Hierarchical fringe tracking

Petrov, R.; Elhalkouj, T.; Boskri, Abdelkarim; Folcher, Jean-Pierre; Lagarde, S.; Bresson, Y.; Benkhaldoun, Z.; Lazrek, M.; Rakshit, Suvendu

doi:10.1117/12.2056677

Cited by 7 publications

(10 citation statements)

References 7 publications

(5 reference statements)

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“…A fringe tracker reaching K 13 would be a major breakthrough by extending the number of GRAVITY targets to about 30 and of OASIS+ targets to about 60 and by improving the accuracy on all measurements. This seems well within the reach of the currently proposed designs (Meisner et al, 2012;Petrov et al, 2014). The full sample of VLTI targets would allow trying a general unification of BLR model by studying for example the cross-relations of the key parameters such as the projection factor f , the BLR thickness ω, the local velocity field parameter σ0 or the rotation-toinflow velocity ratio as a function of the luminosity.…”

Section: Discussion Conclusion and Perspectivesmentioning

confidence: 84%

“…Such a FT would allow increasing the accuracy of the measurements just like the one in GRAVITY, and it would also extend the possibilities of GRAVITY. Currently proposed designs show that FT magnitudes higher than 13 in K-band should be achievable (Meisner et al, 2012;Petrov et al, 2014). The development of such a FT should be a priority for an extended AGN program with the VLTI.…”

Section: Current Incoming and Possible Vlti Instrumentsmentioning

confidence: 99%

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Differential interferometry of QSO broad-line regions - I. Improving the reverberation mapping model fits and black hole mass estimates

Rakshit

Petrov

Meilland

et al. 2015

Monthly Notices of the Royal Astronomical Society

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Reverberation mapping estimates the size and kinematics of broad line regions (BLR) in Quasars and type I AGNs. It yields size-luminosity relation, to make QSOs standard cosmological candles, and mass-luminosity relation to study the evolution of black holes and galaxies. The accuracy of these relations is limited by the unknown geometry of the BLR clouds distribution and velocities. We analyze the independent BLR structure constraints given by super-resolving differential interferometry. We developed a three-dimensional BLR model to compute all differential interferometry and reverberation mapping signals. We extrapolate realistic noises from our successful observations of the QSO 3C273 with AMBER on the VLTI. These signals and noises quantify the differential interferometry capacity to discriminate and measure BLR parameters including angular size, thickness, spatial distribution of clouds, local-toglobal and radial-to-rotation velocity ratios, and finally central black hole mass and BLR distance. A Markov Chain Monte Carlo model-fit, of data simulated for various VLTI instruments, gives mass accuracies between 0.06 and 0.13 dex, to be compared to 0.44 dex for reverberation mapping mass-luminosity fits. We evaluate the number of QSOs accessible to measures with current (AMBER), upcoming (GRAVITY) and possible (OASIS with new generation fringe trackers) VLTI instruments. With available technology, the VLTI could resolve more than 60 BLRs, with a luminosity range larger than four decades, sufficient for a good calibration of RM mass-luminosity laws, from an analysis of the variation of BLR parameters with luminosity.

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Section: Discussion Conclusion and Perspectivesmentioning

confidence: 84%

Section: Current Incoming and Possible Vlti Instrumentsmentioning

confidence: 99%

Differential interferometry of QSO broad-line regions - I. Improving the reverberation mapping model fits and black hole mass estimates

Rakshit

Petrov

Meilland

et al. 2015

Monthly Notices of the Royal Astronomical Society

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“…This offers the advantage to use a well-evaluated device. Finally, figure 4 displays a setup based on our hierarchical fringe tracker concept 11 . Each pair of neighboring telescopes feeds a 2 beams spatial filter (SF2B) that transmits most (typically 75%) of the flux when the input beams are cophased as if it was produced by an unique telescope feeding a single mode beam.…”

