330 research outputs found
A Systems Analysis Approach to Nuclear Facility Siting
In recent years there has been a growing tendency in science to conduct multi-disciplinary studies of large-scale systems. These studies include the entire spectrum of economic, technological, environmental and societal factors which characterize the complex problems of advanced industrialized societies. One of the more promising ways of addressing these problems is the broad research strategy of applied systems analysis. Basically this is a rational approach to problem-solving which attempts to identify and model interactions between the systems under study and all other systems. This results in a thorough understanding of the system being studied which may then serve as an aid in decision-making. This paper attempts to demonstrate an application of the techniques of systems analysis, which have been successful in solving a variety of problems, to the question of nuclear facility siting
The gravitational mass of Proxima Centauri measured with SPHERE from a microlensing event
Proxima Centauri, our closest stellar neighbour, is a low-mass M5 dwarf
orbiting in a triple system. An Earth-mass planet with an 11 day period has
been discovered around this star. The star's mass has been estimated only
indirectly using a mass-luminosity relation, meaning that large uncertainties
affect our knowledge of its properties. To refine the mass estimate, an
independent method has been proposed: gravitational microlensing. By taking
advantage of the close passage of Proxima Cen in front of two background stars,
it is possible to measure the astrometric shift caused by the microlensing
effect due to these close encounters and estimate the gravitational mass of the
lens (Proxima Cen). Microlensing events occurred in 2014 and 2016 with impact
parameters, the closest approach of Proxima Cen to the background star, of
1\farcs6 0\farcs1 and 0\farcs5 0\farcs1, respectively. Accurate
measurements of the positions of the background stars during the last two years
have been obtained with HST/WFC3, and with VLT/SPHERE from the ground. The
SPHERE campaign started on March 2015, and continued for more than two years,
covering 9 epochs. The parameters of Proxima Centauri's motion on the sky,
along with the pixel scale, true North, and centering of the instrument
detector were readjusted for each epoch using the background stars visible in
the IRDIS field of view. The experiment has been successful and the astrometric
shift caused by the microlensing effect has been measured for the second event
in 2016. We used this measurement to derive a mass of
0.150 (an error of 40\%) \MSun for Proxima
Centauri acting as a lens. This is the first and the only currently possible
measurement of the gravitational mass of Proxima Centauri.Comment: 10 pages, 6 figures, accepted by MNRA
Characterization of Spectral Entanglement of Spontaneous Parametric-Down Conversion Biphotons
We verified operational approach based on direct measurement of entanglement
degree for bipartite systems. In particular spectral distributions of single
counts and coincidence for pure biphoton states generated by train of short
pump pulses have been measured and entanglement quantifier calculated. The
approach gives upper bound of entanglement stored in total biphoton states,
which can reach extremely high value up to
Exploring dust around HD142527 down to 0.025" / 4au using SPHERE/ZIMPOL
We have observed the protoplanetary disk of the well-known young Herbig star
HD 142527 using ZIMPOL Polarimetric Differential Imaging with the VBB (Very
Broad Band, ~600-900nm) filter. We obtained two datasets in May 2015 and March
2016. Our data allow us to explore dust scattering around the star down to a
radius of ~0.025" (~4au). The well-known outer disk is clearly detected, at
higher resolution than before, and shows previously unknown sub-structures,
including spirals going inwards into the cavity. Close to the star, dust
scattering is detected at high signal-to-noise ratio, but it is unclear whether
the signal represents the inner disk, which has been linked to the two
prominent local minima in the scattering of the outer disk, interpreted as
shadows. An interpretation of an inclined inner disk combined with a dust halo
is compatible with both our and previous observations, but other arrangements
of the dust cannot be ruled out. Dust scattering is also present within the
large gap between ~30 and ~140au. The comparison of the two datasets suggests
rapid evolution of the inner regions of the disk, potentially driven by the
interaction with the close-in M-dwarf companion, around which no polarimetric
signal is detected.Comment: 11 pages, 7 figures, accepted for publication in A
Azimuthal asymmetries in the debris disk around HD 61005. A massive collision of planetesimals?
