The VLTI fringe sensors: FINITO and PRIMA FSU

Gai, M.; Ménardi, Serge; Cesare, Stefano; Bauvir, Bertrand; Bonino, Donata; Corcione, L.; Dimmler, M.; Massone, G.; Reynaud, François; Wallander, Anders

doi:10.1117/12.551495

Cited by 39 publications

(26 citation statements)

References 7 publications

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“…All data were taken in the medium resolution (MR) mode, while we present the first MR observations of the object taken with the FINITO fringe-tracker (Gai et al 2004). The use of FINITO in this mode extends the observed wavelength range substantially compared to the previous studies, and includes the Na i 2.2 μm doublet which has long been known to be in emission (Thompson & Boroson 1977, and see below).…”

Section: Amber Spectro-interferometrymentioning

confidence: 99%

Neutral and ionised gas around the post-red supergiant IRC +10 420 at AU size scales

Oudmaijer

Wit

2013

A&A

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Context. IRC +10 420 is one of the few known massive stars in rapid transition from the red supergiant phase to the Wolf-Rayet or luminous blue variable phase. Aims. The star has an ionised wind and using the Brγ line we assess the mass-loss on spatial scales of ∼1 AU. Methods. We present new VLT Interferometer AMBER data which are combined with all other AMBER data present in the literature. The final dataset covers a position angle range of ∼180 • and baselines up to 110 m. The spectrally dispersed visibilities, differential phases and line flux are conjointly analysed and modelled. We also present the first AMBER/FINITO observations which cover a larger wavelength range and allow us to observe the Na i doublet at 2.2 μm. The data are complemented by X-Shooter data, which provide a higher spectral resolution view.Results. The Brγ emission line and the Na i doublet are both spatially resolved. After correcting the AMBER data for the fact that the lines are not spectrally resolved, we find that Brγ traces a ring with a diameter of 4.18 mas, in agreement with higher spectral resolution data. We consider a geometric model in which the Brγ emission emerges from the top and bottom rings of an hour-glass shaped structure, viewed almost pole-on. It provides satisfactory fits to most visibilities and differential phases. The fact that we detect line emission from a neutral metal like Na i within the ionised region, a very unusual occurrence, suggests the presence of a dense pseudo-photosphere. Conclusions. The ionised wind can be reproduced with a polar wind, which could well have the shape of an hour-glass. Closer in, the resolved Na i emission is found to occur on scales barely larger than the continuum. This fact and that many yellow hypergiants exhibit this comparatively rare emission hints at the presence of a "Yellow" or even "White Wall" in the Hertzsprung-Russell diagram, preventing them from visibly evolving to the blue.

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Section: Amber Spectro-interferometrymentioning

confidence: 99%

Neutral and ionised gas around the post-red supergiant IRC +10 420 at AU size scales

Oudmaijer

Wit

2013

A&A

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“…We used medium spectral resolution in the K-band (MR, R ∼ 1500, 2.1 μm) and the fringe tracker FINITO (Gai et al 2004) with a frame exposure time of 1 s. Observations were carried out with a maximum projected baseline length of 127.8 m, corresponding to a 3.1 mas spatial resolution, with the atmospheric seeing in the 0.7 ÷ 1.0 range. For the sake of clarity, we distinguish here a Run A (six nights from 2011 Apr.…”

Section: Data Acquisitionmentioning

confidence: 99%

On the binarity of the classical Cepheid X Sagittarii from interferometric observations

Causi

Antoniucci

Bono

et al. 2012

A&A

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Context. Optical-infrared interferometry can provide direct geometrical measurements of the radii of Cepheids and/or reveal any unknown binary companions of these stars. Such information is very important for properly calibrating the period-luminosity relations and determining binary fraction among Cepheids. Aims. We observed the Cepheid X Sgr with VLTI/AMBER in order to confirm or disprove the presence of the hypothesized binary companion and to directly measure the mean stellar radius, possibly detecting its variation along the pulsation cycle. Methods. From AMBER observations in MR mode, we performed a binary model fitting on the closure phase and a limb-darkened model fitting on the visibility. Results. Our analysis indicates that there is a point-like companion at a separation of 10.7 mas, which is 5.6 mag K fainter than the primary and whose flux and position are sharply constrained by the data. The radius pulsation is not detected, whereas the average limb-darkened diameter results in 1.48±0.08 mas, corresponding to 53 ± 3 R at a distance of 333.3 pc.

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“…-Temporal ABCD: it consists in temporally modulating the OPD as for FINITO at VLTI (Gai et al 2004), CHAMP at CHARA (Berger et al 2006), or the Keck Interferometer fringe tracker ). We will consider in the following an implementation using a sampling of both outputs of a beam-splitter (in phase opposition) simultaneously.…”

Section: Phase Estimationmentioning

confidence: 99%

Optimized fringe sensors for the VLTI next generation instruments

Blind

Absil

Bouquin

et al. 2011

A&A

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Context. With the arrival of the next generation of ground-based imaging interferometers combining from four to possibly six telescopes simultaneously, there is also a strong need for a new generation of fringe trackers able to cophase these arrays. These instruments have to be very sensitive and to provide robust operations in quickly varying observational conditions. Aims. We aim at defining the optimal characteristics of fringe sensor concepts operating with four or six telescopes. The current detector limitations lead us to consider solutions based on co-axial pairwise combination schemes. Methods. We independently study several aspects of the fringe sensing process: 1) how to measure the phase and the group delay, and 2) how to combine the telescopes to ensure a precise and robust fringe tracking in real conditions. Thanks to analytical developments and numerical simulations, we define the optimal fringe-sensor concepts and compute the expected performance of the four-telescope one with our dedicated end-to-end simulation tool sim2GFT. Results. We first show that measuring the phase and the group delay by obtaining the data in several steps (i.e. by temporally modulating the optical path difference) is extremely sensitive to atmospheric turbulence and therefore conclude that it is better to obtain the fringe position with a set of data obtained simultaneously. Subsequently, we show that among all co-axial pairwise schemes, moderately redundant concepts increase the sensitivity as well as the robustness in various atmospheric or observing conditions. Merging all these results, end-to-end simulations show that our four-telescope fringe sensor concept is able to track fringes at least 90% of the time up to limiting magnitudes of 7.5 and 9.5 for the 1.8-and 8.2-meter VLTI telescopes respectively.

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The VLTI fringe sensors: FINITO and PRIMA FSU

Cited by 39 publications

References 7 publications

Neutral and ionised gas around the post-red supergiant IRC +10 420 at AU size scales

Neutral and ionised gas around the post-red supergiant IRC +10 420 at AU size scales

On the binarity of the classical Cepheid X Sagittarii from interferometric observations

Optimized fringe sensors for the VLTI next generation instruments

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