R144 revealed as a double-lined spectroscopic binary

H. Sana [1], T. van Boeckel [1], F. Tramper [1], L.E. Ellerbroek [1], A. de Koter [1,2,3], L. Kaper [1], A.F.J. Moffat [4], O. Schnurr [5], F.R.N. Schneider [6], D.R. Gies [7]

1. Astronomical Institute Anton Pannekoek, Amsterdam University, Science Park 904, 1098 XH, Amsterdam, The Netherlands
2. Utrecht University, Princetonplein 5, 3584CC, Utrecht, The Netherlands
3. Instituut voor Sterrenkunde, Universiteit Leuven, Celestijnenlaan 200 D, 3001, Leuven, Belgium
4. Department de Physique, Universite de Montreal and Centre de Recherche en Astrophysique du Quebec, C. P. 6128, succ. centre-ville, Montreal (Qc) H3C 3J7, Canada
5. Leibniz Institut fur Astrophysik Potsdam (AIP), An der Sternwarte 16, 14482 Potsdam, Germany
6. Argelander-Institut fur Astronomie, Universitat Bonn, Auf dem Hugel 71, 53121 Bonn, Germany
7. Center for High Angular Resolution Astronomy and Department of Physics and Astronomy, Georgia State University, P.O. Box 4106, Atlanta, GA 30302-4106, USA

R144 is a WN6h star in the 30 Doradus region. It is suspected to be a binary because of its high luminosity and its strong X-ray ux, but no periodicity could be established so far. Here, we present new X-shooter multi-epoch spectroscopy of R144 obtained at the ESO Very Large Telescope (VLT). We detect variability in position and/or shape of all the spectral lines. We measure radial velocity variations with an amplitude larger than 250 km/s in Niv and Nv lines. Furthermore, the Niii and Nv line Doppler shifts are anti-correlated and the Niv lines show a double-peaked pro file on six of our seven epochs. We thus conclude that R144 is a double-lined spectroscopic binary. Possible orbital periods range from 2 to 6 months, although a period up to one year is allowed if the orbit is highly eccentric. We estimate the spectral types of the components to be WN5-6h and WN6-7h, respectively. The high luminosity of the system (log Lbol/Lsun ~ 6.8) suggests a present-day total mass content in the range of about 200 to 300 M sun, depending on the evolutionary stage of the components. This makes R144 the most massive binary identifi ed so far, with a total mass content at birth possibly as large as 400 M sun. We briefly discuss the presence of such a massive object 60 pc away from the R136 cluster core in the context of star formation and stellar dynamics.

Reference: MNRAS
Status: Manuscript has been accepted

Weblink: http://arxiv.org/abs/1304.4591


Email: H.Sana@uva.nl