Data reduction pipeline for the CHARIS integral-field spectrograph I: Detector readout calibration and data cube extraction

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

Research output: Contribution to journalArticle

18 Scopus citations

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 χ2 fitting. We measure and apply both a detector flatfield and a lenslet flatfield and reconstruct the wavelength-A nd position-dependent lenslet point-spread function (PSF) from images taken with a tunable laser. We use these measured PSFs to implement a χ2-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 χ2 extraction allows us to model and remove correlated read noise, dramatically improving CHARIS's performance. The χ2 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.

Original languageEnglish (US)
Article number048002
JournalJournal of Astronomical Telescopes, Instruments, and Systems
Volume3
Issue number4
DOIs
StatePublished - Oct 1 2017

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Control and Systems Engineering
  • Instrumentation
  • Astronomy and Astrophysics
  • Mechanical Engineering
  • Space and Planetary Science

Keywords

  • Data processing
  • deconvolution
  • infrared spectroscopy
  • multispectral imaging
  • point-spread functions
  • tunable lasers

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    Brandt, T. D., Rizzo, M., Groff, T., Chilcote, J., Greco, J. P., Kasdin, N. J., Limbach, M. A., Galvin, M., Loomis, C., Knapp, G., McElwain, M. W., Jovanovic, N., Currie, T., Mede, K., Tamura, M., Takato, N., & Hayashi, M. (2017). Data reduction pipeline for the CHARIS integral-field spectrograph I: Detector readout calibration and data cube extraction. Journal of Astronomical Telescopes, Instruments, and Systems, 3(4), [048002]. https://doi.org/10.1117/1.JATIS.3.4.048002