unresolved secondaries on diagnostics for Teff and g, and the biases on the determination of interstellar reddening and Mbol. We find that the effects are small and within the observed scatter, but could lead to a small overestimate of the luminosity, of Teff and of g for extreme cases. We conclude that the observed FGLR can, in principle, be well reproduced by close binary evolution models. We outline directions for future work, including rotation and binary population synthesis techniques.
Key words: stars: evolution / binaries: general / stars: massive / supergiants / stars: distances
© ESO 2019
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