49 research outputs found
First experimental results of very high accuracy centroiding measurements for the neat astrometric mission
NEAT is an astrometric mission proposed to ESA with the objectives of
detecting Earth-like exoplanets in the habitable zone of nearby solar-type
stars. NEAT requires the capability to measure stellar centroids at the
precision of 5e-6 pixel. Current state-of-the-art methods for centroid
estimation have reached a precision of about 2e-5 pixel at two times Nyquist
sampling, this was shown at the JPL by the VESTA experiment. A metrology system
was used to calibrate intra and inter pixel quantum efficiency variations in
order to correct pixelation errors. The European part of the NEAT consortium is
building a testbed in vacuum in order to achieve 5e-6 pixel precision for the
centroid estimation. The goal is to provide a proof of concept for the
precision requirement of the NEAT spacecraft. In this paper we present the
metrology and the pseudo stellar sources sub-systems, we present a performance
model and an error budget of the experiment and we report the present status of
the demonstration. Finally we also present our first results: the experiment
had its first light in July 2013 and a first set of data was taken in air. The
analysis of this first set of data showed that we can already measure the pixel
positions with an accuracy of about 1e-4 pixel.Comment: SPIE conference proceeding
A detector interferometric calibration experiment for high precision astrometry
Context: Exoplanet science has made staggering progress in the last two
decades, due to the relentless exploration of new detection methods and
refinement of existing ones. Yet astrometry offers a unique and untapped
potential of discovery of habitable-zone low-mass planets around all the
solar-like stars of the solar neighborhood. To fulfill this goal, astrometry
must be paired with high precision calibration of the detector.
Aims: We present a way to calibrate a detector for high accuracy astrometry.
An experimental testbed combining an astrometric simulator and an
interferometric calibration system is used to validate both the hardware needed
for the calibration and the signal processing methods. The objective is an
accuracy of 5e-6 pixel on the location of a Nyquist sampled polychromatic point
spread function.
Methods: The interferometric calibration system produced modulated Young
fringes on the detector. The Young fringes were parametrized as products of
time and space dependent functions, based on various pixel parameters. The
minimization of func- tion parameters was done iteratively, until convergence
was obtained, revealing the pixel information needed for the calibration of
astrometric measurements.
Results: The calibration system yielded the pixel positions to an accuracy
estimated at 4e-4 pixel. After including the pixel position information, an
astrometric accuracy of 6e-5 pixel was obtained, for a PSF motion over more
than five pixels. In the static mode (small jitter motion of less than 1e-3
pixel), a photon noise limited precision of 3e-5 pixel was reached
Spectral performance of the Microchannel X-ray Telescope on board the SVOM mission
The Microchannel X-ray Telescope (MXT) is an innovative compact X-ray
instrument on board the SVOM astronomical mission dedicated to the study of
transient phenomena such as gamma-ray bursts. During 3 weeks, we have tested
the MXT flight model at the Panter X-ray test facility under the nominal
temperature and vacuum conditions that MXT will undergo in-flight. We collected
data at series of characteristic energies probing the entire MXT energy range,
from 0.28 keV up to 9 keV, for multiple source positions with the center of the
point spread function (PSF) inside and outside the detector field of view
(FOV). We stacked the data of the positions with the PSF outside the FOV to
obtain a uniformly illuminated matrix and reduced all data sets using a
dedicated pipeline. We determined the best spectral performance of MXT using an
optimized data processing, especially for the energy calibration and the charge
sharing effect induced by the pixel low energy thresholding. Our results
demonstrate that MXT is compliant with the instrument requirement regarding the
energy resolution (<80 eV at 1.5 keV), the low and high energy threshold, and
the accuracy of the energy calibration (20 eV). We also determined the
charge transfer inefficiency (~) of the detector and modeled its
evolution with energy prior to the irradiation that MXT will undergo during its
in-orbit lifetime. Finally, we measured the relation of the energy resolution
as function of the photon energy. We determined an equivalent noise charge of
4.9 0.2 e- rms for the MXT detection chain and a Fano factor of 0.131
0.003 in silicon at 208 K, in agreement with previous works. This
campaign confirmed the promising scientific performance that MXT will be able
to deliver during the mission lifetime.Comment: 20 pages, 10 figures, accepted for publication in Experimental
Astronom
Evidence of triggered star formation in G327.3-0.6. Dust-continuum mapping of an infrared dark cloud with P-ArT\'eMiS
Aims. Expanding HII regions and propagating shocks are common in the
environment of young high-mass star-forming complexes. They can compress a
pre-existing molecular cloud and trigger the formation of dense cores. We
investigate whether these phenomena can explain the formation of high-mass
protostars within an infrared dark cloud located at the position of G327.3-0.6
in the Galactic plane, in between two large infrared bubbles and two HII
regions. Methods: The region of G327.3-0.6 was imaged at 450 ? m with the CEA
P-ArT\'eMiS bolometer array on the Atacama Pathfinder EXperiment telescope in
Chile. APEX/LABOCA and APEX-2A, and Spitzer/IRAC and MIPS archives data were
used in this study. Results: Ten massive cores were detected in the P-ArT\'eMiS
image, embedded within the infrared dark cloud seen in absorption at both 8 and
24 ?m. Their luminosities and masses indicate that they form high-mass stars.
