This PDF file contains the front matter associated with SPIE Proceedings Volume 8445, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

The exquisite precision delivered by interferometric techniques is rapidly being applied to more and more branches of optical astronomy. One particularly successful strategy to obtain structures at the scale of the diffraction limit is Aperture Masking Interferometry, which is presently experience a golden age with implementations at a host of large telescopes around the world. This startlingly durable technique, which turns 144 years old this year, presently sets the standard for the recovery of faint companions within a few resolution elements from the core of a stellar point spread function. This invited review will give a historical introduction and overview of the modern status of the technique, the science being delivered, and prospects for new advances and applications.

Aperture-masking interferometry allows diffraction-limited images to be recovered despite the turbulent atmo­ sphere. Here, this approach has been combined with polarimetry to form a novel technique allowing the dusty environments of mass-losing stars (so-called AGB stars) and proto-planetary and debris disks to be imaged, the characterisation of which is key to understanding the recycling of matter and the formation of new planetary systems. Polarimetric aperture-masking interferometry produces images by exploiting the fact that starlight scattered by circumstellar dust becomes strongly polarised. Essentially, aperture-masking allows access to the small spatial scales (rv1Omas) necessary while polarimetry allows light from the dust and star to be differentiated. Furthermore, measurements at multiple wavelengths allow dust grain sizes to be calculated using Mie scattering theory. Excellent results have already been obtained at near-IR wavelengths using the NACO instrument at the VLT. The next step is to leverage the higher spatial resolution and polarisation signal found in the visible, rather than near-IR. To this end, a new instrument allowing precision polarimetric aperture masking interferometry at 600-800nm is being developed for an 8m class telescope, details of which will also be presented.

Kernel-phase is a recently developed paradigm to tackle the classical problem of image deconvolution, based on an interferometric point of view of image formation. Kernel-phase inherits and borrows from the notion of closure-phase, especially as it is used in the context of non-redundant Fizeau interferometry, but extends its application to pupils of arbitrary shape, for diffraction limited images. It can therefore readily be (and is being) used to process existing archival data acquired by space borne telescopes (HST/NICMOS) as well as well corrected AO data from ground based telescopes. The additional calibration brought by kernel-phase boosts the resolution of conventional images and enables the detection of otherwise hidden faint features at the resolution limit and beyond, a regime often refered to as super-resolution. Kernel-phase analysis of archival data leads to new discoveries and/or improved relative astrometry and photometry. The paper also presents how the technique may influence the geometry of new interferometric arrays designed for imaging, dusting off a topic that has known little evolution for the past 40 years; and presents hints of a fast solution to the calibration of non-common path errors in AO systems, using direct focal plane based wavefront sensing.

High contrast imaging techniques such as aperture masking interferometry allow for the detection of faint companions such as substellar companions by utilizing light from the planet itself. This allows access to study a larger population of planetary companions as compared to the transit technique where only systems viewed edge on can be studied, for example. However, aperture masking has several shortcomings including, low throughputs, limited Fourier coverage, and leakage of residual atmospheric noise due to phase corrugations across each sub-apertures. These limitations can be overcome by remapping the pupil with single-mode waveguides. We present an integrated pupil remapping interferometer, known as Dragonfly, that aims to do just that. We discuss the progress we have made over the past year in developing a stable and robust instrument and elucidate challenges and the innovative solutions that were applied. Finally we discuss improvements to the instrument that will enable future scientific endeavors and outline the expected performance limitations.

Extrasolar planets are directly detected most easily when they are young and can have contrasts only a few hundred times fainter than their host stars at near- and mid- infrared wavelengths. However, planets and other solar-system scale structures around solar-type stars in the nearest star forming regions require the full diffraction limit of the world's largest telescopes, and can not be detected with conventional AO imaging techniques. I will describe the recent successes of long-baseline interferometry in detecting planetary-mass companions, focusing on the transitional disk system LkCa 15. I will outline why aperture-masking has been so successful in its resolution and sensitivity niche, and will outline the algorithms needed to calibrate the primary observable of closure/kernel phase to the level needed for extrasolar planet detection.

We report here on some of the major astronomical observations obtained by the Keck Interferometer Nuller (KIN), the high dynamic range instrument recombining the Keck Telescopes at wavelengths of 8 to 13 microns. A few science targets were observed during the commissioning phase (2004-2007). These early observations aimed at demonstrating the KIN’s ability to spatially resolve and characterize circumstellar dust emission around a variety of targets, ranging from evolved stars to young debris disks. Science operations started then in 2008 with the more demanding KIN exozodi key science programs, augmented by observations of YSOs and hot debris disks between 2009 and 2011. The last KIN observations were gathered in 2011B, and the interpretation of some of the results depicted here is still preliminary (exo-zodi survey) or pending (complicated behavior observed in YSOs). We discuss in particular the initial results of the KIN’s exo-zodi observations, which targeted a total of 40 nearby main sequence single stars. We look for trends in this sample, searching for possible correlations between the measured KIN excesses and basic stellar properties such as spectral type or the presence of dust inferred from separate observations.

The Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII) is an 8-meter baseline far-infrared interferometer designed to fly on a high altitude balloon. BETTII uses a double-Fourier Michelson interferometer to simultaneously obtain spatial and spectral information on science targets; the long baseline permits subarcsecond angular resolution, a capability unmatched by other far-infrared facilities. Here, we present key aspects of the overall design of the mission and provide an overview of the current status of the project. We also discuss briefly the implications of this experiment for future space-based far-infrared interferometers.

Interferometry in space has marked advantages: long integration times and observation in spectral bands where the atmosphere is opaque. When installed on separate spacecraft, it also has extended and flexible baselines for better filling of the uv plane. Intensity interferometry has an additional advantage, being insensitive to telescope and path errors, but is unfortunately much less light-sensitive. In planning towards such a mission, we are experimenting with some fundamental research issues. Towards this end, we constructed a system of three vehicles floating on an air table in formation flight, with an autonomous orbit control. Each such device holds its own light collector, detector, and transmitter, to broadcast its intensity signal towards a central receiving station. At this station we implement parallel radio receivers, analogue to digital converters, and a digital three-way correlator. Current technology limits us to ~1GHz transmission frequency, which corresponds to a comfortable 0.3m accuracy in light-bucket shape and in its relative position. Naïve calculations place our limiting magnitude at ~7 in the blue and ultraviolet, where amplitude interferometers are limited. The correlation signal rides on top of this huge signal with its own Poisson noise, requiring a very large dynamic range, which needs to be transmitted in full. We are looking at open questions such as deployable optical collectors and radio antennae of similar size of a few meters, and how they might influence our data transmission and thus set our flux limit.

Interferometry is an affordable way to bring the benefits of high resolution to space far-IR astrophysics. We summarize an ongoing effort to develop and learn the practical limitations of an interferometric technique that will enable the acquisition of high-resolution far-IR integral field spectroscopic data with a single instrument in a future space-based interferometer. This technique was central to the Space Infrared Interferometric Telescope (SPIRIT) and Submillimeter Probe of the Evolution of Cosmic Structure (SPECS) space mission design concepts, and it will first be used on the Balloon Experimental Twin Telescope for Infrared Interferometry (BETTII). Our experimental approach combines data from a laboratory optical interferometer (the Wide-field Imaging Interferometry Testbed, WIIT), computational optical system modeling, and spatio-spectral synthesis algorithm development. We summarize recent experimental results and future plans.

The Wide-Field Imaging Interferometry Testbed (WIIT) is a wide-field spectral imaging Michelson interferometer developed at the NASA/Goddard Space Flight Center. WIIT is operational and effectively demonstrates imaging and spectroscopy over fields-of-view larger than the narrow primary beam footprint of a conventional Michelson interferometer. At the heart of this technique is the "double-Fourier" approach whereby the apertures and a delay line are both moved to collect interferograms over a 2D wide field detector grid simultaneously; one interferogram per detector pixel. This aggregate set of interferograms, as a function of baseline and delay line, is algorithmically processed to construct a single spatial-spectral cube with angular resolution approaching the ratio of the wavelength to the longest baseline. Herein we develop the mathematical spatial-spectral imaging model and the baseline processing algorithm and show results using simulated data and using WIIT testbed data.

The Keck Interferometer (KI) combines the two 10m diameter Keck telescopes providing milliarcsecond angular resolution. KI has unique observing capabilities such as sensitive K-band V², L-band V² and N-band nulling modes. The instrument improvements and status of the Keck Interferometer since the 2010 SPIE meeting are summarized. We discuss the current capabilities of the KI, operational improvements, and the science from the KI during the past two years. We will conclude with a brief note on the closure of the KI facility. Details of dual field phase referencing developments and nulling science results are presented elsewhere at this conference.

The ESO Very Large Telescope Interferometer (VLTI) offers access to the four 8-m Unit Telescopes (UT) and the four 1.8-m Auxiliary Telescopes (AT) of the Paranal Observatory located in the Atacama Desert in northern Chile. The two VLTI instruments, MIDI and AMBER deliver regular scientific results. In parallel to the operation, the instruments developments are pursued, and new modes are studied and commissioned to offer a wider range of scientific possibilities to the community and increase sensitivity. New configurations of the ATs have been offered and are frequently discussed with the science users of the VLTI and implemented to optimize the scientific return. The PRIMA instrument, bringing astrometry capability to the VLTI and phase referencing to the instruments is being commissioned. The visitor instrument PIONIER is now fully operational and bringing imaging capability to the VLTI. The current status of the VLTI is described with successes and scientific results, and prospects on future evolution are presented.

