The Experts below are selected from a list of 161412 Experts worldwide ranked by ideXlab platform
D K Gilmore - One of the best experts on this subject based on the ideXlab platform.
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simulation of astronomical images from optical survey telescopes using a comprehensive photon Monte Carlo Approach
Astrophysical Journal Supplement Series, 2015Co-Authors: J R Peterson, J G Jernigan, S M Kahn, A Rasmussen, E Peng, Z Ahmad, J Bankert, Chihway Chang, Charles F Claver, D K GilmoreAbstract:We present a comprehensive methodology for the simulation of astronomical images from optical survey telescopes. We use a photon Monte Carlo Approach to construct images by sampling photons from models of astronomical source populations, and then simulating those photons through the system as they interact with the atmosphere, telescope, and camera. We demonstrate that all physical effects for optical light that determine the shapes, locations, and brightnesses of individual stars and galaxies can be accurately represented in this formalism. By using large scale grid computing, modern processors, and an efficient implementation that can produce 400,000 photons s−1, we demonstrate that even very large optical surveys can be now be simulated. We demonstrate that we are able to (1) construct kilometer scale phase screens necessary for wide-field telescopes, (2) reproduce atmospheric point-spread function moments using a fast novel hybrid geometric/Fourier technique for non-diffraction limited telescopes, (3) accurately reproduce the expected spot diagrams for complex aspheric optical designs, and (4) recover system effective area predicted from analytic photometry integrals. This new code, the Photon Simulator (PhoSim), is publicly available. We have implemented the Large Synoptic Survey Telescope design, and it can be extended to other telescopes. We expect that because of the comprehensive physics implemented in PhoSim, it will be used by the community to plan future observations, interpret detailed existing observations, and quantify systematics related to various astronomical measurements. Future development and validation by comparisons with real data will continue to improve the fidelity and usability of the code.
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simulation of astronomical images from optical survey telescopes using a comprehensive photon Monte Carlo Approach
arXiv: Instrumentation and Methods for Astrophysics, 2015Co-Authors: J R Peterson, J G Jernigan, S M Kahn, A Rasmussen, E Peng, Z Ahmad, J Bankert, Chihway Chang, Charles F Claver, D K GilmoreAbstract:We present a comprehensive methodology for the simulation of astronomical images from optical survey telescopes. We use a photon Monte Carlo Approach to construct images by sampling photons from models of astronomical source populations, and then simulating those photons through the system as they interact with the atmosphere, telescope, and camera. We demonstrate that all physical effects for optical light that determine the shapes, locations, and brightnesses of individual stars and galaxies can be accurately represented in this formalism. By using large scale grid computing, modern processors, and an efficient implementation that can produce 400,000 photons/second, we demonstrate that even very large optical surveys can be now be simulated. We demonstrate that we are able to: 1) construct kilometer scale phase screens necessary for wide-field telescopes, 2) reproduce atmospheric point-spread-function moments using a fast novel hybrid geometric/Fourier technique for non-diffraction limited telescopes, 3) accurately reproduce the expected spot diagrams for complex aspheric optical designs, and 4) recover system effective area predicted from analytic photometry integrals. This new code, the photon simulator (PhoSim), is publicly available. We have implemented the Large Synoptic Survey Telescope (LSST) design, and it can be extended to other telescopes. We expect that because of the comprehensive physics implemented in PhoSim, it will be used by the community to plan future observations, interpret detailed existing observations, and quantify systematics related to various astronomical measurements. Future development and validation by comparisons with real data will continue to improve the fidelity and usability of the code.
Eric Herbst - One of the best experts on this subject based on the ideXlab platform.
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gas grain chemistry in cold interstellar cloud cores with a microscopic Monte Carlo Approach to surface chemistry
Astronomy and Astrophysics, 2007Co-Authors: Q Chang, H M Cuppen, Eric HerbstAbstract:Aims. We have recently developed a microscopic Monte Carlo Approach to study surface chemistry on interstellar grains and the morphology of ice mantles. The method is designed to eliminate the problems inherent in the rate-equation formalism to surface chemistry. Here we report the first use of this method in a chemical model of cold interstellar cloud cores that includes both gas-phase and surface chemistry. The surface chemical network consists of a small number of diffusive reactions that can produce molecular oxygen, water, carbon dioxide, formaldehyde, methanol and assorted radicals. Methods. The simulation is started by running a gas-phase model including accretion onto grains but no surface chemistry or evaporation. The starting surface consists of either flat or rough olivine. We introduce the surface chemistry of the three species H, O and CO in an iterative manner using our stochastic technique. Under the conditions of the simulation, only atomic hydrogen can evaporate to a significant extent. Although it has little effect on other gas-phase species, the evaporation of atomic hydrogen changes its gas-phase abundance, which in turn changes the flux of atomic hydrogen onto grains. The effect on the surface chemistry is treated until convergence occurs. We neglect all non-thermal desorptive processes. Results. We determine the mantle abundances of assorted molecules as a function of time through 2 $\times$ 10 5 yr. Our method also allows determination of the abundance of each molecule in specific monolayers. The mantle results can be compared with observations of water, carbon dioxide, carbon monoxide, and methanol ices in the sources W33A and Elias 16. Other than a slight underproduction of mantle CO, our results are in very good agreement with observations.
