The Fiber-fed Extended Range Optical Spectrograph

FEROS (the Fiber-fed Extended Range Optical Spectrograph) is a spectrograph installed at the MPG/ESO 2.2-metre telescope located at ESO’s La Silla Observatory. FEROS can collect data with high resolution and in wavelengths from near-ultraviolet to infrared, covering the entire visible spectrum.

The combination of covering a large spectral range with a high resolving power has made FEROS particularly useful for research. Astronomers have used FEROS to study exoplanets in other galaxies and evolved stars on the verge of swallowing orbiting planets. FEROS data were also used to accomplish the first detection of lithium in an exploding star. The instrument can also be used for radial velocity measurements of astronomical objects like exoplanet systems, binary stars, and star clusters.

FEROS is an Échelle spectrograph. Spectrographs separate incoming light into individual wavelengths to produce spectra. Astronomers compare known spectra to those of astronomical objects to discover different characteristics of the object like composition or movement in space. An Échelle spectrograph uses a grating with high-angled cuts, prisms, and lenses to separate the light. These optical components are precisely organised to produce spectra with a high resolution, so astronomers can analyse spectral features of celestial bodies in more detail.

Originally installed on the ESO 1.52-metre telescope, the instrument saw first light on 6 October 1998. A few years later the telescope was decommissioned, and FEROS was then moved to the MPG/ESO 2.2-metre telescope. FEROS continues to be used today by Chilean astronomers and researchers from the Max Planck Society.

Science highlights with FEROS

  • FEROS part of a team of instruments that finds that most very bright high-mass stars, which drive the evolution of galaxies, do not live alone (eso1230)
  • New study finds mysterious lack of dark matter in Sun’s neighbourhood (eso1217)
  • Planet found on the verge of being swallowed by its parent star, showing us the Earth's future (eso0305)



The authoritative technical specifications as offered for astronomical observations are available from the Science Operations page.

Location: La Silla Observatory
Telescope: MPG/ESO 2.2-metre telescope
Focus: Cassegrain (fibre fed)
Type: Visible Spectrograph
Wavelength coverage: ~350nm to ~920nm
Spatial resolution:  
Spectral resolution: R~48 000
First light:

ESO 1.52-metre telescope: 6 October 1998

MPG/ESO 2.2-metre telescope: 25 October 2002

Science goal:
  • Observations of objects requiring high spectral resolution and high stability like:
    • Exoplanetary systems
    • Galactic structure
    • Star clusters
    • Interstellar clouds
    • Chemical composition of stars
Images taken with the instrument: Link
Images of the instrument: Link
Press Releases with the instrument: Link
Data papers:


ESO data citation policy

  • Landessternwarte Heidelberg (LSW), Germany
  • Astronomical Observatory Copenhagen (AOC), Denmark
  • Institut d'Astrophysique de Paris (IAP), Paris
  • Observatoire de Paris/Meudon (OPM), France
  • ESO