Ground-baseed long baselinne interferomeeters have lonng been limiteed in sensitiviity by the shoort integration periods imposed by atmospheric tuurbulence. Thee first observaation fainter thhan this limit wwas performedd on January 222, 2011 when the Keck Interferommeter observedd a K=11.5 taarget, about onne magnitude fainter than iits K=10.3 limmit. This observation wwas made posssible by the Duual Field Phase Referencing instrument of the ASTRA pproject: simultaaneously measuring thhe real-time efffects of the atmmosphere on a nearby bright guide star, andd correcting foor it on the fainnt target, integration tiime longer thaan the turbulennce time scale are made possible. As a preelude to this ddemonstration, we first present the implementatioon of Dual FField Phase RReferencing onn the interferoometer. We tthen detail itss on-sky performance focusing on tthe accuracy oof the turbulennce correction, and on the reesulting fringe contrast stabiility. We conclude witth a presentatioon of early resuults obtained wwith Laser Guidde Star AO andd the interferommeter.

The Phase Referenced Imaging and Micro Arcsecond Astrometry (PRIMA) facility for the Very Large Telescope Interferometer (VLTI), is being installed and tested in the observatory of Paranal. Since January 2011 the integration and individual testing of the different subsystem has come to a necessary minimum. At the same time the astrometric commissioning phase has begun. In this contribution we give an update on the status of the facility and present some highlights and difficulties on our way from first dual-feed fringe detection to first astrometric measurements. We focus on technical and operational aspects. In particular, within the context of the latter we are going to present a modified mode of operation that scans across the fringes. We will show that this mode, originally only intended for calibration purposes, facilitates the detection of dual-fringes.

Rotation plays a crucial role in the shaping and evolution of a star. Widely incorporated into early and late-stage stellar models, rotational effects remain poorly understood in main-sequence stars, mainly due to the absence of observations challenging contemporary models. The Precision Astronomical Visible Observations (PAVO) instrument, located at the Center for High Angular Resolution Astronomy (CHARA) array, provides the highest angular resolution yet achieved (0.3 mas) for stars V=8 magnitude and brighter. We describe instrumental techniques and advances implemented in PAVO@CHARA to observe heavily resolved targets and yield well calibrated closure phases which are key milestones on the pathway to delivery of the first-ever image in the visible of fast-rotating main-sequence star.

The CHARA Array is a six-telescope optical/IR interferometer managed by the Center for High Angular Resolution Astronomy of Georgia State University and located at Mount Wilson Observatory in the San Gabriel Mountains overlooking Pasadena, California. The CHARA Array has the longest operational baselines in the world and has been in regular use for scientific observations since 2005. In this paper we give an update of instrumentation improvements, primarily focused on the beam combiner activity. The CHARA Array supports seven beam combiners: CHARA CLASSIC, a two-way high-sensitivity K/H/J band system; CLIMB, a three-way K/H/J open-air combiner; FLUOR, a two-way K-band high-precision system; MIRC, a four/six-way H/K-band imaging system; CHAMP, a six-way K-band fringe tracker; VEGA, a four-way visible light high spectral resolution system; and PAVO, a three-way visible light high sensitivity system. We also present an overview of science results obtained over the last few years, including some recent imaging results.

The visitor instrument PIONIER provides VLTI with improved imaging capabilities and sensitivity. The in- strument started routinely delivering scientic data in November 2010, that is less than 12 months after being approved by the ESO Science and Technical Committee. We recall the challenges that had to be tackled to design, built and commission PIONIER. We summarize the typical performances and some astrophysical results obtained so far. We conclude this paper by summarizing lessons learned.

In the framework of the understanding of extrasolar systems, the study of host stars is a fundamental point. We need to understand the link between them and the presence of companions, i.e. what makes a star becoming a host star. In this perspective, we used the instrument called VEGA, situated at Mount Wilson (California) on the CHARA array to perform optical interferometric measurements. Interferometry at visible wavelengths allows reaching very high spatial frequencies well adapted for very small (less than 1 millisecond of arc) angular diameters. Therefore, we can access limb darkening measurements which is one of the very few directly measurable constraints on the structure of the atmosphere of a star. From this we can derive stars fundamental parameters. A precise measurement within spectral lines is also a very powerful tool to study the temperature and density structure of the atmosphere of distant stars. Besides, the detection of exoplanets is also related to this method. Combined with the radial velocity method and the transit method, one can study the atmosphere of exoplanets and learn more about their internal structure. We started a large program of observations made of 40 stars hosting exoplanets and observable by VEGA/CHARA. We will measure their limb darkened diameters and derive their parameters. We also aim at better understanding stellar noise sources like spots, and study surface brightness relationships.

