Periodic Reporting for period 4 - HiRISE (High-Resolution Imaging and Spectroscopy of Exoplanets)
Berichtszeitraum: 2022-06-01 bis 2023-11-30
The detection of planets orbiting other stars, known as exoplanets, is one of the greatest astrophysical achievements of the past 30 years. Several thousands of exoplanets of various masses and separation to their host star have been discovered using different observational techniques. One of these techniques is direct imaging, which is a method where the photons coming from an exoplanet are directly measured thanks to a combination of various optical and numerical techniques. Current exoplanet imagers are equipped to correct for the Earth's atmospheric turbulence using extreme adaptive optics and suppress the stellar signal using coronagraphy, but their spectrographs are limited to spectral resolutions of R=50 to 100. From the astrophysical point of view, spectral resolution more than a 1000 times higher are necessary to answer fundamental questions regarding the formation, composition and evolution of young giant exoplanets. High-resolution spectrographs exists but none of the existing instruments include the ExAO and coronagraphy that are required to perform high-contrast imaging and directly image and characterise exoplanets. One such instrument is the CRIRES+ spectrograph, which has recently been reinstalled at the VLT.
With HiRISE, we propose to implement a novel system that enables the characterisation of young giant exoplanets at high spectral resolution. HiRISE aims at implementing a new module inside of SPHERE to pick up the light of a known exoplanet, inject it into an optical fibre, transmit it around the telescope to the CRIRES+ spectrograph, and use the spectrograph to disperse the planet's light at R=100000. HiRISE will use state-of-the-art instrumental concepts to massively augment the capabilities of both SPHERE and CRIRES+. By the end of the project, we aim at having a working prototype instrument installed at the VLT in Chile and use it to characterise a sample of known exoplanet companions.
The goals of the HiRISE project are the following:
1/ Develop innovative instrumental concepts for high-contrast imaging combined with high-resolution spectroscopy
2/ Develop data analysis and signal extraction techniques to detect the signal of planets in data at high spectral resolution, and characterise their physical properties
3/ And finally, design and implement a working prototype at the VLT that enables to combine SPHERE and CRIRES+ for the characterisation of young giant exoplanets at high spectral resolution
With HiRISE, we propose to implement a novel system that enables the characterisation of young giant exoplanets at high spectral resolution. HiRISE aims at implementing a new module inside of SPHERE to pick up the light of a known exoplanet, inject it into an optical fibre, transmit it around the telescope to the CRIRES+ spectrograph, and use the spectrograph to disperse the planet's light at R=100000. HiRISE will use state-of-the-art instrumental concepts to massively augment the capabilities of both SPHERE and CRIRES+. By the end of the project, we aim at having a working prototype instrument installed at the VLT in Chile and use it to characterise a sample of known exoplanet companions.
The goals of the HiRISE project are the following:
1/ Develop innovative instrumental concepts for high-contrast imaging combined with high-resolution spectroscopy
2/ Develop data analysis and signal extraction techniques to detect the signal of planets in data at high spectral resolution, and characterise their physical properties
3/ And finally, design and implement a working prototype at the VLT that enables to combine SPHERE and CRIRES+ for the characterisation of young giant exoplanets at high spectral resolution
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.
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.
HiRISE has already enabled advances for the future characterisation of exoplanets at high spectral resolution. We demonstrated that the driving parameter of an instrument characterising exoplanets at high spectral resolution is the transmission. This is an important discovery that will be a key for the design of future systems. Overall, while designing the HiRISE system for the VLT, the team has gained significant knowledge that will be essential for the development of future instrumentation for the ELT and future space telescopes. This experience will be extremely valuable in the future. The implementation of the system at the telescope is also a key asset for future instrumentation. During commissioning we understood the limitations of the system and how it could be improved on the current instrument, but also for future instrumentation.
Now that the system is operational, we are going to use it for the characterisation of several known companions to study their atmospheric composition, their orbital motion and their rotation. This work is just starting, but with a fully validated instrument we are guaranteed to obtain astrophysical results in the coming year. The science team of HiRISE is already at work on the data and first results can be expected in 2024.
Now that the system is operational, we are going to use it for the characterisation of several known companions to study their atmospheric composition, their orbital motion and their rotation. This work is just starting, but with a fully validated instrument we are guaranteed to obtain astrophysical results in the coming year. The science team of HiRISE is already at work on the data and first results can be expected in 2024.