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Sky emission subtraction for observations without plain sky information

In the near-IR, the sky background is dominated by highly variable airglow emission lines. This is an issue for the sky subtraction in spectra without plain sky, where reference sky spectra taken at a different time as the object spectrum are required. The instrument-independent sky subtraction code Skycorr uses physically motivated line group scaling in the reference sky spectrum by a fitting approach for an improved sky line removal in the object spectrum. Possible wavelength shifts between both spectra are corrected by fitting Chebyshev polynomials and advanced rebinning without resolution decrease. For the correction, the optimised sky line spectrum and the automatically separated sky continuum (without scaling) is subtracted from the input object spectrum.

Tests show that Skycorr performs well (per cent level residuals) for data in different wavelength regimes and of different resolution, even in the cases of relatively long time lags between the object and the reference sky spectrum. Lower quality results are mainly restricted to wavelengths not dominated by airglow lines or pseudo continua by unresolved strong emission bands.

The tool has been developed for ESO by a team of astronomers at the Institute for Astro- and Particle Physics at the University of Innsbruck, as one of three sky modeling and correction tools in an Austrian in-kind contribution to ESO.

The relevant publication for citations is Noll et al. (2014, acc. by A&A).


    11. August 2015: Release of Skycorr 1.1.2.
      support ESO science data products standard (SDP) format for one-dimensional (1D) spectra Note the use of units stored in this format is not yet supported, wlgtomicron still needs to be set correctly in the parameter file. fix regression from 1.1.0 forcing wavelength solution to constant shifts in wavelengths below thermal IR
    27. November 2014: Bugfix release of Skycorr 1.1.1.
      fix regression from 1.1.0 forcing wavelength solution to constant shifts in wavelengths below thermal IR
    7. August 2014: Minor release of Skycorr 1.1.0.
      Avoids runaway of wavelength solution in thermal IR
    1. April 2014: First release of Skycorr 1.0.0 available



Skycorr User Manual


Users of Skycorr are requested to cite the following papers:

Skycorr: A general tool for spectroscopic sky subtraction
S. Noll, W. Kausch, S. Kimeswenger, M. Barden, A. M. Jones, A. Modigliani, C. Szyszka, and J. Taylor, (2014, A&A 567, A25)


Installation packages

The latest version of the installers:

GNU/Linux 32 bit x86
GNU/Linux 64 bit x86
MacOS 64 bit x86

The installers include example data and configurations for FORS, SINFONI and XSHOOTER instruments.

Older versions are available on the FTP server

Installation instructions

The installation procedure is described here.

Source code

Source code required to build Skycorr and its dependencies:

Skycorr source files