284 research outputs found
Detection of the Sgr A* activity at 3.8 and 4.8 microns with NACO
L'-band (lambda=3.8 microns) and M'-band (lambda=4.8 microns) observations of
the Galactic Center region, performed in 2003 at VLT (ESO) with the adaptive
optics imager NACO, have lead to the detection of an infrared counterpart of
the radio source Sgr A* at both wavelengths. The measured fluxes confirm that
the Sgr A* infrared spectrum is dominated by the synchrotron emission of
nonthermal electrons. The infrared counterpart exhibits no significant short
term variability but demonstrates flux variations on daily and yearly scales.
The observed emission arises away from the position of the dynamical center of
the S2 orbit and would then not originate from the closest regions of the black
hole.Comment: 5 pages, 3 figures, accepted in Astronomy & Astrophysic
Optogenetic Recruitment of Dorsal Raphe Serotonergic Neurons Acutely Decreases Mechanosensory Responsivity in Behaving Mice
The inhibition of sensory responsivity is considered a core serotonin function, yet this hypothesis lacks direct support due to methodological obstacles. We adapted an optogenetic approach to induce acute, robust and specific firing of dorsal raphe serotonergic neurons. In vitro, the responsiveness of individual dorsal raphe serotonergic neurons to trains of light pulses varied with frequency and intensity as well as between cells, and the photostimulation protocol was therefore adjusted to maximize their overall output rate. In vivo, the photoactivation of dorsal raphe serotonergic neurons gave rise to a prominent light-evoked field response that displayed some sensitivity to a 5-HT1A agonist, consistent with autoreceptor inhibition of raphe neurons. In behaving mice, the photostimulation of dorsal raphe serotonergic neurons produced a rapid and reversible decrease in the animals' responses to plantar stimulation, providing a new level of evidence that serotonin gates sensory-driven responses.ERC 250334, 5-HT OptogeneticMSCA 220098info:eu-repo/semantics/publishedVersio
Human and environmental controls over aboveground carbon storage in Madagascar
Background: Accurate, high-resolution mapping of aboveground carbon density (ACD, Mg C ha-1) could provide insight into human and environmental controls over ecosystem state and functioning, and could support conservation and climate policy development. However, mapping ACD has proven challenging, particularly in spatially complex regions harboring a mosaic of land use activities, or in remote montane areas that are difficult to access and poorly understood ecologically. Using a combination of field measurements, airborne Light Detection and Ranging (LiDAR) and satellite data, we present the first large-scale, high-resolution estimates of aboveground carbon stocks in Madagascar. Results: We found that elevation and the fraction of photosynthetic vegetation (PV) cover, analyzed throughout forests of widely varying structure and condition, account for 27-67 % of the spatial variation in ACD. This finding facilitated spatial extrapolation of LiDAR-based carbon estimates to a total of 2,372,680 ha using satellite data. Remote, humid sub-montane forests harbored the highest carbon densities, while ACD was suppressed in dry spiny forests and in montane humid ecosystems, as well as in most lowland areas with heightened human activity. Independent of human activity, aboveground carbon stocks were subject to strong physiographic controls expressed through variation in tropical forest canopy structure measured using airborne LiDAR. Conclusions: High-resolution mapping of carbon stocks is possible in remote regions, with or without human activity, and thus carbon monitoring can be brought to highly endangered Malagasy forests as a climate-change mitigation and biological conservation strategy
First direct detection of an exoplanet by optical interferometry; Astrometry and K-band spectroscopy of HR8799 e
To date, infrared interferometry at best achieved contrast ratios of a few
times on bright targets. GRAVITY, with its dual-field mode, is now
capable of high contrast observations, enabling the direct observation of
exoplanets. We demonstrate the technique on HR8799, a young planetary system
composed of four known giant exoplanets. We used the GRAVITY fringe tracker to
lock the fringes on the central star, and integrated off-axis on the HR8799e
planet situated at 390 mas from the star. Data reduction included
post-processing to remove the flux leaking from the central star and to extract
the coherent flux of the planet. The inferred K band spectrum of the planet has
a spectral resolution of 500. We also derive the astrometric position of the
planet relative to the star with a precision on the order of 100as. The
GRAVITY astrometric measurement disfavors perfectly coplanar stable orbital
solutions. A small adjustment of a few degrees to the orbital inclination of HR
8799 e can resolve the tension, implying that the orbits are close to, but not
strictly coplanar. The spectrum, with a signal-to-noise ratio of
per spectral channel, is compatible with a late-type L brown dwarf. Using
Exo-REM synthetic spectra, we derive a temperature of \,K and a
surface gravity of cm/s. This corresponds to a radius
of and a mass of , which is an independent confirmation of mass estimates from evolutionary
models. Our results demonstrate the power of interferometry for the direct
detection and spectroscopic study of exoplanets at close angular separations
from their stars.Comment: published in A&
Single-mode waveguides for GRAVITY II. Single-mode fibers and Fiber Control Unit
The 2nd generation VLTI instrument GRAVITY is a two-field infrared
interferometer operating in the K band between 1.97 and 2.43 m with either
the four 8 m or the four 1.8 m telescopes of the Very Large Telescope (VLT).
