6,491 research outputs found
Mid-infrared imaging- and spectro-polarimetric subarcsecond observations of NGC 1068
We present sub-arcsecond 7.513 m imaging- and spectro-polarimetric
observations of NGC 1068 using CanariCam on the 10.4-m Gran Telescopio
CANARIAS. At all wavelengths, we find:
(1) A 90 60 pc extended polarized feature in the northern ionization
cone, with a uniform 44 polarization angle. Its polarization
arises from dust and gas emission in the ionization cone, heated by the active
nucleus and jet, and further extinguished by aligned dust grains in the host
galaxy. The polarization spectrum of the jet-molecular cloud interaction at
24 pc from the core is highly polarized, and does not show a silicate
feature, suggesting that the dust grains are different from those in the
interstellar medium.
(2) A southern polarized feature at 9.6 pc from the core. Its
polarization arises from a dust emission component extinguished by a large
concentration of dust in the galaxy disc. We cannot distinguish between dust
emission from magnetically aligned dust grains directly heated by the jet close
to the core, and aligned dust grains in the dusty obscuring material
surrounding the central engine. Silicate-like grains reproduce the polarized
dust emission in this feature, suggesting different dust compositions in both
ionization cones.
(3) An upper limit of polarization degree of 0.3 per cent in the core. Based
on our polarization model, the expected polarization of the obscuring dusty
material is 0.1 per cent in the 813 m wavelength range. This
low polarization may be arising from the passage of radiation through aligned
dust grains in the shielded edges of the clumps.Comment: 17 pages, 10 figures, accepted for publication at MNRA
Confirmation of an exoplanet using the transit color signature: Kepler-418b, a blended giant planet in a multiplanet system
We announce confirmation of Kepler-418b, one of two proposed planets in this
system. This is the first confirmation of an exoplanet based primarily on the
transit color signature technique. We used the Kepler public data archive
combined with multicolor photometry from the Gran Telescopio de Canarias and
radial velocity follow-up using FIES at the Nordic Optical Telescope for
confirmation. We report a confident detection of a transit color signature that
can only be explained by a compact occulting body, entirely ruling out a
contaminating eclipsing binary, a hierarchical triple, or a grazing eclipsing
binary. Those findings are corroborated by our radial velocity measurements,
which put an upper limit of ~1 Mjup on the mass of Kepler-418b. We also report
that the host star is significantly blended, confirming the ~10% light
contamination suspected from the crowding metric in the Kepler light curve
measured by the Kepler team. We report detection of an unresolved light source
that contributes an additional ~40% to the target star, which would not have
been detected without multicolor photometric analysis. The resulting
planet-star radius ratio is 0.110 +/- 0.0025, more than 25% more than the 0.087
measured by Kepler, leading to a radius of 1.20 +/- 0.16 Rjup instead of the
0.94 Rjup measured by the Kepler team. This is the first confirmation of an
exoplanet candidate based primarily on the transit color signature,
demonstrating that this technique is viable from ground for giant planets. It
is particularly useful for planets with long periods such as Kepler-418b, which
tend to have long transit durations. Additionally, multicolor photometric
analysis of transits can reveal unknown stellar neighbors and binary companions
that do not affect the classification of the transiting object but can have a
very significant effect on the perceived planetary radius.Comment: accepted by Astronomy & Astrophysic
Near-Infrared Polarimetric Adaptive Optics Observations of NGC 1068: A torus created by a hydromagnetic outflow wind
We present J' and K' imaging linear polarimetric adaptive optics observations
of NGC 1068 using MMT-Pol on the 6.5-m MMT. These observations allow us to
study the torus from a magnetohydrodynamical (MHD) framework. In a 0.5" (30 pc)
aperture at K', we find that polarisation arising from the passage of radiation
from the inner edge of the torus through magnetically aligned dust grains in
the clumps is the dominant polarisation mechanism, with an intrinsic
polarisation of 7.0%2.2%. This result yields a torus magnetic field
strength in the range of 482 mG through paramagnetic alignment, and
139 mG through the Chandrasekhar-Fermi method. The measured
position angle (P.A.) of polarisation at K is found to be similar to the
P.A. of the obscuring dusty component at few parsec scales using infrared
interferometric techniques. We show that the constant component of the magnetic
field is responsible for the alignment of the dust grains, and aligned with the
torus axis onto the plane of the sky. Adopting this magnetic field
configuration and the physical conditions of the clumps in the MHD outflow wind
model, we estimate a mass outflow rate 0.17 M yr at 0.4
pc from the central engine for those clumps showing near-infrared dichroism.
