We present the results of the fifth Interferometric Imaging Beauty Contest. The contest consists in blind imaging of test data sets derived from model sources and distributed in the OIFITS format. Two scenarios of imaging with CHARA/MIRC-6T were offered for reconstruction: imaging a T Tauri disc and imaging a spotted red supergiant. There were eight different teams competing this time: Monnier with the software package MACIM; Hofmann, Schertl and Weigelt with IRS; Thiebaut and Soulez with MiRA ; Young with BSMEM; Mary and Vannier with MIROIRS; Millour and Vannier with independent BSMEM and MiRA entries; Rengaswamy with an original method; and Elias with the radio-astronomy package CASA. The contest model images, the data delivered to the contestants and the rules are described as well as the results of the image reconstruction obtained by each method. These results are discussed as well as the strengths and limitations of each algorithm.
We present the results of the fourth Optical/IR Interferometry Imaging Beauty Contest. The contest consists
of blind imaging of test data sets derived from model sources and distributed in the OI-FITS format. The test
data consists of spectral data sets on an object "observed" in the infrared with spectral resolution. There were 4
different algorithms competing this time: BSMEM the Bispectrum Maximum Entropy Method by Young, Baron
& Buscher; RPR the Recursive Phase Reconstruction by Rengaswamy; SQUEEZE a Markov Chain Monte Carlo
algorithm by Baron, Monnier & Kloppenborg; and, WISARD theWeak-phase Interferometric Sample Alternating
Reconstruction Device by Vannier & Mugnier. The contest model image, the data delivered to the contestants
and the rules are described as well as the results of the image reconstruction obtained by each method. These
results are discussed as well as the strengths and limitations of each algorithm.
A working group on interferometry data standards has been established within IAU Commission 54 (Optical/
Infrared Interferometry). The working group includes members representing the major optical interferometry
projects worldwide, and aims to enhance existing standards and develop new ones to satisfy the broad interests
of the optical interferometry community. We present the initial work of the group to enhance the OIFITS data
exchange standard, and outline the software packages and libraries now available which implement the standard.
MUSTANG is a 90 GHz bolometer camera built for use as a facility instrument on the 100 m Robert C. Byrd
Green Bank radio telescope (GBT). MUSTANG has an 8 by 8 focal plane array of transition edge sensor
bolometers read out using time-domain multiplexed SQUID electronics. As a continuum instrument on a large
single dish MUSTANG has a combination of high resolution (8) and good sensitivity to extended emission
which make it very competitive for a wide range of galactic and extragalactic science. Commissioning finished
in January 2008 and some of the first science data have been collected.
We present the results of the third Optical/IR Interferometry Imaging Beauty Contest. A formal comparison is
presented of the performance of algorithms used for imaging data from optical/infrared long-baseline interferometers.
The contest consists of blind imaging of test data sets derived from model sources and distributed in the
OI-FITS format. The test data consisted of datasets on two objects each "observed" in J, H, and K bands. The
majority of the entries produced accurate reconstructions of the initial models. Each of the methods presented
is discussed.
We present a formal comparison of the performance of algorithms used for synthesis imaging with optical/infrared long-baseline interferometers. Five different algorithms are evaluated based on their performance with simulated test data. Each set of test data is formatted in the OI-FITS format. The data are calibrated power spectra and bispectra measured with an array intended to be typical of existing imaging interferometers. The strengths and limitations of each algorithm are discussed.
This paper describes a standard for exchanging calibrated data from optical (visible/infrared) stellar interferometers. The standard is based on the Flexible Image Transport System (FITS). The formal
definition of the standard is contained in a separate document, the Format Specification. The latest version of the Format Specification is available from the website http://www.mrao.cam.ac.uk/~jsy1001/exchange/. This document gives an overview of the format, and explains some of the decisions taken in designing it.
