1/ Development of a prototype system for the VLT
During the course of course of the project, we developed from scratch a novel prototype instrument, which is implemented as a visitor instrument on the VLT since July 2023. We started with a basic design and simulation model, which was constantly improved over the period 2017-2021. The expected performance of the instrument were an important milestone of the project that enabled convincing the Paranal observatory and its governing bodies to proceed with a visitor instrument. The final design was achieved in 2020-2021, the procurement of the hardware in 2021-2022, the assembly and integration In Europe in 2022-2023, and the installation and commissioning at the telescope in 2023. The first science observing run was done in November 2023, and we have already confirmed detection of three planetary companions in the data. The analysis of the data has already started. The performance of the instrument on sky is within the specifications from design, so we expect important scientific results in the coming years. We have an agreement with the observatory to leave the instrument installed until 2027.
During the development of the HiRISE instrument, we also made significant progress on high-contrast imaging instrumental techniques, such as the Zernike wavefront sensor (ZWFS). This sensor is used to measure the optical aberrations within the SPHERE instrument, which are a known limitation for high-contrast imaging in general, and for the HiRISE instrument in particular. During the course of the project, we validated the use of a ZWFS on the sky and we used it for the characterisation of the temporal variations of aberrations within the SPHERE instrument. These results prefigure the techniques that will be used both for ground-based and space-based observatories to correct and monitor the aberrations in future instruments that will be searching for small telluric exoplanets. The measurements of aberrations in SPHERE with the ZWFS have also helped validating the performance of the HiRISE instrument.
2/ Observations with current instruments
In parallel of the technical aspects of the project, we have investigated scientific observations with existing instruments that provide medium to high spectral resolution. Several observing programmes have been proposed and accepted for the characterisation of known companions on instruments like VLTI/GRAVITY, VLT/SPHERE, VLT/ESPRESSO, CFHT/SPIRou, VLT/MUSE, and VLT/CRIRES+. Due to the Covid-19 epidemic, not all of these programmes have been fully executed, but some data has been acquired and analysed. We also collaborated with colleagues from the Leiden Observatory to obtain interesting CRIRES+ data, and with colleagues from Caltech to get access to KPIC data (equivalent of HiRISE on the Keck Telescope). One publication has been submitted based on the KPIC data and is currently under peer review.
3/ Future instrumentation on large telescopes
The search and characterisation of exoplanets in the future will heavily rely on high-spectral resolution capabilities. In this context, a PhD has worked on the use of the high-contrast imaging mode of the HARMONI instrument for ESO's extremely large telescope (ELT). HARMONI will be the first-light instrument of the European extremely large telescope being built in Chile. His work has demonstrated the very high potential of HARMONI for the detection of young giant exoplanets using the medium resolution of the instrument (Houllé et al. 2021). This work is now used as reference in the HARMONI science group to evaluate the capabilities of the instrument for exoplanet detection and characterisation.