In this paper, we review the current performance of the VEGA/CHARA visible spectrograph and make a review of the most recent astrophysical results. The science programs take benefit of the exceptional angular resolution, the unique spectral resolution and one of the main features of CHARA: Infrared and Visible parallel operation. We also discuss recent developments concerning the tools for the preparation of observations and important features of the data reduction software. A short discussion of the future developments will complete the presentation, directed towards new detectors and possible new beam combination scheme for improved sensitivity and imaging capabilities.

Instrumentation developments at the Navy Precision Optical Interferometer (NPOI, formerly “Navy Optical Interferometer,” and “Navy Prototype Optical Interferometer”) since the last SPIE meeting in 2010 are summarized. The commissioning of new siderostat stations, progress towards the installation of four 1.8m telescopes, and other instrumentation and control systems upgrades, are reviewed.

VISION is the next generation science camera for the Navy Optical Interferometer (NOI). In comparison to the current beam combiner of NOI, VISION will deliver higher precision data products and better exibility by incorporating single mode bers for spatial ltering and by using low-noise detectors. VISION can coherently combine up to six telescope beams using an image-plane combination scheme. This results in simultaneous measurement of 15 visibility amplitudes and 10 independent closure phases that can be used to reconstruct multipixel images of stars.

This paper presents an overview of recent progress at the Sydney University Stellar Interferometer (SUSI). Development of the third-generation PAVO beam combiner has continued. The MUSCA beam combiner for high-precision differential astrometry using visible light phase referencing is under active development and will be the subject of a separate paper. Because SUSI was one of the pioneering interferometric instruments, some of its original systems are old and have become difficult to maintain. We are undertaking a campaign of modernization of systems: (1) an upgrade of the Optical Path Length Compensator IR laser metrology counter electronics from a custom system which uses an obsolete single-board computer to a modern one based on an FPGA interfaced to a Linux computer - in addition to improving maintainability, this upgrade should allow smoother motion and higher carriage speeds; (2) the replacement of the aged single-board computer local controllers for the siderostats and the longitudinal dispersion compensator has been completed; (3) the large beam reducing telescope has been replaced with a pair of smaller units with separate accessible foci. Examples of scientific results are also included.

In the course of our VLTI young stellar object PIONIER imaging program, we have identified a strong visibility chromatic dependency that appeared in certain sources. This effect, rising value of visibilities with decreasing wavelengths over one base, is also present in previous published and archival AMBER data. For Herbig AeBe stars, the H band is generally located at the transition between the star and the disk predominance in flux for Herbig AeBe stars. We believe that this phenomenon is responsible for the visibility rise effect. We present a method to correct the visibilities from this effect in order to allow "gray" image reconstruction software, like Mira, to be used. In parallel we probe the interest of carrying an image reconstruction in each spectral channel and then combine them to obtain the final broadband one. As an illustration we apply these imaging methods to MWC158, a (possibly Herbig) B[e] star intensively observed with PIONIER. Finally, we compare our result with a parametric model fitted onto the data.

The Magdalena Ridge Observatory Interferometer has been designed to be a 10 x 1.4 m aperture long-baseline optical/near-infrared interferometer in an equilateral "Y" configuration, and is being deployed west of Socorro, NM on the Magdalena Ridge. Unfortunately, first light for the facility has been delayed due to the current difficult funding regime, but during the past two years we have made substantial progress on many of the key subsystems for the array. The design of all these subsystems is largely complete, and laboratory assembly and testing, and the installation of many of its components on the Ridge are now underway. This paper serves as an overview and update on the facility's present status, and the plans for future funding and eventual operations of the facilities.

We report recent success to stabilize the VLTI/MIDI-10um beam-combiner with K-band fringe tracking, provided by PRIMA (FSU). After encouraging commissioning results, presented during the last SPIE, we accomplished in November 2011 a successful run of science demonstration. A broad range of targets were observed, from planet-hosting stars over YSO disks to AGN. We will present first results, focussing on the improvements on sensitivity and precision with respect to classical MIDI stand-alone observations. MIDI broad-band dispersion and group-delay can be reliably predicted by the fringe tracker to enable coherent integration beyond coherence time at the lambda/10 precision level.

MATISSE is a mid-infrared spectro-interferometer combining the beams of up to four Unit Telescopes or Auxiliary Telescopes of the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory. MATISSE will constitute an evolution of the two-beam interferometric instrument MIDI. New characteristics present in MATISSE will give access to the mapping and the distribution of the material, the gas and essentially the dust, in the circumstellar environments by using the mid-infrared band coverage extended to L, M and N spectral bands. The four beam combination of MATISSE provides an efficient uv-coverage: 6 visibility points are measured in one set and 4 closure phase relations which can provide aperture synthesis images in the mid-infrared spectral regime. We give an overview of the instrument including the expected performances and a view of the Science Case. We present how the instrument would be operated. The project involves the collaborations of several agencies and institutes: the Observatoire de la Côte d’Azur of Nice and the INSU-CNRS in Paris, the Max Planck Institut für Astronomie of Heidelberg; the University of Leiden and the NOVA-ASTRON Institute of Dwingeloo, the Max Planck Institut für Radioastronomie of Bonn, the Institut für Theoretische Physik und Astrophysik of Kiel, the Vienna University and the Konkoly Observatory.

