CS, HC3N and CH3CCH multi-line analyses towards starburst galaxies. The evolution of cloud structures in the central regions of galaxies

We aim to study the properties of the dense molecular gas towards the inner few 100 pc of four nearby starburst galaxies dominated both by photo dissociation regions (M82) and large-scale shocks (NGC253, IC342 and Maffei2), and to relate the chemical and physical properties of the molecular clouds with the evolutionary stage of the nuclear starbursts. We have carried out multi-transitional observations and analyses of three dense gas molecular tracers, CS, HC3N and CH3CCH, using Boltzmann diagrams in order to determine the rotational temperatures and column densities of the dense gas, and using a Large Velocity Gradients model to calculate the H2 density structure in the molecular clouds. The CS and HC3N data indicate the presence of density gradients in the molecular clouds, showing similar excitation conditions, and suggesting that they arise from the same gas components. In M82, CH3CCH has the highest fractional abundance determined in a extragalactic source (10^-8). The density and the chemical gradients found in all galaxies can be explained in the framework of the starburst evolution. The young shock-dominatedstarburst galaxies, like presumably Maffei2, show a cloud structure with a rather uniform density and chemical composition which suggests low star formation activity. Molecular clouds in galaxies with starburst in an intermediate stage of evolution, such as NGC253 and IC342, show clouds with a large density contrast (two orders of magnitude) between the denser regions (cores) and the less dense regions (halos) of the molecular clouds and relatively constant chemical abundance. Finally, the galaxy with the most evolved starburst, M82, has clouds with a rather uniform density structure, large envelopes of atomic/molecular gas subjected to UV photodissociating radiation from young star clusters, and very different chemical abundances of HC3N and CH3CCH.Comment: 14 pages + 1 appendix of 2 pages; 7 figures. Accepted for publication in Astronomy and Astrophysic

A lambda=3 mm molecular line survey of NGC1068. Chemical signatures of an AGN environment

We aimed to study the molecular composition of the interstellar medium (ISM) surrounding an Active Galactic Nucleus (AGN), by making an inventory of molecular species and their abundances, as well as to establish a chemical differentiation between starburst galaxies and AGN. We used the IRAM-30 m telescope to observe the central 1.5-2 kpc region of NGC1068, covering the frequencies between 86.2 GHz and 115.6 GHz. Using Boltzmann diagrams, we calculated the column densities of the detected molecules. We used a chemical model to reproduce the abundances found in the AGN, to determine the origin of each detected species, and to test the influence of UV fields, cosmic rays, and shocks on the ISM. We identified 24 different molecular species and isotopologues, among which HC3N, SO, N2H+, CH3CN, NS, 13CN, and HN13C are detected for the first time in NGC1068. We obtained the upper limits to the isotopic ratios 12C/13C=49, 16O/18O=177 and 32S/34S=5. Our chemical models suggest that the chemistry in the nucleus of NGC1068 is strongly influenced by cosmic rays, although high values of both cosmic rays and far ultraviolet (FUV) radiation fields also explain well the observations. The gas in the nucleus of NGC1068 has a different chemical composition as compared to starburst galaxies. The distinct physical processes dominating galaxy nuclei (e.g. C-shocks, UV fields, X-rays, cosmic rays) leave clear imprints in the chemistry of the gas, which allow to characterise the nucleus activity by its molecular abundances.Comment: 16 pages, 6 figures, 7 tables. Accepted for publication in Astronomy and Astrophysic

Evaluation of misalignments within a concentrator photovoltaic module by the module optical analyzer: a case of study concerning temperature effects on the module performance

Instituto de Energía Solar, Universidad Politécnica de Madrid (IES-UPM) has developed a method [referred to as the luminescence inverse (LI) method] and equipment [called module optical analyzer (MOA)] to fast measure the optical-angular properties of a CPV module without illumination system nor module movement. This paper presents how the MOA can investigate the optical performance of concentrator photovoltaic (CPV) modules optical-angular performance (in particular, misalignments between the optical components comprising the module) at different temperature conditions

