Karim Agabi

AMBER: the near-infrared focal instrument for the Very Large Telescope Interferometer

AMBER is a focal instrument for the Very Large Telescope Interferometer working in the near infrared from 1.1 to 2.4 micrometers . It has been designed having in mind the General User of interferometric observations and the full range of his possible astrophysical programs. However the three programs used to define the key specifications have been the study of Young Stellar Objects, the study of Active Galactic Nuclei dust tori and broad line regions and the measure of masses and spectra of hot Extra Solar Planets. AMBER combines up to three beams produced by the VLTI 8 m Unit Telescopes equipped with Adaptive Optics and/or by the 1.8 m Auxiliary Telescopes. The fringes are dispersed with resolutions ranging from 35 to 10000. It is optimized for high accuracy single mode measurements of the absolute visibility, of the variation of the visibility and phase with wavelength (differential interferometry) and of phase closure relations with three telescopes. The instrument and its software are designed to allow a highly automated user friendly operation and an easy maintenance.

KEOPS: Kiloparsec Explorer for Optical Planet Search, a direct-imaging optical array at Dome C of Antarctica

Recent site seeing testing campaigns conducted by our team from University of Nice1 show that Dome C represents the best site on Earth for astronomical high angular resolution (HAR) observations at optical and IR wavelengths. The dramatic gain over relevant HAR parameters r0, L0, θ0 and τ0, added to very low temperatures during the polar winter nights (-70°C), the dry atmosphere and the possibility of continuous observations during several nights make Dome C the ideal site for deploying a kilometric optical interferometer before the 2015 horizon. Here we describe the concept of Kiloparsec Explorer for Optical Planet Search (KEOPS) that is studied by our group at LUAN. KEOPS is an interferometric array of 36 off-axis telescopes, each 1.5m in diameter. Its kilometric baselines open sub-mas snap-shot imaging possibilities to detect and characterize extra-solar planetary systems, especially exo-Earths out to 300 parsecs from the visible to the thermal IR. KEOPS can be considered as a DARWIN/TPF challenger but at a much lower cost.

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

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.

Opening a new window on the southern stars for less money: PAIX the first Antarctica polar mission photometer

In this invited paper, we implement a new way to study the stellar oscillations, pulsations and their evolutionary properties with long uninterrupted and continuous precision observations over 150 days from the ground, and without the regular interruptions imposed by the earth rotation. PAIX–First Robotic Antarctica Polar Mission– gives a new insight to cope with unresolved stellar enigma and stellar oscillation challenges and offers a great opportunity to benefit from an access to the best astronomical site on Earth –DomeC–. The project is made of low cost commercial components, and achieves astrophysical measurement time-series of stellar physics fields, challenging photometry from space that shows large gaps in terms of flexibility during the observing runs, the choice of targets, the repair of failures and the inexorable high costs. PAIX has yet more advantages than space missions in observing in UBV RI bands and then collecting unprecedented simultaneous multicolor light curves of several targets. We give a brief history of the Astronomy in Antarctica and describe the first polar robotized mission PAIX and the outcome of stellar physics from the heart of Antarctica during several polar nights. We briefly discuss our first results and perspectives on the pulsating stars and its evolution from Antarctica, especially the connection between temporal hydrodynamic phenomena and cyclic modulations. Finally, we highlight the impact of PAIX on the stellar physics study and the remaining challenges to successfully accomplish the Universe explorations under extreme conditions.

AMBER: a near infrared focal instrument for the VLTI

AMBER is the General User near-infrared focal instrument of the Very Large Telescope interferometer. Its specifications are based on three key programs on Young Stellar Objects, Active Galactic Nuclei central regions, masses and spectra of hot Extra Solar Planets. It has an imaging capacity because it combines up to three beams and very high accuracy measurement are expected from the spatial filtering of beams by single mode fibers and the comparison of measurements made simultaneously in different spectral channels.