Section: Number Of Cophasing Pairs Fed By Each Aperturementioning

confidence: 99%

“…Some authors 10 have proposed to use nλ=1, with the possibility to switch rapidly to a "coherencing mode" with nλ ≥3 but the operational efficiency of such an approach remains unknown. In the Hierarchical Fringe Tracker (HFT) 11 , which is briefly described below, we use nλ=1, because the group delay measurement is obtained from a different device with the photons that are transmitted by the "pair-wise" levels. Optimizing nλ is a key parameter of the design of the PFI fringe tracker and a key motivations for the HFT concept.…”

Section: Number Of Spectral Channels In the Fringe Sensormentioning

confidence: 99%

Co-phasing the planet formation imager

et al. 2016

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The Planet Formation Imager (PFI) is a project for a very large optical interferometer intended to obtain images of the planet formation process at scales as small as the Hill sphere of giant exoplanets. Its main science instruments will work in the thermal infrared but it will be cophased in the near infrared, where it requires also some capacity for scientific imaging. PFI imaging and resolution specifications imply an array of 12 to 20 apertures and baselines up to a few kilometers cophased at near infrared coherent magnitudes as large as 10. This paper discusses various cophasing architectures and the corresponding minimum diameter of individual apertures, which is the dominant element of PFI cost estimates. From a global analysis of the possible combinations of pairwise fringe sensors, we show that conventional approaches used in current interferometers imply the use of prohibitively large telescopes and we indicate the innovative strategies that would allow building PFI with affordable apertures smaller than 2 m in diameter. The approach with the best potential appears to be Hierarchical Fringe Tracking based on "two beams spatial filters" that cophase pairs of neighboring telescopes with all the efficiency of a two telescopes fringe tracker and transmit most of the flux as if it was produced by an unique single mode aperture to cophase pairs of pairs and then pairs of groups of apertures. We consider also the adaptation to PFI of more conventional approaches such as a combination of GRAVITY like fringe trackers or single or multiple chains of 2T fringe trackers.

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“…3 magnitudes, if all other elements are the same, including the detector, the throughput, the exposure time and the control loop. The first idea of Hierarchical Fringe Tracking 10 , illustrated in the figure 1, is to cophase the apertures by pairs, then by pairs of pairs, then by pairs of groups by a cascade of pair-wise FTs. Each FT drives one OPD actuator and it is easy to show that the necessary number of cophasers for nT telescopes is nT-1.…”

Section: Functions and Accuracy Of A Fringe Sensormentioning

confidence: 99%

Hierarchical fringe tracker to co-phase and coherence very large optical interferometers

et al. 2016

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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 UTs and K~7.5 with ATs, for fundamental conceptual reasons: the flux of each telescope is distributed among 3 cophasing pairs and then among 5 spectral channels for coherencing. To overcome this limit we propose a new FT concept, called Hierarchical Fringe Tracker (HFT) that cophase pairs of apertures with all the flux from two apertures and only one spectral channel. When the pair is cophased, most of the flux is transmitted as if it was produced by an unique single mode beam and then used to cophase pairs of pairs and then pairs of groups. At the deeper level, the flux is used in an optimized dispersed fringe device for coherencing. On the VLTI such a system allows a gain of about 3 magnitudes over the GRAVITY FT. On interferometers with more apertures such as CHARA (6 telescopes) or a future Planet Formation Imager (12 to 20 telescopes), the HFT would be even more decisive, as its performance does not decrease with the number of apertures. It would allow building a PFI reaching a coherent magnitude H~10 with 16 apertures with diameters smaller than 2 m. We present the HFT concept, the first steps of its feasibility demonstration from computer simulations and the optical design of a 4 telescopes HFT prototype.

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Hierarchical fringe tracking

Cited by 7 publications

References 7 publications

Differential interferometry of QSO broad-line regions - I. Improving the reverberation mapping model fits and black hole mass estimates

Differential interferometry of QSO broad-line regions - I. Improving the reverberation mapping model fits and black hole mass estimates

Co-phasing the planet formation imager

Hierarchical fringe tracker to co-phase and coherence very large optical interferometers

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