A New Dynamical Model for the Black Hole Binary LMC X-1
Remillard, Ronald A.; McClintock, Jeffrey E.; Gou, Lijun; Levine, Alan M.; Bailyn, Charles D.; Orosz, Jerome A.; Narayan, Ramesh; Steeghs, Danny; Torres, Manuel A. P.; Buxton, Michelle; Bochkov, Ivan; Blaschak, Michael; Dwyer, Morgan M.
United States, United Kingdom
Abstract
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 AV = 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 R sun and a projected rotational velocity of V rotsin i = 129.9 ± 2.2 km s-1. Using these measured properties to constrain the dynamical model, we find an inclination of i = 36fdg38 ± 1fdg92, a secondary star mass of M 2 = 31.79 ± 3.48 M sun, and a black hole mass of 10.91 ± 1.41 M sun. 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 M sun 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.
Based on observations made with the Magellan 6.5 m Clay telescope at Las Campanas Observatory of the Carnegie Institution.