Frédéric P. A. Vogt, Frantz Martinache, Olivier Guyon, Takashi Yoshikawa, Kaito Yokochi, Vincent Garrel, Taro Matsuo
Detection and characterization of exoplanets by direct imaging requires a
coronagraph designed to deliver high contrast at small angular separation. To
achieve this, an accurate control of low order aberrations, such as pointing
and focus errors, is essential to optimize coronagraphic rejection and avoid
the possible confusion between exoplanet light and coronagraphic leaks in the
science image. Simulations and laboratory prototyping have shown that a
Coronagraphic Low Order Wave-Front Sensor (CLOWFS), using a single defocused
image of a reflective focal plane ring, can be used to control tip-tilt to an
accuracy of 10^{-3} lambda/D. This paper demonstrates that the data acquired by
CLOWFS can also be used in post-processing to calibrate residual coronagraphic
leaks from the science image. Using both the CLOWFS camera and the science
camera in the system, we quantify the accuracy of the method and its ability to
successfully remove light due to low order errors from the science image. We
also report the implementation and performance of the CLOWFS on the Subaru
Coronagraphic Extreme AO (SCExAO) system and its expected on-sky performance.
In the laboratory, with a level of disturbance similar to what is encountered
in a post Adaptive Optics beam, CLOWFS post-processing has achieved speckle
calibration to 1/300 of the raw speckle level. This is about 40 times better
than could be done with an idealized PSF subtraction that does not rely on
CLOWFS.
View original:
http://arxiv.org/abs/1112.2817
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