A new dynamical model for the black hole binary LMC X-1

Jerome A. Orosz, Danny Steeghs, Danny Steeghs, Jeffrey E. McClintock, Manuel A P Torres, Ivan Bochkov, Lijun Gou, Ramesh Narayan, Michael Blaschak, Alan M Levine, Ronald A Remillard, Charles D. Bailyn, Morgan M. Dwyer, Michelle M. Buxton

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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 R ⊙ and a projected rotational velocity of V rot sin i = 129.9 2.2kms -1 . Using these measured properties to constrain the dynamical model, we find an inclination of i = 3638 192, a secondary star mass of M 2 = 31.79 3.48 M ⊙ , and a black hole mass of 10.91 1.41 M ⊙ . 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 ⊙ 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.
Original languageEnglish
Pages (from-to)573-591
Number of pages19
JournalThe Astrophysical Journal
Issue number1
Publication statusPublished - 1 Jan 2009


  • Binaries: spectroscopic
  • Black hole physics
  • Stars: early-type
  • X-rays: binaries
  • X-rays: individual (LMC X-1)

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