Beams collected by the telescopes are corrected with adaptive optics systems
and the fringes are stabilized with a fringe-tracking system. A metrology
system allows the measurement of internal path lengths in order to achieve
high-accuracy astrometry. High sensitivity and high interferometric accuracy
are achieved thanks to (i) correction of the turbulent phase, (ii) the use of
low-noise detectors, and (iii) the optimization of photometric and coherence
throughput. Beam combination and most of the beam transport are performed with
single-mode waveguides in vacuum and at low temperature. In this paper, we
present the functions and performance achieved with weakly birefringent
standard single-mode fiber systems in GRAVITY. Fibered differential delay lines
(FDDLs) are used to dynamically compensate for up to 6 mm of delay between the
science and reference targets. Fibered polarization rotators allow us to align
polarizations in the instrument and make the single-mode beam combiner close to
polarization neutral. The single-mode fiber system exhibits very low
birefringence (less than 23{\deg}), very low attenuation (3.6-7 dB/km across
the K band), and optimized differential dispersion (less than 2.04 rad cm2
at zero extension of the FDDLs). As a consequence, the typical fringe contrast
losses due to the single-mode fibers are 6% to 10% in the lowest-resolution
mode and 5% in the medium- and high-resolution modes of the instrument for a
photometric throughput of the fiber chain of the order of 90%. There is no
equivalent of this fiber system to route and modally filter beams with delay
and polarization control in any other K-band beamcombiner.Comment: 14 pages including 2 appendices, 8 figures in the main text plus 2
figures in the appendices, final version published in A&
PREMIUM, a benchmark on the quantification of the uncertainty of the physical models in the system thermal-hydraulic codes: methodologies and data review
The objective of the Post-BEMUSE Reflood Model Input Uncertainty Methods (PREMIUM) benchmark is to progress on the issue of the quantification of the uncertainty of the physical models in system thermalhydraulic codes by considering a concrete case: the physical models involved in the prediction of core reflooding. The present document was initially conceived as a final report for the Phase I “Introduction and Methodology Review” of the PREMIUM benchmark. The objective of Phase I is to refine the definition of the benchmark and publish the available methodologies of model input uncertainty quantification relevant to the objectives of the benchmark. In this initial version the document was approved by WGAMA and has shown its usefulness during the subsequent phases of the project. Once Phase IV was completed, and following the suggestion of WGAMA members, the document was updated adding a few new sections, particularly the description of four new methodologies that were developed during this activity. Such developments were performed by some participants while contributing to PREMIUM progress (which is why this report arrives after those of other phases). After this revision the document title was changed to “PREMIUM methodologies and data review”. The introduction includes first a chapter devoted to contextualization of the benchmark in nuclear safety research and licensing, followed by a description of the PREMIUM objectives. Next, a description of the Phases in which the benchmark is divided and its organization is explained. Chapter two consists of a review of the involvement of the different participants, making a brief explanation of the input uncertainty quantification methodologies used in the activity. The document ends with some conclusions on the development of Phase I, some more general remarks and some statements on the benefits of the benchmark, which can be briefly summarized as it follows:
- Contribution to development of tools and experience related to uncertainty calculation and promotion of the use of BEPU approaches for licensing and safety assessment purposes;
- Contribution to prioritization of improvements to thermal-hydraulic system codes;
- Contribution to a fluent and close interaction between the scientific community and regulatory organizations.
Appendices include the complete description of the experimental data FEBA/SEFLEX used in the benchmark and the methodologies CIRCÉ and FFTBM and the general requirements and description specification used for Phase I. Due to the revision of the document, four extra appendixes have been added related to the methods developed during the activity, MCDA DIPE, Tractebel IUQ and PSI methods
The GRAVITY young stellar object survey XIII. Tracing the time-variable asymmetric disk structure in the inner AU of the Herbig star HD98922
Temporal variability in the photometric and spectroscopic properties of
protoplanetary disks is common in YSO. However, evidence pointing toward
changes in their morphology over short timescales has only been found for a few
sources, mainly due to a lack of high cadence observations at mas resolution.
