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The development and use of a high-speed astronomical photometer


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Hill, KM 1991 , 'The development and use of a high-speed astronomical photometer', PhD thesis, University of Tasmania.

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This dissertation describes the development and implementation of a computer-based
photometric data acquisition system for the Mt Canopus telescope. The high-speed
photometric system allows continuous acquisition of data, for up to —69 min with a
maximum sample rate of 9.8 kHz, while providing a real time display of the counts.
The system was thoroughly tested with a pulsing LED source and with observations of
the Crab pulsar. The results from several observational programs, suited to the
system's capabilities, are also presented. The observational programs involved a study
of the DQ Her type cataclysmic variable EX Hydrae, a fast photometric study of
geostationary spin-stabilised satellites, a monitoring program on SN1987a, and an
occultation program which culminated in a successful observation of a Pluto
occultation and the detection of an atmosphere on this planet.
The Mark I version of the fast-photometer system was used for the photoelectric study
program on the eclipsing cataclysmic variable EX Hya. This program demonstrated the
continued secular decrease in the period of its 67 min modulation. The observed rate of
change of the 67 min period implies a mass transfer rate of the order of —3x10-11Mo
yr-1and a magnetic moment around 8x10 32G cm3 . Two variations in the eclipse
timings are also identified. Firstly, one sees a long-term variation that has been fitted
with an —20 yr period sinusoid. Secondly, one sees a short-term variation which is
correlated with the phase of the 67 min cycle. This second variation has been
interpreted in terms of the eclipse of an accretion column or arc in the region above the
magnetic pole of the white dwarf.
Supplementary to the photometric data, high time resolution spectroscopic data from an
eclipse of EX Hya were obtained with the Anglo-Australian telescope. These data are
compatible with the general spectral characteristics noted by other workers. The V/R
ratio of the spectral lines, around orbital phase 098 = 0, is consistent with the eclipse
of an accretion disk. A sharp peak in the equivalent width of the Balmer lines is seen at
the time of the eclipse. It is comparable in width to the X-ray eclipses, and narrower
than the optical eclipses. Finally, the accretion curtain model of EX Hya is shown to
accommodate, in a qualitative sense, all the observational constraints that must be
imposed on any model of the system.

Item Type: Thesis - PhD
Authors/Creators:Hill, KM
Keywords: Astronomical photometry
Copyright Holders: The Author
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Copyright 1989 the author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Includes bibliographical references (p. 170-176). Thesis (Ph.D.)--University of Tasmania, 1991

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