Mon. Not. R. Astron. Soc., 480, 3706-3717 (2018/November-1)
On the evolutionary state of massive stars in transition phases in M33.
KOURNIOTIS M., KRAUS M., ARIAS M.L., CIDALE L. and TORRES A.F.
Abstract (from CDS):
The advanced stages of several high-mass stars are characterized by episodic mass-loss shed during phases of instability. Key for assigning these stars a proper evolutionary state is to assess the composition and geometry of their ejecta alongside the stellar properties. We selected five hot luminous blue variable candidates in M33 to refine their classification, investigate their circumstellar environments, and explore their evolutionary properties. Being accessible targets in the near-infrared, we conducted medium-resolution spectroscopy with GNIRS/GEMINI in the K-band to investigate their molecular circumstellar environments. Two stars were found to display CO emission, which was modelled to emerge from a circumstellar or circumbinary Keplerian disc/ring. The identification of the carbon isotope 13C and, for one of the two stars, a significantly low 12CO/13CO ratio, implies an evolved stellar state. As both CO emission stars are highly luminous and hence do not undergo a red supergiant phase, we suggest that stripping processes and equatorial high-density ejecta due to fast rotation are responsible for the enrichment of the stellar surface with processed material from the core. A candidate B[e]SG displays an absorption CO profile, which may be attributed to a jet or stellar pulsations. The featureless infrared spectra of two stars suggest a low-density gas shell or dissipation of the molecule due to the ionizing temperature of the star. We propose spectroscopic monitoring of our targets to evaluate the stability of the CO molecule and assess the time-dependent dynamics of the circumstellar gas structures.
© 2018 The Author(s) Published by Oxford University Press on behalf of the Royal Astronomical Society
circumstellar matter - stars: emission line, Be - stars: massive - supergiants - stars: winds, outflows - infrared: stars
View the reference in ADS
To bookmark this query, right click on this link: simbad:2018MNRAS.480.3706K and select 'bookmark this link' or equivalent in the popup menu