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gas grain chemistry in cold interstellar cloud cores with a microscopic Monte Carlo Approach to surface chemistry
arXiv: Astrophysics, 2007Co-Authors: Q Chang, H M Cuppen, Eric HerbstAbstract:AIM: We have recently developed a microscopic Monte Carlo Approach to study surface chemistry on interstellar grains and the morphology of ice mantles. The method is designed to eliminate the problems inherent in the rate-equation formalism to surface chemistry. Here we report the first use of this method in a chemical model of cold interstellar cloud cores that includes both gas-phase and surface chemistry. The surface chemical network consists of a small number of diffusive reactions that can produce molecular oxygen, water, carbon dioxide, formaldehyde, methanol and assorted radicals. METHOD: The simulation is started by running a gas-phase model including accretion onto grains but no surface chemistry or evaporation. The starting surface consists of either flat or rough olivine. We introduce the surface chemistry of the three species H, O and CO in an iterative manner using our stochastic technique. Under the conditions of the simulation, only atomic hydrogen can evaporate to a significant extent. Although it has little effect on other gas-phase species, the evaporation of atomic hydrogen changes its gas-phase abundance, which in turn changes the flux of atomic hydrogen onto grains. The effect on the surface chemistry is treated until convergence occurs. We neglect all non-thermal desorptive processes. RESULTS: We determine the mantle abundances of assorted molecules as a function of time through 2x10^5 yr. Our method also allows determination of the abundance of each molecule in specific monolayers. The mantle results can be compared with observations of water, carbon dioxide, carbon monoxide, and methanol ices in the sources W33A and Elias 16. Other than a slight underproduction of mantle CO, our results are in very good agreement with observations.
H M Cuppen - One of the best experts on this subject based on the ideXlab platform.
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gas grain chemistry in cold interstellar cloud cores with a microscopic Monte Carlo Approach to surface chemistry
Astronomy and Astrophysics, 2007Co-Authors: Q Chang, H M Cuppen, Eric HerbstAbstract:Aims. We have recently developed a microscopic Monte Carlo Approach to study surface chemistry on interstellar grains and the morphology of ice mantles. The method is designed to eliminate the problems inherent in the rate-equation formalism to surface chemistry. Here we report the first use of this method in a chemical model of cold interstellar cloud cores that includes both gas-phase and surface chemistry. The surface chemical network consists of a small number of diffusive reactions that can produce molecular oxygen, water, carbon dioxide, formaldehyde, methanol and assorted radicals. Methods. The simulation is started by running a gas-phase model including accretion onto grains but no surface chemistry or evaporation. The starting surface consists of either flat or rough olivine. We introduce the surface chemistry of the three species H, O and CO in an iterative manner using our stochastic technique. Under the conditions of the simulation, only atomic hydrogen can evaporate to a significant extent. Although it has little effect on other gas-phase species, the evaporation of atomic hydrogen changes its gas-phase abundance, which in turn changes the flux of atomic hydrogen onto grains. The effect on the surface chemistry is treated until convergence occurs. We neglect all non-thermal desorptive processes. Results. We determine the mantle abundances of assorted molecules as a function of time through 2 $\times$ 10 5 yr. Our method also allows determination of the abundance of each molecule in specific monolayers. The mantle results can be compared with observations of water, carbon dioxide, carbon monoxide, and methanol ices in the sources W33A and Elias 16. Other than a slight underproduction of mantle CO, our results are in very good agreement with observations.
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gas grain chemistry in cold interstellar cloud cores with a microscopic Monte Carlo Approach to surface chemistry
arXiv: Astrophysics, 2007Co-Authors: Q Chang, H M Cuppen, Eric HerbstAbstract:AIM: We have recently developed a microscopic Monte Carlo Approach to study surface chemistry on interstellar grains and the morphology of ice mantles. The method is designed to eliminate the problems inherent in the rate-equation formalism to surface chemistry. Here we report the first use of this method in a chemical model of cold interstellar cloud cores that includes both gas-phase and surface chemistry. The surface chemical network consists of a small number of diffusive reactions that can produce molecular oxygen, water, carbon dioxide, formaldehyde, methanol and assorted radicals. METHOD: The simulation is started by running a gas-phase model including accretion onto grains but no surface chemistry or evaporation. The starting surface consists of either flat or rough olivine. We introduce the surface chemistry of the three species H, O and CO in an iterative manner using our stochastic technique. Under the conditions of the simulation, only atomic hydrogen can evaporate to a significant extent. Although it has little effect on other gas-phase species, the evaporation of atomic hydrogen changes its gas-phase abundance, which in turn changes the flux of atomic hydrogen onto grains. The effect on the surface chemistry is treated until convergence occurs. We neglect all non-thermal desorptive processes. RESULTS: We determine the mantle abundances of assorted molecules as a function of time through 2x10^5 yr. Our method also allows determination of the abundance of each molecule in specific monolayers. The mantle results can be compared with observations of water, carbon dioxide, carbon monoxide, and methanol ices in the sources W33A and Elias 16. Other than a slight underproduction of mantle CO, our results are in very good agreement with observations.
