145 research outputs found
Fringe tracking performance monitoring: FINITO at VLTI
Since April 2011, realtime fringe tracking data are recorded simultaneously
with data from the VLTI/AMBER interferometric beam combiner. Not only this
offers possibilities to post-process AMBER reduced data to obtain more accurate
interferometric quantities, it also allows to estimate the performance of the
fringe tracking a function of the conditions of seeing, coherence time, flux,
etc. First we propose to define fringe tracking performance metrics in the
AMBER context, in particular as a function of AMBER's integration time. The
main idea is to determine the optimal exposure time for AMBER: short exposures
are dominated by readout noise and fringes in long exposures are completely
smeared out. Then we present this performance metrics correlated with Paranal
local ASM (Ambient Site Monitor) measurements, such as seeing, coherence time
or wind speed for example. Finally, we also present some preliminary results of
attempts to model and predict fringe tracking performances, using Artificial
Neural Networks.Comment: SPIE conference, Optical and Infrared Interferometry II
Quality control and instruments monitoring for
ABSTRACT The VLTI Data Flow Operations consist in monitoring the performance of the different VLTI instruments offered to the community, in verifying the quality of the calibration and scientific data and their associated products. Since the beginning of MIDI (April 2004) and AMBER (October 2005) Service Mode Operations, scientific as well as calibration data have been accumulated to monitor the instruments and the quality of the observations on different time scales and under different conditions or system configurations. In this presentation, we will describe the Quality Control procedures and give some statistics and results on the different parameters used for instrument monitoring for time scales from hours to years in the case of MIDI. We will show that this includes parameters extracted directly from the instruments (Instrumental Transfer Function, Flux stability, Image Quality, Detector stability …) and parameters extracted from some of the sub-systems associated to the instruments (Adaptive Optics, telescopes used …). We will discuss the development of the monitoring of the instruments once more instrument modes or sub-systems such as PRIMA are offered to the community
CHARM: A Catalog of High Angular Resolution Measurements
Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe
CHARM2: An updated Catalog of High Angular Resolution Measurements
We present an update of the Catalog of High Angular Resolution Measurements (CHARM, Richichi & Percheron 2002, A&A, 386, 492), which includes results available until July 2004. CHARM2 is a compilation of direct measurements by high angular resolution methods, as well as indirect estimates of stellar diameters. Its main goal is to provide a reference list of sources which can be used for calibration and verification observations with long-baseline optical and near-IR interferometers. Single and binary stars are included, as are complex objects from circumstellar shells to extragalactic sources. The present update provides an increase of almost a factor of two over the previous edition. Additionally, it includes several corrections and improvements, as well as a cross-check with the valuable public release observations of the ESO Very Large Telescope Interferometer (VLTI). A total of 8231 entries for 3238 unique sources are now present in CHARM2. This represents an increase of a factor of 3.4 and 2.0, respectively, over the contents of the previous version of CHARM
A List of Bright Interferometric Calibrators measured at the ESO VLTI
In a previous publication (Richichi & Percheron 2005) we described a program
of observations of candidate calibrator stars at the ESO Very Large Telescope
Interferometer (VLTI), and presented the main results from a statistical point
of view. In the present paper, we concentrate on establishing a new homogeneous
group of bright interferometric calibrators, based entirely on publicly
available K-band VLTI observations carried out with the VINCI instrument up to
July 2004. For this, we have defined a number of selection criteria for the
quality and volume of the observations, and we have accordingly selected a list
of 17 primary and 47 secondary calibrators. We have developed an approach to a
robust global fit for the angular diameters using the whole volume of
quality-controlled data, largely independent of a priori assumptions. Our
results have been compared with direct measurements, and indirect estimates
based on spectrophotometric methods, and general agreement is found within the
combined uncertainties. The stars in our list cover the range K=-2.9 to +3.0
mag in brightness, and 1.3 to 20.5 milliarcseconds in uniform-disk diameter.
