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Title: A survey for cool white dwarfs and the age of the galactic disc
Author: Knox, Richard Alan
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1999
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This thesis describes a survey specifically undertaken to obtain a sample of cool white dwarfs directly from original Schmidt plate material. Concerns regarding of the subjectivity of 'eye-blinked' proper motion measures are avoided by using digitised data obtained using the COSMOS and SuperCOSMOS microdensitometers. The observational material is restricted to a single 6 deg field in which an exceptionally large database of over 300 Schmidt plates exists. As a brief aside, the issue of stacking digitised plate data is examined. In particular, recommendations for the correct weighting algorithm and bad pixel rejection algorithm to adopt are made, following detailed experimentation, with a variety of techniques. The plate stacking technique is used for the white dwarf survey material to extend the photometric survey limits, while the optimum proper motion limit to adopt is investigated in detail, with the principal concern being elimination of contaminants while retaining as many genuine proper motion objects as possible. Application of the reduced proper motion population discrimination technique to the resultant proper motion catalogue results in final sample comprising 56 white dwarf candidates. Follow up spectroscopic observations show the survey has been successful in identifying cool white dwarfs, gives no indication of contamination in the white dwarf sample for other stellar types, and also provides two further cool white dwarfs to include in the sample which were marginally excluded by the reduced proper motion survey criteria. Comparison of photographic colours with model predictions allow effective temperatures and bolometric luminosities to be estimated for the sample members. The luminosity function constructed from the sample members is in good agreement with previous work, although the slightly higher space density found for the coolest white dwarfs leads to a modest increase in the age estimate for the Galactic Disc when the luminosity function is compared to theoretical models. The Disc age is found to be 10-1+3 Gyr.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available