The kinematical study of the region suggests that the infrared bubbles expand
toward the infrared dark cloud. Conclusions: Under the influence of expanding
bubbles, star formation occurs in the infrared dark areas at the border of HII
regions and infrared bubbles.Comment: 4 page
The Photodetector Array Camera and Spectrometer (PACS) on the Herschel Space Observatory
The Photodetector Array Camera and Spectrometer (PACS) is one of the three
science instruments on ESA's far infrared and submillimetre observatory. It
employs two Ge:Ga photoconductor arrays (stressed and unstressed) with 16x25
pixels, each, and two filled silicon bolometer arrays with 16x32 and 32x64
pixels, respectively, to perform integral-field spectroscopy and imaging
photometry in the 60-210\mu\ m wavelength regime. In photometry mode, it
simultaneously images two bands, 60-85\mu\ m or 85-125\mu\m and 125-210\mu\ m,
over a field of view of ~1.75'x3.5', with close to Nyquist beam sampling in
each band. In spectroscopy mode, it images a field of 47"x47", resolved into
5x5 pixels, with an instantaneous spectral coverage of ~1500km/s and a spectral
resolution of ~175km/s. We summarise the design of the instrument, describe
observing modes, calibration, and data analysis methods, and present our
current assessment of the in-orbit performance of the instrument based on the
Performance Verification tests. PACS is fully operational, and the achieved
performance is close to or better than the pre-launch predictions
Pilot optical alignment
PILOT (Polarized Instrument for Long wavelength Observations of the Tenuous interstellar medium) is a balloonborne astronomy experiment designed to study the polarization of dust emission in the diffuse interstellar medium in our Galaxy. The PILOT instrument allows observations at wavelengths 240 ÎŒm and 550 ÎŒm with an angular resolution of about two arcminutes. The observations performed during the two first flights performed from Timmins, Ontario Canada, and from Alice-springs, Australia, respectively in September 2015 and in April 2017 have demonstrated the good performances of the instrument. Pilot optics is composed of an off axis Gregorian type telescope combined with a refractive re-imager system. All optical elements, except the primary mirror, which is at ambient temperature, are inside a cryostat and cooled down to 3K. The whole optical system is aligned on ground at room temperature using dedicated means and procedures in order to keep the tight requirements on the focus position and ensure the instrument optical performances during the various phases of a flight. Weâll present the optical performances and the firsts results obtained during the two first flight campaigns. The talk describes the system analysis, the alignment methods, and finally the inflight performances
Characterizing filaments in regions of high-mass star formation: High-resolution submilimeter imaging of the massive star-forming complex NGC 6334 with ArTeMiS
Context. Herschel observations of nearby molecular clouds suggest that interstellar filaments and prestellar cores represent two fundamental steps in the star formation process. The observations support a picture of low-mass star formation according to which filaments of ~0.1 pc width form first in the cold interstellar medium, probably as a result of large-scale compression of interstellar matter by supersonic turbulent flows, and then prestellar cores arise from gravitational fragmentation of the densest filaments. Whether this scenario also applies to regions of high-mass star formation is an open question, in part because the resolution of Herschel is insufficient to resolve the inner width of filaments in the nearest regions of massive star formation.
Aims. In an effort to characterize the inner width of filaments in high-mass star-forming regions, we imaged the central part of the NGC 6334 complex at a resolution higher by a factor of >3 than Herschel at 350 ÎŒm.
Methods. We used the large-format bolometer camera ArTĂ©MiS on the APEX telescope and combined the high-resolution ArTĂ©MiS data at 350 ÎŒm with Herschel/HOBYS data at 70â500 ÎŒm to ensure good sensitivity to a broad range of spatial scales. This allowed us to study the structure of the main narrow filament of the complex with a resolution of 8âł or <0.07 pc at d ~ 1.7 kpc.
Results. Our study confirms that this filament is a very dense, massive linear structure with a line mass ranging from ~500 Mâ/pc to ~2000 Mâ/pc over nearly 10 pc. It also demonstrates for the first time that its inner width remains as narrow as W ~ 0.15 ± 0.05 pc all along the filament length, within a factor of <2 of the characteristic 0.1 pc value found with Herschel for lower-mass filaments in the Gould Belt.
Conclusions. While it is not completely clear whether the NGC 6334 filament will form massive stars in the future, it is two to three orders of magnitude denser than the majority of filaments observed in Gould Belt clouds, and has a very similar inner width. This points to a common physical mechanism for setting the filament width and suggests that some important structural properties of nearby clouds also hold in high-mass star-forming regions
The quasi-universality of nestedness in the structure of quantitative plant-parasite interactions
Understanding the relationships between host range and pathogenicity for parasites, and between the efficiency and scope of immunity for hosts are essential to implement efficient disease control strategies. In the case of plant parasites, most studies have focused on describing qualitative interactions and a variety of genetic and evolutionary models has been proposed in this context. Although plant quantitative resistance benefits from advantages in terms of durability, we presently lack models that account for quantitative interactions between plants and their parasites and the evolution of these interactions. Nestedness and modularity are important features to unravel the overall structure of host-parasite interaction matrices. Here, we analysed these two features on 32 matrices of quantitative pathogenicity trait data gathered from 15 plant-parasite pathosystems consisting of either annual or perennial plants along with fungi or oomycetes, bacteria, nematodes, insects and viruses. The performance of several nestedness and modularity algorithms was evaluated through a simulation approach, which helped interpretation of the results. We observed significant modularity in only six of the 32 matrices, with two or three modules detected. For three of these matrices, modules could be related to resistance quantitative trait loci present in the host. In contrast, we found high and significant nestedness in 30 of the 32 matrices. Nestedness was linked to other properties of plant-parasite interactions. First, pathogenicity trait values were explained in majority by a parasite strain effect and a plant accession effect, with no parasite-plant interaction term. Second, correlations between the efficiency and scope of the resistance of plant genotypes, and between the host range breadth and pathogenicity level of parasite strains were overall positive. This latter result questions the efficiency of strategies based on the deployment of several genetically-differentiated cultivars of a given crop species in the case of quantitative plant immunity