A New Dynamical Model for the Black Hole Binary LMC X-1

• Published in: arXiv.org 2009-03
• Main Authors: Orosz, Jerome A, Steeghs, Danny, McClintock, Jeffrey E, Torres, Manuel A P, Bochkov, Ivan, Gou, Lijun, Narayan, Ramesh, Blaschak, Michael, Levine, Alan M, Remillard, Ronald A, Bailyn, Charles D, Dwyer, Morgan M, Buxton, Michelle
• Format: Article
• Language: English
• Subjects: Binary stars; Inclination; Infrared photometry; Light curve; Luminosity; Mass transfer; Orbits; Photometry; Rotation; Stellar age; Stellar mass; Stellar winds; Thomson scattering; X ray binaries; X ray stars
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.0810.3447

We present a dynamical model of the high mass X-ray binary LMC X-1 based on high-resolution optical spectroscopy and extensive optical and near-infrared photometry. From our new optical data we find an orbital period of P=3.90917 +/- 0.00005 days. We present a refined analysis of the All Sky Monitor data from RXTE and find an X-ray period of P=3.9094 +/- 0.0008 days, which is consistent with the optical period. A simple model of Thomson scattering in the stellar wind can account for the modulation seen in the X-ray light curves. The V-K color of the star (1.17 +/- 0.05) implies A_V = 2.28 +/- 0.06, which is much larger than previously assumed. For the secondary star, we measure a radius of R_2 = 17.0 +/- 0.8 solar radii and a projected rotational velocity of V_rot*sin(i) = 129.9 +/- 2.2 km/s. Using these measured properties to constrain the dynamical model, we find an inclination of i = 36.38 +/- 1.92 deg, a secondary star mass of M_2 = 31.79 +/- 3.48 solar masses, and a black hole mass of 10.91 +/- 1.41 solar masses. The present location of the secondary star in a temperature-luminosity diagram is consistent with that of a star with an initial mass of 35 solar masses that is 5 Myr past the zero-age main sequence. The star nearly fills its Roche lobe (~90% or more), and owing to the rapid change in radius with time in its present evolutionary state, it will encounter its Roche lobe and begin rapid and possibly unstable mass transfer on a timescale of a few hundred thousand years.