887 research outputs found
Crossing the Gould Belt in the Orion vicinity
We present a study of the large-scale spatial distribution of 6482 RASS X-ray
sources in approximately 5000 deg^2 in the direction of Orion. We examine the
astrophysical properties of a sub-sample of ~100 optical counterparts, using
optical spectroscopy. This sub-sample is used to investigate the space density
of the RASS young star candidates by comparing X-ray number counts with
Galactic model predictions. We characterize the observed sub-sample in terms of
spectral type, lithium content, radial and rotational velocities, as well as
iron abundance. A population synthesis model is then applied to analyze the
stellar content of the RASS in the studied area. We find that stars associated
with the Orion star-forming region do show a high lithium content. A population
of late-type stars with lithium equivalent widths larger than Pleiades stars of
the same spectral type (hence younger than ~70-100 Myr) is found widely spread
over the studied area. Two new young stellar aggregates, namely "X-ray Clump
0534+22" (age~2-10 Myr) and "X-ray Clump 0430-08" (age~2-20 Myr), are also
identified. The spectroscopic follow-up and comparison with Galactic model
predictions reveal that the X-ray selected stellar population in the direction
of Orion is characterized by three distinct components, namely the clustered,
the young dispersed, and the widespread field populations. The clustered
population is mainly associated with regions of recent or ongoing star
formation and correlates spatially with molecular clouds. The dispersed young
population follows a broad lane apparently coinciding spatially with the Gould
Belt, while the widespread population consists primarily of active field stars
older than 100 Myr. We expect the "bi-dimensional" picture emerging from this
study to grow in depth as soon as the distance and the kinematics of the
studied sources will become available from the future Gaia mission.Comment: 17 pages, 13 figures, 4 tables. Accepted for publication in Astronomy
and Astrophysics. Abstract shortene
Córdoba taurina : apuntes biográficos de matadores, banderilleros, picadores, puntilleros, maletas, ganaderos, propietarios de plazas, empresarios, aficionados, revisteros y escritores taurinos antig..uos y modernos
Copia digital. Valladolid : Junta de Castilla y León. Consejería de Cultura y Turismo, 2011Del texto se deduce impreso con posterioridad a 189
Hunting for brown dwarf binaries and testing atmospheric models with X-Shooter
The determination of the brown dwarf binary fraction may contribute to the
understanding of the substellar formation mechanisms. Unresolved brown dwarf
binaries may be revealed through their peculiar spectra or the discrepancy
between optical and near-infrared spectral type classification.
We obtained medium-resolution spectra of 22 brown dwarfs with these
characteristics using the X-Shooter spectrograph at the VLT.
We aimed to identify brown dwarf binary candidates, and to test if the
BT-Settl 2014 atmospheric models reproduce their observed spectra.
To find binaries spanning the L-T boundary, we used spectral indices and
compared the spectra of the selected candidates to single spectra and synthetic
binary spectra. We used synthetic binary spectra with components of same
spectral type to determine as well the sensitivity of the method to this class
of binaries.
We identified three candidates to be combination of L plus T brown dwarfs. We
are not able to identify binaries with components of similar spectral type. In
our sample, we measured minimum binary fraction of .
From the best fit of the BT-Settl models 2014 to the observed spectra, we
derived the atmospheric parameters for the single objects. The BT-Settl models
were able to reproduce the majority of the SEDs from our objects, and the
variation of the equivalent width of the RbI (794.8 nm) and CsI (852.0 nm)
lines with the spectral type. Nonetheless, these models did not reproduce the
evolution of the equivalent widths of the NaI (818.3 nm and 819.5 nm) and KI
(1253 nm) lines with the spectral type.Comment: Accepted for publication in MNRA
Diffusion limited aggregation, resetting and large deviations of Brownian motion
Models of fractal growth commonly consider particles diffusing in a medium
and that stick irreversibly to the forming aggregate when making contact for
the first time. As shown by the well-known diffusion limited aggregation (DLA)
model and its generalisations, the fractal dimension is sensitive to the nature
of the stochastic motion of the particles. Here, we study the structures formed
by finite-lived Brownian particles, i.e., particles constrained to find the
aggregate within a prescribed time, and which are removed otherwise. This
motion can be modelled by diffusion with stochastic resetting, a class of
processes which has been widely studied in recent years. In the short lifetime
limit, a very small fraction of the particles manage to reach the aggregate.
Hence, growth is controlled by atypical Brownian trajectories, that move nearly
in straight line according to a large deviation principle. In dimensions,
the resulting fractal dimension of the aggregate decreases from the DLA value
and tends to 1, instead of increasing to as expected from ballistic
aggregation. In the zero lifetime limit one recovers the non-trivial model of
"aggregation by the tips" proposed long ago by R. Jullien [J. Phys. A: Math.
Gen. 19, 2129 (1986)].Comment: 13 pages, 5 figure
Adsorción-desorción de los metales pesados Pb(II) y Hg(II) por modelos de partículas coloidales del suelo
4 páginas, 2 figuras, 1 tabla, 3 referencias.-- Publicado en el Capítulo IV: Contaminación y Medio Ambiente.-- Trabajo presentado a la XVII Reunión Científica de la Sociedad Española de Arcillas, celebrada en Elche (Alicante) y Castellón, del 27-29 de noviembre de 2002.El destino de los metales pesados en el medio ambiente está controlado por las
reacciones de adsorción a los coloides del suelo. Por otro lado, las interacciones entre los
constituyentes del suelo pueden alterar significativamente la cantidad y naturaleza de la
superficie expuesta por los coloides del suelo para la adsorción de contaminantes. Por tanto,
las predicciones sobre la extensión de la adsorción basadas en la suma de las capacidades
adsorbentes de los constituyentes individuales del suelo pueden desviarse de lo que ocurre
en la naturaleza (1). En la bibliografia han sido poco estudiadas las interacciones entre
contaminantes y adsorbentes polifásicos, aunque en la última década ha aumentado la
atención dada al estudio del comportamiento de modelos de asociaciones coloidales para
obtener una interpretación más realista del proceso de adsorción en el suelo (2).