The Extrasolar Planet Search with PRIMA project (ESPRI) aims at characterising and detecting extrasolar planets by measuring the host star's reflex motion using the narrow-angle astrometry capability of the PRIMA facility at the Very Large Telescope Interferometer. A first functional demonstration of the astrometric mode was achieved in early 2011. This marked the start of the astrometric commissioning phase with the purpose of characterising the instrument's performance, which ultimately has to be sufficient for exoplanet detection. We show results obtained from the observation of bright visual binary stars, which serve as test objects to determine the instrument's astrometric precision, its accuracy, and the plate scale. Finally, we report on the current status of the ESPRI project, in view of starting its scientific programme.

We report the first phased images using adaptive optics correction from the Large Binocular Telescope Interferometer. LBTI achieved first fringes in late 2010, with seeing-limited operation. Initial tests verified the feasibility of the setup and allowed us to characterize the phase variations from both the atmosphere and mechanical vibrations. Integration of the secondary-base AO systems was carried out in spring 2011 and spring 2012 for the right and left side respectively. Single aperture, diffraction-limited, operation has been commissioned and is used as a productive mode of the LBTI with the LMIRCam subsystem. We describe the initial observation for dual aperture observations and coherent imaging results.

We present an update on the LINC-NIRVANA (LN) instrument, an innovative Fizeau-mode beam combiner for the Large Binocular Telescope (LBT). LN will deliver 10 mas spatial resolution in the near infrared over a 10 arcsec field of view. In addition to optical-path-difference control, the instrument must correct a wide field of view on the sky using multi-conjugated adaptive optics. This substantially increases sky coverage for fringe tracking reference stars. Subsystem delivery and testing is almost complete, and final Assembly, Integration, and Verification are well advanced. We report on closed-loop control of a number of subsystems, including fine-tuning and optimization of the delay line. Measurement and remediation of instrument flexure are key to the success of LN. Several laboratory performance experiments demonstrate that components are within specification. With several interacting subsystems, LN faces a complexity challenge. A Pathfinder experiment at LBT will verify multiple aspects of LINC-NIRVANA and the telescope starting in winter 2012-2013. Finally, we report on efforts to prepare for early science exploitation in "LINC" mode, which uses single-conjugate adaptive optics.

Unveiling the structure of the Broad Line Region (BLR) of AGNs is critical to understand the quasar phenomenon. Resolving a few BLRs by optical interferometry will bring decisive information to confront, complement and calibrate the reverberation mapping technique, seed of the mass-luminosity relation in quasars. BLRs are much smaller than the angular resolution of the VLT and Keck interferometers and they can be resolved only by differential interferometry very accurate measurements of differential visibility and phase. The latest yields the photocenter variation with λ, and constrains the size, position and velocity law of various regions of the BLR. AGNs are below the magnitude limit for spectrally resolved interferometry set by currently available fringe trackers. A new “blind” observation method and a data processing based on the accumulation of 2D Fourier power and cross spectra permitted us the first spectrally resolved interferometric observation of a BLR, on the K=10 quasar 3C273. A careful bias analysis is still in progress, but we report strong evidence that, as the baseline increases, the differential visibility decreases in the Pa_α line. Combined with a differential phase certainly smaller than 3°, this yields an angular radius of the BLR larger than 0.4 milliarcseconds, or 1000 light days at the distance of 3C273, much larger than the reverberation mapping radius of 300 light days. Explaining the coexistence of these two different scales, and possibly structures and mechanisms, implies very new insights about the BLR of 3C273.

Since our first detection of a resolved near-infrared emission around the main sequence star Vega, which we identified as the signature of hot dust grains close to the sublimation limit, we have been systematically searching for similar signatures around a magnitude-limited sample of nearby main sequence stars with the FLUOR instrument at the CHARA array. About 40 targets with spectral types ranging from A to K have been observed within the last 6 years, leading to first statistical trends on the occurence of the bright exozodi phenomenon as a function of spectral type. Our target sample is balanced between stars known to harbour cold dust populations from space-based missions (e.g., Spitzer, Herschel) and stars without cold dust, so that the occurence of abundant hot dust can also be correlated with the presence of large reservoirs of cold planetesimals. In this paper, we present preliminary conclusions from the CHARA/FLUOR survey. We also discuss the first results obtained in 2011/2012 with the new PIONIER visiting instrument at the VLTI, which is now used to extend our survey sample to the Southern hemisphere and to fainter targets. A first measurement of the exozodi/star flux ratio as a function of wavelength within the H band is presented, thanks to the low spectral resolution capability of PIONIER. Finally, we also briefly discuss our plans for extending the survey to fainter targets in the Northern hemisphere with an upgraded version of the FLUOR beam combiner.

