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To directly image exoplanets and faint circumstellar disks, the noisy stellarhalo must be suppressed to a high level. To achieve this feat, the angulardifferential imaging observing technique and the least-squares LocallyOptimized Combination of Images (LOCI) algorithm have now become the standardin single band direct imaging observations and data reduction. With thedevelopment and commissioning of new high-order high-contrast adaptive opticsequipped with integral field units, the image subtraction algorithm needs to bemodified to allow the optimal use of polychromatic images, field-rotated imagesand archival data. A new algorithm, TLOCI (for Template LOCI), is designed toachieve this task by maximizing a companion signal-to-noise ratio instead ofsimply minimizing the noise as in the original LOCI algorithm. The TLOCItechnique uses an input spectrum and template Point Spread Functions (PSFs,generated from unocculted and unsaturated stellar images) to optimize thereference image least-squares coefficients to minimize the planetself-subtraction, thus maximizing its throughput per wavelength, whilesimultaneously providing a maximum suppression of the speckle noise. The newalgorithm has been developed using on-sky GPI data and has achieved impressivecontrast. This paper presents the TLOCI algorithm, on-sky performance, and willdiscuss the challenges in recovering the planet spectrum with high fidelity.

GPI PSF subtraction with TLOCI: the next evolution in exoplanet/disk high-contrast imaging