We combine GRAVITY multi-epoch observations of HD98922 at mas resolution with
PIONIER archival data covering a total time span of 11 years. We interpret the
interferometric visibilities and spectral energy distribution with geometrical
models and through radiative transfer techniques. We investigated
high-spectral-resolution quantities to obtain information on the properties of
the HI BrG-line-emitting region. The observations are best fitted by a model of
a crescent-like asymmetric dust feature located at 1 au and accounting for 70%
of the NIR emission. The feature has an almost constant magnitude and orbits
the central star with a possible sub-Keplerian period of 12 months, although a
9 month period is another, albeit less probable, solution. The radiative
transfer models show that the emission originates from a small amount of
carbon-rich (25%) silicates, or quantum-heated particles located in a
low-density region. Among different possible scenarios, we favor hydrodynamical
instabilities in the inner disk that can create a large vortex. The high
spectral resolution differential phases in the BrG-line show that the hot-gas
component is offset from the star and in some cases is located between the star
and the crescent feature. The scale of the emission does not favor
magnetospheric accretion as a driving mechanism. The scenario of an asymmetric
disk wind or a massive accreting substellar or planetary companion is
discussed. With this unique observational data set for HD98922, we reveal
morphological variability in the innermost 2 au of its disk region.Comment: 45 pages, 20 figures, accepted by and to be published in Astronomy &
Astrophysics (A&A
Transfusion Related Acute Lung Injury (TRALI) Caused by Red Blood Cell Transfusion Involving Residual Plasma Anti-HLA Antibodies: A report on two Cases and General Considerations
TRALI is considered a serious hazard among immune complications
of blood transfusion and its occurrence is admitted to be globally underestimated.
Each type of blood product is likely to cause TRALI. We report here on two
consecutive observations of TRALI caused by red blood cell concentrates, in
which anti-HLA class I and class II antibodies resulting from post-gravitational
allo-immunization were evidenced in donors. HLA class I and II antigenic
community between recipients and donors' husbands were found and strong
reacting IgG antibodies directed at several of those common antigens were
detected in the donors' serum. Both donors had more than 3 pregnancies, raising
the issue of
blood donor selection or of plasma reduction for cellular products
Using the motion of S2 to constrain vector clouds around SgrA*
The dark compact object at the centre of the Milky Way is well established to
be a supermassive black hole with mass , but the nature of its environment is still under debate. In this
work, we used astrometric and spectroscopic measurements of the motion of the
star S2, one of the closest stars to the massive black hole, to determine an
upper limit on an extended mass composed of a massive vector field around
Sagittarius A*. For a vector with effective mass , our Markov Chain Monte Carlo analysis shows
no evidence for such a cloud, placing an upper bound at confidence level. We show that dynamical
friction exerted by the medium on S2 motion plays no role in the analysis
performed in this and previous works, and can be neglected thus.Comment: 9 pages, 5 figures, accepted to MNRA
Polarimetry and Astrometry of NIR Flares as Event Horizon Scale, Dynamical Probes for the Mass of Sgr A*
We present new astrometric and polarimetric observations of flares from Sgr
A* obtained with GRAVITY, the near-infrared interferometer at ESO's Very Large
Telescope Interferometer (VLTI), bringing the total sample of well-covered
astrometric flares to four and polarimetric ones to six, where we have for two
flares good coverage in both domains. All astrometric flares show clockwise
motion in the plane of the sky with a period of around an hour, and the
polarization vector rotates by one full loop in the same time. Given the
apparent similarities of the flares, we present a common fit, taking into
account the absence of strong Doppler boosting peaks in the light curves and
the EHT-measured geometry. Our results are consistent with and significantly
strengthen our model from 2018: We find that a) the combination of polarization
period and measured flare radius of around nine gravitational radii (, innermost stable circular orbit) is consistent with
Keplerian orbital motion of hot spots in the innermost accretion zone. The mass
inside the flares' radius is consistent with the measured from stellar orbits at several thousand . This
finding and the diameter of the millimeter shadow of Sgr A* thus support a
single black hole model. Further, b) the magnetic field configuration is
predominantly poloidal (vertical), and the flares' orbital plane has a moderate
inclination with respect to the plane of the sky, as shown by the non-detection
of Doppler-boosting and the fact that we observe one polarization loop per
astrometric loop. Moreover, c) both the position angle on sky and the required
magnetic field strength suggest that the accretion flow is fueled and
controlled by the winds of the massive, young stars of the clockwise stellar
disk 1-5 arcsec from Sgr A*, in agreement with recent simulations.Comment: 10 pages, 12 figures. Submitted to A&
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