The UV polarization of x-ray binary systems observed with the Hubble Space Telescope
Abstract
X-ray binary star systems are unique laboratories in which astronomers may observationally refine or confirm some basic principles of astrophysics. Observations of these systems provide information about the geometry, composition, and other physical conditions existing in the accretion structures present in these binaries. The orbital inclination of the binary system may also be inferred from these observations. The High Speed Photometer (HSP) was one of the four axial instruments on the Hubble Space Telescope (HST) from April, 1990 to December, 1993. We used this instrument to observe the X-ray binary systems HD 153919, Vela XR-1 and Cyg XR-1 both photometrically and polarimetrically for the first time ever in the ultraviolet (UV) wavelengths. The photometric and polarimetric light curves of each target have been constructed by measuring the flux and linear polarization in several different wavelength bands, at several different phases in one binary orbit. The UV radiation is believed to originate closer to the compact secondary star, so that observations in these wavelengths enable astronomers to investigate a different region of the gas streams between the stars than could be done from ground based observatories. The results we obtained from these first-ever UV polarimetric observations provide striking confirmation of Rayleigh (recombined material) scattering from gas streams and stellar wind in these systems. This conclusion is based on the dependence of polarimetric variability with wavelength. There is also strong evidence for the existence of polarized bremsstrahlung radiation in the systems with a neutron star secondary. In addition to these results, we derived new estimates for the orbital inclination, location of the scattering structure relative to the line of centers, and orientation of the orbital angular momentum for the system (and associated confidence intervals for each parameter). These results have been compared to previously published ground based observations.
Degree
Ph.D.
Advisors
Moffett, Purdue University.
Subject Area
Astronomy|Astrophysics
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