Hierarchical Fringe Tracking, sky coverage and AGNs at the VLTI

Romain G. Petrov; Fatmé Allouche; Abdelkarim Boskri; James Leftley; Massinissa Hadjara; Sylvain Rousseau; Stéphane Lagarde; Bruno Lopez; Florentin Millour; Xinyang Chen; Yinlei Hao; Thami Elhalkouj; Zouhair Benkhaldoun

doi:10.1117/12.2628250

26 August 2022 Hierarchical Fringe Tracking, sky coverage and AGNs at the VLTI

Romain G. Petrov, Fatmé Allouche, Abdelkarim Boskri, James Leftley, Massinissa Hadjara, Sylvain Rousseau, Stéphane Lagarde, Bruno Lopez, Florentin Millour, Xinyang Chen, Yinlei Hao, Thami Elhalkouj, Zouhair Benkhaldoun

Author Affiliations +

Proceedings Volume 12183, Optical and Infrared Interferometry and Imaging VIII; 121830I (2022) https://doi.org/10.1117/12.2628250
Event: SPIE Astronomical Telescopes + Instrumentation, 2022, Montréal, Québec, Canada

Abstract

Hierarchical Fringe Tracking (HFT) is a fringe tracking concept optimizing the sensitivity in optical long baseline by reducing to an absolute minimum the number of measurements used to correct the OPD fluctuations. By nature, the performances of an HFT do not decreases with the number of apertures of the interferometer and are set only by the flux delivered by the individual telescopes. This a critical feature for future interferometers with large number of apertures both for homodyne and heterodyne operation. Here we report the design and first optical bench tests of integrated optics HFT chips for a 4 telescopes interferometer such as the VLTI. These tests validate the HFT concept and confirm previous estimates that we could track accurately fringes on the VLTI up to nearly K~15.9 with the UTs and K~12.2 with the ATs with a J+H+K fringe tracker with one HFT chip per band. This is typically 2.5 magnitudes fainter than the best potential performance of the current ABCD fringe tracker in the K band. An active longitudinal and transverse chromatic dispersion correction allows the optimization of broad band fiber injections and instrumental contrast. We also present a preliminary evaluation of the potential of such a gain of sensitivity for the observations of AGNs with the VLTI.

Conference Presentation

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Romain G. Petrov, Fatmé Allouche, Abdelkarim Boskri, James Leftley, Massinissa Hadjara, Sylvain Rousseau, Stéphane Lagarde, Bruno Lopez, Florentin Millour, Xinyang Chen, Yinlei Hao, Thami Elhalkouj, and Zouhair Benkhaldoun "Hierarchical Fringe Tracking, sky coverage and AGNs at the VLTI", Proc. SPIE 12183, Optical and Infrared Interferometry and Imaging VIII, 121830I (26 August 2022); https://doi.org/10.1117/12.2628250

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