Imaging polarimetry with the Gemini Planet Imager

The Gemini Planet Imager (GPI), currently under construction for the 8-m Gemini South telescope, is a high contrast adaptive optics instrument intended for direct imaging of extrasolar planets and circumstellar disks. GPI will study circumstellar disks using the polarization of disk-scattered starlight. These observations will be obtained using a novel 'integral field polarimetry' mode, in which the dispersing prism of GPI's integral field spectrograph is replaced by a Wollaston prism, providing simultaneous dual polarimetry for each position in the field of view. By splitting polarizations only after the instrument's lenslet array, this design minimizes wavefront differences between the polarization channels, providing optimal contrast for circumstellar dust. A rotating achromatic waveplate provides modulation. End-to-end numerical modeling indicates that GPI will be sensitive to scattered light from debris disks significantly fainter than can currently be imaged. We discuss the tradeoffs and design decisions for GPI polarimetry, describe the calibration and reduction procedures, and present the current status of the instrument. First light is planned for 2011.

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