A study of NIR atmospheric properties at Paranal Observatory

TL;DR

This study analyzes near-infrared atmospheric properties at Paranal Observatory, quantifying extinction sources and their variability, to improve observational accuracy for telescopic data in the 1.10-2.30 um range.

Contribution

It provides a comprehensive database of atmospheric extinction measurements and models the contributions of water vapor, Rayleigh scattering, and molecular absorption in the NIR.

Findings

Extinction coefficients are less than 0.1 mag/airmass across bands.

Water vapor significantly affects J-band extinction.

Molecular absorption dominates in J, H, Ks bands; Rayleigh scattering in Js.

Abstract

In order to maximize the scientific return of the telescopes located at the Paranal Observatory, we analyse the properties of the atmosphere above Paranal in the near-infrared (NIR). We estimate atmospheric extinction in the spectral range 1.10-2.30 um (J, Js, H, and Ks) using standard stars that were observed during photometric and clear nights with ISAAC on the Very Large Telescope UT1 between 2000 and 2004. We have built a database consisting of hundreds of observations, which allows us to examine how extinction varies with airmass and the column density of water vapour. In addition, we use theoretical models of the atmosphere to estimate Rayleigh scattering and molecular absorption in order to quantify their fractional contribution to the total extinction in each filter. Finally, we have observed 8 bright red standard stars to evaluate filter color terms. We find that extinction coefficients are < 0.1 mag/airmass in all the considered bands. The extinction coefficient in the J-band strongly depends on the column density of water vapour. Molecular absorption dominates the extinction in J, H and Ks, while Rayleigh scattering contributes most to the extinction in Js. We have found negligible color terms for J, H and Ks and a non-negligible color term for Js.