77 research outputs found
Reims – 32-34 rue de Sébastopol
Le diagnostic archéologique, conduit sur une surface totale de 1 532 m2 (118 m2 ouverts, soit 7,7 %), a révélé la présence de remblais récents contenant du mobilier contemporain. Le départ d’un creusement de nature indéterminée a été remarqué dans la partie nord-ouest de la zone diagnostiquée
Reims – 32-34 rue Sébastopol
Un diagnostic archéologique a été mené à Reims, 32-34 rue de Sébastopol, par le service archéologique de Reims Métropole sur une emprise totale de 1 532 m2. Les quelques 118 m2 ouverts (7,7 % de l’emprise) ont permis de documenter la présence de remblais récents contenant du mobilier contemporain. Le départ d’un creusement de nature indéterminé a été remarqué dans la partie nord-est de la zone diagnostiquée
Une statuette inédite dans un contexte de sépulture à crémation gallo-romaine à Châlons-en-Champagne (Marne)
Les fouilles préventives menées au « 28-32 rue du Général Féry » à Châlons-en-Champagne (Marne) ont permis la découverte, au sein d'une sépulture secondaire à incinération, d'une statuette en calcaire. Cette dernière se démarque du corpus habituellement mis au jour en contexte funéraire par le matériau employé, sa taille mais aussi sa représentation qui semble inédite par rapport au répertoire iconographique actuellement connu.Rescue excavations at 28-32 rue du Général Féry, Châlons-en-Champagne (Marne), led to the discovery of a limestone statuette in an incineration grave. The statuette is unusual for a burial context on account of its material and size, but also for its subject, which is uncommon in the iconography in its current state of knowledge.Bei den „28-32 rue du Général Féry“ in Châlons-en-Champagne (Departement Marne) durchgeführten Präventivgrabungen wurde in einer sekundären Brandbestattung eine Statuette aus Kalkstein entdeckt. Sie unterscheidet sich von den üblichen in Bestattungskontexten gefundenen Statuetten nicht nur durch das Material und ihre Größe, sondern auch durch ihre Darstellungsweise, die im heute bekannten ikonographischen Programm einmalig zu sein scheint
Searching for faint companions with VLTI/PIONIER. II. 92 main sequence stars from the Exozodi survey
The Exozodi survey aims to determine the occurrence rate of bright
exozodiacal discs around nearby main sequence stars using infrared
interferometry. Although the Exozodi survey targets have been carefully
selected to avoid the presence of binary stars, the results of this survey can
still be biased by the presence of unidentified stellar companions. Using the
PIONIER data set collected within the Exozodi survey, we aim to search for the
signature of point-like companions around the Exozodi target stars. We use both
the closure phases and squared visibilities collected by PIONIER to search for
companions within the ~100 mas interferometric field of view. The presence of a
companion is assessed by computing the goodness of fit to the data for a series
of binary models with various separations and contrasts. Five stellar
companions are resolved for the first time around five A-type stars: HD 4150,
HD 16555, HD 29388, HD 202730, and HD 224392 (although the companion to HD
16555 was independently resolved by speckle interferometry while we were
carrying out the survey). In the most likely case of main sequence companions,
their spectral types range from A5V to K4V. Three of these stars were already
suspected to be binaries from Hipparcos astrometric measurements, although no
information was available on the companions themselves so far. In addition to
debiasing the statistics of the Exozodi survey, these results can also be used
to revise the fraction of visual binaries among A-type stars, suggesting that
an extra ~13% A-type stars are visual binaries in addition to the ones detected
in previous direct imaging surveys. We estimate that about half the population
of nearby A-type stars could be resolved as visual binaries using a combination
of state-of-the-art interferometry and single-aperture imaging, and we suggest
that a significant fraction of these binaries remains undetected to date.Comment: Accepted for publication in A&
Unveiling new stellar companions from the PIONIER exozodi survey
The main goal of the EXOZODI survey is to detect and characterize
circumstellar dust and to propose the first statistical study of exozodiacal
disks in the near-infrared using telescopes in both hemispheres. For this
purpose, Ertel et al. have conducted in 2012 a survey of nearby main sequence
stars with VLTI/PIONIER to search for the presence of circumstellar dust. This
survey, carried out during 12 nights, comprises about 100 stars. For each star,
we obtained typically three OBs and we searched for circumstellar emission
