The VLT-FLAMES Tarantula Survey

XXVII. Physical parameters of B-type main-sequence binary systems in the Tarantula nebula^⋆,⋆⋆

¹ Astrophysics Research Centre, School of Mathematics and Physics, Queen’s University Belfast, Belfast BT7 1NN, UK
² Sub-department of Atmospheric, Oceanic and Planetary Physics, Department of Physics, University of Oxford, Oxford, OX1 3RH, UK
e-mail: ryan.garland@physics.ox.ac.uk
³ UK Astronomy Technology Centre, Royal Observatory Edinburgh, Blackford Hill, Edinburgh, EH9 3HJ, UK
⁴ Department of Physics and Astronomy, Hounsfield Road, University of Sheffield, S3 7RH, UK
⁵ Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
⁶ Anton Pannenkoek Institute for Astronomy, University of Amsterdam, 1090 GE Amsterdam, The Netherlands
⁷ Argelander-Institut für Astronomie der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁸ European Space Astronomy Centre (ESAC), Camino bajo del Castillo, s/n Urbanizacion Villafranca del Castillo, Villanueva de la Cañada, 28692 Madrid, Spain
⁹ King’s College London, Graduate School, Waterloo Bridge Wing, Franklin Wilkins Building, 150 Stamford Street, London SE1 9NH, UK
¹⁰ Instituut voor Sterrenkunde, Universiteit Leuven, Celestijnenlaan 200 D, 3001 Leuven, Belgium
¹¹ Department of Physics, University of Oxford, Keble Road, Oxford OX1 3RH, UK
¹² Instituto de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
¹³ Departamento de Astrofísica, Universidad de La Laguna, 38205 La Laguna, Tenerife, Spain
¹⁴ Armagh Observatory, College Hill, Armagh, BT61 9DG, UK

Received: 31 October 2016
Accepted: 10 April 2017

Abstract

A spectroscopic analysis has been undertaken for the B-type multiple systems (excluding those with supergiant primaries) in the VLT-FLAMES Tarantula Survey (VFTS). Projected rotational velocities, v_esini, for the primaries have been estimated using a Fourier Transform technique and confirmed by fitting rotationally broadened profiles. A subset of 33 systems with v_esini ≤ 80 km s^-1 have been analysed using a TLUSTY grid of model atmospheres to estimate stellar parameters and surface abundances for the primaries. The effects of a potential flux contribution from an unseen secondary have also been considered. For 20 targets it was possible to reliably estimate their effective temperatures (T_eff) but for the other 13 objects it was only possible to provide a constraint of 20 000 ≤ T_eff ≤ 26 000 K – the other parameters estimated for these targets will be consequently less reliable. The estimated stellar properties are compared with evolutionary models and are generally consistent with their membership of 30 Doradus, while the nature of the secondaries of 3 SB2 system is discussed. A comparison with a sample of single stars with v_esini ≤ 80 km s^-1 obtained from the VFTS and analysed with the same techniques implies that the atmospheric parameters and nitrogen abundances of the two samples are similar. However, the binary sample may have a lack of primaries with significant nitrogen enhancements, which would be consistent with them having low rotational velocities and having effectively evolved as single stars without significant rotational mixing. This result, which may be actually a consequence of the limitations of the pathfinder investigation presented in this paper, should be considered as a motivation for spectroscopic abundance analysis of large samples of binary stars, with high quality observational data.