Cassegrain Echelle Spectrograph

The Cassegrain Echelle Spectrograph (CASPEC) instrument was the first major ESO-built instrument at the Cassegrain focus of the ESO 3.6-metre telescope at La Silla Observatory, in Chile. The decision to build such an instrument was taken in 1974, but due to ESO’s move from Geneva, Switzerland to Garching, Germany and the difficulties in procuring a suitable 2D detector, tests at the ESO 3.6-metre telescope only started in June 1983. Visiting astronomers could observe with CASPEC from 1 April 1984.

CASPEC was able to obtain high-resolution spectroscopic observations of stars, nuclei of galaxies and quasi-stellar objects (QSOs) as faint as magnitude 16 with its signal-to-noise ratio, that were only then possible to obtain with large coudé instruments. This gave ESO astronomers the possibility to carry out detailed observations of the physical conditions and abundances of faint stars and extragalactic observations at this spectral resolution for the first time.

Over time, CASPEC was upgraded to optical cameras and several CCDs of increasing sensitivity and resolution. During its 15-year lifetime, CASPEC was used for a large variety of scientific programs and contributed to many important discoveries. In 1987, for example, CASPEC helped in the discovery of the most distant known object in the Universe at that time. About ten years later CASPEC helped studying a major transition period in the early Universe, providing a high-resolution spectrum of a bright southern quasar.

CASPEC was decommissioned in 1999.

Science highlights with CASPEC

  • Newly discovered quasar is most distant known object in the Universe (eso8713)
  • Detailed observations of a bright supernova in Centaurus A suggest that this galaxy is much closer than previously thought (eso8608)



This table lists the global capabilities of the instrument.

Location: Decommissioned
Telescope: ESO 3.6-m telescope
Focus: Cassegrain
Type: Optical Echelle spectrograph
Wavelength range: 350–1000 nm
Special resolution: seeing limited
Spectral resolution: R ~20000-65000
First light: June 1983
Science goals:
  • Physical conditions and abundances of faint stars
  • Nuclei of galaxies
  • QSOs
Images taken with the instrument: Link
Images of the instrument: Link
Press Releases with the instrument: Link
  • ESO