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

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

Numerical Modeling of Physic-Chemical Processes of Multicore Cable in the Polymerization

There are developed mathematical model of physical and chemical processes of polymerization adhesive coating stranded cable. There are found time of full polymerization in the shell of the multicore cable product. There are compared with the single-core cable. Also the necessity of changing the speed of the cable pulling the multilayer product compared with single-core

SimCADO - an instrument data simulator package for MICADO at the E-ELT

MICADO will be the first-light wide-field imager for the European Extremely Large Telescope (E-ELT) and will provide difiraction limited imaging (7mas at 1.2mm) over a ~53 arcsecond field of view. In order to support various consortium activities we have developed a first version of SimCADO: an instrument simulator for MICADO. SimCADO uses the results of the detailed simulation efforts conducted for each of the separate consortium-internal work packages in order to generate a model of the optical path from source to detector readout. SimCADO is thus a tool to provide scientific context to both the science and instrument development teams who are ultimately responsible for the final design and future capabilities of the MICADO instrument. Here we present an overview of the inner workings of SimCADO and outline our plan for its further development.Comment: to appear in Ground-based and Airborne Instrumentation for Astronomy VI, eds. Evans C., Simard L., Takami H., Proc. SPIE vol. 9908 id 73; 201

Carbonic Acid Revisited: Vibrational Spectra, Energetics and the Possibility of Detecting an Elusive Molecule

We calculate harmonic frequencies of the three most abundant carbonic acid conformers. For this, different model chemistries are investigated with respect to their benefits and shortcomings. Based on these results we use perturbation theory to calculate anharmonic corrections at the {\omega}B97XD/aug-cc-pVXZ, X=D,T,Q, level of theory and compare them with recent experimental data and theoretical predictions. A discrete variable representation method is used to predict the large anharmonic contributions to the frequencies of the stretching vibrations in the hydrogen bonds in the carbonic acid dimer. Moreover, we re-investigate the energetics of the formation of the carbonic acid dimer from its constituents water and carbon dioxide using a high-level extrapolation method. We find that the {\omega}B97XD functional performs well in estimating the fundamental frequencies of the carbonic acid conformers. Concerning the reaction energetics, the accuracy of {\omega}B97XD is even comparable to the high-level extrapolation method. We discuss possibilities to detect carbonic acid in various natural environments such as Earth's and Martian atmospheres.Comment: 22 pages, 2 figures, 5 tables. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. The following article appeared in AIP Advances 2, 032180 (2012) and may be found at http://link.aip.org/link/?ADV/2/03218

Fusion Algebras of Fermionic Rational Conformal Field Theories via a Generalized Verlinde Formula

We prove a generalization of the Verlinde formula to fermionic rational conformal field theories. The fusion coefficients of the fermionic theory are equal to sums of fusion coefficients of its bosonic projection. In particular, fusion coefficients of the fermionic theory connecting two conjugate Ramond fields with the identity are either one or two. Therefore, one is forced to weaken the axioms of fusion algebras for fermionic theories. We show that in the special case of fermionic W(2,d)-algebras these coefficients are given by the dimensions of the irreducible representations of the horizontal subalgebra on the highest weight. As concrete examples we discuss fusion algebras of rational models of fermionic W(2,d)-algebras including minimal models of the $N=1$ super Virasoro algebra as well as $N=1$ super W-algebras SW(3/2,d).Comment: 28 pages (Plain TeX), BONN-HE-93-0

SimCADO - a Python Package for Simulating Detector Output for MICADO at the E-ELT

SimCADO is the instrument data simulation software for the E-ELT's near-infrared wide-field imaging camera - MICADO. Written in Python, SimCADO allows the user to simulate possible future observations of astronomical objects with the 39m European Extremely Large Telescope (E-ELT). In these proceedings we present a brief introduction into how to use SimCADO