The CHARA Array possesses the longest baselines in the world for infrared and visible interferometry, while the Michigan Infrared Combiner (MIRC) is the most advanced beam combiner for imaging. CHARA+MIRC has allowed imaging the surfaces of rapid rotators, interacting binary stars, and magnetically-active stars all for the first time. In this presentation, I will give an overview of the discoveries made by MIRC over the past five years and discuss technical and scientific lessons learned.

Michigan InfraRed Combiner (MIRC) is a near-infrared image-plane combiner at the CHARA array which consists of six 1-m diameter telescopes with the longest baseline of 330m. MIRC was upgraded from a 4-beam to a full 6-beam combiner in July 2011, which now records interferometry data of 15 baselines and 20 triangles simultaneously. The improved snapshot UV coverage has greatly boosted the ability for imaging complicated targets such as the asymmetry of circumstellar disks, interacting binaries and the surfaces of spotted stars. In addition, the Photometric Channels subsystem, which directly measures the real time flux of individual beams, has been upgraded to increase the light throughput to improve the visibility and closure phase calibration. The system sensitivity has been improved as well to allow fainter objects such as Young Stellar Objects (YSOs) to be observable with MIRC for the first time. Our presentation will conclude with first preliminary results of imaging two Be binaries observed by the upgraded MIRC.

For information-rich direct images at high resolution, hypertelescopes combine light from a sparse array of many subapertures, using pupil densification. Among the possible architectures, the Arecibo-like spherical class has fixed mirrors arrayed as elements of a common spherical locus, matching approximately the natural curvature of a crater or valley. A focal gondola suspended on the focal sphere, is tracking the primary star image, and several more can be added for independent observations of di.erent sources. Since no delay lines are needed, hundred of mirrors can be used for reaching the theoretical information gain with respect to fewer apertures. The aperture size of such instruments may range from 50 to perhaps 1200m at available terrestrial sites. As an example of their broad science capabilities, we have simulated the resolved and spectro-imaging- of an exoplanet transiting across the disk of its parent star, achievable with adaptive optics. Faint cosmological sources may also become observable if a Laser Guide Star can be fitted. We describe the current construction and in situ opto-mechanical testing of a 57m hypertelescope, later expandable to 200 with 100 or more sub-apertures. The preliminary operating experience gained in a year, without stellar fringes yet, indicates the likely feasibility of larger versions at suitable sites. Labeyrie et al., (this conference) discuss an "Extremely Large Hypertelescope" (ELHyT) having 1200m sparse aperture and, at similar cost, a larger collection area and higher limiting magnitude than a 40m ELT.

The hypertelescope construction initiated in the Southern Alps (Labeyrie et al., this conference) has provided some preliminary operating experience indicating that larger versions, up to perhaps 1200m, are probably feasible at suitable sites. The Arecibo-like architecture of such instruments does not require the large mount and dome which dominate the cost of a 40m ELT. For the same cost, an "Extremely Large Hyper Telescope” ( ELHyT) may therefore have a larger collecting area. It may thus in principle reach higher limiting magnitudes, both for seeing-limited and, if equipped with a Laser Guide Star and adaptive phasing, for high-resolution imaging with gain as the size ratio, i.e. about 30 with respect to a 40m ELT. Like the radio arrays of antennas, such instruments can be grown progressively. Also, they can be up-graded with several focal gondolas, independently tracking different sources. Candidate sites have been identified in the Himalaya and the Andes. We describe several design options and compare the science achievable for both instruments, ELTs and ELHyTs. The broad science addressed by an ELHyT covers stellar chromospheres, transiting exoplanets and those requiring a high dynamic range, achieved by array apodization or coronagraphy. With a Laser Guide Star, it extends to faint compact sources beyond the limits of telescopes having a smaller collecting area, supernovae, active galactic nuclei, gamma ray bursts. The sparse content of remote galaxies seen in the Hubble Deep Field appears compatible with the crowding limitations of an ELHyT having 1000 apertures.

GAME is a recent concept for a small/medium class mission aimed at Fundamental Physics tests in the Solar system, by means of an optimised instrument in the visible, based on smart combination of coronagraphy and Fizeau interferometry. The targeted precision on the γ and β parameters of the Parametrised Post-Newtonian formulation of General Relativity are respectively in the 10^-7-10^-8 and 10^-5-10^-6 range, improving by one or two orders of magnitude with respect to the expectations on current or near future experiments. Such precision is suitable to detect possible deviations from the unity value, associated to generalised Einstein models for gravitation, with potentially huge impacts on the cosmological distribution of dark matter and dark energy from a Solar system scale experiment. The measurement principle is based on the differential astrometric signature on the stellar positions, i.e. based on the spatial component of the effect rather than the temporal component as in the most recent experiments using radio link delay timing variation (Cassini). The instrument concept is based on multiple field, multiple aperture Fizeau interferometry, observing simultaneously regions close to the Solar limb (requiring the adoption of coronagraphic techniques), and others in opposition to the Sun. The diluted optics approach is selected for achieving an efficient rejection of the scattered solar radiation, while retaining an acceptable angular resolution on the science targets. The multiple field observation is aimed at cost-effective control of systematic effects through simultaneous calibration. We describe the science motivation, the proposed mission profile, the instrument concept and the expected performance.

