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Wavelength self-calibration and sky subtraction for Fabry–Pérot interferometers: applications to OSIRIS


T. Weinzirl


Professor of Astronomy

A.L. Chies-Santos


We describe techniques concerning wavelength calibration and sky subtraction to maximize the scientific utility of data from tunable filter instruments. While we specifically address data from the Optical System for Imaging and low Resolution Integrated Spectroscopy instrument (OSIRIS) on the 10.4-m Gran Telescopio Canarias telescope, our discussion is generalizable to data from other tunable filter instruments. A key aspect of our methodology is a coordinate transformation to polar coordinates, which simplifies matters when the tunable filter data are circularly symmetric around the optical centre. First, we present a method for rectifying inaccuracies in the wavelength calibration using OH sky emission rings. Using this technique, we improve the absolute wavelength calibration from an accuracy of ∼5 to 1 Å, equivalent to ∼7 per cent of our instrumental resolution, for 95 per cent of our data. Then, we discuss a new way to estimate the background sky emission by median filtering in polar coordinates. This method suppresses contributions to the sky background from the outer envelopes of distant galaxies, maximizing the fluxes of sources measured in the corresponding sky-subtracted images. We demonstrate for data tuned to a central wavelength of 7615 Å that galaxy fluxes in the new sky-subtracted image are ∼37 per cent higher, versus a sky-subtracted image from existing methods for OSIRIS tunable filter data.


Weinzirl, T., Aragón-Salamanca, A., Bamford, S., Rodríguez del Pino, B., Gray, M., & Chies-Santos, A. (2015). Wavelength self-calibration and sky subtraction for Fabry–Pérot interferometers: applications to OSIRIS. Monthly Notices of the Royal Astronomical Society, 454(2),

Journal Article Type Article
Acceptance Date Aug 27, 2015
Publication Date Dec 1, 2015
Deposit Date Apr 20, 2017
Publicly Available Date Apr 20, 2017
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 0035-8711
Publisher Oxford University Press
Peer Reviewed Peer Reviewed
Volume 454
Issue 2
Keywords instrumentation: interferometers – techniques: imaging spectroscopy – galaxies: clusters: individual: Abell 901/902 – galaxies: distances and redshifts
Public URL
Publisher URL
Additional Information This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society Published by Oxford University Press on behalf of the Royal Astronomical Society.


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