Development of a near-infrared polarimeter and its application to the continuum polarization of magnetic white dwarfs
Thesis/Dissertation
·
OSTI ID:6452227
A new type of astronomical polarimeter is presented that incorporates a fused-silica stress-birefringent modulator which simultaneously allows the selection of chopping frequency (less than or equal to 5Hz) and spectral tuning (1 less than or equal to lambda less than or equal to 2.5 ..mu..m) with very high modulation efficiency. Two integrating detector packages are discussed. The first uses a single germanium photodiode and HR polaroid analyzer and achieves sigma/sub v/ = 1% for a J = 14.5 object in 0.5 hr with the MMT. The second package uses a 12 x 30 pixel HgCdTe array and MgF/sub 2/ Wollaston prism to provide four simultaneous polarimetric channels that properly eliminate the systematic errors resulting from staring mode operation. The continuum polarizations of five isolated highly magnetic white dwarfs were investigated both observationally and theoretically. The most complete broad-band polarimetric survey throughout the spectral region 0.35 less than or equal to lambda less than or equal to 1.65 ..mu..m was performed. An apparent correlation in the linear polarizations of Grw + 70/sup 0/8247, GD229, and G240-72 was discovered. In addition, no evidence for time-dependent rotation of position angle is found for any of the stars. New observations of BG C Mi reveal the first definitive discovery of polarized cyclotron emission in any intermediate polar and confirms that the long-held basic model of a magnetically accreting white dwarf is correct.
- Research Organization:
- Arizona Univ., Tucson (USA)
- OSTI ID:
- 6452227
- Country of Publication:
- United States
- Language:
- English
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