The models used were able to create the torus in a timescale of 10
yr with a rotational velocity of 1228 km s at 0.4 pc. We conclude
that the evolution, morphology and kinematics of the torus in NGC 1068 can be
explained within a MHD framework.Comment: 14 pages, 4 figures, Accepted by MNRA
Spatial effects on species persistence and implications for biodiversity
Natural ecosystems are characterized by striking diversity of form and
functions and yet exhibit deep symmetries emerging across scales of space, time
and organizational complexity. Species-area relationships and species-abundance
distributions are examples of emerging patterns irrespective of the details of
the underlying ecosystem functions. Here we present empirical and theoretical
evidence for a new macroecological pattern related to the distributions of
local species persistence times, defined as the timespans between local
colonizations and extinctions in a given geographic region. Empirical
distributions pertaining to two different taxa, breeding birds and herbaceous
plants, analyzed in a new framework that accounts for the finiteness of the
observational period, exhibit power-law scaling limited by a cut-off determined
by the rate of emergence of new species. In spite of the differences between
taxa and spatial scales of analysis, the scaling exponents are statistically
indistinguishable from each other and significantly different from those
predicted by existing models. We theoretically investigate how the scaling
features depend on the structure of the spatial interaction network and show
that the empirical scaling exponents are reproduced once a two-dimensional
isotropic texture is used, regardless of the details of the ecological
interactions. The framework developed here also allows to link the cut-off
timescale with the spatial scale of analysis, and the persistence-time
distribution to the species-area relationship. We conclude that the inherent
coherence obtained between spatial and temporal macroecological patterns points
at a seemingly general feature of the dynamical evolution of ecosystems.Comment: 5 pages, 5 figures. Supplementary materials avaliable on
http://www.pnas.org/content/108/11/434
The Effect of Aqueous Alteration in Antarctic Carbonaceous Chondrites from Comparative ICP-MS Bulk Chemistry
Terrestrial ages of Antarctic carbonaceous chondrites (CC) indicate that these meteorites have been preserved in or on ice for, at least, tens of thousands of years. Due to the porous structure of these chondrites formed by the aggregation of silicate-rich chondrules, refractory inclusions, metal grains, and fine-grained matrix materials, the effect of pervasive terrestrial water is relevant. Our community defends that pristine CC matrices are representing samples of scarcely processed protoplanetary disk materials as they contain stellar grains, but they might also trace parent body processes. It is important to study the effects of terrestrial aqueous alteration in promoting bulk chemistry changes, and creating distinctive alteration minerals. Particularly because it is thought that aqueous alteration has particularly played a key role in some CC groups in modifying primordial bulk chemistry, and homogenizing the isotopic content of fine-grained matrix materials. Fortunately, the mineralogy produced by parent-body and terrestrial aqueous alteration processes is distinctive. With the goal to learn more about terrestrial alteration in Antarctica we are obtaining reflectance spectra of CCs, but also performing ICP-MS bulk chemistry of the different CC groups. A direct comparison with the mean bulk elemental composition of recovered falls might inform us on the effects of terrestrial alteration in finds. With such a goal, in the current work we have analyzed some members representative of CO and CM chondrite groups
Infrared heater system for warming tropical forest understory plants and soils
The response of tropical forests to global warming is one of the largest uncertainties in predicting the future carbon balance of Earth. To determine the likely effects of elevated temperatures on tropical forest understory plants and soils, as well as other ecosystems, an infrared (IR) heater system was developed to provide in situ warming for the Tropical Responses to Altered Climate Experiment (TRACE) in the Luquillo Experimental Forest in Puerto Rico. Three replicate heated 4‐m‐diameter plots were warmed to maintain a 4°C increase in understory vegetation compared to three unheated control plots, as sensed by IR thermometers. The equipment was larger than any used previously and was subjected to challenges different from those of many temperate ecosystem warming systems, including frequent power surges and outages, high humidity, heavy rains, hurricanes, saturated clayey soils, and steep slopes. The system was able to maintain the target 4.0°C increase in hourly average vegetation temperatures to within ± 0.1°C. The vegetation was heterogeneous and on a 21° slope, which decreased uniformity of the warming treatment on the plots; yet, the green leaves were fairly uniformly warmed, and there was little difference among 0–10 cm depth soil temperatures at the plot centers, edges, and midway between. Soil temperatures at the 40–50 cm depth increased about 3°C compared to the controls after a month of warming. As expected, the soil in the heated plots dried faster than that of the control plots, but the average soil moisture remained adequate for the plants. The TRACE heating system produced an adequately uniform warming precisely controlled down to at least 50‐cm soil depth, thereby creating a treatment that allows for assessing mechanistic responses of tropical plants and soil to warming, with applicability to other ecosystems. No physical obstacles to scaling the approach to taller vegetation (i.e., trees) and larger plots were observed
Characterization of Mycobacterium tuberculosis Beijing isolates from the Mediterranean area
<p>Abstract</p> <p>Background</p> <p>The Beijing lineage of <it>Mycobacterium tuberculosis </it>is causing concern due to its global distribution and its involvement in severe outbreaks. Studies focused on this lineage are mainly restricted to geographical settings where its prevalence is high, whereas those in other areas are scarce. In this study, we analyze Beijing isolates in the Mediterranean area, where this lineage is not prevalent and is mainly associated with immigrant cases.</p> <p>Results</p> <p>Only 1% (N = 26) of the isolates from two population-based studies in Spain corresponded to Beijing strains, most of which were pan-susceptible and from Peruvian and Ecuadorian patients. Restriction fragment length polymorphism typing with the insertion sequence IS<it>6110 </it>identified three small clusters (2-3 cases). Mycobacterial interspersed repetitive unit-variable number tandem repeat typing (MIRU-15) offered low discriminatory power, requiring the introduction of five additional loci. A selection of the Beijing isolates identified in the Spanish sample, together with a sample of Beijing strains from Italy, to broaden the analysis context in the Mediterranean area, were assayed in an infection model with THP-1 cells. A wide range of intracellular growth rates was observed with only two isolates showing an increased intracellular replication, in both cases associated with contained production of TNF-α. No correlation was observed between virulence and the Beijing phylogenetic group, clustered/orphan status, or resistance. The Beijing strain responsible for extensive spread on Gran Canaria Island was also identified in Madrid, but did not lead to secondary cases and did not show high infectivity in the infection model.</p> <p>Conclusions</p> <p>The Beijing lineage in our area is a non-homogeneous family, with only certain highly virulent representatives. The specific characterization of Beijing isolates in different settings could help us to accurately identify the virulent representatives before making general assumptions about this lineage.</p
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