Time domain astronomy from Dome C: results from ASTEP

ASTEP (Antarctic Search for Transiting Exo Planets) is a research program funded mainly by French ANR grants and by the French Polar Institute (IPEV), dedicated to the photometric study of exoplanetary transits from Antarctica. The preliminary “pathfinder” instrument ASTEP–South is described in another communication (Crouzet et al., these proceedings), and we focus in this presentation on the main instrument of the ASTEP program : “ASTEP–400”, a 40 cm robotized and thermally-controlled photometric telescope operated from the French-Italian Concordia station (Dome C, Antarctica). ASTEP–400 has been installed at Concordia during the 2009-2010 summer campaign. Since, the telescope has been operated in nominal conditions during 2010 and 2011 winters, and the 2012 winterover is presently in progress. Data from the first two winter campaigns are available and processed. We give a description of the ASTEP–400 telescope from the mechanical, optical and thermal point of view. Control and software issues are also addressed. We end with a discussion of some astronomical results obtained with ASTEP–400.

The LUCAS program: detecting vegetation and traces of life in the Earthshine

The aim of the LUCAS program is to observe chlorophyll and atmospheric molecules in the Earthshine spectrum in order to prepare the detection of life in terrestrial extrasolar planets to be discovered. Actually, observations from Antarctica offer a unique possibility to study the variations of Earthshine spectrum during Earth rotation while various parts of Earth are facing the Moon. Special instrumentation for the LUCAS program was designed and put in the Concordia station in the Dome C. Observations are in progress.

Multi-aperture interferometry at Concordia

2. KEOPS – the concept The DomeC site astronomical qualities begin to be well bracketed. After several summers and now almost two winter-over site testing campaigns, it is clear that it is, for many astronomical parameters, the best, or one of the very best sites on Earth. Some of these parameters still demand additional investigation or more statistics. But the global quality has been proved to be enough out of range for attracting an ever increasing scientific community. French and Italian funding has started to be raised, so that beyond the site testing, real astronomical programmes are expected to be operated in 2008 (IRAIT from Italy and A-STEP from France). On the longer term range, medium and far infrared imaging on one hand, and on the other hand Extremely High Resolution Imaging even in visible light are among the favorite targets in the prospect studies. Some are thinking of an Antarctic ELT, to be set above the 30-m turbulent surface boundary layer, others would prefer an multi mirror interferometer. Such an interferometer, that could be called an optical equivalent to the VLA in radio waves or ALMA in millimetric, can possibly be regarded as the next generation, post-VLTI, of large size optical interferometry. Of course, optical long baseline imaging interferometry is extremely difficult, as the technical challenges go more or less as the inverse of the wavelength, and that means a factor 100 to 1000 for optical or near-IR as compared to the millimetric case of ALMA. However and to some extent, it can now be regarded as a mature observing technique. Several optical arrays are able to provide 2-D maps: NPOI in Arizona, COAST at Cambridge, UK, CHARA at Mount Wilson, California and of course the VLTI at Paranal, Chile. At the 2004 Liege International Astrophysical Colloquium devoted to the Science case for next generation optical/infrared interferometric facilities (the post-VLTI era), it was recognised by Pierre Lena that on one hand “the next interferometer generation should operate at least from 1 to 12μm and have kilometric baselines (1 to 10 km at most)”, and on the other hand “the Dome C site characteristics, as far as they are known today, appear to be of an entirely different class than any other ground-based site: in fact, this site classifies as an intermediate one between space and conventional ground.

CORONA: progress report on the Dome C prototype APKC coronagraph

We outline the concept and laboratory results of our coronagraphic testbed which has been shipped on automn 2005 to Dome C in Antarctica. We also describe the principle of our coronagraph achromatization and the laboratory first data like the coronographic nulling results which attain more than 103 at least. The future development of our experiment for a much larger telescope is also outlined. We finally present CORONAs on-sky first results.