1,963 research outputs found
Where is the warm H2 ? A search for H2 emission from disks around Herbig Ae/Be stars
Mid-IR emission lines of H2 are useful probes to determine the mass of warm
gas present in the surface layers of disks. Numerous observations of Herbig
Ae/Be stars (HAeBes) have been performed, but only 2 detections of mid-IR H2
toward HD97048 and AB Aur have been reported. We aim at tracing the warm gas in
the disks of 5 HAeBes with gas-rich environments and physical characteristics
close to those of AB Aur and HD97048, to discuss whether the detections toward
these 2 objects are suggestive of peculiar conditions for the gas. We search
for the H2 S(1) emission line at 17.035 \mu\m with VISIR, and complemented by
CH molecule observations with UVES. We gather the H2 measurements from the
literature to put the new results in context and search for a correlation with
some disk properties. None of the 5 VISIR targets shows evidence for H2
emission. From the 3sigma upper limits on the integrated line fluxes we
constrain the amount of optically thin warm gas to be less than 1.4 M_Jup in
the disk surface layers. There are now 20 HAeBes observed with VISIR and TEXES
instruments to search for warm H2, but only two detections (HD97048 and AB Aur)
were made so far. We find that the two stars with detected warm H2 show at the
same time high 30/13 \mu\m flux ratios and large PAH line fluxes at 8.6 and
11.3 \mu\m compared to the bulk of observed HAeBes and have emission CO lines
detected at 4.7 \mu\m. We detect the CH 4300.3A absorption line toward both
HD97048 and AB Aur with UVES. The CH to H2 abundance ratios that this would
imply if it were to arise from the same component as well as the radial
velocity of the CH lines both suggest that CH arises from a surrounding
envelope, while the detected H2 would reside in the disk. The two detections of
the S(1) line in the disks of HD97048 and AB Aur suggest either peculiar
physical conditions or a particular stage of evolution.Comment: accepted for publication in A&A : 10 pages, 6 figure
A survey for near-infrared H2 emission in Herbig Ae/Be stars: emission from the outer disks of HD 97048 and HD 100546
We report on a sensitive search for H2 1-0 S(1), 1-0 S(0) and 2-1 S(1)
ro-vibrational emission at 2.12, 2.22 and 2.25 micron in a sample of 15 Herbig
Ae/Be stars employing CRIRES, the ESO-VLT near-infrared high-resolution
spectrograph, at R~90,000. We detect the H2 1-0 S(1) line toward HD 100546 and
HD 97048. In the other 13 targets, the line is not detected. The H2 1-0 S(0)
and 2-1 S(1) lines are undetected in all sources. This is the first detection
of near-IR H2 emission in HD 100546. The H2 1-0 S(1) lines observed in HD
100546 and HD 97048 are observed at a velocity consistent with the rest
velocity of both stars, suggesting that they are produced in the circumstellar
disk. In HD 97048, the emission is spatially resolved and it is observed to
extend at least up to 200 AU. We report an increase of one order of magnitude
in the H2 1-0 S(1) line flux with respect to previous measurements taken in
2003 for this star, which suggests line variability. In HD 100546 the emission
is tentatively spatially resolved and may extend at least up to 50 AU. Modeling
of the H2 1-0 S(1) line profiles and their spatial extent with flat keplerian
disks shows that most of the emission is produced at a radius >5 AU. Upper
limits to the H2 1-0 S(0)/ 1-0 S(1) and H2 2-1 S(1)/1-0 S(1) line ratios in HD
97048 are consistent with H2 gas at T>2000 K and suggest that the emission
observed may be produced by X-ray excitation. The upper limits for the line
ratios for HD 100546 are inconclusive. Because the H2 emission is located at
large radii, for both sources a thermal emission scenario (i.e., gas heated by
collisions with dust) is implausible. We argue that the observation of H2
emission at large radii may be indicative of an extended disk atmosphere at
radii >5 AU. This may be explained by a hydrostatic disk in which gas and dust
are thermally decoupled or by a disk wind caused by photoevaporation.Comment: Accepted by A&A. 16 pages, 7 figure
Spectral Evolution and Radial Dust Transport in the Prototype Young Eruptive System EX Lup
EX Lup is the prototype of a class of pre-main sequence eruptive stars
defined by their repetitive outbursts lasting several months. In 2008
January-September EX Lup underwent its historically largest outburst,
brightening by about 4 magnitudes in visual light. In previous studies we
discovered on-going silicate crystal formation in the inner disk during the
outburst, but also noticed that the measured crystallinity fraction started
decreasing after the source returned to the quiescent phase. Here we present
