Astron. Astrophys. Suppl. Ser. 144, 39-44

Optical parameters relevant for High Angular Resolution at Paranal from GSM instrument and surface layer contribution

F. Martin¹ - R. Conan¹ - A. Tokovinin³ - A. Ziad¹ - H. Trinquet¹ - J. Borgnino¹ - A. Agabi¹ - M. Sarazin²

Send offprint request: F. Martin,
e-mail: Francois.MARTIN@unice.fr

1 - U.M.R. Astrophysique No. 6525, Université de Nice-Sophia Antipolis, F-06108 Nice Cedex 2, France
2 - European Southern Observatory, Karl-Schwarzschild-Str. 2, D-85748 Garching bei München, Germany
3 - Sternberg Astronomical Institute, Universitestsky prosp. 13, 119899 Moscow, Russia

Received January 12; accepted February 25, 2000

Abstract:

Main atmospheric parameters characterizing the turbulence were measured at the Paranal ESO Observatory (Chile) with the Generalized Seeing Monitor (GSM) during 19 nights in November-December 1998. The median seeing for this period was 0.88'', a little worse than average, the spatial coherence outer scale of the wavefront $\mbox{${\cal{L}}_0 $ }= 22.0$ m and the median isoplanatic angle $\mbox{$\theta_0 $ }~=~1.90''$. A very good agreement with seeing values given by ESO DIMM was found. Effects of ground layer turbulence were estimated from measurements of temperature micro-fluctuations at several altitudes. These measurements revealed that the first 21 m above ground account for 12.5% of the total turbulent energy. Comparison between GSM and ESO DIMM values have permitted to highlight a local phenomenon which occurs sometimes at the site in the middle of the night. Statistics of the refractive index structure constant C_n² in the surface layer is also studied.

Key words: turbulence -- atmospheric effects -- site testing