On the orbital and physical parameters of the HDE 226868/Cygnus X-1 binary system (original) (raw)
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Abstract
In this paper we explore the consequences of the recent determination of the mass m=(8.7±0.8)M⊙ of Cygnus X-1, obtained from the Quasi-Periodic Oscillation (QPO)-photon index correlation scaling, on the orbital and physical properties of the binary system HDE 226868/Cygnus X-1. By using such a result and the latest spectroscopic optical data of the HDE 226868 supergiant star we get M=(24±5)M⊙ for its mass. It turns out that deviations from the third Kepler law significant at more than 1-sigma level would occur if the inclination i of the system's orbital plane to the plane of the sky falls outside the range ≈41–56 deg: such deviations cannot be due to the first post-Newtonian (1PN) correction to the orbital period because of its smallness; interpreted in the framework of the Newtonian theory of gravitation as due to the stellar quadrupole mass moment Q, they are unphysical because Q would take unreasonably large values. By conservatively assuming that the third Kepler law is an adequate model for the orbital period we obtain i=(48±7) deg which yields for the relative semimajor axis a=(42±9)R⊙ (≈0.2 AU).
Publication:
Astrophysics and Space Science
Pub Date:
June 2008
DOI:
arXiv:
Bibcode:
Keywords:
- Black holes: individual (Cyg X-1);
- Stars: individual (HDE 226868);
- X-rays: binaries;
- X-rays: individual (Cyg X-1);
- General Relativity and Quantum Cosmology;
- Astrophysics
E-Print:
Latex2e, 7 pages, 1 table, 4 figures. To appear in ApSS (Astrophysics and Space Science)