Fundamental parameters of four massive eclipsing binaries in Westerlund 1

¹ SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen ; Kapteyn Institute, University of Groningen, The Netherlands
e-mail: e.koumpia@sron.nl
² National Observatory of Athens, Institute of Astronomy, Astrophysics, Space Applications & Remote Sensing, I. Metaxa & Vas. Pavlou St., Palaia Penteli, 15236 Athens, Greece
e-mail: bonanos@astro.noa.gr

Received: 24 April 2012
Accepted: 11 September 2012

Abstract

Context. Only a small number of high mass stars (>30   M_⊙) have fundamental parameters (i.e. masses and radii) measured with high enough accuracy from eclipsing binaries to constrain formation and evolutionary models of massive stars.

Aims. This work aims to increase this limited sample, by studying the four massive eclipsing binary candidates discovered by Bonanos in the young massive cluster Westerlund 1.

Methods. We present new follow-up echelle spectroscopy of these binaries and models of their light and radial velocity curves.

Results. We obtain fundamental parameters for the eight component stars, finding masses that span a range of 10−40 M_⊙, and contributing accurate fundamental parameters for one additional very massive star, the 33 M_⊙ component of W13. WR77o is found to have a  ~40 M_⊙ companion, which provides a second dynamical constraint on the mass of the progenitor of the magnetar known in the cluster. We also use W13 to estimate the first, direct, eclipsing binary distance to Westerlund 1 and therefore the magnetar and find it to be at 3.7  ±  0.6 kpc.

Conclusions. Our results confirm previous evidence for a high mass for the progenitor of the magnetar. In addition, the availability of eclipsing binaries with accurate parameters opens the way for direct, independent, high precision eclipsing binary distance measurements to Westerlund 1.