based on the measurement of squared visibilities at short baselines. A drop in
the measured visibilities with respect to the expected photospheric visibility
indicates the presence of resolved emission around the target star. It is
however generally not possible to conclude on the morphology of the detected
emission based solely on the squared visibilities. Here, we focus on closure
phases to search for faint companions around the whole sample. Indeed, to
derive robust statistics on the occurrence rate of bright exozodiacal disks, we
need to discriminate between companions and disks. For this reason, the main
goal of this paper is to discriminate between circumstellar disks (which show
no closure phase provided that they are point-symmetric) and faint companions
(point-like sources, creating non-zero closure phases). We also aim to reveal
new companions that do not necessarily produce a significant signature in the
squared visibilities, as the signature of the companion may show up more
prominently in the closure phases. In this process, we reveal four new stellar
companions with contrasts ranging from 2% to 95% (i.e., up to equal flux
binaries). We also tentatively detect faint companions around one other target
that will require follow-up observations to be confirmed or infirmed. We
discuss the implications of these discoveries on the results of the exozodi
survey.Comment: To appear in SPIE proceedings vol. 914
A near-infrared interferometric survey of debris-disc stars. IV. An unbiased sample of 92 southern stars observed in H-band with VLTI/PIONIER
Context. Detecting and characterizing circumstellar dust is a way to study
the architecture and evolution of planetary systems. Cold dust in debris disks
only traces the outer regions. Warm and hot exozodiacal dust needs to be
studied in order to trace regions close to the habitable zone.
Aims. We aim to determine the prevalence and to constrain the properties of
hot exozodiacal dust around nearby main-sequence stars.
Methods. We search a magnitude limited (H < 5) sample of 92 stars for bright
exozodiacal dust using our VLTI visitor instrument PIONIER in the H-band. We
derive statistics of the detection rate with respect to parameters such as the
stellar spectral type and age or the presence of a debris disk in the outer
regions of the systems. We derive more robust statistics by combining our
sample with the results from our CHARA/FLUOR survey in the K-band. In addition,
our spectrally dispersed data allows us to put constraints on the emission
mechanism and the dust properties in the detected systems.
Results. We find an over-all detection rate of bright exozodiacal dust in the
H-band of 11% (9 out of 85 targets) and three tentative detections. The
detection rate decreases from early type to late type stars and increases with
the age of the host star. We do not confirm the tentative correlation between
the presence of cold and hot dust found in our earlier analysis of the FLUOR
sample alone. Our spectrally dispersed data suggest that either the dust is
extremely hot or the emission is dominated by the scattered light in most
cases. The implications of our results for the target selection of future
terrestrial planet finding missions using direct imaging are discussed.Comment: 20 pages, 16 figures, 4 tables, updated references and minor changes
to the text, accepted for publication in A&
Exploiting spatial sparsity for multi-wavelength imaging in optical interferometry
Optical interferometers provide multiple wavelength measurements. In order to
fully exploit the spectral and spatial resolution of these instruments, new
algorithms for image reconstruction have to be developed. Early attempts to
deal with multi-chromatic interferometric data have consisted in recovering a
gray image of the object or independent monochromatic images in some spectral
bandwidths. The main challenge is now to recover the full 3-D (spatio-spectral)
brightness distribution of the astronomical target given all the available
data. We describe a new approach to implement multi-wavelength image
reconstruction in the case where the observed scene is a collection of
point-like sources. We show the gain in image quality (both spatially and
spectrally) achieved by globally taking into account all the data instead of
dealing with independent spectral slices. This is achieved thanks to a
regularization which favors spatial sparsity and spectral grouping of the
sources. Since the objective function is not differentiable, we had to develop
a specialized optimization algorithm which also accounts for non-negativity of
the brightness distribution.Comment: This version has been accepted for publication in J. Opt. Soc. Am.
