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D. Potter, M. Graham (Steward Observatory)
PEPPER is an instrument designed to perform very accurate, photon-noise limited self calibrated differential photometry and polarimetry. The limiting problem of detector gain variation in these high contrast applications is overcome through a combination of fast response ferro-electric liquid crystal (FLC) polarization rotators in series with a high speed, high gain electron multiplying CCD (EMCCD). The instrument has two modes, a differential photometer mode, and an imaging polarimetry mode. The differential photometer mode is self calibrated by splitting the beam using a polarizing beam splitter and passing the beams through different narrow band spectral filters. The two beams are recombined creating a single beam containing two colors of light distinguished by the polarization encoding. This beam is then modulated through a FLC and resolved with another polarizing beamsplitter. This allows for the measurement of the two spectral bands using the same pixels on the modulation frequency of the FLC or about 100-500 Hz. This technique is being applied to monitor the phase variations of short period radial velocity planets using narrow band filters centered on the Na and K absorption lines for photometric reference. The polarization mode incorporates a half wave FLC in series with a quarter wave FLC and an analyzer to produce a measurement of all Stokes parameters at a frequency of about 100 Hz. This mode is designed to detect the polarization signature of debris disks at high contrast. Here we present the results from the first on-sky observations using the EMCCD as the detector.
This work is supported by the NSF ATI award 0352989 and NSF
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.