Abdelkrim Agabi

First Whole Atmosphere Nighttime Seeing Measurements at Dome C, Antarctica

ABSTRACT We report site‐testing results obtained in the nighttime during the polar autumn and winter at Dome C. These results were collected during the first Concordia winterover by A. Agabi. They are based on seeing and isoplanatic angle monitoring, as well as in situ balloon measurements of the refractive index structure constant profiles documentclass{aastex} usepackage{amsbsy} usepackage{amsfonts} usepackage{amssymb} usepackage{bm} usepackage{mathrsfs} usepackage{pifont} usepackage{stmaryrd} usepackage{textcomp} usepackage{portland,xspace} usepackage{amsmath,amsxtra} usepackage[OT2,OT1]{fontenc} newcommandcyr{ renewcommandrmdefault{wncyr} renewcommandsfdefault{wncyss} renewcommandencodingdefault{OT2} normalfont selectfont} DeclareTextFontCommand{textcyr}{cyr} pagestyle{empty} DeclareMathSizes{10}{9}{7}{6} begin{document} landscape

Theoretical spatiotemporal analysis of angle of arrival induced by atmospheric turbulence as observed with the grating scale monitor experiment

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ASTEP 400: a telescope designed for exoplanet transit detection from Dome C, Antarctica

end{document} . Atmosphere is divided into two regions: (1) a 36 m high surface layer responsible for 87% of the turbulence, a...

Optimized spectral bandwidth in high angular resolution imaging effect of a finite spatial-coherence outer scale

Theoretical investigations of the statistical properties of the wave frontnperturbed by atmospheric turbulence are presented. They are deduced from thencalculation of the two-dimensional spatial covariance and the temporal crossnspectrum of the angle-of-arrival fluctuations with a finite outer scale overna pair of circular pupils as in the case of the grating scale monitor or anynother Shack–Hartmann-type sensor. Both calculations lead to integralnexpressions that are numerically evaluated and hold for any baseline vectornin the mean wave-front plane. It is proposed to retrieve the wave-front outernscale L0 from estimations ofnthis two-dimensional spatial covariance, normalized by the angle-of-arrivalnstructure function. To eliminate instrument vibration errors, the covariancenand the structure function are estimated from measurements obtained by mechanicallynindependent and mechanically coupled devices, respectively. The angle-of-arrivalntemporal cross spectrum is calculated for any mean wind velocity vector. Itnis shown that the baseline component in the mean wind direction affects thenphase of the angle-of-arrival temporal cross spectrum, whereas the componentnin the perpendicular direction affects the modulus. From simultaneous measurementsnof the phase of the angle-of-arrival temporal cross spectrum obtained withntwo nonparallel baselines, one can calculate the mean wind speed and direction,nwhich allows estimation of the coherence time for techniques of optical observationnat high angular resolution through the atmosphere.

Estimation of the spatial-coherence inner scale of the wavefronts perturbed by the atmospheric turbulence from first order angle-of-arrival statistics

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. The ASTEP project (Antarctic Search for Transiting ExoPlanets) is a pilot project which seeks to identify transiting planets and understand the limits of visible photometry from this site. ASTEP 400 is an optical 40cm telescope with a field of view of 1° x 1°. The expected photometric sensitivity is 1E-3, per hour for at least 1,000 stars. The optical design guarantees high homogeneity of the PSF sizes in the field of view. The use of carbon fibers in the telescope structure guarantees high stability. The focal optics and the detectors are enclosed in a thermally regulated box which withstands extremely low temperatures. The telescope designed to run at -80°C (-110°F) was set up at Dome C during the southern summer 2009- 2010. It began its nightly observations in March 2010.

ASTEP South: A first photometric analysis

In the case of high angular resolution techniques (speckle interferometry, long baseline Michelson interferometry), one has studied how varies the signal-to-noise ratio (SNR) in terms of the spectral bandwidth Δλ. For values of Δλ varying from 0 up to 100 nanometers, it is shown that the SNR, contrary to the predictions, has no maximum value. In addition, in the case of the high frequency approximation, the effects of a finite spatial-coherence outer scale, the influence of the turbulence model used and of the “optical energy” of the turbulence on the optimal spectral bandwidth have been analyzed and discussed.

Optical turbulence and outer scales above Dome C in Antarctica

The variance of the angle-of-arrival fluctuations is theoretically calculated taking into account the effects of limit scales for the spatial coherence of the wavefronts perturbed by an atmospheric turbulence described by the Von Karman model. A technique is proposed allowing the estimation of the spatial-coherence inner scale from measurements of the angle-of-arrival fluctuations (variance) with and without spatio-angular filterings. In order to support the theoretical study, a numerical simulation is performed. In addition the possibility to use in situ measurements has been evaluated introducing the vertical turbulence profiles, in the theory. A method is presented allowing, by means of spatial filters with linear amplitude transmittance, the observation of the angle-of-arrival fluctuations without spatial filtering, and afterwards an experimental concept is derived. Finally, the influence of the model used to describe atmospheric turbulence is discussed.

G.S.M.: a Grating Scale Monitor for atmospheric turbulence measurements. I. The instrument and first results of angle of arrival measurements.

The ASTEP project aims at detecting and characterizing transiting planets from Dome C, Antarctica, and qualifying this site for photometry in the visible. The first phase of the project, ASTEP South, is a fixed 10 cm diameter instrument pointing continuously towards the celestial South pole. Observations were made almost continuously during 4 winters, from 2008 to 2011. The point-to-point RMS of 1-day photometric lightcurves can be explained by a combination of expected statistical noises, dominated by the photon noise up to magnitude 14. This RMS is large, from 2.5 mmag at R=8 to 6% at R=14, because of the small size of ASTEP South and the short exposure time (30 s). Statistical noises should be considerably reduced using the large amount of collected data. A 9.9-day period eclipsing binary is detected, with a magnitude R=9.85. The 2-season lightcurve folded in phase and binned into 1000 points has a RMS of 1.09 mmag, for an expected photon noise of 0.29 mmag. The use of the 4 seasons of data with a better detrending algorithm should yield a sub-millimagnitude precision for this folded lightcurve. Radial velocity follow-up observations are conducted and reveal a F-M binary system. The detection of this 9.9-day period system with a small instrument such as ASTEP South and the precision of the folded lightcurve show the quality of Dome C for continuous photometric observations, and its potential for the detection of planets with orbital period longer than those usually detected from the ground.

KEOPS: towards exo-Earths from Dome C of Antarctica

Dome C in Antarctica is a particular astronomical site when considering the optical turbulence conditions. From the first winterover campaign performed in 2005 at Dome C, the set of 34 meteorological balloon profiles has been analyzed. The meteorological balloons were equipped with microthermal sensors used to sense the vertical profile of the optical turbulence intensity C2n. The C2n median profile, mean temperature and mean horizontal wind speed are given. The C2n median profile is characterized by a very strong and thin turbulent surface layer. The surface layer height is defined. The median outer scale profile at Dome C is computed using the Tatarski definition. The von Karman outer scale is also deduced. The integrated parameters as Fried parameter r0, coherence time τ0, isoplanatic angle θ0 and the spatial-coherence outer scale L0 used to define astronomical site quality, are computed at 8 m above the ground and above the turbulent surface layer.