Accurate fundamental parameters and distance to a massive early-type eclipsing binary in the Danks 2 cluster^⋆

¹ IAASARS, National Observatory of Athens, 15236 Penteli, Greece
e-mail: mkourniotis@astro.noa.gr
² Section of Astrophysics, Astronomy and Mechanics, Faculty of Physics, University of Athens, Panepistimiopolis, 15784 Zografos, Athens, Greece
³ Argelander-Institut für Astronomie der Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁴ SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands
⁵ Kapteyn Institute, University of Groningen, 9712 Groningen, The Netherlands
⁶ Núcleo de Astronomía de la Facultad de Ingeniería, Universidad Diego Portales, Av. Ejército 441, Santiago, Chile
⁷ Millennium Institute of Astrophysics, Santiago, Chile

Received: 14 June 2015
Accepted: 5 August 2015

Abstract

We present a study of the properties of the O-type, massive eclipsing binary 2MASS J13130841-6239275 located in the outskirts of the Danks 2 cluster in the G305 star-forming complex, using near-infrared spectroscopy from VLT/ISAAC. We derive the masses and radii to be 24.5 ± 0.9 M_⊙ and 9.2 ± 0.1 R_⊙ for the primary and 21.7 ± 0.8 M_⊙ and 8.7 ± 0.1 R_⊙ for the secondary component. In addition, we evaluate the sensitivity of our parameters to the choice of the spectral features used to determine the radial velocities. Both components appear to be main-sequence O6.5−O7 type stars at an age of ~5 Myr, which is in agreement with the age of the cluster. A high visual extinction of A₅₄₉₅ = 11.9 ± 0.1 mag is reported, which is likely attributed to the cold molecular gas contaminating the northeast region of the cluster. By fitting the spectral energy distribution of the system to the available BVI_cJHK_s photometry, we determine a distance to the system of 3.52 ± 0.08 kpc with a precision of 2%, which is the most well-determined distance to the Danks 2 cluster and the host complex reported in the literature.