Alain Blazit

ASTEP South: an Antarctic Search for Transiting ExoPlanets around the celestial south pole

Context. The Concordia base in Dome C, Antarctica, is an extremely promising site for photometric astronomy due to the 3-month long night during the Antarctic winter, favorable weather conditions, and low scintillation. Aims. The ASTEP project (Antarctic Search for Transiting ExoPlanets) is a pilot project to discover transiting planets and understand the limits of visible photometry from the Concordia site. Methods. ASTEP South is the first phase of the ASTEP project. The instrument is a fixed 10 cm refractor with a 4k × 4k CCD camera in a thermalized box, pointing continuously a 3.88 × 3.88° 2 field of view centered on the celestial south pole. We describe the project and report results of a preliminary data analysis. Results. ASTEP South became fully functional in June 2008 and obtained 1592 hours of data during the 2008 Antarctic winter. The data are of good quality but the analysis has to account for changes in the PSF (point spread function) due to rapid ground seeing variations and instrumental effects. The pointing direction is stable within 10 arcsec on a daily timescale and drifts by only 34 arcsec in 50 days. A truly continuous photometry of bright stars is possible in June (the noon sky background peaks at a magnitude R ≈ 15 arcsec -2 on June 22), but becomes challenging in July (the noon sky background magnitude is R ≈ 12.5 arcsec -2 on July 20). The weather conditions are estimated from the number of stars detected in the field. For the 2008 winter, the statistics are between 56.3% and 68.4% of excellent weather, 17.9% to 30% of veiled weather (when the probable presence of thin clouds implies a lower number of detected stars) and 13.7% of bad weather. Using these results in a probabilistic analysis of transit detection, we show that the detection efficiency of transiting exoplanets in one given field is improved at Dome C compared to a temperate site such as La Silla. For example we estimate that a year-long campaign of 10 cm refractor could reach an efficiency of 69% at Dome C versus 45% at La Silla for detecting 2-day period giant planets around target stars from magnitude 10 to 15. The detection efficiency decreases for planets with longer orbital periods, but in relative sense it is even more favorable to Dome C. Conclusions. This shows the high potential of Dome C for photometry and future planet discoveries.

New generation photon-counting cameras: algol and CPNG

Algol and Comptage de Photons Nouvelle Génération (CPNG) are new generation photon counting cameras developed for high angular resolution in the visible by means of optical aperture synthesis and speckle interferometry and for photon noise limited fast imaging of biological targets. They are intensified CCDs. They have been built to benefit from improvements in photonic commercial components, sensitivity, and personal computer workstations processing power. We present how we achieve optimal performances (sensitivity and spatiotemporal resolution) by the combination of proper optical and electronics design, and real-time elaborated data processing. The number of pixels is 532 x 516 and 1024(2) read at a frame rate of 262 and 100 Hz for CPNG and Algol, respectively. The dark current is very low: 5.5 x 10(-4) e(-) .pixel(-1). s(-1). The saturation flux is approximately 7 photon events /pixel/s. Quantum efficiencies reach up to 36% and 26% in the visible with the GaAsP photocathodes and in the red with the GaAs ones, respectively, thanks to the sensitivity of the photocathodes and to the photon centroiding algorithm; they are likely the highest values reported for intensified CCDs.

Status report on the GI2T interferometer

The GI2T interferometer has been recently equipped with a new beam combiner called REGAIN, including a dedicated visible spectrograph for enhanced spectral capabilities. The control system, the fringe tracking processor, the photon counting detectors as well as the data reduction pipeline have been refurbished or changed. After a long phase of qualification, the whole system is now ready for scientific operations. We will describe the main new features of the system.

GI2T/REGAIN interferometer

This paper presents the optical layout of the REGAIN beam combiner including the optical delay line LAROCA with its variable curvature mirror, the field rotator devices, the image and pupil tracking systems and the dedicated visible spectrography. Preliminary studies of foreseen improvements, such as adaptive optics, IR spectrograph and addition of a third telescope, will be discussed.

The GI2T/REGAIN interferometer

Abstract After five years of development, the REGAIN project has obtained its first light during summer 1999. The main goals were improving the quality and quantity of data through a complete re-designing and re-building of the central beam combiner. The REGAIN interferometric bonnette delivers two coherent foci, one at visible wavelengths and one in the IR bands (J, H and K). The visible focus is equipped with a dedicated visible spectrograph and two photon counting detectors. The infrared focus can be equipped with different instruments. The main technical issues that have been chosen will be discussed here.

CPng: a high sensitivity photon-counting camera

CPng is a photon-counting camera currently under final development at Observatoire de Lyon, France and Observatoire de la Cote d Azur, France. Its goal is to provide quantum efficiency as high as possible at visible wavelengths up to 30-35 %under very low light level conditions and with a very short exposure time, approximately 4ms. Five CPng devices are under construction for astronomical and bio-medical imaging.

Application of adaptive optics to the GI2T/REGAIN interferometer

The GI2T is a multi-speckle Michelson stellar interferometer of two 1.5 m telescopes operating in the visible and near infrared wavelengths. The REGAIN project (REcombinateur du GrAnd INterferometre) which consists of the renewal of the whole instrument is now nearly completed and the next step of the developments on GI2T will be the implantation of adaptive optics systems in each interferometric arm. In this paper we show that the data reduction methods of speckle interferometry that have been applied to the GI2T under pure turbulence, are also valid when the images are partially corrected by adaptive optics. Some simulation results show the expected performances in terms of signal-to-noise ratio for typical observation conditions. We also tackle the problem of piston control by a bimorph deformable mirror. The last section presents instrumental aspects of the foreseen AO system and the current status of the integration of the first wavefront sensor.

First tests for a low-cost curvature-oriented AO

Since a few years we are developing a low cost adaptive optics system for the GI2T optical interferometer. Our AO is based on a curvature sensor and a 31 actuator bimorphe mirror. We designed a wavefront sensor using an array of prisms to split the pupil image and photon counting avalanche photodiodes modules as detectors. We present here the design and the first results obtained on a test bench. This AO system will be used for the tests of a laser guide star and for observations of stars and asteroids. Latter, another system will be built to equip GI2T-Regain with two AO.