Francois Martin

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

Contribution to the space-time study of stellar speckle patterns

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Measurements of the wavefront outer scale at Paranal: influence of this parameter in interferometry

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

WIMPs and solar evolution code

The temporal behavior of stellar speckle patterns is statistically analyzed. The time-only power spectrum is shown to be the sum of two exponentially decreasing functions defining two characteristic time constants. The corresponding correlation is the sum of two Lorentzian functions. This is consistent with the first-order expansion of the power spectrum deduced from the multiple-layer model for atmospheric turbulence. However, this model fails to account for the experimental data that show a strong correlation between the spatial structure of a speckle pattern and its temporal behavior. This leads to the introduction of a new empirical model, called the randomly jittered speckle pattern model, which gives a preponderant place to image motion. The speckle lifetime then appears to be substantially longer than the corresponding measured time constant. As a consequence, a preliminary compensation of the image motion appears to be particularly interesting in speckle interferometry or active optics experiments.

San Pedro Mártir: astronomical site evaluation

The Generalized Seeing Monitor (GSM) has undertaken a campaign of measurement of the optical turbulent parameters: the Frieds parameter, the outer scale (L0) and the isoplanatic patch, at Paranal, the site of the VLT, in December 1998. The principle aim of this mission was to measure L0 values at Paranal. In a first part, we present the GSM, the results of the mission and particularly the statistics of L0. In a second part, we emphasize the effect of L0 on the optical path difference (OPD) values for the co-phasing of an interferometer. We derive the exact formulation of the OPD for the Von Karman model and we give the expected OPD at Paranal with L0 values measured by the GSM. We give also the expression of the residual OPD at the output of a fringe tracker system as a function of L0, of the exposure time of the fringe sensor and of the frequency of the closed-loop of the system.

Wavefront outer-scale monitoring at La Silla

The Saclay solar evolution code is used to check the effect of WIMPs on solar evolution. In this paper we study the effects of various types of Cosmion-matter interactions, give constraints on the crosssections compatible with the measured neutrino rate of 2 SNU on chlorine, and relate these constraints to ongoing dark matter detection experiments.

Simulation of pupil-plane observation of angle-of-arrival fluctuations in daytime turbulence

The Observatorio Astronomico Nacional at San Pedro Martir is situated on the summit of the San Pedro Martir Sierra in the Baja California peninsula of Mexico, at 2800m above sea level. For as long as three decades, a number of groups and individuals have gathered extremely valuable data leading to the site characterization for astronomical observations. Here we present a summary of the most important results obtained so far. The aspects covered are: weather, cloud coverage, local meteorology, atmospheric optical extinction, millimetric opacity, geotechnical studies, seeing, optical turbulence profiles, wind profiles and 3D simulations of atmospheric turbulence. The results place San Pedro Martir among the most favorable sites in the world for astronomical observations. It seems to be particularly well-suited for extremely large telescopes because of the excellent turbulence and local wind conditions, to mention but two characteristics. Long-term monitoring of some parameters still have to be undertaken. The National University of Mexico (UNAM) and other international institutions are putting a considerable effort in that sense.

Estimation of turbulence parameters from solar observations

The effective wavefront outer scale L0 was monitored continuously during 16 nights in August-September 1997 using the new Grating Scale Monitor (GSM) instrument. Simultaneous comparison with the data form open-loop adaptive optics system on the ESO 3.6 m telescope revealed a good agreement of the L0 derived by both methods. The GSM principle is similar to the Shack-Hartmann sensor: angle of arrival fluctuations are measured with four 10-cm telescopes and the outer scale is computed from their normalized covariances. The seeing and effective wavefront velocity are measured as well. GSM does not suffer form dome and mirror seeing effects and can be used anywhere for site evaluation. Outer scale has log-normal distribution, its median is found to be 24 m, with a rms scatter of log L0 of +/- 0.22. Short isolated bursts of high L0 values were sometimes observed. A weak correlation of L0 and seeing angle exists for some nights. Decametric values of L0 found here imply that at baselines of few meters the influence of finite L0 on the energy balance between tip-tilt and higher-order modes must be properly taken into account. This can sensibly modify the predicted performance of adaptive optics systems.

Comments on the low-wavenumber power of granulation brightness fluctuations

High angular resolution observations of the sun are limited by atmospheric turbulence. The MISOLFA seeing monitor (still under construction) is developed to obtain spatial and temporal statistical properties of optical turbulence by analyzing local motions observed on solar edge images. The solar flying shadows used for angle-of-arrival spatio-temporal analysis are observed in the pupil plane image by mean of a rectangular thin slit positioned on the solar edge image. A numerical simulation of the light propagation in both the atmospheric turbulence medium and the MISOLFA optical system is carried out studying the relation of the measured intensity variations in the pupil plane to angle-of-arrival fluctuations in the non-isoplanatic case. First results are presented and discussed.

Generalized seeing monitor (GSM): a dedicated monitor for wavefront optical parameter measurements

The one-dimensional point spread function for long-exposure frames of the whole system atmosphere - instrument is calculated from solar limb observations using data recorded at OCA Observatory (France). It is then compared to the theoretical one deduced from the Von Karman model and various wave-front structure functions. Good agreement is found allowing to deduce the spatial coherence outer scale L0 and the Fried parameter r0.