Polarimetry of magnetic cataclysmic variables

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dc.contributor.advisorWarner, Brianen_ZA
dc.contributor.authorCropper, Mark Scotten_ZA
dc.date.accessioned2016-02-15T07:15:09Z
dc.date.available2016-02-15T07:15:09Z
dc.date.issued1985en_ZA
dc.descriptionBibliography: pages 136-138.en_ZA
dc.description.abstractThe design and construction of an astronomical polarimeter is described and an evaluation made of its performance. Extensive observations of cataclysmic variables with emphasis on the AM Her and DQ Her classes are then presented. After consideration of the basic principles involved in the development of an efficient and accurate polarimeter, a design using two super-achromatic retarders (a 1/4 wave and a 1/2 wave) rotating above a fixed analyser was adopted. This permitted simultaneous linear and circular polarisation measurements, or, by rearranging the order of the retarders in the beam, linear polarisation measurements alone, or circular polarisation measurements alone, with enhanced efficiency. The polarimeter was found to have extremely low instrumental polarisations and, because of the superachromatic retarders used, the efficiency correction factors were very close to 1 at all wavelengths. The polarisations are calculated at the telescope and the light curve at a higher time resolution may also be recorded if this is required. Extensive sets of observations using the polarimeter were obtained for six of the ten AM Her variables (or "polars"). EF Eri and El405-451 were observed most. Evidence was found in El405-451 for movement of the apparent location of the accretion region on the primary star and the inclination and magnetic dipole off set from the rotation axis was determined. This allowed a comparison to be made between the competing models for the cyclotron emission, showing that those which take into account the temperature structure of the accretion region provide the best results. Observations and an analysis of the polarisation data from H0139-68, E2003+225, VV Puppis and PG1550+191 are also presented in some detail. A final chapter presents results from observations made to detect a modulation in the polarisation at the rotation period of the primary in the DQ Her variables. Upper limits are set for 4 members of the class and the implications of the results are discussed.en_ZA
dc.identifier.apacitationCropper, M. S. (1985). <i>Polarimetry of magnetic cataclysmic variables</i>. (Thesis). University of Cape Town ,Faculty of Science ,Department of Astronomy. Retrieved from http://hdl.handle.net/11427/17034en_ZA
dc.identifier.chicagocitationCropper, Mark Scott. <i>"Polarimetry of magnetic cataclysmic variables."</i> Thesis., University of Cape Town ,Faculty of Science ,Department of Astronomy, 1985. http://hdl.handle.net/11427/17034en_ZA
dc.identifier.citationCropper, M. 1985. Polarimetry of magnetic cataclysmic variables. University of Cape Town.en_ZA
dc.identifier.ris TY - Thesis / Dissertation AU - Cropper, Mark Scott AB - The design and construction of an astronomical polarimeter is described and an evaluation made of its performance. Extensive observations of cataclysmic variables with emphasis on the AM Her and DQ Her classes are then presented. After consideration of the basic principles involved in the development of an efficient and accurate polarimeter, a design using two super-achromatic retarders (a 1/4 wave and a 1/2 wave) rotating above a fixed analyser was adopted. This permitted simultaneous linear and circular polarisation measurements, or, by rearranging the order of the retarders in the beam, linear polarisation measurements alone, or circular polarisation measurements alone, with enhanced efficiency. The polarimeter was found to have extremely low instrumental polarisations and, because of the superachromatic retarders used, the efficiency correction factors were very close to 1 at all wavelengths. The polarisations are calculated at the telescope and the light curve at a higher time resolution may also be recorded if this is required. Extensive sets of observations using the polarimeter were obtained for six of the ten AM Her variables (or "polars"). EF Eri and El405-451 were observed most. Evidence was found in El405-451 for movement of the apparent location of the accretion region on the primary star and the inclination and magnetic dipole off set from the rotation axis was determined. This allowed a comparison to be made between the competing models for the cyclotron emission, showing that those which take into account the temperature structure of the accretion region provide the best results. Observations and an analysis of the polarisation data from H0139-68, E2003+225, VV Puppis and PG1550+191 are also presented in some detail. A final chapter presents results from observations made to detect a modulation in the polarisation at the rotation period of the primary in the DQ Her variables. Upper limits are set for 4 members of the class and the implications of the results are discussed. DA - 1985 DB - OpenUCT DP - University of Cape Town LK - https://open.uct.ac.za PB - University of Cape Town PY - 1985 T1 - Polarimetry of magnetic cataclysmic variables TI - Polarimetry of magnetic cataclysmic variables UR - http://hdl.handle.net/11427/17034 ER - en_ZA
dc.identifier.urihttp://hdl.handle.net/11427/17034
dc.identifier.vancouvercitationCropper MS. Polarimetry of magnetic cataclysmic variables. [Thesis]. University of Cape Town ,Faculty of Science ,Department of Astronomy, 1985 [cited yyyy month dd]. Available from: http://hdl.handle.net/11427/17034en_ZA
dc.language.isoengen_ZA
dc.publisher.departmentDepartment of Astronomyen_ZA
dc.publisher.facultyFaculty of Scienceen_ZA
dc.publisher.institutionUniversity of Cape Town
dc.subject.otherAstronomyen_ZA
dc.titlePolarimetry of magnetic cataclysmic variablesen_ZA
dc.typeDoctoral Thesis
dc.type.qualificationlevelDoctoral
dc.type.qualificationnamePhDen_ZA
uct.type.filetypeText
uct.type.filetypeImage
uct.type.publicationResearchen_ZA
uct.type.resourceThesisen_ZA
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