RISTRETTO: coronagraph and AO designs enabling High Dispersion Coronagraphy at 2 lambda/D

TL;DR

RISTRETTO is a specialized instrument designed to enable high-contrast, high-resolution spectroscopy of nearby exoplanets at small angular separations, advancing direct atmospheric characterization capabilities.

Contribution

It introduces a novel coronagraphic IFU and adaptive optics system optimized for high dispersion coronagraphy at 2 lambda/D, with potential for high coupling efficiency and contrast.

Findings

Potential to reach > 50% coupling efficiency

Achieves <1E-4 contrast at 2lambda/D in median seeing

Design modifications enable nulling on the first diffraction ring

Abstract

RISTRETTO is the evolution of the original idea of coupling the VLT instruments SPHERE and ESPRESSO, 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. 2lambda/D at lambda=750nm. The instrument is composed of an extreme adaptive optics, a coronagraphic Integral Field Unit, and a diffraction-limited spectrograph (R=140.000, lambda=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 <1E-4 contrast at 2lambda/D in median seeing conditions.