Dome C site testing: surface layer, free atmosphere seeing and isoplanatic angle statistics

This paper analyses 3.5 years of site testing data obtained at Dome C, Antarctica, based on measurements obtained with three DIMMs located at three different elevations. Basic statistics of the seeing and the isoplanatic angle are given, as well as the characteristic time of temporal fluctuations of these two parameters, which we found to around 30 minutes at 8 m. The 3 DIMMs are exploited as a profiler of the surface layer, and provide a robust estimation of its statistical properties. It appears to have a very sharp upper limit (less than 1 m). The fraction of time spent by each telescope above the top of the surface layer permits us to deduce a median height of between 23 m and 27 m. The comparison of the different data sets led us to infer the statistical properties of the free atmosphere seeing, with a median value of 0.36 arcsec. The C_n^2 profile inside the surface layer is also deduced from the seeing data obtained during the fraction of time spent by the 3 telescopes inside this turbulence. Statistically, the surface layer, except during the 3-month summer season, contributes to 95 percent of the total turbulence from the surface level, thus confirming the exceptional quality of the site above it

First whole atmosphere night-time seeing measurements at Dome C, Antarctica

We report site testing results obtained in night-time during the polar autumn and winter at Dome C. These results were collected during the first Concordia winterover by A. Agabi. They are based upon seeing and isoplanatic angle monitoring, as well as in-situ balloon measurements 2 of the refractive index structure constant profiles Cn (h). Atmosphere is divided into two regions: (i) a 36 m high surface layer responsible of 87% of the turbulence and (ii) a very stable free atmosphere above with a median seeing of 0.36+-0.19 arcsec at an elevation of h = 30 m. The median seeing measured with a DIMM placed on top of a 8.5 m high tower is 1.3+-0.8 arcsec.Comment: accepted for publication in PASP (oct 2005

The Fresnel Diffraction: A Story of Light and Darkness

This book is a collection of 19 articles which reflect the courses given at the Collège de France/Summer school “Reconstruction d'images − Applications astrophysiques“ held in Nice and Fréjus, France, from June 18 to 22, 2012. The articles presented in this volume address emerging concepts and methods that are useful in the complex process of improving our knowledge of the celestial objects, including Earth

Nulling interferometry: performance comparison between Antarctica and other ground-based sites

Detecting the presence of circumstellar dust around nearby solar-type main sequence stars is an important pre-requisite for the design of future life-finding space missions such as ESA's Darwin or NASA's Terrestrial Planet Finder (TPF). The high Antarctic plateau may provide appropriate conditions to perform such a survey from the ground. We investigate the performance of a nulling interferometer optimised for the detection of exozodiacal discs at Dome C, on the high Antarctic plateau, and compare it to the expected performance of similar instruments at temperate sites. Based on the currently available measurements of the turbulence characteristics at Dome C, we adapt the GENIEsim software (Absil et al. 2006, A&A 448) to simulate the performance of a nulling interferometer on the high Antarctic plateau. To feed a realistic instrumental configuration into the simulator, we propose a conceptual design for ALADDIN, the Antarctic L-band Astrophysics Discovery Demonstrator for Interferometric Nulling. We assume that this instrument can be placed above the 30-m high boundary layer, where most of the atmospheric turbulence originates. We show that an optimised nulling interferometer operating on a pair of 1-m class telescopes located 30 m above the ground could achieve a better sensitivity than a similar instrument working with two 8-m class telescopes at a temperate site such as Cerro Paranal. The detection of circumstellar discs about 20 times as dense as our local zodiacal cloud seems within reach for typical Darwin/TPF targets in a integration time of a few hours. Moreover, the exceptional turbulence conditions significantly relax the requirements on real-time control loops, which has favourable consequences on the feasibility of the nulling instrument.Comment: 10 pages, accepted for publication in A&

Eléments orbitaux d'étoiles doubles: ADS 10279 etADS 16650

Nous présentons de nouveaux éléments orbitaux pour les étoiles doubles visuelles ADS 10279 et 16650. Ces éléments ont été obtenus en utilisant les dernières mesures que nous avons effectuées avec le tavelographe PISCO et le télescope Bernard Lyot de 2 m du Pic du Midi, et celles déjà disponibles dans la littérature

Eléments orbitaux d'étoiles doubles: ADS 7307 et ADS 17030

Nous présentons de nouveaux éléments orbitaux pour les étoiles doubles visuelles ADS 7307 et 17030. Ces éléments ont été obtenus en utilisant les dernières mesures que nous avons effectuées avec le tavelographe PISCO et le télescope Bernard Lyot de 2 m du Pic du Midi, et celles déjà disponibles dans la littérature