En este trabajo se han determinado las capacidades adsorbentes de modelos de
partículas coloidales binarias y ternarias que contienen montmorillonita (SW), ferrihidrita (Fh)
y ácido húmico (AH) para dos contaminantes inorgánicos, los metales pesados Pb(lI) y
Hg(II), Y se compararon con las capacidades de adsorción de los constituyentes
individuales. Las partículas modelos se prepararon en el laboratorio y se caracterizaron por
análisis elemental, espectroscopía infrarroja, difracción de rayos X y medidas de superficie
específica. Se estudió la adsorción-desorción de Pb(lI) y Hg(ll) por parte de los diferentes
adsorbentes y se utilizaron las técnicas de espectroscopía infrarroja y difracción de rayos X
para analizar los mecanismos de interacción.Este trabajo ha sido financiado por el proyecto del MCYT REN2001-1700-C02-
01/TECNO y por el grupo RNM124 del PAI de la Junta de AndalucíaPeer reviewe
Accretion-ejection connection in the young brown dwarf candidate ISO-Cha1 217
As the number of observed brown dwarf outflows is growing it is important to
investigate how these outflows compare to the well studied jets from young
stellar objects. A key point of comparison is the relationship between outflow
and accretion activity and in particular the ratio between the mass outflow and
accretion rates (/). The brown dwarf candidate
ISO-ChaI 217 was discovered by our group, as part of a spectro-astrometric
study of brown dwarfs, to be driving an asymmetric outflow with the
blue-shifted lobe having a position angle of 20. The aim here
is to further investigate the properties of ISO-ChaI 217, the morphology and
kinematics of its outflow, and to better constrain
(/). The outflow is spatially resolved in the
lines and is detected out to 1\farcs6
in the blue-shifted lobe and ~ 1" in the red-shifted lobe. The asymmetry
between the two lobes is confirmed although the velocity asymmetry is less
pronounced with respect to our previous study. Using thirteen different
accretion tracers we measure log() [M/yr]= -10.6
0.4. As it was not possible to measure the effect of extinction on the ISO-ChaI
217 outflow was derived for a range of values of A, up to
a value of A = 2.5 mag estimated for the source extinction. The logarithm
of the mass outflow () was estimated in the range -11.7 to -11.1
for both jets combined. Thus / [\Msun/yr] lies
below the maximum value predicted by magneto-centrifugal jet launching models.
Finally, both model fitting of the Balmer decrements and spectro-astrometric
analysis of the H line show that the bulk of the H I emission comes
from the accretion flow.Comment: accepted by Astronomy & Astrophysic
Estudio comparativo de los parámetros calidad de la leche, características tecnológicas y producción quesera de la Raza Merina de Grazalema frente al cruce con razas foráneas
En los últimos años se están incorporando masivamente
en España, en general, y en Andalucía, en
particular, razas ovinas foráneas de aptitud lechera,
fundamentalmente las razas Assaf, Awassi y Lacaune.
Su introducción está fomentando, asimismo, la realización
de cruces indiscriminados con nuestras razas
ovinas autóctonas, de aptitud lechera pero de menor
especialización, al menos cuantitativamente (Casas et
al., 2005).
El objetivo de este estudio ha sido analizar en dos
grupos de animales de un mismo rebaño (ovejas puras
de raza Merina de Grazalema, y ovejas cruzadas
Merina de Grazalema x Awassi) las características de
la producción lechera, y proceder a la elaboración de
quesos para estudiar las posibles diferencias tecnológicas
de los quesos derivados de ambas elaboraciones.
A través del mismo se ha comprobado una mayor producción
lechera de las ovejas cruzadas (167.35±13.20
kg frente a 136.84±4.25 kg) pero con un porcentaje de
grasa (6.25±0.34 % frente a 8.27±0.22 %), proteína
(4.71±0.14 % frente a 5.80±0.09 %) y extracto seco
(10.97±0.46 % frente a 14.07±0.28 %), estadísticamente
inferior. En cuanto a los parámetros de aptitud tecnológica,
los valores de tiempo de coagulación medio (24.70±0.77
minutos), dureza media (dureza del coágulo a los 30 minutos)
de 25.03±2.27 mm, y el rendimiento en cuajada
(327.50±5.70 g/l), mostraron cifras inferiores a las referenciadas
por Casas et al. (2005) para la raza ovina Merina de
Grazalema. Finalmente, la velocidad de endurecimiento
resultó mayor a los valores obtenidos en el trabajo citado
anteriormente (4.59±0.54 min.). Por otro lado, estos mismos
parámetros mostraron valores inferiores en el tiempo
de coagulación (19.60±0.62 minutos), velocidad de endurecimiento
(3.97±0.38 min.) y rendimiento en cuajada
(290.55±6.67), mientras que la dureza media (32.85±2.03
mm) fue superior en las ovejas cruzadas, respecto a los
valores encontrados en esta misma explotación para los
animales puros.
Como consecuencia de todo ello, el rendimiento quesero
real fue del 30.25 % para las ovejas puras frente al
23.70 % de las cruzadas.
Esto determina que la producción quesera real que
se obtiene por oveja pura, sea superior al de la cruzada
(41.38 kg queso fresco/lactación frente a los 39.70 de la
cruzada)
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