We present a formal comparison of the performance of algorithms used for synthesis imaging with optical/infrared long-baseline interferometers. Five different algorithms are evaluated based on their performance with simulated test data. Each set of test data is formatted in the OI-FITS format. The data are calibrated power spectra and bispectra measured with an array intended to be typical of existing imaging interferometers. The strengths and limitations of each algorithm are discussed.
The 74 MHz system on the National Radio Astronomy Observatory's Very
Large Array (VLA) has opened a high-resolution, high-sensitivity
window on the electromagnetic spectrum at low frequencies. It
provides us with a unique glimpse into both the possibilities and
challenges of planned low-frequency radio interferometers such as
LOFAR, the LWA, and the SKA. Observations of bright, resolved radio
sources at 74 MHz provide new scientific insights into the structure,
history, and energy balances of these systems. However many of these
scientifically motivated observations will also be critical to testing
the scientific fidelity of new instruments, by providing a set of
well-known standard sources. We are also using the 74 MHz system to
conduct a sky survey, called the VLA Low-frequency Sky Survey (VLSS).
When complete it will cover the entire sky above -30 degrees
declination, at a 5σ sensitivity of 0.5 Jy/bm-1, and a resolution of 80" (B-configuration). Among its various uses, this
survey will provide an initial grid of calibrator sources at low
frequency. Finally, practical experience with calibration and data
reduction at 74 MHz has helped to direct and shape our understanding
of the design needs of future instruments. In particular, we have
begun experimenting with angle-variant calibration techniques which
are essential to properly calibrate the wide field of view at low
frequencies.
Ionospheric phase errors degrade high-resolution radio images below
100 MHz, and they differ significantly from the tropospheric errors
which dominate at high frequencies. The ionosphere is so high
(~400 km) and the VLA primary beam is so wide (~0.2 rad) that
the intersection of the beam with the ionospheric screen is larger
than the "isoplanatic patch" size, a phase coherent region on the
sky. Antenna-based calibration techniques developed at higher
frequencies cannot be used because ionospheric phase errors vary
significantly across the field-of-view of each antenna. This paper
describes the "field-based calibration" technique adopted for the
74 MHz VLA Low--frequency Sky Survey (VLSS) being made with the 10 km
"B" configuration. This technique is useful for a range of array
sizes but fails on baselines longer than the linear size of the
isoplanatic patch, a few 10s of km at 74 MHz. Implications for
designing larger low-frequency arrays are discussed.
Installed at the heart of the Very Large Telescope Interferometer (VLTI), VINCI combines coherently the infrared light coming from two telescopes. The first fringes were obtained in March 2001 with the VLTI test siderostats, and in October of the same year with the 8 meters Unit Telescopes (UTs). After more than one year of operation, it is now possible to evaluate its behavior and performances with a relatively long timescale. During this period, the technical downtime has been kept to a very low level. The most important parameters of the instrument (interferometric efficiency, mechanical stability,...) have been followed regularly, leading to a good understanding of its performances and characteristics. In addition to a large number of laboratory measurements, more than 3000 on-sky observations have been recorded, giving a precise knowledge of the behavior of the system under various conditions. We report in this paper the main characteristics of the VINCI instrument hardware and software. The differences between observations with the siderostats and the UTs are also briefly discussed.
The mid-infrared interferometric instrument MIDI is currently undergoing testing in preparation for commissioning on the Very Large Telescope Interferometer VLTI at the end of this year 2002. It will perform interferometric observations over the 8 μm - 13 μm wavelength range, with a spatial resolution of 20 milliarcsec, a spectral resolution of up to 250, and an anticipated point source sensitivity of N = 4 mag or 1 Jy for self-fringe tracking, which will be the only observing mode during the first months of operation. We describe the layout of the instrument and the performance during laboratory tests, both for broadband and spectrally resolved observing modes. We also briefly outline the planned guaranteed time observations.
