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Measurements of the wave-front outer scale at Paranal. Influence of this parameter in interferometry. R. Conan, A. Ziad, J. Borgnino and F. Martin UMR 6525 Astrophysique, Université de Nice-Sophia Antipolis, F-06108 Nice Cedex 2, France A. Tokovinin

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measurements of the wave front outer scale at paranal

Measurements of the wave-front outer scale at Paranal

Influence of this parameter in interferometry

R. Conan, A. Ziad, J. Borgnino and F. Martin

UMR 6525 Astrophysique, Université de Nice-Sophia Antipolis,

F-06108 Nice Cedex 2, France

A. Tokovinin

Sternberg Astronomical Institute, Universitestsky prosp., 13,

119899 Moscow, Russia

the generalized seeing monitor
The Generalized Seeing Monitor
  • Four telescopes (Ø=10cm, L-shape layout)
  • Simultaneous measurement of one component of the angle of arrival
  • Real-time computation of :
    • the Fried’s parameter : r0
    • the spatial coherence outer scale : L0
    • the isoplanatic patch : q0

SPIE\'s International Symposium - Astronomical Telescopes and Instrumentation 2000

gsm at paranal 27 nov 20 dec 1998
GSM at Paranal27 Nov./20 Dec. 1998
  • GSM has worked during 19 clear nights
  • 1884 measurements of each parameter :
    • median seeing : 0.9 as,
    • median L0 : 22 m,
    • median q0 : 1.9 as.

SPIE\'s International Symposium - Astronomical Telescopes and Instrumentation 2000

co phasing outer scale theory
Co-phasing & outer scaleTheory
  • Standard deviation of the Optical Path Difference (OPD) : where is the structure function and is the spectrum of the phase fluctuations (Von Karman).

SPIE\'s International Symposium - Astronomical Telescopes and Instrumentation 2000

co phasing outer scale theory1
Co-phasing & outer scaleTheory
  • Solutions to the structure function
    • without aperture filtering :
    • with aperture filtering :
        • 1.
        • 2.
        • 3.

SPIE\'s International Symposium - Astronomical Telescopes and Instrumentation 2000

co phasing outer scale theory2
Co-phasing & outer scaleTheory
  • Structure function of the phase fluctuations

SPIE\'s International Symposium - Astronomical Telescopes and Instrumentation 2000

co phasing outer scale theory3
Co-phasing & outer scaleTheory
  • Isolines of the OPD in units of wavelength as a function of B and L0
  • D = 10m and r0 = 10cm

SPIE\'s International Symposium - Astronomical Telescopes and Instrumentation 2000

co phasing outer scale application to vlti
Co-phasing & outer scaleApplication to VLTI
  • OPD in units of the wavelength
  • Diameter : 8.2m
  • Baselines : 40, 100 and 200 m
  • r0 and L0 measured by the GSM

SPIE\'s International Symposium - Astronomical Telescopes and Instrumentation 2000

opd residual after correction by a fringe tracker
OPD residual after correctionby a fringe tracker
  • Structure function of the residual phase (residual piston) : with :

SPIE\'s International Symposium - Astronomical Telescopes and Instrumentation 2000

opd residual after correction by a fringe tracker1
OPD residual after correctionby a fringe tracker
  • OPD residual =

with

and

SPIE\'s International Symposium - Astronomical Telescopes and Instrumentation 2000

summary
Summary
  • Longest set of continuous nights of outer scale measurements at Paranal (median L0 : 22 m)
  • Derivation of mathematical formulas for OPD with and without the filtering effect of a finite size aperture
  • OPD values expected at Paranal (D=8.2m, B=40, 100 and 200m) are 10 timeslower than for a model with an infinite L0. The OPD is independent of baseline values.

SPIE\'s International Symposium - Astronomical Telescopes and Instrumentation 2000

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