On the orbital and physical parameters of the HDE 226868/Cygnus X-1 binary system

Iorio, Lorenzo

doi:10.1007/s10509-008-9839-y

General Relativity and Quantum Cosmology

arXiv:0707.3525 (gr-qc)

[Submitted on 24 Jul 2007 (v1), last revised 26 May 2008 (this version, v2)]

Title:On the orbital and physical parameters of the HDE 226868/Cygnus X-1 binary system

Authors:Lorenzo Iorio

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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_Sun 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_Sun 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_Sun. Our estimate for the Roche's lobe of HDE 226868 is r_M = (21 +/- 6)R_Sun.

Comments:	Latex2e, 7 pages, 1 table, 4 figures. To appear in ApSS (Astrophysics and Space Science)
Subjects:	General Relativity and Quantum Cosmology (gr-qc); Astrophysics (astro-ph)
Cite as:	arXiv:0707.3525 [gr-qc]
	(or arXiv:0707.3525v2 [gr-qc] for this version)
	https://doi.org/10.48550/arXiv.0707.3525
Journal reference:	Astrophys.SpaceSci.315:335-340,2008
Related DOI:	https://doi.org/10.1007/s10509-008-9839-y

Submission history

From: Lorenzo Iorio [view email]
[v1] Tue, 24 Jul 2007 11:00:19 UTC (422 KB)
[v2] Mon, 26 May 2008 16:01:24 UTC (28 KB)

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