Piston control with adaptive optics in stellar interferometry

Vérinaud, Christophe; Cassaing, F.

doi:10.1051/0004-6361:20000185

Cited by 14 publications

(7 citation statements)

References 16 publications

(15 reference statements)

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“…-Bimorph piston effect: this is the OPD induced by resonances of the adaptive optics deformable mirror (Vérinaud & Cassaing 2001). This contribution has been evaluated for the MACAO adaptive optics at VLTI, and turns out to be dominant above 100 Hz despite the use of a "piston-free" algorithm for the control of the deformable mirror.…”

Section: The Piston Effectmentioning

confidence: 99%

Performance study of ground-based infrared Bracewell interferometers

Absil¹,

Hartog

Gondoin

et al. 2006

A&A

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Nulling interferometry, a powerful technique for high-resolution imaging of the close neighbourhood of bright astrophysical objets, is currently considered for future space missions such as Darwin or the Terrestrial Planet Finder Interferometer (TPF-I), both aiming at Earth-like planet detection and characterization. Ground-based nulling interferometers are being studied for both technology demonstration and scientific preparation of the Darwin/TPF-I missions through a systematic survey of circumstellar dust disks around nearby stars. In this paper, we investigate the influence of atmospheric turbulence on the performance of ground-based nulling instruments, and deduce the major design guidelines for such instruments. End-to-end numerical simulations allow us to estimate the performance of the main subsystems and thereby the actual sensitivity of the nuller to faint exozodiacal disks. Particular attention is also given to the important question of stellar leakage calibration. This study is illustrated in the context of GENIE, the Ground-based European Nulling Interferometer Experiment, to be installed at the VLTI and working in the L band. We estimate that this instrument will detect exozodiacal clouds as faint as about 50 times the Solar zodiacal cloud, thereby placing strong constraints on the acceptable targets for Darwin/TPF-I.

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Section: The Piston Effectmentioning

confidence: 99%

Performance study of ground-based infrared Bracewell interferometers

Absil¹,

Hartog

Gondoin

et al. 2006

A&A

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“…Such effect would reduce the fringe contrast at the recombination laboratory and be detrimental to the performance of the Interferometer. The piston mode removal algorithm implemented had been first described in 6 . Most of the piston characterization & tune-up takes place in the laboratory where a setup has been designed in order to do so.…”

Section: Piston Performancementioning

confidence: 99%

MACAO-VLTI adaptive optics systems performance

Arsenault¹,

Donaldson²,

Dupuy³

et al. 2004

Advancements in Adaptive Optics

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In April and August '03 two MACAO-VLTI curvature AO systems were installed on the VLT telescopes unit 2 and 3 in Paranal (Chile). These are 60 element systems using a 150mm bimorph deformable mirror and 60 APD's as WFS detectors. Valuable integration & commissioning experience has been gained during these 2 missions. Several tests have been performed in order to evaluate system performance on the sky. The systems have proven to be extremely robust, performing in a stable fashion in extreme seeing condition (seeing up to 3"). Strehl ratio of 0.65 and residual tilt smaller than 10 mas have been obtained on the sky in 0.8" seeing condition. Weak guide source performance is also excellent with a strehl of 0.26 on a V~16 magnitude star. Several functionalities have been successfully tested including: chopping, off-axis guiding, atmospheric refraction compensation etc. The AO system can be used in a totally automatic fashion with a small overhead: the AO loop can be closed on the target less than 60 sec after star acquisition by the telescope. It includes reading the seeing value given by the site monitor, evaluate the guide star magnitude (cycling through neutral density filters) setting the close-loop AO parameters (system gain and vibrating membrane mirror stroke) including calculation of the command-matrix. The last 2 systems will be installed in August '04 and in the course of 2005.

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“…where A and B are constants and Φ i (ν) is chosen randomly for each sampled temporal frequency ν. For Kolmogorov turbulence, the fast scan ( 1 s) regime has B = 17/6 (Conan et al 1995) but there is experimental evidence (di Folco et al 2003) that the slope is not as steep at VLTI, with simulations by Absil et al (2006) explaining it in terms of the piston induced at high frequency by the adaptive optics (imperfect) correction ("bimorph piston", see Vérinaud & Cassaing 2001) and wavefront errors produced by the injection into single-mode waveguides ("coupled piston", see Ruilier & Cassaing 2001). Linfield et al (1999) have also measured a deviation from the Kolmogorov behaviour at PTI.…”

Section: Numerical Modellingmentioning

confidence: 99%

Bandwidth smearing in infrared long-baseline interferometry. Application to stellar companion search in fringe-scanning mode

Lachaume¹,

Berger²

2013

Monthly Notices of the Royal Astronomical Society

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In long-baseline interferometry, bandwidth smearing of an extended source occurs at finite bandwidth when its different components produce interference packets that only partially overlap. In this case, traditional model fitting or image reconstruction using standard formulas and tools lead to biased results.In this paper, we propose and implement a method to overcome this effect by calculating analytically a corrective term for the conventional interferometric observables: the visibility amplitude and closure phase. For that purpose, we model the interferogram taking into account the finite bandwidth and the instrumental differential phase. We obtain generic expressions for the visibility and closure phase in the case of temporally-modulated interferograms, either processed using Fourier analysis or with the ABCD method. The expressions can be used to fit arbitrary models to the data. We then apply our results to the search and characterisation of stellar companions with PIONIER at the Very Large Telescope Interferometer, assessing the bias on observables and model-fitted parameters of a binary star. Finally, we consider the role of the atmosphere, first with an analytic model to identify the main contributions to bias and, secondly, by confirming the model with a numerical simulation of the atmospheric turbulence.In addition to the analytic expressions, the main results of our study are: (i) the chromatic dispersion in the beam transport in the instrument has a strong impact on the closure phase and introduces additional biases even at separations where smearing is not expected to play an important role; (ii) the atmospheric turbulence introduces additional biases when smearing is present, but the impact is important only at very low spectral resolution; (iii) the bias on the observables strongly depends on the recombination scheme and data processing; (iv) the goodness of model fits is improved by modelling a Gaussian bandpass as long as the smearing is moderate.

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Piston control with adaptive optics in stellar interferometry

Cited by 14 publications

References 16 publications

Performance study of ground-based infrared Bracewell interferometers

Performance study of ground-based infrared Bracewell interferometers

MACAO-VLTI adaptive optics systems performance

Bandwidth smearing in infrared long-baseline interferometry. Application to stellar companion search in fringe-scanning mode

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