Methodology of quantifying curvature of Fresnel lenses and its effect on CPV module performance

Fresnel lenses used as primary optics in concentrating photovoltaic modules may show warping produced by lens manufacturing or module assembly (e.g., stress during molding or weight load) or due to stress during operation (e.g., mismatch of thermal expansion between different materials). To quantify this problem, a simple method called “checkerboard method” is presented. The proposed method identifies shape errors on the front surface of primary lenses by analyzing the Fresnel reflections. This paper also deals with the quantification of the effects these curvatures have on their optical performance and on the electrical performance of concentrating modules incorporating them. This method can be used to perform quality control of Fresnel lenses in scenarios of high volume production

Assessment of the optical efficiency of a primary lens to be used in a CPV system

This article summarizes experimental methods to evaluate the performance and to assess the efficiency of a lens that will be used as primary optics in a concentrating photovoltaic system comprising multijunction solar cells. The methods are classified into two groups: those intended to quantify the transmission losses and those that estimate the size and shape of the light spot. In addition, the optical efficiency definition is reviewed and a systematic procedure to evaluate it is proposed

A novel scanning lens instrument for evaluating Fresnel lens performance: equipment development and initial results

A system dedicated to the optical transmittance characterization of Fresnel lenses has been developed at NREL, in collaboration with the UPM. The system quantifies the optical efficiency of the lens by generating a performance map. The shape of the focused spot may also be analyzed to understand change in the lens performance. The primary instrument components (lasers and CCD detector) have been characterized to confirm their capability for performing optical transmittance measurements. Measurements performed on SoG and PMMA lenses subject to a variety of indoor conditions (e.g., UV and damp heat) identified differences in the optical efficiency of the evaluated lenses, demonstrating the ability of the Scanning Lens Instrument (SLI) to distinguish between the aged lenses

Hybrid dome with total internal reflector as a secondary optical element for CPV

Secondary optical elements (SOEs) are used in Concentrator Photovoltaic (CPV) modules to allow the concentration ratio to exceed those typically achievable by Fresnel lenses, reducing cell costs, without sacrificing tolerance to tracking errors. One option is a “dome” SOE: a simple, single surface refractive optic that images the primary lens onto the cell while immersing it. In this article, we explore the limits of this type of SOE and propose an evolved version, which we dub the Hybrid Dome Reflector (HDR), which offers advantages especially for high concentration modules with large cells, where reflective secondaries do not offer sufficient acceptance angle, but other dielectric secondaries, such as the Dielectric Totally Internally Reflecting Concentrator DTIRC, may be too large for economical manufacture. We discuss aspects of HDR design and share selected ray-tracing simulations and experimental results. We show that the new HDR design improves acceptance angle and tolerances to manufacturing error and lens temperature as compared to a reflective SOE built while offering similar efficiencies

Understanding causes and effects of non-uniform light distributions on multi-junction solar cells: Procedures for estimating efficiency losses

This paper presents the mechanisms of efficiency losses that have to do with the non-uniformity of the irradiance over the multi-junction solar cells and different measurement techniques used to investigate them. To show the capabilities of the presented techniques, three different concentrators (that consist of an acrylic Fresnel lens, different SOEs and a lattice matched multi-junction cell) are evaluated. By employing these techniques is possible to answer some critical questions when designing concentrators as for example which degree of non-uniformity the cell can withstand, how critical the influence of series resistance is, or what kind of non-uniformity (spatial or spectral) causes more losses

Concentration photovoltaic optical system irradiance distribution measurements and its effect on multi-junction solar cells

This paper proposes an indoor procedure based on charge-coupled device camera measurements to characterize the non-uniform light patterns produced by optical systems used in concentration photovoltaic (CPV) systems. These irradiance patterns are reproduced on CPV solar cells for their characterization at concentrated irradiances by using a concentrator cell tester and placing high-resolution masks over the cells. Measured losses based on the masks method are compared with losses in concentrator optical systems measured by using the Helios 3198 solar simulator for CPV module