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| Paper: |
Prospects for Mid-infrared Imaging and Polarimetry with Denver's TNTCAM2 |
| Volume: |
199, Asymmetrical Planetary Nebulae II: From Origins to Microstructures |
| Page: |
101 |
| Authors: |
Stencel, Robert E. |
| Abstract: |
Structural detail of asymmetric planetary nebulae is conditioned by the mass loss history of central stars (and their planets?). Much of this outlying structure can be mapped with thermal infrared imaging and polarimetry - both of which are capabilities designed into our second generation, NSF-sponsored Ten and Twenty micron CAMera, featuring collaborative access to the community of interested researchers. The University of Denver is now completing construction of a mid-infrared imaging polarimeter dubbed TNTCAM Mark II. The instrument will be the only one of its kind capable of attaining polarimetric accuracy of 0.2 % across the 5 - 25 micron spectral interval. This sensitivity is only attainable by cooling the transmissive polarizing optics to liquid helium (LHe) temperatures. A major technical challenge in the design of this instrument has been finding a way to modulate the polarization signature of the incoming beam at a rate sufficient to combat the degrading effects of the atmosphere. Our group has chosen to quickly rotate a half-waveplate situated on the cold (i.e. 4 degrees Kelvin) work-surface. The waveplate is rotated between two fixed positions separated by 45 degrees at a rate of 1 Hz to obtain one of the two Stoke's parameters required to measure linear polarization. The waveplate is then offset by 22.5 degrees and then rotated again at 1 Hz between two positions separated by 45 degrees to obtain the other Stoke's parameter. In addition to rotating the waveplate, the waveplate itself must be moved out of the beam during normal imaging applications. This instrument is being developed under NSF grant AST-9724506 to the University of Denver and is slated for community access after January 2000. |
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