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Atmospheric Sounding for Site Testing of the European Extremely Large Telescope: Precipitable Water Vapour and More

Florian Kerber

In support of characterization of potential sites for the European Extremely Large Telescope (E-ELT) the European Southern Observatory (ESO), the Institute for Space Imaging Science (ISIS) and the astrometeorology group of the Universidad Valparaiso have jointly established an improved understanding of atmospheric precipitable water vapour (PWV) above ESO’s La Silla Paranal Observatory. In a first step, 8 years worth of high resolution near-IR spectra taken with VLT-UVES have been statistically analysed to reconstruct the PWV history above Paranal. In order to better understand the systematics involved three dedicated campaigns were conducted in May, August and November 2009. Several methods for determining the water column were employed, including radiosonde launches, continuous measurements by infrared radiometer, and VLT instruments operating at various wavelengths: CRIRES, UVES, VISIR and X-shooter. In a first for astronomical instruments all methods have been evaluated with respect to the radiosondes, the established standard in atmospheric research. Agreement between the radiosondes and the IR radiometer (IRMA) is excellent while all other astronomical methods covering a wavelength range from 700 – 20000 nm have also been successfully validated in a quantitative manner. In a collaboration with CAUP we are now exploiting these data for another scientific application. Oxygen lines in the HARPS spectra are analysed in order to deduce bulk motion in the atmosphere. This atmospheric wind structure is then compared to the in-situ data taken by the radiosonde during the HARPS observations. Such a combination of independent atmospheric sounding is done for the first time with the goal to make a quantitative comparison.

2011 January 19, 13:30

Centro de Astrofísica da Universidade do Porto (Auditorium)
Rua das Estrelas, 4150-762 Porto

Faculdade de Ciências da Universidade de Lisboa Universidade do Porto Faculdade de Ciências e Tecnologia da Universidade de Coimbra
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia