An advanced scattered moonlight model for Cerro Paranal

The largest natural source of light at night is the Moon, and it is the major contributor to the astronomical sky background. Being able to accurately predict the sky background, including scattered moonlight is important for scheduling astronomical observations. We have developed an improved scattered moonlight model, in which the components are computed with a better physical understanding as opposed to the simple empirical fit in the frequently used photometric model of Krisciunas & Schaefer (1991). Our spectroscopic model can better trace the spectral trends of scattered moonlight for any position of the Moon and target observation. This is the first scattered moonlight model that we know of which is this physical and versatile. We have incorporated an observed solar spectrum, accurate lunar albedo fit, and elaborate scattering and absorption calculations that include scattering off of molecules and aerosols. It was designed for Cerro Paranal, but can be modified for any location with known atmospheric properties. Throughout the optical range, the uncertainty is less than 20%. This advanced scattered moonlight model can predict the amount of scattered moonlight for any given geometry of the Moon and target, and lunar phase for the entire optical spectrum.Comment: 12 pages, 13 figures, accepted for publication in A&

Study of the atmospheric conditions at Cerro Armazones using astronomical data

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 Cherenkov Telescope Array (CTA). Methods: Spectroscopic data from the Bochum Echelle Spectroscopic Observer (BESO) instrument were investigated by using line-by-line radiative transfer model (LBLRTM) radiative transfer models for the Earths 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 Nino event registered in the period 2009-2010. Models of the 3D Global Data Assimilation System (GDAS) were used for further comparison. Moreover, for those days with coincidence of data from a similar study with VLT/X-shooter and microwave radiometer LHATPRO data at Cerro Paranal, a direct comparison is presented. 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 method for predicting of local atmospheric conditions - they usually systematically overestimate the PWV values. Due to the large sample, we were furthermore able to characterize the site with respect to symmetry across the sky and variation with the years and within the seasons. This kind of technique of studying the atmospheric conditions is shown to be a promising step into a possible monitoring equipment for CTA.Comment: Accepted for publication in Astronomy and Astrophysics, 7 pages, 9 figure

15 years of VLT/UVES OH intensities and temperatures in comparison with TIMED/SABER data

The high-resolution echelle spectrograph UVES of the Very Large Telescope at Cerro Paranal in Chile has been regularly operated since April 2000. Thus, UVES archival data originally taken for astronomical projects but also including sky emission can be used to study airglow variations on a time scale longer than a solar cycle. Focusing on OH emission and observations until March 2015, we considered about 3,000 high-quality spectra from two instrumental set-ups centred on 760 and 860 nm, which cover about 380 nm each. These data allowed us to measure line intensities for several OH bands in order to derive band intensities and rotational temperatures for different upper vibrational levels as a function of solar activity and observing date. The results were compared with those derived from emission and temperature profile data of the radiometer SABER on the TIMED satellite taken in the Cerro Paranal area between 2002 and 2015. In agreement with the SABER data, the long-term variations in OH intensity and temperature derived from the UVES data are dominated by the solar cycle, whereas secular trends appear to be negligible. Combining the UVES and SABER results, the solar cycle effects for the OH intensity and temperature are about 12 to 17% and 4 to 5 K per 100 sfu and do not significantly depend on the selected OH band. The data also reveal that variations of the effective OH emission layer height and air density can cause significant changes in the OH rotational temperatures due to a varying ratio of OH thermalising collisions by air molecules and OH radiation, deactivation, and destruction processes which impede the rotational relaxation. However, this effect appears to be of minor importance for the explanation of the rotational temperature variations related to the solar activity cycle, which causes only small changes in the OH emission profile.Comment: preprint with 22 pages and 11 figures, accepted for publication in JAST

The Stellar Population of High Redshift Galaxies

Using the VLT we have obtained high quality spectra of about 70 high redshift (1- 4.6) galaxies within the FORS Deep Field (FDF). As expected most of them turn out to be (bright) starburst galaxies and the observed spectra agree with synthetic ones. The equivalent width of the CIV(1550) absorption line turns out to be a good indicator for the galaxies metallicity. Furthermore our high-z starburst galaxies show increasing metal content with decreasing redshift. Compared with local starburst galaxies they tend to be overliminous for their metallicity.Comment: 3 pages, including 4 eps-figures, Latex2e, to appear in proceedings of MPA/ESO/MPE/USM Joint Astronomy Conference on "Lighthouses of the Universe" (Eds.: R. Sunyaev, M. Gilfanov, E. Churazov

A Semantic-Based Information Management System to Support Innovative Product Design

International competition and the rapidly global economy, unified by improved communication and transportation, offer to the consumers an enormous choice of goods and services. The result is that companies now require quality, value, time to market and innovation to be successful in order to win the increasing competition. In the engineering sector this is traduced in need of optimization of the design process and in maximization of re-use of data and knowledge already existing in the company. The “SIMI-Pro” (Semantic Information Management system for Innovative Product design) system addresses specific deficiencies in the conceptual phase of product design when knowledge management, if applied, is often sectorial. Its main contribution is in allowing easy, fast and centralized collection of data from multiple sources and in supporting the retrieval and re-use of a wide range of data that will help stylists and engineers shortening the production cycle. SIMI-Pro will be one of the first prototypes to base its information management and its knowledge sharing system on process ontology and it will demonstrate how the use of centralized network systems, coupled with Semantic Web technologies, can improve inter-working activities and interdisciplinary knowledge sharing

Mechanical Design of the MID Split-and-Delay Line at the European XFEL

A new split-and-delay line (SDL) is under development for the Materials Imaging and Dynamics (MID) end station at the European XFEL.* The device utilises Bragg reflection to provide pairs of X-ray pulses with an energy of (5 - 10) keV and a continuously tunable time delay of (-10 - 800) ps - thus allowing zero-crossing of the time delay. The mechanical concept features separate positioning stages for each optical element. Those are based on a serial combination of coarse motion axes and a fine alignment 6 DoF Cartesian parallel kinematics**. That allows to meet the contradictory demands of a fast long-range travel of up to 1000 mm and in the same time a precise alignment with a resolution in the nanometer range. Multiple laser interferometers monitor the position of the optical elements and allow an active control of their alignment. All optical elements and mechanics will be installed inside an UHV chamber, including the interferometer and about 100 stepper motors. With this paper we present the mechanical design for the SDL. It will additionally show the design of a prototype of a positioning stage which allows extensive testing of the implemented concepts and techniques

Bolometric Night Sky Temperature and Subcooling of Telescope Structures

Context. The term sky temperature is used in the literature in different contexts which often leads to confusion. In this work, we study $T_\text{sky}$, the effective bolometric sky temperature at which a hemispherical black body would radiate the same power onto a flat horizontal structure on the ground as the night sky, integrated over the entire thermal wavelength range of $1-100\,\mu$m. We then analyze the thermal physics of radiative cooling with special focus on telescopes and discuss mitigation strategies. Aims. The quantity $T_\text{sky}$ is useful to quantify the subcooling in telescopes which can deteriorate the image quality by introducing an Optical Path Difference (OPD) and induce thermal stress and mechanical deflections on structures. Methods. We employ the Cerro Paranal Sky Model of the European Southern Observatory to derive a simple formula of $T_\text{sky}$ as a function of atmospheric parameters. The structural subcooling and the induced OPD are then expressed as a function of surface emissivity, sky view factor, local air speed and structure dimensions. Results. At Cerro Paranal (2600 m) and Cerro Armazones (3060 m) in the Atacama desert, $T_\text{sky}$ towards the zenith mostly lies $20-50$ Kelvin below the ambient temperature near the ground, depending strongly on the precipitable water vapor (PWV) column in the atmosphere. The temperature difference can decrease by several Kelvin for higher zenith distances. The subcooling OPD scales linearly to quadratically with the telescope diameter and is inversely proportional to the local air speed near the telescope structure.Comment: 14 pages, 16 figure

CIGALEMC: Galaxy Parameter Estimation using a Markov Chain Monte Carlo Approach with Cigale

We introduce a fast Markov Chain Monte Carlo (MCMC) exploration of the astrophysical parameter space using a modified version of the publicly available code CIGALE (Code Investigating GALaxy emission). The original CIGALE builds a grid of theoretical Spectral Energy Distribution (SED) models and fits to photometric fluxes from Ultraviolet (UV) to Infrared (IR) to put contraints on parameters related to both formation and evolution of galaxies. Such a grid-based method can lead to a long and challenging parameter extraction since the computation time increases exponentially with the number of parameters considered and results can be dependent on the density of sampling points, which must be chosen in advance for each parameter. Markov Chain Monte Carlo methods, on the other hand, scale approximately linearly with the number of parameters, allowing a faster and more accurate exploration of the parameter space by using a smaller number of efficiently chosen samples. We test our MCMC version of the code CIGALE (called CIGALEMC) with simulated data. After checking the ability of the code to retrieve the input parameters used to build the mock sample, we fit theoretical SEDs to real data from the well known and studied SINGS sample. We discuss constraints on the parameters and show the advantages of our MCMC sampling method in terms of accuracy of the results and optimization of CPU time.Comment: 12 pages, 8 figures, 4 tables, updated to match the version accepted for publication in ApJ; code available at http://www.oamp.fr/cigale

OH level populations and accuracies of Einstein-A coefficients from hundreds of measured lines

OH airglow is an important nocturnal emission of the Earth's mesopause region. As it is chemiluminescent radiation in a thin medium, the population distribution over the various roto-vibrational OH energy levels of the electronic ground state is not in local thermodynamic equilibrium (LTE). In order to better understand these non-LTE effects, we studied hundreds of OH lines in a high-quality mean spectrum based on observations with the high-resolution Ultraviolet and Visual Echelle Spectrograph at Cerro Paranal in Chile. Our derived populations cover vibrational levels between v = 3 and 9, rotational levels up to N = 24, and individual $\Lambda$-doublet components when resolved. As the reliability of these results critically depends on the Einstein-A coefficients used, we tested six different sets and found clear systematic errors in all of them, especially for Q-branch lines and individual $\Lambda$-doublet components. In order to minimise the deviations in the populations for the same upper level, we used the most promising coefficients from Brooke et al. (2016) and further improved them with an empirical correction approach. The resulting rotational level populations show a clear bimodality for each v, which is characterised by a probably fully thermalised cold component and a hot population with rotational temperatures between about 700 (v = 9) and 7,000 K (v = 4). The latter causes non-LTE contributions at low N, which can be estimated quite robustly based on the two-temperature model. The bimodality is also clearly indicated by the different dependence of the populations on changes in the effective height of the OH emission layer.Comment: 37 single-column pages and 14 figures, replacement due to publication of final paper in Atmos. Chem. Phys., changes related to DOI and journal referenc