Measurements of the wave front outer scale at paranal
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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 Paranal Instrumentation 200027 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 scale Instrumentation 2000Theory

  • 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 scale Instrumentation 2000Theory

  • 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 scale Instrumentation 2000Theory

  • Structure function of the phase fluctuations

SPIE's International Symposium - Astronomical Telescopes and Instrumentation 2000


Co phasing outer scale theory3
Co-phasing & outer scale Instrumentation 2000Theory

  • 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 scale Instrumentation 2000Application 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 correction Instrumentation 2000by 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 correction Instrumentation 2000by a fringe tracker

  • OPD residual =

with

and

SPIE's International Symposium - Astronomical Telescopes and Instrumentation 2000



Summary
Summary Instrumentation 2000

  • 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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