Swiss 1.2-metre Leonhard Euler Telescope

Lore & Background

The Euler telescope uses the CORALIE instrument to search for exoplanets. CORALIE is an echelle-type spectrograph, a copy of the ELODIE spectrograph used by Michel Mayor and Didier Queloz to detect the planet orbiting a star. It was built and installed at the Euler Telescope in April 1998, and upgraded in 2007 by Didier Queloz and his team to support the Wide Angle Search for Planets program and the Next-Generation Transit Survey. The instrument is optimized to measure the Doppler effect on a star's electromagnetic spectrum with great precision to detect the gravitational tug of an orbiting exoplanet, an indirect detection method also known as radial velocity or wobble method. The mass of the planet can be estimated from these measurements. The spectrograph participates in the Southern Sky extrasolar Planet search Programme initiated by Michel Mayor.

Reader's Guide

The Euler telescope's significance lies in its contributions to exoplanet discovery and characterization. Its first discovery was a planet in orbit around Gliese 86, determined to be a hot Jupiter with an orbital period of only 15.8 Earth days and about four times the mass of Jupiter. Since then, many other exoplanets have been discovered or examined in follow-up observations. Together with the Mercator Telescope, Euler was part of the Southern Sky extrasolar Planet search Programme, which has discovered numerous extrasolar planets. It has also been frequently employed for follow-up characterization to determine the mass of exoplanets discovered by the Wide Angle Search for Planets (SuperWASP). In 2010, the visible camera EulerCam was installed by Didier Queloz, with the main objective to measure planets by the transit method, supporting ground-based programs such as Wide Angle Search for Planets. By combining the measured size from the transit method and mass from radial velocity, it can be determined whether an observed exoplanet is gaseous or rocky. The CORALIE spectrograph has a fixed resolution of R = 50,000 with three-pixel sampling, and its detector is a 2k × 2k charge-coupled device with 15 micrometer pixel size.

Did You Know?

• The Euler telescope saw its first light on 12 April 1998.
• Its first discovered exoplanet was a hot Jupiter around Gliese 86 with a 15.8-day orbital period and about four times Jupiter's mass.
• In 2010, the EulerCam was installed to measure exoplanets by the transit method.

A Swiss Instrument on Chilean Soil

The Leonhard Euler Telescope stands as a testament to international astronomical collaboration, pairing Swiss engineering with the exceptional observing conditions of the Chilean Norte Chico region. Built and operated by the Geneva Observatory, this fully automatic 1.2-metre reflecting telescope sits at an altitude of 2,375 metres on ESO's La Silla Observatory site, roughly 460 kilometres north of Santiago de Chile. The high elevation and dry climate of the location minimize atmospheric interference, granting the instrument the stable skies its precision work demands. The telescope achieved first light on 12 April 1998 and carries the name of Leonhard Paul Euler, the celebrated Swiss mathematician whose contributions to science spanned centuries. As a national asset of Switzerland, it operates autonomously, freeing Geneva-based astronomers from the need to travel to Chile for routine observations. Its compact 47-inch aperture, while modest compared to giant modern telescopes, is perfectly suited to the precision spectroscopic and photometric work that defines its exoplanet-hunting mission.

The CORALIE Spectrograph and the Wobble Method

At the heart of the Euler Telescope's exoplanet-detection capability lies CORALIE, an echelle-type spectrograph built and installed in April 1998. CORALIE is a direct copy of the ELODIE spectrograph, the very instrument Michel Mayor and Didier Queloz used to detect a planet orbiting a star. This lineage gives CORALIE a proven pedigree in radial velocity work. The instrument is optimized to measure the Doppler shift in a star's electromagnetic spectrum with extraordinary precision, detecting the subtle gravitational tug that an orbiting planet exerts on its host star. This indirect detection technique, often called the wobble method, allows astronomers to estimate a planet's mass from the periodic shifts in spectral lines. CORALIE operates at a fixed resolution of R = 50,000 with three-pixel sampling, using a 2k by 2k charge-coupled device with 15-micrometre pixels. In 2007, Didier Queloz and his team upgraded the spectrograph to enhance its performance in support of the Wide Angle Search for Planets and the Next-Generation Transit Survey.

Hunting Worlds Beyond the Solar System

The Euler Telescope's discovery record is anchored by its very first exoplanet detection: a hot Jupiter orbiting Gliese 86, with an orbital period of just 15.8 Earth days and a mass approximately four times that of Jupiter. This milestone formed part of the broader Southern Sky extrasolar Planet search Programme, a collaborative effort initiated by Michel Mayor in which Euler worked alongside the Mercator Telescope to uncover numerous additional extrasolar planets. Beyond its primary survey role, the telescope has been frequently called upon for follow-up characterization work, particularly to measure the masses of exoplanets initially identified by the Wide Angle Search for Planets, known as SuperWASP. This complementary role is crucial: while SuperWASP's wide-field cameras can spot transiting planets across vast stretches of sky, Euler's precision spectroscopy provides the radial velocity data needed to confirm and quantify those discoveries. Since its 1998 first light, the telescope has contributed to the detection and examination of many other exoplanets, cementing its place in the growing catalogue of worlds beyond our solar system.

Combining Mass and Size to Reveal a Planet's Nature

Euler's scientific power extends well beyond a single instrument. In addition to CORALIE, the telescope hosts EulerCam, a high-precision photometry camera installed in 2010 by Didier Queloz, and a smaller piggyback-mounted telescope nicknamed Pisco. EulerCam's primary mission is to measure exoplanets via the transit method, supporting ground-based programs such as SuperWASP by recording the slight dimming of a star as a planet passes in front of it. This technique yields an estimate of the planet's physical size. When that size measurement is combined with the mass derived from CORALIE's radial velocity observations, astronomers can determine whether an exoplanet is predominantly gaseous or rocky in composition. This dual-method approach transforms Euler from a mere planet-finder into a tool for characterizing planetary physics. The multi-instrument configuration allows the telescope to tackle different aspects of exoplanet science in a single observing session, maximizing the scientific return from each night of clear Chilean sky.