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High-contrast imaging instruments are now being equipped with integral fieldspectrographs (IFS) to facilitate the detection and characterization of faintsubstellar companions. Algorithms currently envisioned to handle IFS data, suchas the Locally Optimized Combination of Images (LOCI) algorithm, rely uponaggressive point-spread-function (PSF) subtraction, which is ideal forinitially identifying companions but results in significantly biased photometryand spectroscopy due to unwanted mixing with residual starlight. Thisspectro-photometric issue is further complicated by the fact that algorithmiccolor response is a function of the companion's spectrum, making it difficultto calibrate the effects of the reduction without using iterations involving aseries of injected synthetic companions. In this paper, we introduce a new PSFcalibration method, which we call "damped LOCI", that seeks to alleviate theseconcerns. By modifying the cost function that determines the weightingcoefficients used to construct PSF reference images, and also forcing thosecoefficients to be positive, it is possible to extract companion spectra with aprecision that is set by calibration of the instrument response andtransmission of the atmosphere, and not by post-processing. We demonstrate theutility of this approach using on-sky data obtained with the Project 1640 IFSat Palomar. Damped-LOCI does not require any iterations on the underlyingspectral type of the companion, nor does it rely upon priors involving thechromatic and statistical properties of speckles. It is a general techniquethat can readily be applied to other current and planned instruments thatemploy IFS's.

the astrophysical journal. supplement series/astrophysical journal. supplement series

Application of a damped Locally Optimized Combination of Images method  to the spectral characterization of faint companions using an Integral Field  Spectrograph