The planar optics phase sensor: a study for the VLTI 2nd generation fringe tracker
In a few years, the second generation instruments of the Very Large Telescope Interferometer (VLTI) will routinely provide observations with 4 to 6 telescopes simultaneously. To reach their ultimate performance, they will need a fringe sensor capable to measure in real time the randomly varying optical paths differences. A collaboration between LAOG (PI institute), IAGL, OCA and GIPSA-Lab has proposed the Planar Optics Phase Sensor concept to ESO for the 2[SUP]nd[/SUP] Generation Fringe Tracker. This concept is based on the integrated optics technologies, enabling the conception of extremely compact interferometric instruments naturally providing single-mode spatial filtering. It allows operations with 4 and 6 telescopes by measuring the fringes position thanks to a spectrally dispersed ABCD method. We present here the main analysis which led to the current concept as well as the expected on-sky performance and the proposed design
Multiple star systems in the Orion nebula
This is the author accepted manuscript. The final fersion is available from EDP Sciences via the DOI in this record.This work presents an interferometric study of the massive-binary fraction in the Orion Trapezium cluster with the recently comissioned GRAVITY instrument. We observed a total of 16 stars of mainly OB spectral type. We find three previously unknown companions for θ1 Ori B, θ2 Ori B, and θ2 Ori C. We determined a separation for the previously suspected companion of NU Ori. We confirm four companions for θ1 Ori A, θ1 Ori C, θ1 Ori D, and θ2 Ori A, all with substantially improved astrometry and photometric mass estimates. We refined the orbit of the eccentric high-mass binary θ1 Ori C and we are able to derive a new orbit for θ1 Ori D. We find a system mass of 21.7 M⊙ and a period of 53 days. Together with other previously detected companions seen in spectroscopy or direct imaging, eleven of the 16 high-mass stars are multiple systems. We obtain a total number of 22 companions with separations up to 600 AU. The companion fraction of the early B and O stars in our sample is about two, significantly higher than in earlier studies of mostly OB associations. The separation distribution hints toward a bimodality. Such a bimodality has been previously found in A stars, but rarely in OB binaries, which up to this point have been assumed to be mostly compact with a tail of wider companions. We also do not find a substantial population of equal-mass binaries. The observed distribution of mass ratios declines steeply with mass, and like the direct star counts, indicates that our companions follow a standard power law initial mass function. Again, this is in contrast to earlier findings of flat mass ratio distributions in OB associations. We excluded collision as a dominant formation mechanism but find no clear preference for core accretion or competitive accretion.Marie Skłodowska-Curie Grant AgreementFCT-PortugalERC Starting Gran
The GRAVITY+ Project: Towards All-sky, Faint-Science, High-Contrast Near-Infrared Interferometry at the VLTI
The GRAVITY instrument has been revolutionary for near-infrared
interferometry by pushing sensitivity and precision to previously unknown
limits. With the upgrade of GRAVITY and the Very Large Telescope Interferometer
(VLTI) in GRAVITY+, these limits will be pushed even further, with vastly
improved sky coverage, as well as faint-science and high-contrast capabilities.
This upgrade includes the implementation of wide-field off-axis
fringe-tracking, new adaptive optics systems on all Unit Telescopes, and laser
guide stars in an upgraded facility. GRAVITY+ will open up the sky to the
measurement of black hole masses across cosmic time in hundreds of active
galactic nuclei, use the faint stars in the Galactic centre to probe General
Relativity, and enable the characterisation of dozens of young exoplanets to
study their formation, bearing the promise of another scientific revolution to
come at the VLTI.Comment: Published in the ESO Messenge
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