395 research outputs found
Near-infrared spectroscopy of 1999 JU3, the target of the Hayabusa 2 mission
Context. Primitive asteroids contain complex organic material and ices
relevant to the origin of life on Earth. These types of asteroids are the
target of several-sample return missions to be launched in the next years. 1999
JU3 is the target of the Japanese Aerospace Exploration Agency's Hayabusa 2
mission. Aims. 1999 JU3 has been previously identified as a C-class asteroid.
Spectroscopic observations at longer wavelengths will help to constrain its
composition. Methods. We obtained spectroscopy of 1999 JU3 from 0.85 to 2.2
microns, with the 3.6 m Telescopio Nazionale Galileo using the low resolution
mode of the Near Infrared Camera Spectrograph. Results. We present a
near-infrared spectrum of 1999 JU3 from 0.85 to 2.2microns that is consistent
with previously published spectra and with its C-type classification.
Conclusions. Our spectrum confirms the primitive nature of 1999 JU3 and its
interest as target of the sample-return mission Hayabusa 2.Comment: Research Note: 3 pages 1 Figure Received December 2012; accepted 4
March 201
An efficient technique of texture representation in segmentation-based image coding schemes
In segmentation-based image coding techniques the image to be compressed is first segmented. Then, the information is coded describing the shape and the interior of the regions. A new method to encode the texture obtained in segmentation-based coding schemes is presented. The approach combines 2-D linear prediction and stochastic vector quantization. To encode a texture, a linear predictor is computed first. Next, a codebook following the prediction error model is generated and the prediction error is encoded with VQ. In the decoder, the error image is decoded first and then filtered as a whole, using the prediction filter. Hence, correlation between pixels is not lost from one block to another and a good reproduction quality can be achieved.Peer ReviewedPostprint (published version
Infrared observations of faint comets
Infrared observations of the periodic comets Encke, Stephan-Oterma and Chernykh indicate that the dusty component in this class of comets is not radically different from the dusty component found in nonperiodic comets. The differences in the infrared behavior among these three comets suggest that a range of behaviors rather than a single behavior typifies the cometary activity. The range in albedo (0.02 to 0.10) of the dust calculated for the periodic comets is similar to the range in albedos seen among the asteroids
Testing the comet nature of main belt comets. The spectra of 133P/Elst-Pizarro and 176P/LINEAR
We present the visible spectrum of MBCs 133P/Elst-Pizarro and 176P/LINEAR, as
well as three Themis family asteroids: (62) Erato, (379), Huenna and (383)
Janina, obtained in 2007 using three telescopes at "El Roque de los Muchachos"'
Observatory, in La Palma, Spain, and the 8m Kueyen (UT2) VLT telescope at Cerro
Paranal, Chile.
The spectra of 133P and 176P resemble best those of B-type asteroid and are
very similar to those of Themis family members and are significantly different
from the spectrum of comet 162P/Siding-Spring and most of the observed cometary
nuclei. CN gas emission is not detected in the spectrum of 133P. We determine
an upper limit for the CN production rate Q(CN) = mol/s,
three orders of magnitude lower than the Q(CN) of Jupiter family comets
observed at similar heliocentric distances.
The spectra of 133P/Elst-Pizarro and 176P/LINEAR confirm that they are likely
members of the Themis family of asteroids, fragments that probably retained
volatiles, and unlikely have a cometary origin in the trans-neptunian belt or
the Oort cloud.Comment: Paper sumbmited to A&A. 7 pages and 6 figure
Additional spectra of asteroid 1996 FG3, backup target of the ESA MarcoPolo-R mission
Near-Earth binary asteroid (175706) 1996 FG3 is the current backup target of
the ESA MarcoPolo-R mission, selected for the study phase of ESA M3 missions.
