1982•Monthly Notices of the Royal Astronomical SocietyRequires access
The effect of orbital eccentricity on polarimetric binary diagnostics
J. C. Brown, C. Aspin⋆, J. F. L. Simmons, Ian S. McLean
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Abstract
The assumption of corotation implicit in all previous modelling of phase-locked polarization variations from close binaries, is relaxed and the simple case of a localized scattering region in an eccentric orbit about a point light source is developed. We find that where previously only second harmonic variations of polarization were present (when the scattering geometry is symmetric about the orbital plane of the system) first and third harmonics are added when the eccentricity e ≠ 0. We show that erroneous model parameter values (such as the orbital inclination) can occur if a circular orbit model is assumed when analysing the data from an eccentric orbit binary. Extension of the equations to fitting of noisy data is briefly discussed and for illustration is applied to the polarimetric data for Cygnus X-1. We find that the polarimetric variations (at harmonics other than second) observed in Cygnus X-1 cannot be caused solely by any orbital eccentricity but could contain a contribution due to it.