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Journal of Astronomical Telescopes, Instruments, and Systems • Open Access • new

Data reduction pipeline for the CHARIS integral-field spectrograph I: detector readout calibration and data cube extraction
Author(s): Timothy D. Brandt; Maxime Rizzo; Tyler Groff; Jeffrey Chilcote; Johnny P. Greco; N. Jeremy Kasdin; Mary Anne Limbach; Michael Galvin; Craig Loomis; Gillian Knapp; Michael W. McElwain; Nemanja Jovanovic; Thayne Currie; Kyle Mede; Motohide Tamura; Naruhisa Takato; Masahiko Hayashi

Paper Abstract

We present the data reduction pipeline for CHARIS, a high-contrast integral-field spectrograph for the Subaru Telescope. The pipeline constructs a ramp from the raw reads using the measured nonlinear pixel response and reconstructs the data cube using one of three extraction algorithms: aperture photometry, optimal extraction, or χ 2 fitting. We measure and apply both a detector flatfield and a lenslet flatfield and reconstruct the wavelength- and position-dependent lenslet point-spread function (PSF) from images taken with a tunable laser. We use these measured PSFs to implement a χ 2 -based extraction of the data cube, with typical residuals of 5 % due to imperfect models of the undersampled lenslet PSFs. The full two-dimensional residual of the χ 2 extraction allows us to model and remove correlated read noise, dramatically improving CHARIS’s performance. The χ 2 extraction produces a data cube that has been deconvolved with the line-spread function and never performs any interpolations of either the data or the individual lenslet spectra. The extracted data cube also includes uncertainties for each spatial and spectral measurement. CHARIS’s software is parallelized, written in Python and Cython, and freely available on github with a separate documentation page. Astrometric and spectrophotometric calibrations of the data cubes and PSF subtraction will be treated in a forthcoming paper.

Paper Details

Date Published: 24 November 2017
PDF: 18 pages
J. Astron. Telesc. Instrum. Syst. 3(4) 048002 doi: 10.1117/1.JATIS.3.4.048002
Published in: Journal of Astronomical Telescopes, Instruments, and Systems Volume 3, Issue 4
Show Author Affiliations
Timothy D. Brandt, Univ. of California, Santa Barbara (United States)
Maxime Rizzo, NASA Goddard Space Flight Ctr. (United States)
Tyler Groff, NASA Goddard Space Flight Ctr. (United States)
Jeffrey Chilcote, Stanford Univ. (United States)
Johnny P. Greco, Princeton Univ. (United States)
N. Jeremy Kasdin, Princeton Univ. (United States)
Mary Anne Limbach, Princeton Univ. (United States)
Michael Galvin, Princeton Univ. (United States)
Craig Loomis, Princeton Univ. (United States)
Gillian Knapp, Princeton Univ. (United States)
Michael W. McElwain, NASA Goddard Space Flight Ctr. (United States)
Nemanja Jovanovic, California Institute of Technology (United States)
Thayne Currie, Subaru Telescope, National Astronomical Observatory of Japan (United States)
Kyle Mede, Rakuten, Inc. (Japan)
Motohide Tamura, The Univ. of Tokyo (Japan)
National Astronomical Observatory of Japan (Japan)
Astrobiology Ctr., National Institutes of Natural Sciences (Japan)
Naruhisa Takato, Subaru Telescope, National Astronomical Observatory of Japan (United States)
Masahiko Hayashi, National Astronomical Observatory of Japan (Japan)

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