ontext. Debris disks offer valuable insights into the latest stages of circumstellar disk evolution, and can possibly help us to trace the outcomes of planetary formation processes. In the age range 10 to 100 Myr, most of the gas is expected to have been removed from the system, giant planets (if any) must have already been formed, and the formation of terrestrial planets may be on-going. Pluto-sized planetesimals, and their debris released in a collisional cascade, are under their mutual gravitational influence, which may result into non-axisymmetric structures in the debris disk. Aims. High angular resolution observations are required to investigate these effects and constrain the dynamical evolution of debris disks. Furthermore, multi-wavelength observations can provide information about the dust dynamics by probing different grain sizes. Methods. Here we present new VLT/SPHERE and ALMA observations of the debris disk around the 40 Myr-old solar-type star HD 61005. We resolve the disk at unprecedented resolution both in the near-infrared (in scattered and polarized light) and at millimeter wavelengths. We perform a detailed modeling of these observations, including the spectral energy distribution. Results. Thanks to the new observations, we propose a solution for both the radial and azimuthal distribution of the dust grains in the debris disk. We find that the disk has a moderate eccentricity (e ∼ 0.1) and that the dust density is two times larger at the pericenter compared to the apocenter. Conclusions. With no giant planets detected in our observations, we investigate alternative explanations besides planet- disk interactions to interpret the inferred disk morphology. We postulate that the morphology of the disk could be the consequence of a massive collision between ∼ 1000 km-sized bodies at ∼ 61 au. If this interpretation holds, it would put stringent constraints on the formation of massive planetesimals at large distances from the star
Variable dynamics in the inner disk of HD 135344B revealed with multi-epoch scattered light imaging
This is the author accepted manuscript. The final version is available from American Astronomical Society via the DOI in this record.MB acknowledges funding from ANR of France under
contract number ANR-16-CE31-0013 (Planet Forming
Disks). SP acknowledges support from CONICYTGemini
grant 32130007. SK acknowledges support from
an STFC Rutherford fellowship (ST/J004030/1) and an
ERC Starting Grant (Grant Agreement No. 639889)
Shadows cast on the transition disk of HD 135344B. Multiwavelength VLT/SPHERE polarimetric differential imaging
The protoplanetary disk around the F-type star HD 135344B (SAO 206462) is in
a transition stage and shows many intriguing structures both in scattered light
and thermal (sub-)millimeter emission which are possibly related to planet
formation processes. We study the morphology and surface brightness of the disk
in scattered light to gain insight into the innermost disk regions, the
formation of protoplanets, planet-disk interactions traced in the surface and
midplane layers, and the dust grain properties of the disk surface. We have
carried out high-contrast polarimetric differential imaging (PDI) observations
with VLT/SPHERE and obtained polarized scattered light images with ZIMPOL in R-
and I-band and with IRDIS in Y- and J-band. The scattered light images reveal
with unprecedented angular resolution and sensitivity the spiral arms as well
as the 25 au cavity of the disk. Multiple shadow features are discovered on the
outer disk with one shadow only being present during the second observation
epoch. A positive surface brightness gradient is observed in the stellar
irradiation corrected images in southwest direction possibly due to an
azimuthally asymmetric perturbation of the temperature and/or surface density
by the passing spiral arms. The disk integrated polarized flux, normalized to
the stellar flux, shows a positive trend towards longer wavelengths which we
attribute to large aggregate dust grains in the disk surface. Part of the the
non-azimuthal polarization signal in the Uphi image of the J-band observation
could be the result of multiple scattering in the disk. The detected shadow
features and their possible variability have the potential to provide insight
into the structure of and processes occurring in the innermost disk regions.Comment: Accepted for publication in A&A, 20 pages, 15 figure
Generation of degenerate, factorizable, pulsed squeezed light at telecom wavelengths
We characterize a periodically poled KTP crystal that produces an entangled,
two-mode, squeezed state with orthogonal polarizations, nearly identical,
factorizable frequency modes, and few photons in unwanted frequency modes. We
focus the pump beam to create a nearly circular joint spectral probability
distribution between the two modes. After disentangling the two modes, we
observe Hong-Ou-Mandel interference with a raw (background corrected)
visibility of 86 % (95 %) when an 8.6 nm bandwidth spectral filter is applied.
We measure second order photon correlations of the entangled and disentangled
squeezed states with both superconducting nanowire single-photon detectors and
photon-number-resolving transition-edge sensors. Both methods agree and verify
that the detected modes contain the desired photon number distributions
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