Upgrading the high contrast imaging facility SPHERE: science drivers and instrument choices

TL;DR

SPHERE+ aims to upgrade the VLT instrument to enhance exoplanet detection and characterization, enabling observations of fainter targets, broader spectral analysis, and serving as a prototype for future ELT instruments.

Contribution

This paper presents the science goals, technical requirements, and instrumental trade-offs for the SPHERE+ upgrade, outlining its novel features and expected performance improvements.

Findings

Enhanced infrared sensitivity and bandwidth for better exoplanet detection.

Implementation of a second-stage AO system with pyramid wavefront sensor.

Development of a medium resolution integral field spectrograph for detailed atmospheric studies.

Abstract

SPHERE+ is a proposed upgrade of the SPHERE instrument at the VLT, which is intended to boost the current performances of detection and characterization for exoplanets and disks. SPHERE+ will also serve as a demonstrator for the future planet finder (PCS) of the European ELT. The main science drivers for SPHERE+ are 1/ to access the bulk of the young giant planet population down to the snow line ($3-10$ au), to bridge the gap with complementary techniques (radial velocity, astrometry); 2/ to observe fainter and redder targets in the youngest ($1-10$\,Myr) associations compared to those observed with SPHERE to directly study the formation of giant planets in their birth environment; 3/ to improve the level of characterization of exoplanetary atmospheres by increasing the spectral resolution in order to break degeneracies in giant planet atmosphere models. Achieving these objectives requires to increase the bandwidth of the xAO system (from $\sim$1 to 3\,kHz) as well as the sensitivity in the infrared (2 to 3\,mag). These features will be brought by a second stage AO system optimized in the infrared with a pyramid wavefront sensor. As a new science instrument, a medium resolution integral field spectrograph will provide a spectral resolution from 1000 to 5000 in the J and H bands. This paper gives an overview of the science drivers, requirements and key instrumental trade-off that were done for SPHERE+ to reach the final selected baseline concept.