4,383 research outputs found
J-PLUS: analysis of the intracluster light in the Coma cluster
The intracluster light (ICL) is a luminous component of galaxy clusters
composed of stars that are gravitationally bound to the cluster potential but
do not belong to the individual galaxies. Previous studies of the ICL have
shown that its formation and evolution are intimately linked to the
evolutionary stage of the cluster. Thus, the analysis of the ICL in the Coma
cluster will give insights into the main processes driving the dynamics in this
highly complex system. Using a recently developed technique, we measure the ICL
fraction in Coma at several wavelengths, using the J-PLUS unique filter system.
The combination of narrow- and broadband filters provides valuable information
on the dynamical state of the cluster, the ICL stellar types, and the
morphology of the diffuse light. We use the Chebyshev-Fourier Intracluster
Light Estimator (CICLE) to disentangle the ICL from the light of the galaxies,
and to robustly measure the ICL fraction in seven J-PLUS filters. We obtain the
ICL fraction distribution of the Coma cluster at different optical wavelengths,
which varies from , showing the highest values in the narrowband
filters J0395, J0410, and J0430. This ICL fraction excess is distinctive
pattern recently observed in dynamically active clusters (mergers), indicating
a higher amount of bluer stars in the ICL compared to the cluster galaxies.
Both the high ICL fractions and the excess in the bluer filters are indicative
of a merging state. The presence of younger/lower-metallicity stars the ICL
suggests that the main mechanism of ICL formation for the Coma cluster is the
stripping of the stars in the outskirts of infalling galaxies and, possibly,
the disruption of dwarf galaxies during past/ongoing mergers.Comment: 10 pages, 3 figures, 1 table. Accepted for publication in A&
J-PLUS: Identification of low-metallicity stars with artificial neural networks using SPHINX
We present a new methodology for the estimation of stellar atmospheric
parameters from narrow- and intermediate-band photometry of the Javalambre
Photometric Local Universe Survey (J-PLUS), and propose a method for target
pre-selection of low-metallicity stars for follow-up spectroscopic studies.
Photometric metallicity estimates for stars in the globular cluster M15 are
determined using this method. By development of a neural-network-based
photometry pipeline, we aim to produce estimates of effective temperature,
, and metallicity, [Fe/H], for a large subset of stars in the
J-PLUS footprint. The Stellar Photometric Index Network Explorer, SPHINX, is
developed to produce estimates of and [Fe/H], after training on a
combination of J-PLUS photometric inputs and synthetic magnitudes computed for
medium-resolution (R ~ 2000) spectra of the Sloan Digital Sky Survey. This
methodology is applied to J-PLUS photometry of the globular cluster M15.
Effective temperature estimates made with J-PLUS Early Data Release photometry
exhibit low scatter, \sigma() = 91 K, over the temperature range
4500 < (K) < 8500. For stars from the J-PLUS First Data Release
with 4500 < (K) < 6200, 85 3% of stars known to have [Fe/H]
<-2.0 are recovered by SPHINX. A mean metallicity of [Fe/H]=-2.32 0.01,
with a residual spread of 0.3 dex, is determined for M15 using J-PLUS
photometry of 664 likely cluster members. We confirm the performance of SPHINX
within the ranges specified, and verify its utility as a stand-alone tool for
photometric estimation of effective temperature and metallicity, and for
pre-selection of metal-poor spectroscopic targets.Comment: 18 pages, 12 figure
Construction and Performance of Large-Area Triple-GEM Prototypes for Future Upgrades of the CMS Forward Muon System
At present, part of the forward RPC muon system of the CMS detector at the
CERN LHC remains uninstrumented in the high-\eta region. An international
collaboration is investigating the possibility of covering the 1.6 < |\eta| <
2.4 region of the muon endcaps with large-area triple-GEM detectors. Given
their good spatial resolution, high rate capability, and radiation hardness,
these micro-pattern gas detectors are an appealing option for simultaneously
enhancing muon tracking and triggering capabilities in a future upgrade of the
CMS detector. A general overview of this feasibility study will be presented.
The design and construction of small (10\times10 cm2) and full-size trapezoidal
(1\times0.5 m2) triple-GEM prototypes will be described. During detector
assembly, different techniques for stretching the GEM foils were tested.
Results from measurements with x-rays and from test beam campaigns at the CERN
SPS will be shown for the small and large prototypes. Preliminary simulation
studies on the expected muon reconstruction and trigger performances of this
proposed upgraded muon system will be reported.Comment: 7 pages, 25 figures, submitted for publication in conference record
of the 2011 IEEE Nuclear Science Symposium, Valencia, Spai
Goedel-type Universes and the Landau Problem
We point out a close relation between a family of Goedel-type solutions of
3+1 General Relativity and the Landau problem in S^2, R^2 and H_2; in
particular, the classical geodesics correspond to Larmor orbits in the Landau
problem. We discuss the extent of this relation, by analyzing the solutions of
the Klein-Gordon equation in these backgrounds. For the R^2 case, this relation
was independently noticed in hep-th/0306148. Guided by the analogy with the
Landau problem, we speculate on the possible holographic description of a
single chronologically safe region.Comment: Latex, 21 pages, 1 figure. v2 missing references to previous work on
the subject adde
Climate change challenges, plant science solutions
Climate change is a defining challenge of the 21st century, and this decade is a critical time for action to mitigate the worst effects on human populations and ecosystems. Plant science can play an important role in developing crops with enhanced resilience to harsh conditions (e.g. heat, drought, salt stress, flooding, disease outbreaks) and engineering efficient carbon-capturing and carbon-sequestering plants. Here, we present examples of research being conducted in these areas and discuss challenges and open questions as a call to action for the plant science community
Uma proposta alternativa para a análise de experimentos de campo utilizando a geoestatística
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