SO Colloquium – Atmospheric Dispersion Correction to detect Exo-Earths: EXOTICA, ANDES, and RISTRETTO

Astronomical observations with ground-based telescopes are affected by wavelength-dependent atmospheric dispersion, due to the variation of the refractive index of the atmosphere with wavelength. In high-resolution imagers and spectrographs, as used in exoplanet searches, the use of an atmospheric dispersion corrector (ADC) is mandatory.

State-of-the art ADCs will thus be implemented in EXOTICA, ANDES and RISTRETTO. EXOTICA, the recently proposed EXOplanet Tracker Instrument at Calar Alto, is a high-resolution spectrograph for radial velocity monitoring of exoplanet candidates. ANDES, the ArmazoNes high Dispersion Echelle Spectrograph, is the high-resolution optical and near-infrared spectrograph for the ESO Extremely Large Telescope (ELT). RISTRETTO is a visible high-resolution spectrograph fed by an extreme adaptive optics (XAO) system, to be proposed as a visitor instrument on ESO VLT.

The atmospheric dispersion has a strong impact on acquired images even after ADC correction. Fiber-fed seeing-limited spectrographs, like EXOTICA and ANDES, have different ADC requirements than diffraction limited instruments, like RISTRETTO, that imposes requirements at the level of few milli-arcseconds. On the other hand, for planet-hunting spectrographs like ESPRESSO, the ADC were over-engineered to reduce systematics to the cm/s-level. These very stringent requirements are almost impossible to achieve with traditional ADCs, and as such the field is an area of active research.

In this talk, I will present the three instruments as case studies for how ADC requirements are set and understood, what is the traditional way to correct atmospheric dispersion, and present the new concept we will adopt for RISTRETTO.

Fecha y lugar: 02/06/2026 – 12:30 | Salón de Actos
Bachar Wehbe
Institute of Astrophysics and Space Sciences (Portugal)