Direct Planet Imaging with NICI: Combining Angular and Spectral Difference Imaging

The NICI(Near Infrared Coronagraphic Imager)/Gemini South Campaign is the most ambitious direct extrasolar planet imaging campaign to date, achieving median contrasts of 13 and 15 magnitudes at 0.5 and 1.0'' respectively. Starting in December of 2008, we have begun looking for both methane- bearing candidates (T < 1400 K) and non-methanated substellar companions around several hundred nearby stars chosen on the basis of youth, proximity, spectral type, etc. Here, I present the data reduction techniques optimized for NICI, and also discuss the instrument's strengths and limitations. NICI is the combination of an 85 element adaptive optics system, a Lyot coronagraph, and a dual channel camera capable of simultaneous spectral difference imaging (SDI) on and off the 1.6um methane feature and angular difference imaging (ADI) where the cassegrain rotator is turned off. We have developed a novel method of reducing the data which takes advantage of both SDI and ADI techniques. Speckles with long correlation times are removed by subtracting a "Static" PSF, possible because of ADI. Short-lived speckles are removed by the subtracting the simultaneously imaged channel, possible because of SDI.