Research Note

A study of NIR atmospheric properties at Paranal Observatory

¹ European Southern Observatory, Casilla 19001, Santiago 19, Chile
e-mail: glombard@eso.org
² ESA-STScI, 3700 San Martin Drive, MD 21218, Baltimore, USA
³ Australian Astronomical Observatory, PO Box 296, Epping NSW 1710, Australia
⁴ Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway

Received: 23 December 2010
Accepted: 29 January 2011

Abstract

Aims. 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).

Methods. We estimate atmospheric extinction in the spectral range 1.10–2.30 μm (J, J_s, H, and K_s) 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.

Results. We find that extinction coefficients are  < 0.1 mag airmass^-1 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 K_s, while Rayleigh scattering contributes most to the extinction in J_s. We have found negligible color terms for J, H and K_s and a non-negligible color term for J_s.