35 research outputs found
Extragalactic Fields Optimized for Adaptive Optics
In this paper we present the coordinates of 67 55' x 55' patches of sky which
have the rare combination of both high stellar surface density (>0.5
arcmin^{-2} with 13<R<16.5 mag) and low extinction (E(B-V)<0.1). These fields
are ideal for adaptive-optics based follow-up of extragalactic targets. One
region of sky, situated near Baade's Window, contains most of the patches we
have identified. Our optimal field, centered at RA: 7h24m3s, Dec: -1deg27'15",
has an additional advantage of being accessible from both hemispheres. We
propose a figure of merit for quantifying real-world adaptive optics
performance, and use this to analyze the performance of multi-conjugate
adaptive optics in these fields. We also compare our results to those that
would be obtained in existing deep fields. In some cases adaptive optics
observations undertaken in the fields given in this paper would be orders of
magnitude more efficient than equivalent observations undertaken in existing
deep fields.Comment: 28 pages, 15 figures, 1 table; accepted for publication in PAS
The Next Generation Virgo Cluster Survey - Infrared (NGVS-IR): I. A new Near-UV/Optical/Near-IR Globular Cluster selection tool
The NGVS-IR project (Next Generation Virgo Survey - Infrared) is a contiguous
near-infrared imaging survey of the Virgo cluster of galaxies. It complements
the optical wide-field survey of Virgo (NGVS). The current state of NGVS-IR
consists of Ks-band imaging of 4 deg^2 centered on M87, and J and Ks-band
imaging of 16 deg^2 covering the region between M49 and M87. In this paper, we
present the observations of the central 4 deg^2 centered on Virgo's core
region. The data were acquired with WIRCam on the Canada-France-Hawaii
Telescope and the total integration time was 41 hours distributed in 34
contiguous tiles. A survey-specific strategy was designed to account for
extended galaxies while still measuring accurate sky brightness within the
survey area. The average 5\sigma limiting magnitude is Ks=24.4 AB mag and the
50% completeness limit is Ks=23.75 AB mag for point source detections, when
using only images with better than 0.7" seeing (median seeing 0.54"). Star
clusters are marginally resolved in these image stacks, and Virgo galaxies with
\mu_Ks=24.4 AB mag arcsec^-2 are detected. Combining the Ks data with optical
and ultraviolet data, we build the uiK color-color diagram which allows a very
clean color-based selection of globular clusters in Virgo. This diagnostic plot
will provide reliable globular cluster candidates for spectroscopic follow-up
campaigns needed to continue the exploration of Virgo's photometric and
kinematic sub-structures, and will help the design of future searches for
globular clusters in extragalactic systems. Equipped with this powerful new
tool, future NGVS-IR investigations based on the uiK diagram will address the
mapping and analysis of extended structures and compact stellar systems in and
around Virgo galaxies.Comment: 23 pages, 18 figures. Accepted for publication in ApJ
Évolution cosmologique des propriétés physiques des galaxies
BORDEAUX1-Observatoire (331672201) / SudocTOULOUSE3-BU Sciences (315552104) / SudocTOULOUSE-Observ. Midi Pyréné (315552299) / SudocMEUDON-Observatoire (920482302) / SudocAIX-MARSEILLE1.OAMP.Le Verrier (130552205) / SudocSudocFranceF
DĂ©tection et analyse par effet de lentille gravitationnelle d'amas de galaxies
TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF
Modeling of the He Density Evolution Inside the CABRI Transient Rods During Power Transients
International audienceCABRI is an experimental pulse reactor, funded by the French Nuclear Safety and Radioprotection Institute and operated by CEA at the Cadarache research center. It is designed to study fuel behavior under reactivity-initiated accident conditions. In order to produce the power transients, reactivity is injected by depressurization of a neutron absorber (He) situated in transient rods inside the reactor core. The shapes of power transients depend on the total amount of reactivity injected and on the injection speed. The injected reactivity can be calculated by conversion of the He gas density into units of reactivity. So, it is of upmost importance to properly model gas density evolution in transient rods during a power transient. The He depressurization was studied by computational fluid dynamics (CFD) calculations validated by measurements using pressure transducers. The CFD calculations show that the density evolution is slower than the pressure drop. Studies also show that it is harder to predict the depressurization during the power transients because of neutron/He capture reactions that induce a gas heating. Surrogate models were built based on CFD calculations and validated against preliminary tests in the CABRI transient system. Two methods were identified to evaluate the gas density evolution: CFD calculations and reverse point kinetics (PKs). The first one consists in adding a heat source in transient rods based on the experimental power conversion. The second one consists in using the measured power by boron ionization chambers to evaluate the net reactivity by a reverse PKs method and to subtract the reactivity feedbacks calculated with the DULCINEE multiphysics code
