The VLT-FLAMES Tarantula Survey

XXIII. Two massive double-lined binaries in 30 Doradus^⋆,⋆⋆

¹ Department of Physics & Astronomy, University College London, Gower Street, London, WC1E 6BT, UK
² Astrophysics Research Centre, Queen’s University Belfast, BT7 1NN, Northern Ireland, UK
³ UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ, UK
⁴ Department of Physics & Astronomy, Johns Hopkins University, Bloomberg Center for Physics and Astronomy, Room 520, 3400 N. Charles Street, Baltimore, MD 21218, USA
⁵ Instituto de Astronomia, Geofísica e Ciências, Rua do Matão 1226, Cidade Universitária São Paulo, 05508-090 São Paulo SP, Brasil
⁶ IAASARS, National Observatory of Athens, 15236 Penteli, Greece
⁷ Department of Physics & Astronomy, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
⁸ Argelander Institut für Astronomie der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁹ ESA/STScI, 3700 San Martin Drive, Baltimore, MD 21218, USA
¹⁰ Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
¹¹ Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
¹² Warsaw University Observatory, Al. Ujazdowskie 4, 00-478 Warszawa, Poland

Received: 25 April 2015
Accepted: 24 August 2015

Abstract

Aims. We investigate the characteristics of two newly discovered short-period, double-lined, massive binary systems in the Large Magellanic Cloud, VFTS 450 (O9.7 II–Ib + O7::) and VFTS 652 (B1 Ib + O9: III:).

Methods. We perform model-atmosphere analyses to characterise the photospheric properties of both members of each binary (denoting the “primary” as the spectroscopically more conspicuous component). Radial velocities and optical photometry are used to estimate the binary-system parameters.

Results. We estimate T_eff = 27 kK, log g = 2.9 (cgs) for the VFTS 450 primary spectrum (34 kK, 3.6: for the secondary spectrum); and T_eff = 22 kK, log g = 2.8 for the VFTS 652 primary spectrum (35 kK, 3.7: for the secondary spectrum). Both primaries show surface nitrogen enrichments (of more than 1 dex for VFTS 652), and probable moderate oxygen depletions relative to reference LMC abundances. We determine orbital periods of 6.89 d and 8.59 d for VFTS 450 and VFTS 652, respectively, and argue that the primaries must be close to filling their Roche lobes. Supposing this to be the case, we estimate component masses in the range ~20–50 M_⊙.

Conclusions. The secondary spectra are associated with the more massive components, suggesting that both systems are high-mass analogues of classical Algol systems, undergoing case-A mass transfer. Difficulties in reconciling the spectroscopic analyses with the light-curves and with evolutionary considerations suggest that the secondary spectra are contaminated by (or arise in) accretion disks.