Robust determination of optical path difference: fringe tracking at the Infrared Optical Telescope Array interferometer

Pedretti, E.; Traub, Wesley A.; Monnier, John D.; Millan-Gabet, R.; Carleton, N. P.; Schloerb, F. Peter; Brewer, Michael K.; Berger, J.‐P.; Lacasse, M. G.; Ragland, Sam

doi:10.1364/ao.44.005173

Cited by 24 publications

(18 citation statements)

References 25 publications

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“…To estimate the GD OPDs, we use an algorithm similar to the double Fourier interferometry used at IOTA (Pedretti et al 2005). The 16-element coherence vectorĈ l n is estimated at time step n for each spectral channel l using the calibrated P2VM l :…”

Section: Group Delay Estimationmentioning

confidence: 99%

Comparison of fringe-tracking algorithms for single-mode near-infrared long-baseline interferometers

Choquet

Perrin

et al. 2014

A&A

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To enable optical long baseline interferometry toward faint objects, long integrations are necessary despite atmospheric turbulence. Fringe trackers are needed to stabilize the fringes and thus increase the fringe visibility and phase signal-to-noise ratio (S/N), with efficient controllers robust to instrumental vibrations and to subsequent path fluctuations and flux drop-outs. We report on simulations, analysis, and comparison of the performances of a classical integrator controller and of a Kalman controller, both optimized to track fringes under realistic observing conditions for different source magnitudes, disturbance conditions, and sampling frequencies. The key parameters of our simulations (instrument photometric performance, detection noise, turbulence, and vibrations statistics) are based on typical observing conditions at the Very Large Telescope observatory and on the design of the GRAVITY instrument, a 4-telescope single-mode long-baseline interferometer in the near-infrared, next in line to be installed at VLT Interferometer. We find that both controller performances follow a two-regime law with the star magnitude, a constant disturbance limited regime, and a diverging regime limited by both the detector and photon-noise. Moreover, we find that the Kalman controller is optimal in the high and medium S/N regime owing to its predictive commands based on an accurate disturbance model. In the low S/N regime, the model is not accurate enough to be more robust than an integrator controller. Identifying the disturbances from high S/N measurements improves the Kalman performances in the case of strong optical path difference disturbances.

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Section: Group Delay Estimationmentioning

confidence: 99%

Comparison of fringe-tracking algorithms for single-mode near-infrared long-baseline interferometers

Choquet

Perrin

et al. 2014

A&A

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“…The result is a single interferometric signal per baseline represented in red in Fig. 3; 2. at the end of the scan, the signal is processed by the algorithm presented by Pedretti et al (2005). It provides an SNR and a group-delay position for each baseline; 3. then these six group-delay measurements are converted into offsets for the four input beams.…”

Section: Quick-look and Fringe Trackingmentioning

confidence: 99%

PIONIER: a 4-telescope visitor instrument at VLTI

Bouquin

Berger

Lazareff

et al. 2011

A&A

253

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Context. PIONIER stands for PrecisionAims. In this paper, we explain the instrumental concept and describe the standard operational modes and the data reduction strategy. We present the typical performance and discuss how to improve them. Methods. This paper is based on laboratory data obtained during the integrations at IPAG, as well as on-sky data gathered during the commissioning at VLTI. We illustrate the imaging capability of PIONIER on the binaries δ Sco and HIP11231. Results. PIONIER provides six visibilities and three independent closure phases in the H band, either in a broadband mode or with a low spectral dispersion (R = 40), using natural light (i.e. unpolarized). The limiting magnitude is Hmag = 7 in dispersed mode under median atmospheric conditions (seeing <1 , τ 0 > 3 ms) with the 1.8 m Auxiliary Telescopes. We demonstrate a precision of 0.5 deg on the closure phases. The precision on the calibrated visibilities ranges from 3% to 15% depending on the atmospheric conditions. Conclusions. PIONIER was installed and successfully tested as a visitor instrument for the VLTI. It permits high angular resolution imaging studies at an unprecedented level of sensitivity. The successful combination of the four 8 m Unit Telescopes in March 2011 demonstrates that VLTI is ready for four-telescope operation.

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“…Closure phases are computed as the phase of the complex triple amplitude, also called bispectrum (Baldwin et al 1996). These measurements were recorded when interferences occurred on the three baselines taking advantage of the baseline bootstrapping technique (Pedretti et al 2005). This method makes it possible to record fringes on a long baseline at low visibility when fringes on the shorter baselines are detected.…”

Section: Observation and Data Reductionmentioning

confidence: 99%

Imaging the spotty surface of Betelgeuse in theHband

Haubois¹,

Perrin²,

Lacour³

et al. 2009

A&A

161

171

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Aims. This paper reports on H-band interferometric observations of Betelgeuse made at the three-telescope interferometer IOTA. We image Betelgeuse and its asymmetries to understand the spatial variation of the photosphere, including its diameter, limb darkening, effective temperature, surrounding brightness, and bright (or dark) star spots. Methods. We used different theoretical simulations of the photosphere and dusty environment to model the visibility data. We made images with parametric modeling and two image reconstruction algorithms: MIRA and WISARD. Results. We measure an average limb-darkened diameter of 44.28 ± 0.15 mas with linear and quadratic models and a Rosseland diameter of 45.03 ± 0.12 mas with a MARCS model. These measurements lead us to derive an updated effective temperature of 3600 ± 66 K. We detect a fully-resolved environment to which the silicate dust shell is likely to contribute. By using two imaging reconstruction algorithms, we unveiled two bright spots on the surface of Betelgeuse. One spot has a diameter of about 11 mas and accounts for about 8.5% of the total flux. The second one is unresolved (diameter < 9 mas) with 4.5% of the total flux. Conclusions. Resolved images of Betelgeuse in the H band are asymmetric at the level of a few percent. The MOLsphere is not detected in this wavelength range. The amount of measured limb-darkening is in good agreement with model predictions. The two spots imaged at the surface of the star are potential signatures of convective cells.

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Robust determination of optical path difference: fringe tracking at the Infrared Optical Telescope Array interferometer

Cited by 24 publications

References 25 publications

Comparison of fringe-tracking algorithms for single-mode near-infrared long-baseline interferometers

Comparison of fringe-tracking algorithms for single-mode near-infrared long-baseline interferometers

PIONIER: a 4-telescope visitor instrument at VLTI

Imaging the spotty surface of Betelgeuse in theHband

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