CRIRES⁺

CRIRES⁺, short for Cryogenic high-resolution InfraRed Echelle Spectrograph, is an upgrade to the original CRIRES that resulted from a six-year collaboration between researchers at ESO and several European institutes.

Located at UT3 on the Very Large Telescope (VLT) at ESO's Paranal Observatory, the CRIRES⁺ is an instrument based on the backbone of the original CRIRES spectrograph. This instrument worked on the VLT for eight years achieving great scientific results, among them, the measurement of length of an exoplanet day for the first time or the creation of the first weather map for the nearest brown dwarf to Earth.

By increasing the wavelength range that is covered simultaneously by a factor of ten, the upgrade project gave new capabilities to the instrument and more ambitious scientific goals. “This was done by turning CRIRES into a cross-dispersed echelle spectrograph,” says ESO project manager for the CRIRES⁺, Reinhold Dorn.

Since October 2021, the astronomy community is able to use this improved instrument to search for super-Earths in habitable zones of low-mass stars, where the chance of finding planets that can support life is higher. CRIRES⁺ can also be used to search and describe the chemical composition of exoplanet atmospheres and to study the origin and evolution of stellar magnetic fields.

Like it is predecessor, CRIRES⁺ consists of both a spectrograph and an adaptive optics system. The spectrograph's application is to split the light into its separate components for individual analysis. Inside of the instrument, the light is divided in the same way that rain droplets disperse the light to form a rainbow. This process allows astronomers to capture essential information of different elements encoded in the light. 

The adaptive optics system, called MACAO (Multi-Applications Curvature Adaptive Optics), uses a reference star to measure the distortions of the image caused by the turbulence of the atmosphere, computes the corrections needed, and applies them to a deformable mirror. MACAO corrects up to 1000 frames/second, resulting in sharper images. Thanks to a complete upgrade to MACAO, the lifetime of this system will be of at least ten years.

Other main additions are new gas cells, which are part of a new calibration module, new large state-of-the-art detectors, and a polarimetry module allowing new science to be made with the instrument.

These new features are all supported by a dedicated data reduction software, which allows the astronomers using the instrument to take full advantage of the new capabilities offered by CRIRES⁺.

In 2023, the VLT was equipped with a new fibre-optics tool, HiRISE, coupling SPHERE and CRIRES⁺. HiRISE combines the capabilities of the two instruments to carry out in-depth spectroscopic studies of exoplanets.