The relative accuracy of the angular diameter values is on average 0.4% and 2%
for the primary and secondary calibrators respectively. Our calibrators are
well suited for interferometric observations in the near-infrared on baselines
between ~20m and ~200m, and their accuracy is superior, at least for the
primary calibrators, to other similar catalogues. Therefore, the present list
of calibrators has the potential to lead to significantly improved
interferometric scientific results
An overview of the mid-infrared spectro-interferometer MATISSE: science, concept, and current status
MATISSE is the second-generation mid-infrared spectrograph and imager for the
Very Large Telescope Interferometer (VLTI) at Paranal. This new interferometric
instrument will allow significant advances by opening new avenues in various
fundamental research fields: studying the planet-forming region of disks around
young stellar objects, understanding the surface structures and mass loss
phenomena affecting evolved stars, and probing the environments of black holes
in active galactic nuclei. As a first breakthrough, MATISSE will enlarge the
spectral domain of current optical interferometers by offering the L and M
bands in addition to the N band. This will open a wide wavelength domain,
ranging from 2.8 to 13 um, exploring angular scales as small as 3 mas (L band)
/ 10 mas (N band). As a second breakthrough, MATISSE will allow mid-infrared
imaging - closure-phase aperture-synthesis imaging - with up to four Unit
Telescopes (UT) or Auxiliary Telescopes (AT) of the VLTI. Moreover, MATISSE
will offer a spectral resolution range from R ~ 30 to R ~ 5000. Here, we
present one of the main science objectives, the study of protoplanetary disks,
that has driven the instrument design and motivated several VLTI upgrades
(GRA4MAT and NAOMI). We introduce the physical concept of MATISSE including a
description of the signal on the detectors and an evaluation of the expected
performances. We also discuss the current status of the MATISSE instrument,
which is entering its testing phase, and the foreseen schedule for the next two
years that will lead to the first light at Paranal.Comment: SPIE Astronomical Telescopes and Instrumentation conference, June
2016, 11 pages, 6 Figure
Mid-infrared sizes of circumstellar disks around Herbig Ae/Be stars measured with MIDI on the VLTI
We present the first long baseline mid-infrared interferometric observations of the circumstellar disks surrounding Herbig Ae/Be stars. The observations were obtained using the mid-infrared interferometric instrument MIDI at the European Southern Observatory (ESO) Very Large Telescope Interferometer VLTI on Cerro Paranal. The 102 m baseline given by the telescopes UT1 and UT3 was employed, which provides a maximum full spatial resolution of 20 milli-arcsec (mas) at a wavelength of 10 μm. The interferometric signal was spectrally dispersed at a resolution of 30, giving spectrally resolved visibility information from 8 μm to 13.5 μm. We observed seven nearby Herbig Ae/Be stars and resolved all objects. The warm dust disk of HD 100546 could even be resolved in single-telescope imaging. Characteristic dimensions of the emitting regions at 10 μm are found to be from 1 AU to 10 AU. The 10 μm sizes of our sample stars correlate with the slope of the 10–25 μm infrared spectrum in the sense that the reddest objects are the largest ones. Such a correlation would be consistent with a different geometry in terms of flaring or flat (self-shadowed) disks for sources with strong or moderate mid-infrared excess, respectively. We compare the observed spectrally resolved visibilities with predictions based on existing models of passive centrally irradiated hydrostatic disks made to fit the SEDs of the observed stars. We find broad qualitative agreement of the spectral shape of visibilities corresponding to these models with our observations. Quantitatively, there are discrepancies that show the need for a next step in modelling of circumstellar disks, satisfying both the spatial constraints such as are now available from the MIDI observations and the flux constraints from the SEDs in a consistent way
First light for GRAVITY: Phase referencing optical interferometry for the Very Large Telescope Interferometer
This is the author accepted manuscript. the final version is available from EDP Sciences via the DOI in this recordGRAVITY is a new instrument to coherently combine the light of the European Southern Observatory Very Large Telescope Interferometer to form a telescope with an equivalent 130 m diameter angular resolution and a collecting area of 200 m2. The instrument comprises fiber fed integrated optics beam combination, high resolution spectroscopy, built-in beam analysis and control, near-infrared wavefront sensing, phase-tracking, dual-beam operation, and laser metrology. GRAVITY opens up to optical/infrared interferometry the techniques of phase referenced imaging and narrow angle astrometry, in many aspects following the concepts of radio interferometry. This article gives an overview of GRAVITY and reports on the performance and the first astronomical observations during commissioning in 2015/16. We demonstrate phase-tracking on stars as faint as mK ≈ 10 mag, phase-referenced interferometry of objects fainter than mK ≈ 15 mag with a limiting magnitude of mK ≈ 17 mag, minute long coherent integrations, a visibility accuracy of better than 0.25%, and spectro-differential phase and closure phase accuracy better than 0.5°, corresponding to a differential astrometric precision of better than ten microarcseconds (μas). The dual-beam astrometry, measuring the phase difference of two objects with laser metrology, is still under commissioning. First observations show residuals as low as 50 μas when following objects over several months. We illustrate the instrument performance with the observations of archetypical objects for the different instrument modes. Examples include the Galactic center supermassive black hole and its fast orbiting star S2 for phase referenced dual-beam observations and infrared wavefront sensing, the high mass X-ray binary BP Cru and the active galactic nucleus of PDS 456 for a few μas spectro-differential astrometry, the T Tauri star S CrA for a spectro-differential visibility analysis, ξ Tel and 24 Cap for high accuracy visibility observations, and η Car for interferometric imaging with GRAVITY.Agence Nationale de la RechercheAlexander von Humboldt FoundationEuropean Union, Seventh Framework Programm
The Enhanced Resolution Imager and Spectrograph for the VLT
ERIS, the Enhanced Resolution Imager and Spectrograph, is an instrument that
both extends and enhances the fundamental diffraction limited imaging and
spectroscopy capability for the VLT. It replaces two instruments that were
being maintained beyond their operational lifetimes, combines their
functionality on a single focus, provides a new wavefront sensing module for
natural and laser guide stars that makes use of the Adaptive Optics Facility,
and considerably improves on their performance. The observational modes ERIS
provides are integral field spectroscopy at 1-2.5 {\mu}m, imaging at 1-5 {\mu}m
with several options for high contrast imaging, and longslit spectroscopy at
3-4 {\mu}m, The instrument is installed at the Cassegrain focus of UT4 at the
VLT and, following its commissioning during 2022, has been made available to
the community.Comment: 19 pages with 29 figures; submitted to A&
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