On the interpretation of polarimetric observations of close binary stars

Aspin, Colin (1981) On the interpretation of polarimetric observations of close binary stars. PhD thesis, University of Glasgow.

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Abstract

Over the last few years the problem of determining orbital and physical parameters of close binaries has become paramount in interpreting the complex nature of these systems. Photometry and spectroscopy have in many cases combined to give reasonably accurate values of such parameters as the binary inclination and orbital eccentricity. In some cases however the two methods have provided conflicting values of the inclination i, for example, and it remains to obtain independent estimates to confirm or not the previous values. The development of techniques to interpret the variable linear polarization observed in certain binaries has proceeded hand in hand with the improvement of observational techniques and the continuing discovery of new 'polarimetric binaries'. A relatively simple model was presented by Brown,McLean and Emslie (1978) whereby the variation inpolarization of the light from binaries is caused by the orbital motion of a scattering region situated within the system and corotating with it. This scattering region is assumed optically thin and under the corotation assumption to be in a circular orbit about the primary star. The behaviour of the polarization is phase locked to the orbital period of the system and variation occurs, in the general case at both the first and second harmonic of that period (i.e. at the period itself and half that period). If the scattering region is of a form symmetric about the orbital plane of the system then the polarization has a second harmonic structure only (i.e. it varies a half the binary period) and produces a double looped ellipse figure in the Q,U plane. In this thesis we extend this simple, and hence 'canonical' model to enable an optimum set of JONILP.6.0 parameters to be obtained in the presence of noisy data. The optimum inclination iopt is found when the chi2 statistic is minimized and an eror or uncertainty in this value is estimated by forming a Relative Confidence Interval at a particular (i.e. chosen) significance level. This model optimization technique is then applied to Cygnus X-1 data with the result that the uncertainty in iopt is significantly larger than previous estimates. (cf. Chapter 2) thorough statistical and numerical analysis of the determination of inclinations by this method is undertaken in Chapter 3 and Chapter It where we establish the severe nature of the bias of the inclination estimator in the canonical model and show that a high degree of accuracy is needed in polarimetric measurements before reasonable (i.e. + 5

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: J C Brown
Keywords: Astronomy
Date of Award: 1981
Depositing User: Enlighten Team
Unique ID: glathesis:1981-74209
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 23 Sep 2019 15:33
Last Modified: 23 Sep 2019 15:33
URI: http://theses.gla.ac.uk/id/eprint/74209

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