Atmospheric conditions at Cerro Armazones derived from astronomical data^⋆,⋆⋆

¹ Instituto de Astronomía, Universidad Católica del Norte, Av. Angamos, 0610 Antofagasta, Chile
e-mail: mlakicevic@ucn.cl; skimeswenger@ucn.cl
² Institute for Astro- and Particle Physics, University of Innsbruck, Technikerstr. 258, 6020 Innsbruck, Austria
³ University of Vienna, Department of Astrophysics, Türkenschanzstr. 17 (Sternwarte), 1170 Vienna, Austria
⁴ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching bei München, Germany

Received: 15 December 2015
Accepted: 30 January 2016

Abstract

Aims. We studied the precipitable water vapour (PWV) content near Cerro Armazones and discuss the potential use of our technique of modelling the telluric absorbtion lines for the investigation of other molecular layers. The site is designated for the European Extremely Large Telescope (E-ELT) and the nearby planned site for the Čerenkov Telescope Array (CTA).

Methods. Spectroscopic data from the Bochum Echelle Spectroscopic Observer (BESO) instrument were investigated by using a line-by-line radiative transfer model (LBLRTM) for the Earth’s atmosphere with the telluric absorption correction tool molecfit. All observations from the archive in the period from December 2008 to the end of 2014 were investigated. The dataset completely covers the El Niño event registered in the period 2009–2010. Models of the 3D Global Data Assimilation System (GDAS) were used for further comparison. Moreover, we present a direct comparison for those days for which data from a similar study with VLT/X-Shooter and microwave radiometer LHATPRO at Cerro Paranal are available.

Results. This analysis shows that the site has systematically lower PWV values, even after accounting for the decrease in PWV expected from the higher altitude of the site with respect to Cerro Paranal, using the average atmosphere found with radiosondes. We found that GDAS data are not a suitable basis for predicting local atmospheric conditions – they usually systematically overestimate the PWV values. The large sample furthermore enabled us to characterize the site with respect to symmetry across the sky and variation with the years and within the seasons. This technique of studying the atmospheric conditions is shown to be a promising step into a possible monitoring equipment for the CTA.