1,171 research outputs found
Rotationally resolved spectroscopy of (20000) Varuna in the near-infrared
Models of the escape and retention of volatiles by minor icy objects exclude
any presence of volatile ices on the surface of TNOs smaller than ~1000km in
diameter at the typical temperature in this region of the solar system, whereas
the same models show that water ice is stable on the surface of objects over a
wide range of diameters. Collisions and cometary activity have been used to
explain the process of surface refreshing of TNOs and Centaurs. These processes
can produce surface heterogeneity that can be studied by collecting information
at different rotational phases. The aims of this work are to study the surface
composition of (20000)Varuna, a TNO with a diameter ~650km and to search for
indications of rotational variability. We observed Varuna during two
consecutive nights in January 2011 with NICS@TNG obtaining a set of spectra
covering the whole rotation period of Varuna. After studying the spectra
corresponding to different rotational phases, we did not find any indication of
surface variability. In all the spectra, we detect an absorption at 2{\mu}m,
suggesting the presence of water ice on the surface. We do not detect any other
volatiles on the surface, although the S/N is not high enough to discard their
presence. Based on scattering models, we present two possible compositions
compatible with our set of data and discuss their implications in the frame of
the collisional history of the Kuiper Belt. We find that the most probable
composition for the surface of Varuna is a mixture of amorphous silicates,
complex organics, and water ice. This composition is compatible with all the
materials being primordial. However, our data can also be fitted by models
containing up to a 10% of methane ice. For an object with the characteristics
of Varuna, this volatile could not be primordial, so an event, such as an
energetic impact, would be needed to explain its presence on the surface.Comment: 6 pages, 5 figures, to be published in A&
The Spectrum of Pluto, 0.40 - 0.93 m I. Secular and longitudinal distribution of ices and complex organics
Context. During the last 30 years the surface of Pluto has been
characterized, and its variability has been monitored, through continuous
near-infrared spectroscopic observations. But in the visible range only few
data are available. Aims. The aim of this work is to define the Pluto's
relative reflectance in the visible range to characterize the different
components of its surface, and to provide ground based observations in support
of the New Horizons mission. Methods. We observed Pluto on six nights between
May and July 2014, with the imager/spectrograph ACAM at the William Herschel
Telescope (La Palma, Spain). The six spectra obtained cover a whole rotation of
Pluto (Prot = 6.4 days). For all the spectra we computed the spectral slope and
the depth of the absorption bands of methane ice between 0.62 and 0.90 m.
To search for shifts of the center of the methane bands, associated with
dilution of CH4 in N2, we compared the bands with reflectances of pure methane
ice. Results. All the new spectra show the methane ice absorption bands between
0.62 and 0.90 m. The computation of the depth of the band at 0.62 m
in the new spectra of Pluto, and in the spectra of Makemake and Eris from the
literature, allowed us to estimate the Lambert coefficient at this wavelength,
at a temperature of 30 K and 40 K, never measured before. All the detected
bands are blue shifted, with minimum shifts in correspondence with the regions
where the abundance of methane is higher. This could be indicative of a
dilution of CH4:N2 more saturated in CH4. The longitudinal and secular
variations of the parameters measured in the spectra are in accordance with
results previously reported in the literature and with the distribution of the
dark and bright material that show the Pluto's albedo maps from New Horizons.Comment: This manuscript may change and improve during the reviewing process.