Assessment of the
CABRI is an experimental pulse reactor, funded by the French Nuclear Safety and Radioprotection Institute (IRSN) and operated by CEA at the Cadarache research center. It is designed to study fuel behavior under RIA conditions. In order to produce the power transients, reactivity is injected by depressurization of a neutron absorber (3He) situated in transient rods inside the reactor core. The shapes of power transients depend on the total amount of reactivity injected and on the injection speed. The injected reactivity can be calculated by conversion of the 3He gas density into units of reactivity. So, it is of upmost importance to properly master gas density evolution in transient rods during a power transient. The 3He depressurization was studied by CFD calculations and completed with measurements using pressure transducers. The CFD calculations show that the density evolution is slower than the pressure drop. Surrogate models were built based on CFD calculations and validated against preliminary tests in the CABRI transient system. Studies also show that it is harder to predict the depressurization during the power transients because of neutron/3He capture reactions that induce a gas heating. This phenomenon can be studied by a multiphysics approach based on reaction rate calculation thanks to Monte Carlo code and study the resulting heating effect with the validated CFD simulation
Assessment of the 3He pressure inside the CABRI transient rods - Development of a surrogate model based on measurements and complementary CFD calculations
CABRI is an experimental pulse reactor, funded by the French Nuclear Safety and Radioprotection Institute (IRSN) and operated by CEA at the Cadarache research center. It is designed to study fuel behavior under RIA conditions. In order to produce the power transients, reactivity is injected by depressurization of a neutron absorber (3He) situated in transient rods inside the reactor core. The shapes of power transients depend on the total amount of reactivity injected and on the injection speed. The injected reactivity can be calculated by conversion of the 3He gas density into units of reactivity. So, it is of upmost importance to properly master gas density evolution in transient rods during a power transient. The 3He depressurization was studied by CFD calculations and completed with measurements using pressure transducers. The CFD calculations show that the density evolution is slower than the pressure drop. Surrogate models were built based on CFD calculations and validated against preliminary tests in the CABRI transient system. Studies also show that it is harder to predict the depressurization during the power transients because of neutron/3He capture reactions that induce a gas heating. This phenomenon can be studied by a multiphysics approach based on reaction rate calculation thanks to Monte Carlo code and study the resulting heating effect with the validated CFD simulation
Coupled Experimental and Computational Approach for CABRI Power Transients Analysis
International audienceCABRI is an experimental pulse reactor, funded by the French Nuclear Safety and Radioprotection Institute and operated by Commissariat à l'Énergie Atomique et aux Énergies Alternatives at the Cadarache Research Center. It is designed to study fuel behavior under reactivity-initiated accident conditions. In order to produce the power transients, reactivity is injected by depressurization of a neutron absorber (3 He) situated in the so-called transient rods inside the reactor core. The CABRI reactivity injection system allows us to generate structured tran-sients based on specific sequences of depressurization. For such transients, the time difference between the openings of two valves of the reactivity injection system has an important impact on the power pulse shape. A kinetic point code, SPARTE, was developed in order to replace the older DULCINEE code dedicated to the modeling and prediction of CABRI power transients. The SPARTE code includes new models of 3 He depressurization based on CFD calculations, variable Doppler coefficient based on Monte Carlo calculations, and variable axial neutron flux profile. The density and Doppler models have a large impact on power transient prediction. For low initial pressure transients, the major uncertainty comes from the reactivity injected by the 3 He depressurization. For high initial pressure transients, the 3 He heating during the power pulse ("TOP effect") is responsible of an additional injection of reactivity that needs to be modeled precisely