new observations of the 10 m silicate feature, obtained with the MIDI and
VISIR instruments at Paranal Observatory. The observations demonstrate that
within five years practically all crystalline forsterite disappeared from the
surface of the inner disk. We reconstruct this process by presenting a series
of parametric axisymmetric radiative transfer models of an expanding dust cloud
that transports the crystals from the terrestrial zone to outer disk regions
where comets are supposed to form. Possibly the early Sun also experienced
similar flare-ups, and the forming planetesimals might have incorporated
crystalline silicate material produced by such outbursts. Finally, we discuss
how far the location of the dust cloud could be constrained by future JWST
observations.Comment: 12 pages, 4 figures, accepted for publication in Ap
The molecular basis of defective lens development in the Iberian mole
Background:
Fossorial mammals face natural selection pressures that differ from those acting on surface dwelling animals, and these may lead to reduced visual system development. We have studied eye development in a species of true mole, the Iberian mole Talpa occidentalis, and present the molecular basis of abnormal lens development. This is the first embryological developmental study of the eyes of any fossorial mammal at the molecular level.
Results:
Lens fibre differentiation is not completed in the Iberian mole. Although eye development starts normally (similar to other model species), defects are seen after closure of the lens vesicle. PAX6 is not down-regulated in developing lens fibre nuclei, as it is in other species, and there is ectopic expression of FOXE3, a putative downstream effector of PAX6, in some, but not all lens fibres. FOXE3-positive lens fibres continue to proliferate within the posterior compartment of the embryonic lens, but unlike in the mouse, no proliferation was detected anywhere in the postnatal mole lens. The undifferentiated status of the anterior epithelial cells was compromised, and most of them undergo apoptosis. Furthermore, β-crystallin and PROX1 expression patterns are abnormal and our data suggest that genes encoding β-crystallins are not directly regulated by PAX6, c-MAF and PROX1 in the Iberian mole, as they are in other model vertebrates.
Conclusion:
In other model vertebrates, genetic pathways controlling lens development robustly compartmentalise the lens into a simple, undifferentiated, proliferative anterior epithelium, and quiescent, anuclear, terminally differentiated posterior lens fibres. These pathways are not as robust in the mole, and lead to loss of the anterior epithelial phenotype and only partial differentiation of the lens fibres, which continue to express 'epithelial' genes. Paradigms of genetic regulatory networks developed in other vertebrates appear not to hold true for the Iberian mole.This work was supported by the Alfonso Martín Escudero Foundation and Junta de Andalucía through Group PAI CVI-109 (BIO-109). Work in JMC's laboratory is supported by Wellcome Trust grant 074127 and BBSRC grant BB/E015840/1
Analysis on the feasability of airborne GNSS-R receivers for weather nowcasting and target detection
Weather forecast relies to a large extent on data acquired by satellite. LEO polar satellites provide global coverage, but poor spatial resolution. GEO satellites provide a better coverage and revisit time, at expenses of poorer spatial resolution. LEO constellations of small satellites offer the promise of global coverage with good spatial resolution and revisit time. However, hosted payloads on aircrafts offer the potential of very high resolution and very low revisit time for regional applications. In this work, the idea of equipping commercial airliners with low-cost Global Navigation Satellite System - Reflectometer (GNSS-R) receivers is explored, with emphasis on real-world data and the implications the expected scientific yield would offer.This work has received funding from project Spanish Ministerio de Ciencia, Innovacion y Universidades and EU ERDF project ref. RTI2018-099008-B-C21 ”SENSING WITH PIONEERING OPPORTUNISTIC TECHNIQUES,“ , and support grant MDM-2016-0600 to “María de Maeztu Excellence Units” CommSensLab, from Spanish Ministerio de Economía y Competitividad (MINECO/FEDER).Peer ReviewedPostprint (published version
Monitorización con vídeo-EEG y ECG simultáneo para el diagnóstico diferencial de trastornos de conciencia transitorios. A propósito de un caso
We present the case of a 36 year-old woman, with history of transient
consciousness disorders with vegetative state, interpreted as epileptic crises
and treated with valproate for two years. After nine asymptomatic years, they
reappeared associated with migraine, vomiting and some generalized convulsions.
