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Adaptive Lyot Mask. In order to optimize the occulting process of a Lyot coronograph , a new kind of occulting disk as been developped at the National Observatory of Rio de Janeiro, to provides a high dynamic imaging .

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Adaptive lyot mask
Adaptive Lyot Mask

In order to optimize the occulting process of a Lyot coronograph , a new kind of occulting disk as been developped at the National Observatory of Rio de Janeiro, to provides a high dynamic imaging .

A mercury (Hg) drop glueded on to an optical window by molecular cohesion and compressed by a pellicular film is used as the occulting disk. The minimum of the superficial tension potential function provides an optical precision (lambda/100) of the toric free surface of the mercury.

This process provides a size control for the adaptation to the seeing conditions and to the apparent diameter of a resolved object, and in the case of adaptive optics, to the Airy diameter fraction needed. The occultation is a three dimensional process near the focal plane on the toric free surface that provides an apodization of the occultation.

The Hg-Mask coronograph has been projected for astrometric observations of the inner Neptunian satellite Proteus and works since 2000 at the 1.6m telescope of the Pico dos Dias Observatory (Minas Gerais – Brazil).

“A coronograph with a variable diameter occulting disk” Bourget et al. (2001), PASP 113.

“Coronographie de Lyot a masque de mercure” Bourget et al. (2003). Deuxiemes Journées d´Imagerie à Très Haute Dynamique, Nice, France.


Second prototype at the 1.6m Telescope of the OPD – Brasil.

Astrometric observations program of Jovian satellites since 2000.

  • -Hg Mask size control.

  • -Internal Flat.

  • Intensified way for the Mask centering process and pupil image visualisation.


5’*5’Field Brasil.

for the astrometric calibration

Proteus -

Neptune – Proteus

10‾5 Dynamic

2000-2002: 66 astrometric positions


V (Neptune) = 7.8 Brasil.

V (Proteus) = 20.3

Texp = 10 – 20 s

Separation 5´´


Uranus – Puck Brasil.

1.5 10‾6 Dynamic

V (Uranus) = 5.7

V (Puck) = 20.4

Separation 5´´

Oberon

Miranda Umbriel

Ariel

Titan

Miranda Puck Umbriel


Construction of an Hg-Mask coronograph for the Pic Du Midi Observatory (France), delivery in February 2004.

First tests October 2003, at the T1m telescope:

Pleione (Hα)

HR1180-280

HD 23 862

Bourget, Colas, Assus

Observations realised for Farrokh vakili (LUAN – Nice)

Rotational gradient visu


Hg-Mask Observatory (France), delivery in February 2004.

Mercury drops compression range:

Duplication of the diameter

Precompressed Compression limit

Nitrocellulose pellicle

Toric free surface

of mercury

Optical window

Example of Hg-Drops

50 μm to 250 μm

Size : limit max 1.5mm

limit min 10μm


Construction of a tip-tilt correction and automatic centring system of the coronograph (first light in 2002). The originality of this system in development is to use the dynamic diffraction signal behind the occulting disk as a tilt parameter. A “loop” on the Hg-Mask size provides an optimization of the dynamic correction of the tip-tilt.

Optical quality distorssion : 20*20 mm field:


First Light 2002 system of the coronograph (first light in 2002). The originality of this system in development is to use the dynamic diffraction signal behind the occulting disk as a tilt parameter. A

First cavity

Hg-Mask

CCD

Tip-Tilt fiber sensor

Carbon fiber structure


Tip-Tilt sensor- First test system of the coronograph (first light in 2002). The originality of this system in development is to use the dynamic diffraction signal behind the occulting disk as a tilt parameter. A

Small field coronograph

Fiber entrance__

APD

Quadrant fiber guide

50μm fiber quadrant

Four APD as quadrant


Inductive control system of the coronograph (first light in 2002). The originality of this system in development is to use the dynamic diffraction signal behind the occulting disk as a tilt parameter. A Tip-Tilt Mirror


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