The data reduction and calibration is reliable and has been checked
independently using different reduction approaches. The data will be made
publicily available when the paper is accepted. If you need them before,
please, contact the autho
Time-resolved photometry of the young dipper RX~J1604.3-2130A:Unveiling the structure and mass transport through the innermost disk
Context. RX J1604.3-2130A is a young, dipper-type, variable star in the Upper Scorpius association, suspected to have an inclined inner disk, with respect to its face-on outer disk. Aims. We aim to study the eclipses to constrain the inner disk properties. Methods. We used time-resolved photometry from the Rapid Eye Mount telescope and Kepler 2 data to study the multi-wavelength variability, and archival optical and infrared data to track accretion, rotation, and changes in disk structure. Results. The observations reveal details of the structure and matter transport through the inner disk. The eclipses show 5 d quasi-periodicity, with the phase drifting in time and some periods showing increased/decreased eclipse depth and frequency. Dips are consistent with extinction by slightly processed dust grains in an inclined, irregularly-shaped inner disk locked to the star through two relatively stable accretion structures. The grains are located near the dust sublimation radius (similar to 0.06 au) at the corotation radius, and can explain the shadows observed in the outer disk. The total mass (gas and dust) required to produce the eclipses and shadows is a few % of a Ceres mass. Such an amount of mass is accreted/replenished by accretion in days to weeks, which explains the variability from period to period. Spitzer and WISE infrared variability reveal variations in the dust content in the innermost disk on a timescale of a few years, which is consistent with small imbalances (compared to the stellar accretion rate) in the matter transport from the outer to the inner disk. A decrease in the accretion rate is observed at the times of less eclipsing variability and low mid-IR fluxes, confirming this picture. The v sin i = 16 km s(-1) confirms that the star cannot be aligned with the outer disk, but is likely close to equator-on and to be aligned with the inner disk. This anomalous orientation is a challenge for standard theories of protoplanetary disk formation.Science & Technology Facilities Council (STFC): ST/S000399/1.
ESO fellowship.
European Union (EU): 823 823.
German Research Foundation (DFG): FOR 2634/1 TE 1024/1-1.
French National Research Agency (ANR): ANR-16-CE31-0013.
Alexander von Humboldt Foundation.
European Research Council (ERC): 678 194.
European Research Council (ERC): 742 095.
National Aeronautics & Space Administration (NASA).
National Science Foundation (NSF).
National Aeronautics & Space Administration (NASA): NNG05GF22G.
National Science Foundation (NSF): AST-0909182, AST-1 313 422
Plasmon enhanced energy-transfer up-conversion in Yb3+-Er3+ co-doped LiNbO3 crystal
We have analyzed the effect of linear chains of metallic Ag nanoparticles on the optical properties of a periodically poled Yb 3+ -Er 3+ co-doped LiNbO 3 crystal. By exploiting the broad plasmonic response supported by linear chains of strongly coupled Ag nanoparticles, we demonstrate a 50% of enhancement of the up-converted Er 3+ emission under excitation in the f-f transition of Yb 3+ ions. The observed intensification is explained in terms of the broad plasmonic spectral response supported by the Ag chains, which overlaps both the Er 3+ visible emissions and the Yb 3+ absorption band, and the two-photon character of the Yb 3+ → Er 3+ energy-transfer up-conversion process. The results are of interest for applications involving luminescence up-conversion such as sensing, solar energy conversion, biological imaging or solid-state nanolasersThis work has been supported by the Spanish Ministry of
Economy and Competitiveness (MINECO) under project MAT2013-
43301-R and Comunidad de Madrid under grant S2013/MIT-274
Double quantum dot with tunable coupling in an enhancement-mode silicon metal-oxide semiconductor device with lateral geometry
We present transport measurements of a tunable silicon
metal-oxide-semiconductor double quantum dot device with lateral geometry.