We have built at the Haute-Provence observatory (France) the rst diluted telescope in the world. We describe this prototype called Carlina, made of three 25 cm mirrors separated by a maximum baseline of 10.5 m. The three mirrors in place are already coherenced and rst light is scheduled for June-July 2012. In this article, we will mainly describe the focal gondola. We propose to build in the near future a 100 m aperture Large Diluted Telescope. This diluted telescope will be more sensitive than regular interferometers (Keck, VLTI, etc.), with higher imaging capabilities. A LDT will open new elds of research in astrophysics thanks to very high angular resolution imaging of the surface of supergiant stars, AGN, gravitational micro-lens systems, exo-planets, etc.

This article reports the advances on the development of mid-infrared integrated optics for stellar interferometry. The devices are fabricated by laser writing techniques on chalcogenide glasses. Laboratory characterizaton is reported and analyzed.

We present the experimental results of a 3D photonic component designed for the determination of coherence properties of astronomical targets in optical interferometry. The component is based on the properties of two dimensional arrays of evanescently coupled waveguides and has the potential of being scalable to arbitrary large arrays of telescopes. Simulations and rst experimental results will be presented together with perspectives for implementation of future instruments combining multiple telescopes.

In this communication an extraction procedure that takes into account the spectral dispersion function (the spectral analog of the PSF) is presented. The method is named least-squares deconvolution. It allows the recovery of the relative line-to-continuum visibility amplitude ratio and the relative line to continuum visibility phase difference. The method only uses as input the AMBER data making the sole hypotheses that the spectral broadening of the spectra in the photometric channel is the same as that of the interferometric data. A subset of this hypothesis is the case of unresolved lines. It is extremely robust being able to recover line to continuum visibility and phase at very low signal-to-noise ratio. It is shown that it is superior to other differential visibility and phase methods presented in the literature, which in certain conditions are biased. The method can be trivially generalized to similar instruments as those available at CHARA and Keck-I. Least squares deconvolution opens the possibility of delivering legacy quality measurements from the AMBER archive without relying on visibility calibration or environmental effects such as vibrations. It is a key tool for the astrophysical exploitation of this instrument.

Optical Interferometry has long been limited by low SNR making it nearly impossible to measure the small visibilities required to make resolved images. Although the SNR exists in the raw data, much SNR is lost in the conventional squared-visibility processing. In modern interferometers fringes are recorded simultaneously at many wavelengths and baselines. This makes phase-referencing possible, which is the key to coherent integration, which in turns can greatly improve the SNR of measurements, making small-amplitude resolving measurements possible. In this paper we will detail the theory of coherent integration. We will also explain why coherent integration should, in most cases, be carried out during post-processing in software rather than in real-time in hardware. We will then compare it to conventional processing approaches for some data from the Navy Optical Interferometer. We will demonstrate how coherent integration can improve the accuracy of observations.

We developed the tool GEM-FIND that allows to constrain the morphology and brightness distribution of ob- jects. The software fits geometrical models to spectrally dispersed interferometric visibility measurements in the N-band using the Levenberg-Marquardt minimization method. Each geometrical model describes the bright- ness distribution of the object in the Fourier space using a set of wavelength-independent and/or wavelength- dependent parameters. In this contribution we numerically analyze the stability of our nonlinear fitting approach by applying it to sets of synthetic visibilities with statistically applied errors, answering the following questions: How stable is the parameter determination with respect to (i) the number of uv-points, (ii) the distribution of points in the uv-plane, (iii) the noise level of the observations?

We present here three recipes for getting better images with optical interferometers. Two of them, Low- Frequencies Filling and Brute-Force Monte Carlo were used in our participation to the Interferometry Beauty Contest this year and can be applied to classical imaging using V² and closure phases. These two addition to image reconstruction provide a way of having more reliable images. The last recipe is similar in its principle as the self-calibration technique used in radio-interferometry. We call it also self-calibration, but it uses the wavelength-differential phase as a proxy of the object phase to build-up a full-featured complex visibility set of the observed object. This technique needs a first image-reconstruction run with an available software, using closure-phases and squared visibilities only. We used it for two scientific papers with great success. We discuss here the pros and cons of such imaging technique.

