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Astron. Astrophys. 336, L49-L52 (1998)

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Letter to the Editor

First statistical data on wavefront outer scale at La Silla observatory from the GSM instrument

F. Martin 1, A. Tokovinin 2, A. Ziad 1, R. Conan 1, J. Borgnino 1, R. Avila 1, A. Agabi 1 and M. Sarazin 3

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

Received 9 March 1998 / Accepted 8 July 1998


Results of the first monitoring of the wavefront outer scale [FORMULA] during 16 nights at La Silla, Chile, are presented. This parameter is of importance for high angular resolution observing techniques like adaptive optics and optical interferometry. It was measured with the Grating Scale Monitor (GSM) instrument which is based on the analysis of the spatial covariance of angle of arrival fluctuations simultaneously detected at several points on the wavefront. The outer scale distribution is found to be log-normal, with median value of 24 m and rms scatter of [FORMULA][FORMULA] of [FORMULA]. Short-duration bursts of [FORMULA] are noted. During 1 hour the [FORMULA] and seeing were simultaneously measured with the ADONIS adaptive optics system at the 3.6 m telescope, and a good agreement with our data was noted.

Our measurements of the seeing were found to agree with the ESO DIMM seeing data. Effective wavefront velocity was also found in order to estimate the adaptive optics time constant.

Key words: seeing – adaptive optics – interferometry

Send offprint requests to: F. Martin

© European Southern Observatory (ESO) 1998

Online publication: July 27, 1998