Correction tools for telluric absorption and emission

The following software tools to correct astronomical observations for telluric absorption and emission are provided. The tools have been developed for ESO by a team of astronomers at the Institute for Astro- and Particle Physics at the University of Innsbruck, as part of an in-kind contribution to ESO, which includes as well a model of the sky emission and transmission spectrum at Cerro Paranal.

Correcting observations for telluric absorption


Molecfit is an instrument-independent software tool to correct astronomical observations for atmospheric absorption features, based on fitting synthetic transmission spectra to the astronomical data. It can also estimate molecular abundances, especially the water vapour content of the Earth’s atmosphere.

Sky emission subtraction for observations without plain sky information


Skycorr provides an advanced instrument-independent sky-correction tool that removes sky emission in science spectra by means of sky spectra taken at a different time and sky location. The algorithm adapts a reference sky spectrum to a science spectrum by correcting differences due to temporal and spatial airglow variability and issues related with the instrument or the data reduction. A similar but less sophisticated method was developed by Davies (2007) for SINFONI near-IR spectroscopic data.

Cerro Paranal Sky Model


The Austrian in-kind contributions to ESO also include an advanced model of the sky emission and transmission spectrum at Cerro Paranal, in particular developed to be used in the ESO Exposure Time Calculators. The web application SkyCalc provides an interface to obtain models of transmission and radiance spectra in physical units, calculated with this model for various observation configurations and conditions.

Please refer to the document The Cerro Paranal Sky Model for more information.

New! A command-line interface to SkyCalc skycalc_cli is available!

A library of telluric transmission spectra with various resolutions and atmospheric conditions has been calculated with the Cerro Paranal sky model. A description of the usage of the spectra can be found in the article Moehler et al. (2014, A&A 568, A9).


Users of molecfit/skycorr are requested to cite the following paper(s)

Molecfit: A general tool for telluric absorption correction I. Method and application to ESO instruments
A. Smette, H. Sana, S. Noll, H. Horst, W. Kausch, S. Kimeswenger, M.Barden, C. Szyszka, A. M. Jones, A. Gallene, J. Vinther, P. Ballester and J. Taylor (2015, A&A 576, A77)

Molecfit: A general tool for telluric absorption correction II. Quantitative evaluation on ESO-VLT/X-Shooter spectra
W. Kausch, S. Noll, A. Smette, S. Kimeswenger, M. Barden, C. Szyszka, A. M. Jones, H. Sana, H. Horst, and F. Kerber, (2015, A&A 576, A78).

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, acc. by A&A.