Interacting massive binaries, HR-diagram of the LMC and SN1987A

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Session 19 -- Supernovae and SNRs
Oral presentation, Monday, 2:30-4:00, Zellerbach Auditorium Room

[19.06] Interacting massive binaries, HR-diagram of the LMC and SN1987A

N. Rathnasree (UVM)

The observational constraints on massive star models for the LMC arise essentially from (1) the distribution of stars in the HR-diagram of the LMC, (2) the observations of SN 1987A and its progenitor and (3) from the determinations of surface abundances of certain blue supergiants in the LMC which are seen to be helium and nitrogen enriched. The standard physical inputs used in single star evolutionary models do not give good agreement with these observational constraints. The study of interacting binary stars, taking into account the effect of the transfer of CNO processed and helium enriched material to the secondaries in these systems, reveals that the presence of a substantial fraction of such stars in the BSG region in the HR-diagram of the LMC gives good agreement with the observational constraints discussed above. Mass transfer to the secondary while it is still within its main-sequence could give an evolutionary model at $ 20 M_{\sun}$ which stays in the blue through out its lifetime and yet could show helium enrichment and CNO processing in its circumstellar material and the envelope of the star consistent with the observations of SN1987A. However, a more consistent model for the progenitor is obtained if the component masses are nearly equal and the secondary star accretes matter from the primary after it evolves to the Hayashi track. The presence of highly helium and nitrogen enriched BSG stars at high temperatures is shown to arise as a natural consequence of interacting binary star evolution, a feature in general difficult to reconcile with all the existing evolutionary models. It is predicted that these stars should be abundant at high temperatures close to the main-sequence while lower temperature regions should be populated by stars with moderate helium and nitrogen enrichment. This research was partially supported by $8^{th}$ Five year plan project 8P-45 at TIFR, India. Supercomputing time on the CRAY XMP and YMP at the University of Illinois is acknowledged.

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