RISTRETTO: coronagraph and AO designs enabling High Dispersion Coronagraphy at 2 λ/D
RISTRETTO: conception du coronographe et de l'optique adaptative permettant de la coronographie à haute dispersion à 2 λ/D
Résumé
RISTRETTO is the evolution of the original idea of coupling the VLT instruments SPHERE and ESPRESSO,1 aiming at High Dispersion Coronagraphy. RISTRETTO is a visitor instrument that should enable the characterization of the atmospheres of nearby exoplanets in reflected light, by using the technique of high-contrast, high-resolution spectroscopy. Its goal is to observe Prox Cen b and other planets placed at about 35mas from their star, i.e. 2λ/D at λ=750nm. The instrument is composed of an extreme adaptive optics, a coronagraphic Integral Field Unit, and a diffraction-limited spectrograph (R=140.000, λ =620-840 nm). We present the status of our studies regarding the coronagraphic IFU and the XAO system. The first in particular is based on a modified version of the PIAA apodizer, allowing nulling on the first diffraction ring. Our proposed design has the potential to reach ≥ 50% coupling and ≤ 10−4 contrast at 2λ/D in median seeing conditions.
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