Topic
Closure phase
About: Closure phase is a research topic. Over the lifetime, 256 publications have been published within this topic receiving 6824 citations.
Papers published on a yearly basis
Papers
TL;DR: GRAVITY as discussed by the authors 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.
Abstract: GRAVITY 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.
503 citations
TL;DR: AMBER as mentioned in this paper is one of the VLTI instruments that combines up to three beams with low, moderate and high spectral resolutions in order to provide milli-arcsecond spatial resolution for compact astrophysical sources in the near-infrared wavelength domain.
Abstract: Context: Optical long-baseline interferometry is moving a crucial step forward with the advent of general-user scientific instruments that equip large aperture and hectometric baseline facilities, such as the Very Large Telescope Interferometer (VLTI). Aims: AMBER is one of the VLTI instruments that combines up to three beams with low, moderate and high spectral resolutions in order to provide milli-arcsecond spatial resolution for compact astrophysical sources in the near-infrared wavelength domain. Its main specifications are based on three key programs on young stellar objects, active galactic nuclei central regions, masses, and spectra of hot extra-solar planets. Methods: These key science goals led to scientific specifications, which were used to propose and then validate the instrument concept. AMBER uses single-mode fibers to filter the entrance signal and to reach highly accurate, multiaxial three-beam combination, yielding three baselines and a closure phase, three spectral dispersive elements, and specific self-calibration procedures. Results: The AMBER measurements yield spectrally dispersed calibrated visibilities, color-differential complex visibilities, and a closure phase allows astronomers to contemplate rudimentary imaging and highly accurate visibility and phase differential measurements. AMBER was installed in 2004 at the Paranal Observatory. We describe here the present implementation of the instrument in the configuration with which the astronomical community can access it. Conclusions: .After two years of commissioning tests and preliminary observations, AMBER has produced its first refereed publications, allowing assessment of its scientific potential.
488 citations
TL;DR: In this article, a review describes self-calibration methods and their application to both conventional and very long baseline arrays and includes examples of the high-quality images that they produce.
Abstract: This review describes these self-calibration methods and their application to both conventional and very long baseline arrays and includes examples of the high-quality images that they produce. After first defining closure phase and closure amplitude in Section 2, we review conventional aperture synthesis methods in Sections 3 and 4. The new iterative self-calibration algorithms are the subject of Section 5. In Section 6 we consider the capabilities and limitations of these algorithms. Finally, in Section 7 we mention some applications in optical and infrared astronomy and in new radio instruments presently planned or under construction.
400 citations
TL;DR: In this paper, an innovative data reduction method for single-mode interferometry is presented based on a direct modelling of the fringes in the detector plane, which is specifically developed for the AMBER instrument, the three-beam combiner of the Very Large Telescope Interferometer.
Abstract: We present in this paper an innovative data reduction method for single-mode interferometry. It has been specifically developed for the AMBER instrument, the three-beam combiner of the Very Large Telescope Interferometer, but can be derived for any single-mode interferometer. The algorithm is based on a direct modelling of the fringes in the detector plane. As such, it requires a preliminary calibration of the instrument in order to obtain the calibration matrix which builds the linear relationship between the interferogram and the interferometric observable, that is the complex visibility. Once the calibration procedure has been performed, the signal processing appears to be a classical least square determination of a linear inverse problem. From the estimated complex visibility, we derive the squared visibility, the closure phase and the spectral differential phase. The data reduction procedures are gathered into the so-called amdlib software, now available for the community, and presented in this paper. Furthermore, each step of this original algorithm is illustrated and discussed from various on-sky observations conducted with the VLTI, with a focus on the control of the data quality and the effective execution of the data reduction procedures. We point out the present limited performances of the instrument due to VLTI instrumental vibrations, difficult to calibrate.
273 citations
TL;DR: In this paper, a 1.3 mm very long baseline interferometry (VLBI) was used to study Sagittarius A*, a black hole candidate at the Galactic center.
Abstract: Sagittarius A*, the ~4 × 10^6 M_⊙ black hole candidate at the Galactic center, can be studied on Schwarzschild
radius scales with (sub)millimeter wavelength very long baseline interferometry (VLBI). We report on 1.3 mm
wavelength observations of Sgr A* using a VLBI array consisting of the JCMT on Mauna Kea, the Arizona Radio
Observatory’s Submillimeter Telescope on Mt. Graham in Arizona, and two telescopes of the CARMA array at
Cedar Flat in California. Both Sgr A* and the quasar calibrator 1924−292 were observed over three consecutive
nights, and both sources were clearly detected on all baselines. For the first time, we are able to extract 1.3mmVLBI
interferometer phase information on Sgr A* through measurement of closure phase on the triangle of baselines. On
the third night of observing, the correlated flux density of Sgr A* on all VLBI baselines increased relative to the
first two nights, providing strong evidence for time-variable change on scales of a few Schwarzschild radii. These
results suggest that future VLBI observations with greater sensitivity and additional baselines will play a valuable
role in determining the structure of emission near the event horizon of Sgr A*.
244 citations
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2021 | 5 |
| 2020 | 10 |
| 2019 | 6 |
| 2018 | 10 |
| 2017 | 10 |
| 2016 | 17 |