This thesis explores the photometric variability in isolated magnetic white dwarfs (MWDs) to search for spin periods. Approximately 40% of MWDs exhibit photometric modulations as the star rotates due to the effects from a strong magnetic field or star spots. A sample of 77 MWDs is studied to discover periods on timescales of minutes to one week. Well-defined periods are determined in 12 MWDs, with periods of roughly an hour to a few days, and variability with poorly constrained periods is found in a further 13 stars. MWD spin periods can provide important constraints for their post main-sequence evolution and formation, and in particular, potential information on the influence magnetism plays on the mass and angular momentum loss of the evolving star. A correlation has emerged between the spin period and magnetic field strength and temperature, suggesting hotter MWDs spin faster and have higher field strengths, characteristics possibly associated with MWDs that might have formed in binary mergers. A similar investigation is carried out on longer timescales (months – years) for ten single MWDs, which are stable on short timescales but were previously found to display modulations between observing seasons. However, no significant variability is detected in the sample, although G240-72 may display variations over months. Finally, the spin period evolution over ∼ 20 years is studied in the hot, massive, highly magnetic, rapidly rotating MWD, RE J0317-853. A rate of period change is measured as Ṗ = (9.6 ± 1.4) × 10[superscript −14] s/s which is most likely due to the orbital motion of the wide binary pair of RE J0317-853 and LB9802. Spin-down from magnetic dipole radiation is ruled out as a possible mechanism. Periodic variations in the expected arrival times of maximum flux tentatively suggest a low-mass planetary companion may be orbiting RE J0317-853.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:579224 |
| Date | January 2013 |
| Creators | Lawrie, Katherine Anne |
| Contributors | Burleigh, Matthew; Goad, Michael |
| Publisher | University of Leicester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/2381/28179 |
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