DISCOVERY OF THE MASSIVE OVERCONTACT BINARY VFTS 352: EVIDENCE FOR ENHANCED INTERNAL MIXING

Author(s):Show less -

Almeida, L. A. ^{[1, 2]} ; Sana, H. ^{[3, 4]} ; de Mink, S. E. ^[5] ; Tramper, F. ^[5] ; Soszynski, I. ^[6] ; Langer, N. ^[7] ; Barba, R. H. ^[8] ; Cantiello, M. ^[9] ; Damineli, A. ^[2] ; de Koter, A. ^{[5, 10]} ; Garcia, M. ^[11] ; Graefener, G. ^[12] ; Herrero, A. ^{[13, 14]} ; Howarth, I. ^[15] ; Maiz Apellanz, J. ^[11] ; Norman, C. ^[1] ; Ramirez-Agudelo, O. H. ^[5] ; Vink, J. S. ^[12]

Affiliation:Show less -

^[1] Johns Hopkins Univ, Dept Phys & Astron, Bloomberg Ctr Phys & Astron, Baltimore, MD 21218 - USA

^[2] Inst Astron Geofis & Ciencias, BR-05508090 Sao Paulo, SP - Brazil

^[3] European Space Agcy, Space Telescope Sci Inst, Baltimore, MD 21218 - USA

^[4] Katholieke Univ Leuven, Inst Astron, B-3001 Leuven - Belgium

^[5] Univ Amsterdam, Anton Pannenkoek Astron Inst, NL-1090 GE Amsterdam - Netherlands

^[6] Univ Warsaw Observ, PL-00478 Warsaw - Poland

^[7] Univ Bonn, Argelander Inst Astron, D-53121 Bonn - Germany

^[8] Univ La Serena, Dept Fis & Astron, La Serena - Chile

^[9] Univ Calif Santa Barbara, Kavli Inst Theoret Phys, Santa Barbara, CA 93106 - USA

^[10] Univ Leuven, Inst Sterrenkunde, B-3001 Leuven - Belgium

^[11] Ctr Astrobiol INTA CSIC, Dept Astrofis, Madrid 28691 - Spain

^[12] Armagh Observ, Armagh BT61 9DG - North Ireland

^[13] Inst Astrofis Canarias, E-38200 Tenerife - Spain

^[14] Univ La Laguna, Dept Astrofis, E-38071 Tenerife - Spain

^[15] UCL, Dept Phys Astron, London WC1E 6BT - England

• Document type: Journal article
• Source: ASTROPHYSICAL JOURNAL; v. 812, n. 2 OCT 20 2015.
• Web of Science Citations: 13

Abstract

The contact phase expected to precede the coalescence of two massive stars is poorly characterized due to the paucity of observational constraints. Here we report on the discovery of VFTS 352, an O-type binary in the 30 Doradus region, as the most massive and earliest spectral type overcontact system known to date. We derived the 3D geometry of the system, its orbital period P-orb = 1.1241452(4) day, components' effective temperatures-T-1 = 42 540 +/- 280 K and T-2 = 41 120 +/- 290 K-and dynamical masses-M-1 = 28.63 +/- 0.30 M-circle dot and M-2= 28.85 +/- 0.30 M-circle dot. Compared to single-star evolutionary models, the VFTS 352 components are too hot for their dynamical masses by about 2700 and 1100 K, respectively. These results can be explained naturally as a result of enhanced mixing, theoretically predicted to occur in very short-period tidally locked systems. The VFTS 352 components are two of the best candidates identified so far to undergo this so-called chemically homogeneous evolution. The future of VFTS 352 is uncertain. If the two stars merge, a very rapidly rotating star will be produced. Instead, if the stars continue to evolve homogeneously and keep shrinking within their Roche Lobes, coalescence can be avoided. In this case, tides may counteract the spin down by winds such that the VFTS 352 components may, at the end of their life, fulfill the requirements for long gamma-ray burst (GRB) progenitors in the collapsar scenario. Independently of whether the VFTS 352 components become GRB progenitors, this scenario makes VFTS 352 interesting as a progenitor of a black hole binary, hence as a potential gravitational wave source through black hole-black hole merger. (AU)

• FAPESP's process: 12/09716-6 - Accurate distances to young clusters through massive eclipsing binaries
• Grantee: Leonardo Andrade de Almeida
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 13/18245-0 - Full spectroscopic orbital solutions for more than 100 massive binaries in the high-mass starburst region 30 Doradus
• Grantee: Leonardo Andrade de Almeida
• Support Opportunities: Scholarships abroad - Research Internship - Post-doctor