The first science instrument for the Very Large Telescope Interferometer (VLTI), the Mid-infrared instrument MIDI, will be commissioned in November 2002 with anticipated first fringe during that commissioning run on the 40-cm Siderostats and the 8.2-meter Unit Telescopes. In this paper we describe scientific and technical observing modes (also referred to as observation procedures) developed for MIDI and discuss in detail how an observing run with the instrument is planned.
MIDI is built by a consortium lead by the Max Planck Institute for Astronomy (MPIA Heidelberg), with contributions from among others ASTRON (Dwingeloo, The Netherlands), Leiden Observatory, University of Amsterdam, Paris Observatory, University of Groningen, the Kiepenheuer-Institut fur Sonnenpysik at Freiburg, Thuringer Landessternwarte Tautenburg, and the Observatoire de la Cote d'Azur.
On March 17, 2001, the VLT interferometer saw for the first time interferometric fringes on sky with its two test siderostats on a 16m baseline. Seven months later, on October 29, 2001, fringes were found with two of the four 8.2m Unit Telescopes (UTs), named Antu and Melipal, spanning a baseline of 102m. First shared risk science operations with VLTI will start in October 2002. The time between these milestones is used for further integration as well as for commissioning of the interferometer with the goal to understand all its characteristics and to optimize performance and observing procedures. In this article we will describe the various commissioning tasks carried out and present some results of our work.
The start of NEVEC was initiated by the opportunity in the Netherlands to reinstate instrumental efforts in astronomy through a funding program for 'Top Research Schools,’ which brought about the creation of NOVA. The fact that considerable experience exists in Radio Astronomical imaging through interferometry (the Westerbork Synthesis Radio Telescope started in 1970), and the relatively small size at the time of ESO's VLTI Team made it opportune to aim for a win-win situation through collaboration. So presently an MOU between ESO and NOVA is in force, which stipulates that 10 out of the 18 man-years funded by NOVA for NEVEC until 2005 [new personnel, in university setting (Leiden) but on project money] shall be used on tasks that are mutually agreed between NOVA and ESO.
The tasks presently are found in the domain of observing modes, calibration and modeling, as well as contributing to the commissioning of new instruments and thinking about future instruments. Another task, outside these 10 FTE, has been the data handling and analysis software for MIDI, and again contributing to its commissioning. Delivery of the first operational version in Heidelberg has just taken place (summer 2002) contributing to the successful Preliminary Acceptance in Europe for MIDI on September 10, 2002. The actual state of 'products and deliveries' and the future outlook are reviewed.
The Data Flow System is the VLT end-to-end system for handling astronomical observations from the initial observation proposal phase through the acquisition, processing and control of the astronomical data. The VLT Data Flow System has been in place since the opening of the first VLT Unit Telescope in 1998. When completed the VLT Interferometer will make it possible to coherently combine up to three beams coming from the four VLT 8.2m telescopes as well as from a set of initially three 1.8m Auxiliary Telescopes, using a Delay Line tunnel and four interferometry instruments. The Data Flow system is now in the process of installation and adaptation for the VLT Interferometer. Observation preparation for a multi-telescope system, handling large data volume of several tens of gigabytes per night are among the new challenges offered by this system. This introduction paper presents the VLTI Data Flow system installed during the initial phase of VLTI commissioning. Observation preparation, data archival, and data pipeline processing are addressed.
MIDI is a two channel mid-infrared interferometric instrument developed for the Very Large Telescopes (VLT) Interferometer (VLTI). A control system with real-time capabilities integrates the various VLTI subsystems. Based on the VLTI control architecture and its interferometric extension, the VLTI control system, the MIDI control system will use synchronized VME computers running Tornado to control time critical subsystems such as delay lines and detector control electronics. Standard Unix workstations run high-level coordinating, monitoring, and data pre-processing tasks as well as graphical user interfaces. We describe the MIDI control architecture, the data flow and storage concept, and the self fringe tracking option. Furthermore we introduce a software package currently under development to simulate observations with MIDI.
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