The isolation of luminous blue variables resembles aging B-type supergiants, not the most massive unevolved stars

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Abstract

Luminous blue variables (LBVs) are suprisingly isolated from the massive O-type stars that are their putative progenitors in single-star evolution, implicating LBVs as binary evolution products. Aadland et al. found that LBVs are, however, only marginally more dispersed than a photometrically selected sample of bright blue stars (BBS) in the Large Magellanic Cloud (LMC), leading them to suggest that LBV environments may not exclude a single-star origin. In both comparisons, LBVs have the same median separation, confirming that any incompleteness in the O-star sample does not fabricate LBV isolation. Instead, the relative difference arises because the photometric BBS sample is farmore dispersed than known O-type stars. Evidence suggests that the large BBS separation arises because it traces less massive (∼20 M), aging blue supergiants. Although photometric criteria used by A19 aimed to select only the most massive unevolved stars, visual-wavelength colour selection cannot avoid contamination because O and early B stars have almost the same intrinsic colour. Spectral types confirm that the BBS sample contains many B supergiants. Moreover, the observed BBS separation distribution matches that of spectroscopically confirmed early B supergiants, not O-type stars, and matches predictions for a roughly 10 Myr population, not a 3-4 Myr population. A broader implication for ages of stellar populations is that bright blue stars are not a good tracer of the youngest massive O-type stars. Bright blue stars in nearby galaxies (and unresolved blue light in distant galaxies) generally trace evolved blue supergiants akin to SN 1987A's progenitor.

Original languageEnglish (US)
Pages (from-to)4378-4388
Number of pages11
JournalMonthly Notices of the Royal Astronomical Society
Volume489
Issue number3
DOIs
StatePublished - Jan 1 2019

Keywords

  • Binaries: General
  • Blue stragglers
  • Stars: Evolution
  • Stars: Massive
  • Stars: Wolf-Rayet

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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