2,109 research outputs found
Multimodal Differential Emission Measure in the Solar Corona
The Atmospheric Imaging Assembly (AIA) telescope on board the Solar Dynamics
Observatory (SDO) provides coronal EUV imaging over a broader temperature
sensitivity range than the previous generations of instruments (EUVI, EIT, and
TRACE). Differential emission measure tomography (DEMT) of the solar corona
based on AIA data is presented here for the first time. The main product of
DEMT is the three-dimensional (3D) distribution of the local differential
emission measure (LDEM). While in previous studies, based on EIT or EUVI data,
there were 3 available EUV bands, with a sensitivity range
MK, the present study is based on the 4 cooler AIA bands (aimed at studying the
quiet sun), sensitive to the range MK. The AIA filters allow
exploration of new parametric LDEM models. Since DEMT is better suited for
lower activity periods, we use data from Carrington Rotation 2099, when the Sun
was in its most quiescent state during the AIA mission. Also, we validate the
parametric LDEM inversion technique by applying it to standard bi-dimensional
(2D) differential emission measure (DEM) analysis on sets of simultaneous AIA
images, and comparing the results with DEM curves obtained using other methods.
Our study reveals a ubiquitous bimodal LDEM distribution in the quiet diffuse
corona, which is stronger for denser regions. We argue that the nanoflare
heating scenario is less likely to explain these results, and that alternative
mechanisms, such as wave dissipation appear better supported by our results.Comment: 52 pages, 18 figure
Quasinormal modes and Stability Analysis for 4-dimensional Lifshitz Black Hole
We study the Lifshitz black hole in 4-dimensions with dynamical exponent z=2
and we calculate analytically the quasinormal modes of scalar perturbations.
These quasinormal modes allows to study the stability of the Lifshitz black
hole and we have obtained that Lifshitz black hole is stable.Comment: 7 pages, 2 figures. arXiv admin note: text overlap with
arXiv:1205.058
High resolution spectroscopic analysis of seven giants in the bulge globular cluster NGC 6723
Globular clusters associated with the Galactic bulge are important tracers of
stellar populations in the inner Galaxy. High resolution analysis of stars in
these clusters allows us to characterize them in terms of kinematics,
metallicity, and individual abundances, and to compare these fingerprints with
those characterizing field populations. We present iron and element ratios for
seven red giant stars in the globular cluster NGC~6723, based on high
resolution spectroscopy. High resolution spectra () of seven K
giants belonging to NGC 6723 were obtained with the FEROS spectrograph at the
MPG/ESO 2.2m telescope. Photospheric parameters were derived from FeI
and FeII transitions. Abundance ratios were obtained from line-to-line spectrum
synthesis calculations on clean selected features. An intermediate metallicity
of [Fe/H] dex and a heliocentric radial velocity of
were found for NGC 6723. Alpha-element
abundances present enhancements of dex,
dex, dex, and
dex. Similar overabundance is found for the iron-peak Ti with
dex. Odd-Z elements Na and Al present abundances of
dex and dex, respectively. Finally,
the s-element Ba is also enhanced by dex. The enhancement
levels of NGC 6723 are comparable to those of other metal-intermediate bulge
globular clusters. In turn, these enhancement levels are compatible with the
abundance profiles displayed by bulge field stars at that metallicity. This
hints at a possible similar chemical evolution with globular clusters and the
metal-poor of the bulge going through an early prompt chemical enrichment
Estimating the mass of CMEs from the analysis of EUV dimmings
Context. Reliable estimates of the mass of coronal mass ejections (CMEs) are required to quantify their energy and predict how they affect space weather. When a CME propagates near the observer's line of sight, these tasks involve considerable errors, which motivated us to develop alternative means for estimating the CME mass. Aims. We aim at further developing and testing a method that allows estimating the mass of CMEs that propagate approximately along the observer's line of sight. Methods. We analyzed the temporal evolution of the mass of 32 white-light CMEs propagating across heliocentric heights of 2.5-15 R, in combination with that of the mass evacuated from the associated low coronal dimming regions. The mass of the white-light CMEs was determined through existing methods, while the mass evacuated by each CME in the low corona was estimated using a recently developed technique that analyzes the dimming in extreme-UV (EUV) images. The combined white-light and EUV analyses allow the quantification of an empirical function that describes the evolution of CME mass with height. Results. The analysis of 32 events yielded reliable estimates of the masses of front-side CMEs. We quantified the success of the method by calculating the relative error with respect to the mass of CMEs determined from white-light STEREO data, where the CMEs propagate close to the plane of sky. The median for the relative error in absolute values is ≈30%; 75% of the events in our sample have an absolute relative error smaller than 51%. The sources of uncertainty include the lack of knowledge of piled-up material, subsequent additional mass supply from the dimming region, and limitations in the mass-loss estimation from EUV data. The proposed method does not rely on assumptions of CME size or distance to the observer's plane of sky and is solely based on the determination of the mass that is evacuated in the low corona. It therefore represents a valuable tool for estimating the mass of Earth-directed events.Fil: López, F. M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; ArgentinaFil: Cremades Fernandez, Maria Hebe. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Tecnológica Nacional; ArgentinaFil: Balmaceda, Laura Antonia. George Mason University; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio. Universidad Nacional de San Juan. Instituto de Ciencias Astronómicas, de la Tierra y del Espacio; ArgentinaFil: Nuevo, Federico Alberto. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; ArgentinaFil: Vásquez, A. M.. Consejo Nacional de Investigaciónes Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Astronomía y Física del Espacio. - Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Astronomía y Física del Espacio; Argentina. Universidad Nacional de Tres de Febrero; Argentin
