Evolution of binary stars in the LMC with helium enrichment

• Published in: Monthly notices of the Royal Astronomical Society Vol. 250; no. 2; pp. 453 - 457
• Main Authors: Ray, A., Rathnasree, N.
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford University Press 15.05.1991; Blackwell Science
• Subjects: Astronomy; Earth, ocean, space; Exact sciences and technology; Giant and subgiant stars; Normal stars (by class): general or individual; Stars; Massive star; Data analysis; Spatial distribution; Digital simulation; Color magnitude diagram; Binary star; X ray binary; Stellar evolution; Supergiant; Large Magellanic Cloud
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/250.2.453

Recent surveys of supergiant stars in the LMC indicate that the post-main-sequence region of the colour–magnitude diagram is well populated, although numerical evolution of massive stars with normal surface hydrogen indicates to the contrary. Supergiant stars having surface enrichment of helium acquired for example from a previous phase of accretion from a binary companion, however, evolve in a way so that the evolved models and observed data are consistent – an observation first made by Tuchman & Wheeler. We compare the available data with computed evolutionary tracks of massive stars of metallicity relevant to the LMC with and without helium-enriched envelopes and conclude that a large fraction ( ≈ 60 per cent) of supergiant stars may occur in binaries. Since these binaries will later evolve into massive X-ray binaries, the observed number and orbital period distribution of the latter in the LMC can constrain the evolutionary scenarios of the supergiant binaries. The distribution of post-main-sequence binaries and closely related systems like WR + O stars obtained from these constraints, is bimodal consisting of close and wide binaries. Single radio pulsars which arise out of long-period binaries may cluster around OB associations in the LMC because of their low velocity of ejection after a second supernova explosion.