Experimentally extracted gate-to-dot capacitances show that the device is
largely symmetric under the gate voltages applied. Intriguingly, these gate
voltages themselves are not symmetric. Comparison with numerical simulations
indicates that the applied gate voltages serve to offset an intrinsic asymmetry
in the physical device. We also show a transition from a large single dot to
two well isolated coupled dots, where the central gate of the device is used to
controllably tune the interdot coupling.Comment: 4 pages, 3 figures, to be published in Applied Physics Letter
The Evolution of Dust Disk Sizes from a Homogeneous Analysis of 1-10 Myr old Stars
We utilize ALMA archival data to estimate the dust disk size of 152
protoplanetary disks in Lupus (1-3 Myr), Chamaeleon I (2-3 Myr), and Upper-Sco
(5-11 Myr). We combine our sample with 47 disks from Tau/Aur and Oph whose dust
disk radii were estimated, as here, through fitting radial profile models to
visibility data. We use these 199 homogeneously derived disk sizes to identify
empirical disk-disk and disk-host property relations as well as to search for
evolutionary trends. In agreement with previous studies, we find that dust disk
sizes and millimeter luminosities are correlated, but show for the first time
that the relationship is not universal between regions. We find that disks in
the 2-3 Myr-old Cha I are not smaller than disks in other regions of similar
age, and confirm the Barenfeld et al. (2017) finding that the 5-10 Myr USco
disks are smaller than disks belonging to younger regions. Finally, we find
that the outer edge of the Solar System, as defined by the Kuiper Belt, is
consistent with a population of dust disk sizes which have not experienced
significant truncation
Stability of schizophrenia diagnosis in a ten-year longitudinal study on first episode of non-affective psychosis: conclusions from the PAFIP cohort
OBJECTIVE: To evaluate the ten-year stability of schizophrenia diagnosis in a cohort of first-episode psychosis (FEP) patients and the factors associated with it. METHODS: Changes in diagnosis of 209 FEP patients were described during ten years of follow-up. Related factors with maintenance or change of schizophrenia diagnosis were evaluated in prospective and retrospective approaches through Binary Logistic Regressions, ROC and survival curves. RESULTS: Out of the 209 patients, 126 were diagnosed of schizophrenia six months after their inclusion in the clinical program. Prospective analyses showed that eight of those 126 schizophrenia patients had changed to a different diagnosis after ten years, and predictors of change were better childhood premorbid adjustment, less severity of clinical global impression at baseline, and diagnosis of comorbid personality disorder during follow-up. Retrospectively, out of the 154 patients with schizophrenia in the ten-year assessment, 36 had a different diagnosis at baseline, and those factors related with a different prior diagnosis than schizophrenia were better socioeconomic status and shorter duration of untreated psychosis (DUP). A survival analysis on the timing of schizophrenia diagnosis showed that male gender and longer DUP were predictors of earlier definite diagnosis. CONCLUSIONS: Diagnostic stability of schizophrenia in our FEP sample is high, especially prospective stability, and the group of patients with diagnostic change corresponded to a milder psychopathological profile before and at the onset of disease. Moreover, we observed a cautious attitude in the diagnosis of schizophrenia in patients with shorter DUP who had schizophrenia diagnosis after ten years
Biological and chemical factors controlling the patchy distribution of soil water repellency among plant species in a Mediterranean semiarid forest
Natural soil water repellency is a property that has already been observed in forest soils and is characterized by its patchy distribution. There are many factors involved in its development. In this work, we have studied a large number of chemical and biological factors under the influence of different plant species (. Pinus halepensis, Quercus rotundifolia, Cistus albidus and Rosmarinus officinalis) to learn which has the greatest responsibility for its presence and persistence in the top-soil layer. We observed strong and significant correlations between ergosterol, glomalin related soil protein (GRSP), extractable lipids, soil organic matter (SOM) content and water repellency (WR). Our results suggested lipid fraction as the principal factor. Moreover, apart from Pinus, fungal biomass seems to be also related to the SOM content. Soil WR found under Pinus appears to be the most influenced by fungi. Quality of SOM, to be precise, lipid fraction could be responsible for WR and its relationship with fungal activity.Ministerio de EconomĂa y Competitividad CGL2010- 21670-C02-01, CGL2012-38655-C04-0
A Major Asymmetric Dust Trap in a Transition Disk
The statistics of discovered exoplanets suggest that planets form
efficiently. However, there are fundamental unsolved problems, such as
excessive inward drift of particles in protoplanetary disks during planet
formation. Recent theories invoke dust traps to overcome this problem. We
report the detection of a dust trap in the disk around the star Oph IRS 48
using observations from the Atacama Large Millimeter/submillimeter Array
(ALMA). The 0.44-millimeter-wavelength continuum map shows high-contrast
crescent-shaped emission on one side of the star originating from
millimeter-sized grains, whereas both the mid-infrared image (micrometer-sized
dust) and the gas traced by the carbon monoxide 6-5 rotational line suggest
rings centered on the star. The difference in distribution of big grains versus
small grains/gas can be modeled with a vortex-shaped dust trap triggered by a
companion.Comment: 25 pages, 7 figures (accepted version prior to language editing
- …