Lacour, S., Dembet, R., Abuter, R., Fedou, P., Perrin, G., Choquet, E., Pfuhl, O., Eisenhauer, F., Woillez, J., Cassaing, F., Wieprecht, E., Ott, T. E., Wiezorrek, E., Tristram, K. R. W., Wolff, B., Ramirez, A., Haubois, X., Perraut, K., Straubmeier, C., Brandner, W. and Amorim, A. (2019). The GRAVITY fringe tracker. Astron. Astrophys., 624. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Context. The GRAVITY instrument was commissioned on the VLTI in 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 possible through the fringe tracker, which compensates the differential piston based on measurements of a brighter off-axis astronomical reference source. Aims. The goal of this paper is to describe the main developments made in the context of the GRAVITY fringe tracker. This could serve as basis for future fringe-tracking systems. Methods. The paper therefore covers all aspects of the fringe tracker, from hardware to control software and on-sky observations. Special emphasis is placed on the interaction between the group-delay controller and the phase-delay controller. The group-delay control loop is a simple but robust integrator. The phase-delay controller is a state-space control loop based on an auto-regressive representation of the atmospheric and vibrational perturbations. A Kalman filter provides the best possible determination of the state of the system. Results. The fringe tracker shows good tracking performance on sources with coherent K magnitudes of 11 on the Unit Telescopes (UTs) and 9.5 on the Auxiliary Telescopes (ATs). It can track fringes with a signal-to-noise ratio of 1.5 per detector integration time, limited by photon and background noises. During good seeing conditions, the optical path delay residuals on the ATs can be as low as 75 nm root mean square. The performance is limited to around 250 nm on the UTs because of structural vibrations.

Item Type: Journal Article
Creators:
CreatorsEmailORCIDORCID Put Code
Lacour, S.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Dembet, R.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Abuter, R.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Fedou, P.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Perrin, G.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Choquet, E.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Pfuhl, O.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Eisenhauer, F.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Woillez, J.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Cassaing, F.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Wieprecht, E.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Ott, T. E.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Wiezorrek, E.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Tristram, K. R. W.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Wolff, B.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Ramirez, A.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Haubois, X.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Perraut, K.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Straubmeier, C.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Brandner, W.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
Amorim, A.UNSPECIFIEDUNSPECIFIEDUNSPECIFIED
URN: urn:nbn:de:hbz:38-150596
DOI: 10.1051/0004-6361/201834981
Journal or Publication Title: Astron. Astrophys.
Volume: 624
Date: 2019
Publisher: EDP SCIENCES S A
Place of Publication: LES ULIS CEDEX A
ISSN: 1432-0746
Language: English
Faculty: Unspecified
Divisions: Unspecified
Subjects: no entry
Uncontrolled Keywords:
KeywordsLanguage
INTERFEROMETRY; OPTICS; PHASE; AMBER; VLTIMultiple languages
Astronomy & AstrophysicsMultiple languages
Refereed: Yes
URI: http://kups.ub.uni-koeln.de/id/eprint/15059

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