It is a primitive (C-type) asteroid that shows significant variation in its
visible and near-infrared spectra. Here we present new spectra of 1996 FG3 and
we compare our new data with other published spectra, analysing the variation
in the spectral slope. The asteroid will not be observable again over the next
three years at least. We obtained the spectra using DOLORES and NICS
instruments at the Telescopio Nazionale Galileo (TNG), a 3.6m telescope located
at El Roque de los Muchachos Observatory in La Palma, Spain. To compare with
other published spectra of the asteroid, we computed the spectral slope S', and
studied any plausible correlation of this quantity with the phase angle
(alpha). In the case of visible spectra, we find a variation in spectral slope
of Delta S' = 0.15 +- 0.10 %/10^3 A/degree for 3 < alpha < 18 degrees, in good
agreement with the values found in the literature for the phase reddening
effect. In the case of the near-infrared, we find a variation in the slope of
Delta S' = 0.04 +- 0.08 %/10^3 A/degree for 6 < alpha < 51 degrees. Our
computed variation in S' agrees with the only two values found in the
literature for the phase reddening in the near-infrared. The variation in the
spectral slope of asteroid 1996 FG3 shows a trend with the phase angle at the
time of the observations, both in the visible and the near-infrared. It is
worth noting that, to fully explain this spectral variability we should take
into account other factors, like the position of the secondary component of the
binary asteroid 1999 FG3 with respect to the primary, or the spin axis
orientation at the time of the observations. More data are necessary for an
analysis of this kind.Comment: 4 pages, 3 figures, Accepted in A&A 25 June 201
Time variability of cyclonic geostrophic circulation in the Mediterranean
Interannual variability and trends of the surface geostrophic cyclonic circulation and cyclone frequency in Western and Eastern Mediterranean areas are analyzed, based on a cyclone data base derived from the ERA-40 ECWMF reanalysis (within the MEDEX project tasks), spanning from September/1957 to August/2002. In this 45 years, the cyclonic circulation show a significant decrease in the Western Mediterranean, mostly in winter and spring, and an increase in the Eastern, mainly due to the summer and autumn increase in the frequency of thermal lows
Intense storms in the Mediterranean: a first description from the ERA-40 perspective
International audienceThe study of the Mediterranean cyclones from a climatological point of view has been one of the objectives of the first phase of WMO WWRP MEDEX (MEDiterranean EXperiment) project. It has been revealing itself like a good procedure for extracting conclusions about their characteristics and behaviour. The implementation on ECMWF ERA-40 reanalysis of the method for detecting and tracking the cyclones developed at the Centro Meteorológico Territorial (CMT) in Illes Balears of the Instituto Nacional de Meteorología (INM, Spain) has allowed the selection of the most intense storms occurred for the last 45 years. This selection has been based on the value of the cyclones' circulation. The areas of maximum intensification for those cyclones have been obtained and the existence of preferential zones of intensification has been verified. Finally a first sight of those cases has allowed to initiate the check up of the ability of the ERA-40 re-analyses for reproducing these intense Mediterranean storms
Detection and thermal description of medicanes from numerical simulation
Tropical-like cyclones rarely affect the Mediterranean region but they can
produce strong winds and heavy precipitations. These warm-core cyclones,
called MEDICANES (MEDIterranean hurriCANES), are small in size, develop over
the sea and are infrequent. For these reasons, the detection and forecast of
medicanes are a difficult task and many efforts have been devoted to identify
them.
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The goals of this work are to contribute to a proper description of these
structures and to develop some criteria to identify medicanes from numerical
weather prediction (NWP) model outputs. To do that, existing methodologies
for detecting, characterizating and tracking cyclones have been adapted to
small-scale intense cyclonic perturbations. First, a mesocyclone detection
and tracking algorithm has been modified to select intense cyclones. Next,
the parameters that define the Hart's cyclone phase diagram are tuned and
calculated to examine their thermal structure.
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Four well-known medicane events have been described from numerical simulation
outputs of the European Centre for
Medium-Range Weather Forecast (ECMWF) model. The predicted cyclones and their evolution have
been validated against available observational data and numerical analyses
from the literature
Towards a climatology of sensitivities of Mediterranean high impact weather ? first approach
International audienceDuring recent years, great interest has grown within the operational weather community on the adaptable component of observational networks. Decisions regarding where to deploy new observations of special value under threatening weather, or regarding permanent changes in observational strategies need support from sensitivity studies that determine areas where the addition of observations would optimally improve the skill of numerical predictions. Within the context of the MEDEX project (http://medex.inm.uib.es), the sensitivities of a collection of severe weather episodes in the Mediterranean have been computed using the MM5 Adjoint Modeling system. Various approaches are explored trying to summarize the results for the diversity of cases that produce high impact weather (HIW; mainly heavy rain and strong winds) in the Mediterranean region. A first attempt uses an objective classification of the trajectories of the most intense cyclone types from the ERA-40 reanalyses. Sensitivities are then computed for each group of frequent trajectories, providing a prototype sensitivity field for each of the most frequent intense cyclones in the Mediterranean. However, a large portion of HIW episodes in the Mediterranean are not linked to significantly intense cyclones within the climatology. Consequently, a subjective classification of HIW events is also performed and the sensitivity fields for an example case is shown to complete the study. Although the sensitive areas for Mediterranean HIW are not particularly confined, it is remarkable how poorly sampled areas by the regular observing networks such as North Africa and the eastern North-Atlantic are highlighted in the results
Heavy rain events in the Western Mediterranean: an atmospheric pattern classification
International audienceHeavy rain is one of the most important high-impact weather phenomena that occasionally affect Mediterranean areas. The aim of this study is to achieve a classification of atmospheric patterns related to heavy rain events in both French and Spanish Mediterranean regions. The classification is made on some atmospheric fields (geopotential at 1000 hPa and at 500 hPa and temperature at 850 hPa) of HIRLAM-INM-0.5° operational analysis, for heavy rain events included in the High Impact Weather MEDEX database. It covers a period of roughly 7 and a half years, from January 1997 to May 2004. A Principal Components Analysis was conducted to reduce the number of variables. After that, by means of a Cluster Analysis, the heavy rain events are classified into 8 atmospheric patterns. The results show a good relationship between regions affected by heavy rain and atmospheric patterns, in the sense that the same atmospheric patterns usually produce heavy rain in different regions, and heavy rain in different regions is usually due to specific atmospheric patterns
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