Optical interferometers provide multiple wavelength measurements. In order to fully exploit the spectral and spatial resolution of these instruments, new algorithms for image reconstruction have to be developed. Early attempts to deal with multi-chromatic interferometric data have consisted in recovering a gray image of the object or independent monochromatic images in some spectral bandwidths. The main challenge is now to recover the full 3-D (spatio-spectral) brightness distribution of the astronomical target given all the available data. We describe a new approach to implement multi-wavelength image reconstruction in the case where the observed scene is a collection of point-like sources. We show the gain in image quality (both spatially and spectrally) achieved by globally taking into account all the data instead of dealing with independent spectral slices. This is achieved thanks to a regularization which favors spatially sparsity and spectral grouping of the sources. Since the objective function is not dierentiable, we had to develop a specialized optimization algorithm which also takes into account the non-negativity of the brightness distribution.

We report on our progress toward a flexible image reconstruction software for optical interferometry capable of "5D imaging" of stellar surfaces. 5D imaging is here defined as the capability to image directly one or several stars in three dimensions, with both the time and wavelength dependencies taken into account during the reconstruction process. Our algorithm makes use of the Healpix (Gorski et al., 2005) sphere partition scheme to tesselate the stellar surface, 3D Open Graphics Language (OpenGL) to model the spheroid geometry, and the Open Compute Language (OpenCL) framework for all other computations. We use the Monte Carlo Markov Chain software SQUEEZE to solve the image reconstruction problem on the surfaces of these stars. Finally, the Compressed Sensing and Bayesian Evidence paradigms are employed to determine the best regularization for spotted stars. Our algorithm makes use of the Healpix (reference needed) sphere partition scheme to tesselate the stellar surface, 3D Open Graphics Language (OpenGL) to model the spheroid, and the Open Compute Language (OpenCL) framework to model the Roche gravitational potential equation.

We present the results of the fifth Interferometric Imaging Beauty Contest. The contest consists in blind imaging of test data sets derived from model sources and distributed in the OIFITS format. Two scenarios of imaging with CHARA/MIRC-6T were offered for reconstruction: imaging a T Tauri disc and imaging a spotted red supergiant. There were eight different teams competing this time: Monnier with the software package MACIM; Hofmann, Schertl and Weigelt with IRS; Thiebaut and Soulez with MiRA ; Young with BSMEM; Mary and Vannier with MIROIRS; Millour and Vannier with independent BSMEM and MiRA entries; Rengaswamy with an original method; and Elias with the radio-astronomy package CASA. The contest model images, the data delivered to the contestants and the rules are described as well as the results of the image reconstruction obtained by each method. These results are discussed as well as the strengths and limitations of each algorithm.

The super-massive 4 million solar mass black hole (SMBH) SgrA* shows variable emission from the millimeter to the X-ray domain. A detailed analysis of the infrared light curves allows us to address the accretion phenomenon in a statistical way. The analysis shows that the near-infrared flux density excursions are dominated by a single state power law, with the low states of SgrA* are limited by confusion through the unresolved stellar background. We show that for 8-10m class telescopes blending effects along the line of sight will result in artificial compact star-like objects of 0.5-1 mJy that last for about 3-4 years. We discuss how the imaging capabilities of GRAVITY at the VLTI, LINC-NIRVANA at the LBT and METIS at the E-ELT will contribute to the investigation of the low variability states of SgrA*.

The VLTI/MIDI AGN Large Programme comprises 14 AGNs for which torus properties are being determined. Observations and data reduction are finished and show resolved dust emission in almost all of the sources. Questions addressed with this programme range from unification to the physics of accreting galactic nuclei. In particular, the observations allow us to dissect the parsec-scale infrared emission and to determine the sizes and fluxes of the various components. These AGNs are among the faintest objects ever studied with MIDI and require the data reduction software to be adjusted.

Latest-generation spectro-interferometric instruments combine a milliarcsecond angular resolution with spectral capabilities, resulting in an immensely increased information content. Here, I present methodological work and results that illustrate the fundamentally new scientific insights provided by spectro-interferometry with very high spectral dispersion or in multiple line transitions (Brackett and Pfund lines). In addition, I discuss some pitfalls in the interpretation of spectro-interferometric data. In the context of our recent studies on the classical Be stars β CMi and ζ Tau, I present the first position-velocity diagram obtained with optical interferometry and provide a physical interpretation for a phase inversion, which has in the meantime been observed for several classical Be-stars. In the course of our study on the Herbig B[e] star V921 Sco, we combined, for the first time, spectro-interferometry and spectro-astrometry, providing a powerful and resource-efficient way to constrain the spatial distribution as well as the kinematics of the circumstellar gas with an unprecedented velocity resolution up to R = λ/Δλ = 100,000. Finally, I discuss our phase sign calibration procedure, which has allowed us to calibrate AMBER differential phases and closure phases for all spectral modes, and derive from the gained experience science-driven requirements for future instrumentation projects.