J R Peterson - One of the best experts on this subject based on the ideXlab platform.
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simulation of astronomical images from optical survey telescopes using a comprehensive photon Monte Carlo Approach
Astrophysical Journal Supplement Series, 2015Co-Authors: J R Peterson, J G Jernigan, S M Kahn, A Rasmussen, E Peng, Z Ahmad, J Bankert, Chihway Chang, Charles F Claver, D K GilmoreAbstract:We present a comprehensive methodology for the simulation of astronomical images from optical survey telescopes. We use a photon Monte Carlo Approach to construct images by sampling photons from models of astronomical source populations, and then simulating those photons through the system as they interact with the atmosphere, telescope, and camera. We demonstrate that all physical effects for optical light that determine the shapes, locations, and brightnesses of individual stars and galaxies can be accurately represented in this formalism. By using large scale grid computing, modern processors, and an efficient implementation that can produce 400,000 photons s−1, we demonstrate that even very large optical surveys can be now be simulated. We demonstrate that we are able to (1) construct kilometer scale phase screens necessary for wide-field telescopes, (2) reproduce atmospheric point-spread function moments using a fast novel hybrid geometric/Fourier technique for non-diffraction limited telescopes, (3) accurately reproduce the expected spot diagrams for complex aspheric optical designs, and (4) recover system effective area predicted from analytic photometry integrals. This new code, the Photon Simulator (PhoSim), is publicly available. We have implemented the Large Synoptic Survey Telescope design, and it can be extended to other telescopes. We expect that because of the comprehensive physics implemented in PhoSim, it will be used by the community to plan future observations, interpret detailed existing observations, and quantify systematics related to various astronomical measurements. Future development and validation by comparisons with real data will continue to improve the fidelity and usability of the code.
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simulation of astronomical images from optical survey telescopes using a comprehensive photon Monte Carlo Approach
arXiv: Instrumentation and Methods for Astrophysics, 2015Co-Authors: J R Peterson, J G Jernigan, S M Kahn, A Rasmussen, E Peng, Z Ahmad, J Bankert, Chihway Chang, Charles F Claver, D K GilmoreAbstract:We present a comprehensive methodology for the simulation of astronomical images from optical survey telescopes. We use a photon Monte Carlo Approach to construct images by sampling photons from models of astronomical source populations, and then simulating those photons through the system as they interact with the atmosphere, telescope, and camera. We demonstrate that all physical effects for optical light that determine the shapes, locations, and brightnesses of individual stars and galaxies can be accurately represented in this formalism. By using large scale grid computing, modern processors, and an efficient implementation that can produce 400,000 photons/second, we demonstrate that even very large optical surveys can be now be simulated. We demonstrate that we are able to: 1) construct kilometer scale phase screens necessary for wide-field telescopes, 2) reproduce atmospheric point-spread-function moments using a fast novel hybrid geometric/Fourier technique for non-diffraction limited telescopes, 3) accurately reproduce the expected spot diagrams for complex aspheric optical designs, and 4) recover system effective area predicted from analytic photometry integrals. This new code, the photon simulator (PhoSim), is publicly available. We have implemented the Large Synoptic Survey Telescope (LSST) design, and it can be extended to other telescopes. We expect that because of the comprehensive physics implemented in PhoSim, it will be used by the community to plan future observations, interpret detailed existing observations, and quantify systematics related to various astronomical measurements. Future development and validation by comparisons with real data will continue to improve the fidelity and usability of the code.
R S Thorne - One of the best experts on this subject based on the ideXlab platform.
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study of Monte Carlo Approach to experimental uncertainty propagation with mstw 2008 pdfs
Journal of High Energy Physics, 2012Co-Authors: G. Watt, R S ThorneAbstract:We investigate the Monte Carlo Approach to propagation of experimental un- certainties within the context of the established "MSTW 2008" global analysis of parton distribution functions (PDFs) of the proton at next-to-leading order in the strong coupling. We show that the Monte Carlo Approach using replicas of the original data gives PDF un- certainties in good agreement with the usual Hessian Approach using the standard �χ 2 = 1 criterion, then we explore potential parameterisation bias by increasing the number of free parameters, concluding that any parameterisation bias is likely to be small, with the ex- ception of the valence-quark distributions at low momentum fractions x. We motivate the need for a larger tolerance, �χ 2 > 1, by making fits to restricted data sets and idealised consistent or inconsistent pseudodata. Instead of using data replicas, we alternatively pro- duce PDF sets randomly distributed according to the covariance matrix of fit parameters including appropriate tolerance values, then we demonstrate a simpler method to produce an arbitrary number of random predictions on-the-fly from the existing eigenvector PDF sets. Finally, as a simple example application, we use Bayesian reweighting to study the effect of recent LHC data on the lepton charge asymmetry from W boson decays.