Electroencephalogram and cerebral magnetic resonance turned out normal, and
treatment with zonisamide was started, without beneficial results. Later
cardiological studies objectified a blockage of the left branch that coincided
with dizziness. The study was completed with Video-EGG monitoring, where there
was an episode that showed temporary right epileptiform activity, with a
diagnosis established of focal epilepsy of unknown cause. At present, she remains
asymptomatic with oxycarbazepine
Evidence for CO depletion in the inner regions of gas-rich protoplanetary disks
We investigate the physical properties and spatial distribution of Carbon
Monoxide (CO) gas in the disks around the Herbig Ae/Be stars HD 97048 and HD
100546.
Using high-spectral-resolution 4.588-4.715 m spectra containing
fundamental CO emission taken with CRIRES on the VLT, we probe the
circumstellar gas and model the kinematics of the emission lines. By using
spectro-astrometry on the spatially resolved targets, we constrain the physical
size of the emitting regions in the disks. We resolve, spectrally and
spatially, the emission of the CO v(1-0) vibrational band and the
CO and vibrational bands in both targets,
as well as the CO band in HD 100546. Modeling of the CO emission
with a homogeneous disk in Keplerian motion, yields a best fit with an inner
and outer radius of the CO emitting region of 11 and 100 AU for HD
97048. HD 100546 is not fit well with our model, but we derive a lower limit on
the inner radius of 8 AU. The fact that gaseous [OI] emission was previously
detected in both targets at significantly smaller radii suggests that CO may be
effectively destroyed at small radii in the surface layers of these disksComment: v2: Letter format has been changed to Paper format; Change in the
focus of the paper towards CO depletion; Major changes in text; Change of
title. Submitted to A&A, 14/10/2008. Accepted by A&A, 17/04/200
Random walks associated with symmetric M-matrices
In this paper we generalize the transition probability matrix for a random walk on a finite network by defining the transition probabilities througha symmetric M-matrix. Usually, the walker jumps from a vertex to a neighboraccording to the probabilities given by the adjacency matrix. Moreover, we can find in the literature the relation between random walks and the normalized laplacian or the combinatorial laplacian that are singular and symmetric M-matrices. Our model takes into consideration not only the probability of transitioning given by the adjacency matrix but also some added probability that depends on a node property. This also includes the probability of remaining in each node, when the M-matrix is not singular. The nodes importance is taking into account by considering the lower eigenvalue and its associated eigenfunction for the given M-matrix. We give expressions for the mean first passage time and Kemeny’s constant for such a random walks in terms of 1-inverses of the considered Mmatrix.This work has been partly supported by the Spanish Research Council (Ministerio de Ciencia e Innovación) under project PID2021-122501NB-I00 and by the Universitat Politècnica de Catalunya under funds AGRUPS-2022 and AGRUPS-2023.Peer ReviewedPostprint (author's final draft
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