Related papers: Potential and sky coverage for off-axis fringe tra…

The GRAVITY instrument has been commissioned on the VLTI during 2016 and is now available to the astronomical community. It is the first optical interferometer capable of observing sources as faint as magnitude 19 in K-band. This is…

The limiting magnitude is a key issue for optical interferometry. Pairwise fringe trackers based on the integrated optics concepts used for example in GRAVITY seem limited to about K=10.5 with the 8m Unit Telescopes of the VLTI, and there…

As part of the GRAVITY$^{+}$ project, the near-infrared beam combiner GRAVITY and the VLTI are currently undergoing a series of significant upgrades to further improve the performance and sky coverage. The instrumental changes will be…

Context: MATISSE, the mid-infrared spectro-imaging instrument of VLTI, was designed to deliver its advertised performance when paired with an external second generation fringe tracker. Science observation started in 2019, demonstrating…

Aims. As part of the ongoing GRAVITY+ upgrade of the Very Large Telescope Interferometer infrastructure, we aim to improve the performance of the GRAVITY Fringe-Tracker, and to enable its use by other instruments. Methods. We modify the…

GRAVITY+ is the upgrade of GRAVITY and the Very Large Telescope Interferometer (VLTI) with wide-separation fringe tracking, new adaptive optics, and laser guide stars on all four 8~m Unit Telescopes (UTs), for ever fainter, all-sky, high…

The full scientific potential of the VLTI with its second generation instruments MATISSE and GRAVITY require fringe tracking up to magnitudes K>14 with the UTs and K>10 with the ATs. The GRAVITY fringe tracker (FT) will be limited to K~10.5…

With the advent of GRAVITY+, the upgrade to the beam combiner GRAVITY at the Very Large Telescope Interferometer (VLTI), fainter and higher redshift active galactic nuclei (AGNs) are becoming observable, opening an unprecedented opportunity…

The implementation of fringe tracking for optical interferometers is inevitable when optimal exploitation of the instrumental capacities is desired. Fringe tracking allows continuous fringe observation, considerably increasing the…

Optical variability is a key observational probe for studying the accretion dynamics and central engine physics of Active Galactic Nuclei (AGNs). The quality and completeness of light curves have a direct impact on variability studies,…

After the first year of observations with the GRAVITY fringe tracker, we compute correlations between the optical path residuals and atmospheric and astronomical parameters. The median residuals of the optical path residuals are 180 nm on…

Context. It will soon become possible to directly link the most accurate radio reference frame with the Gaia optical reference frame using many common extragalactic objects. It is important to know the level of coincidence between the radio…

Global Navigation Satellite System (GNSS) receivers provide ubiquitous and precise position, navigation, and time (PNT) to a wide gamut of civilian and tactical infrastructures and devices. Due to the low GNSS received signal power, even…

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…

The optical structure of several AGN has been studied using the Fine Guidance Sensors (FGS) on the Hubble Space Telescope (HST). The FGSs are interferometric devices which can resolve structure on scales of 20 milliarcsecs or less and hence…

The high spectral resolution and sensitivity of FUSE have enabled far-ultraviolet studies of AGN and QSOs that are a natural complement to observations using HST, Chandra, and XMM-Newton. Through synergistic use of the large sample of…

Context. With the arrival of the next generation of ground-based imaging interferometers combining from 4 to possibly 6 telescopes simultaneously, there is also a strong need for a new generation of fringe trackers able to cophase such…

Variability has proven to be a powerful tool to detect active galactic nuclei (AGN) in multi-epoch surveys. The new-generation facilities expected to become operational in the next few years will mark a new era in time-domain astronomy and…

We describe the fringe packet tracking system used to equalise the optical path lengths at the Infrared Optical Telescope Array (IOTA) interferometer. The measurement of closure phases requires obtaining fringes on three baselines…

VLT-Interferometry will allow imaging of the Galactic Center (GC) and the nuclei of extragalactic sources at an angular resolution of a few milliarcseconds. VLTI will be a prime instrument to study the immediate environment of the massive…