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Astron. Astrophys. 364, 587-596 (2000)

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Simulations of polarization from accretion disks

J. Schultz

000014 University of Helsinki, Observatory, P.O. Box 14, Finland (juho.schultz@astro.helsinki.fi)

Received 17 January 2000 / Accepted 19 October 2000

Abstract

The Monte Carlo Method was used to estimate the level of polarization from axisymmetric accretion disks similar to those in low-mass X-ray binaries and some classes of cataclysmic variables. In low-mass X-ray binaries electron scattering is supposed to be the dominant opacity source in the inner disk, and most of the optical light is produced in the disk. Thompson scattering occuring in the disk corona produces linear polarization. Detailed theoretical models of accretion disks are numerous, but simple mathematical disk models were used, as the accuracy of polarization measurements does not allow distinction of the fine details of disk models. Stokes parameters were used for the radiative transfer. The simulations indicate that the vertical distribution of emissivity has the greatest effect on polarization, and variations of radial emissivity distribution have no detectable effect on polarization. Irregularities in the disk may reduce the degree of polarization. The polarization levels produced by simulations are detectable with modern instruments. Polarization measurements could be used to get rough constraints on the vertical emissivity distribution of an accretion disk, provided that a reasonably accurate disk model can be constructed from photometric or spectrosopic observations in optical and/or X-ray wavelengths.

Key words: accretion, accretion disks – polarization – methods: numerical

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© European Southern Observatory (ESO) 2000

Online publication: January 29, 2001
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