Instrument Information
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| IDENTIFIER |
urn:nasa:pds:context:instrument:mcdonald.struve2m1.molp::1.1
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| NAME |
MCDONALD OBSERVATORY LINEAR POLARIMETER
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| TYPE |
POLARIMETER
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| DESCRIPTION |
The Linear Polarimeter was put into service at McDonald Observatory in 1978. Themain element is a Glan-Air prism, rapidly rotating to counteract atmospherictransparency fluctuations. The Glan prism was chosen as an analyzer due to its veryhigh throughput, achromatic nature, optical precision, and low cost. A slightdisadvantageresults from the presence of an air gap inside the prism and the resultant lateralimage displacement (less than 0.1mm). A slight image rotation causes an instrumentalpolarization of 0.05% which varies slightly with wavelength, is constant in time, andcan easily be subtracted out. Other sources of instrumental polarization, includingthe aluminized telescope mirrors, have turned out to be less than 10^-4.Tests have shown that under ideal observing conditions, the polarimeter can measureaccurately to a precision on the order 10^-4. In practice, therefore, the precisionof the polarimeter is limited by photon statistics.For more information about the instrument, including a schematic diagram, see Breger(1979).Breger, M., Interstellar grain size: A look at the deviant four, AstrophysicalJournal 233, 97-101, 1979.
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| REFERENCES |
Breger, M., Interstellar grain size: A look at the deviant four, AstrophysicalJournal 233, 97-101, 1979.
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