The Higgs boson in the MSSM in light of the LHC
We investigate the expectations for the light Higgs signal in the MSSM in
different search channels at the LHC. After taking into account dark matter and
flavor constraints in the MSSM with eleven free parameters, we show that the
light Higgs signal in the channel is expected to be at most at
the level of the SM Higgs, while the from W fusion
and/or the can be enhanced. For the main discovery
mode, we show that a strong suppression of the signal occurs in two different
cases: low or large invisible width. A more modest suppression is
associated with the effect of light supersymmetric particles. Looking for such
modification of the Higgs properties and searching for supersymmetric partners
and pseudoscalar Higgs offer two complementary probes of supersymmetry.Comment: 19 pages, 8 figure
The WHI Corona from Differential Emission Measure Tomography
A three dimensional (3D) tomographic reconstruction of the local differential
emission measure (LDEM) of the global solar corona during the whole heliosphere
interval (WHI, Carrington rotation CR-2068) is presented, based on STEREO/EUVI
images. We determine the 3D distribution of the electron density, mean
temperature, and temperature spread, in the range of heliocentric heights 1.03
to 1.23 Rsun. The reconstruction is complemented with a potential field source
surface (PFSS) magnetic-field model. The streamer core, streamer legs, and
subpolar regions are analyzed and compared to a similar analysis previously
performed for CR-2077, very near the absolute minimum of the Solar Cycle 23. In
each region, the typical values of density and temperature are similar in both
periods. The WHI corona exhibits a streamer structure of relatively smaller
volume and latitudinal extension than during CR-2077, with a global
closed-to-open density contrast about 6% lower, and a somewhat more complex
morphology. The average basal electron density is found to be about 2.23 and
1.08 x 10^8 cm^-3, in the streamer core and subpolar regions, respectively. The
electron temperature is quite uniform over the analyzed height range, with
average values of about 1.13 and 0.93 MK, in the streamer core and subpolar
regions, respectively. Within the streamer closed region, both periods show
higher temperatures at mid-latitudes and lower temperatures near the equator.
Both periods show beta>1 in the streamer core and beta<1 in the surrounding
open regions, with CR-2077 exhibiting a stronger contrast. Hydrostatic fits to
the electron density are performed, and the scale height is compared to the
LDEM mean electron temperature. Within the streamer core, the results are
consistent with an isothermal hydrostatic plasma regime, with the temperatures
of ions and electrons differing by up to about 10% .. (continues)..Comment: 13 Figure
New universality class for the three-dimensional XY model with correlated impurities: Application to He in aerogels
Encouraged by experiments on He in aerogels, we confine planar spins in
the pores of simulated aerogels (diffusion limited cluster-cluster aggregation)
in order to study the effect of quenched disorder on the critical behavior of
the three-dimensional XY model. Monte Carlo simulations and finite-size scaling
are used to determine critical couplings and exponents. In agreement with
experiments, clear evidence of change in the thermal critical exponents
and is found at nonzero volume fractions of impurities. These changes
are explained in terms of {\it hidden} long-range correlations within disorder
distributions.Comment: 4 pages, 4 figures, submitted to Phys. Rev. Let
Correlation between magnetic interactions and domain structure in A1 FePt ferromagnetic thin films
We have investigated the relationship between the domain structure and the
magnetic interactions in a series of FePt ferromagnetic thin films of varying
thickness. As-made films grow in the magnetically soft and chemically
disordered A1 phase that may have two distinct domain structures. Above a
critical thickness nm the presence of an out of plane
anisotropy induces the formation of stripes, while for planar
domains occur.
Magnetic interactions have been characterized using the well known DCD-IRM
remanence protocols, plots, and magnetic viscosity measurements. We
have observed a strong correlation between the domain configuration and the
sign of the magnetic interactions. Planar domains are associated with positive
exchange-like interactions, while stripe domains have a strong negative
dipolar-like contribution. In this last case we have found a close correlation
between the interaction parameter and the surface dipolar energy of the stripe
domain structure. Using time dependent magnetic viscosity measurements, we have
also estimated an average activation volume for magnetic reversal, nm which is approximately
independent of the film thickness or the stripe period.Comment: 25 pages, 11 figure
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