Abstract
Context.The improvement of large size detectors permitted the development of integral field spectrographs (IFSs) in astronomy. Spectral information for each spatial element of a two-dimensional field of view is obtained thanks to integral field units that spread the spectra on the 2D grid of the sensor.Aims.Here we aim to solve the inherent issues raised by standard data-reduction algorithms based on direct mapping of the 2D + λdata cube: the spectral cross-talk due to the overlap of neighbouring spectra, the spatial correlations of the noise due to the re-interpolation of the cube on a Cartesian grid, and the artefacts due to the influence of defective pixels.Methods.The proposed method, Projection, Interpolation, and Convolution (PIC), is based on an “inverse-problems” approach. By accounting for the overlap of neighbouring spectra as well as the spatial extension in a spectrum of a given wavelength, the model inversion reduces the spectral cross-talk while deconvolving the spectral dispersion. Considered as missing data, defective pixels undetected during the calibration are discarded on-the-fly via a robust penalisation of the data fidelity term.Results.The calibration of the proposed model is presented for the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument (SPHERE). This calibration was applied to extended objects as well as coronagraphic acquisitions dedicated to exoplanet detection or disc imaging. Artefacts due to badly corrected defective pixels or artificial background structures observed in the cube reduced by the SPHERE data reduction pipeline are suppressed while the reconstructed spectra are sharper. This reduces the false detections by the standard exoplanet detection algorithms.Conclusions.These results show the pertinence of the inverse-problems approach to reduce the raw data produced by IFSs and to compensate for some of their imperfections. Our modelling forms an initial building block necessary to develop methods that can reconstruct and/or detect sources directly from the raw data.
Highlights
The pertinence of single-field spectroscopy has been demonstrated in numerous fields in astrophysics, such as stellar classification, chemical analysis, velocity measurement, magnetic field probing, and so on
Many integral field spectrographs (IFSs) are based on this principle, such as for example the Optically Adaptive System for Imaging Spectroscopy (OASIS), the Spectrographic Areal Unit for Research on Optical Nebulae (SAURON, Bacon et al 2001), the SuperNovae Integral Field Spectrograph (SNIFS, Lantz et al 2004), and the OH-Suppressing Infrared Integral Field Spectrograph (OSIRIS, Larkin et al 2006)
With the development of extreme adaptive optics (Jovanovic et al 2015), in the last few years we have witnessed the results of a new generation of IFSs, such as those incorporated into the Project 1640 IFS (Hinkley et al 2011, Hale Telescope), the Gemini Planet Imager (GPI, Macintosh et al 2008, Gemini South Telescope), the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument (SPHERE, Beuzit et al 2019, Very Large Telescope; VLT), and the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS, Groff et al 2016, Subaru Telescope)
Summary
The pertinence of single-field spectroscopy has been demonstrated in numerous fields in astrophysics, such as stellar classification, chemical analysis, velocity measurement, magnetic field probing, and so on. An integral field spectrograph (IFS) combines this spatial sampling of an object with its spectral information resolved in different points of the field of view in a single exposure to obtain 2D + λ data This new technique became available with the rise of large detectors. With the development of extreme adaptive optics (Jovanovic et al 2015), in the last few years we have witnessed the results of a new generation of IFSs, such as those incorporated into the Project 1640 IFS (Hinkley et al 2011, Hale Telescope), the Gemini Planet Imager (GPI, Macintosh et al 2008, Gemini South Telescope), the Spectro-Polarimetric High-contrast Exoplanet REsearch instrument (SPHERE, Beuzit et al 2019, Very Large Telescope; VLT), and the Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS, Groff et al 2016, Subaru Telescope) These are based on lenslet arrays that limit the non-common path aberrations compared to slicer concepts. Special care is taken on the detector characterisation (Appendix A) and on the chromatic model of the spectral dispersion (Appendix B)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
