ESO's Fibre-fed, Extended Range, Échelle Spectrograph (FEROS) is a bench-mounted, thermally controlled, prism-crossdispersed échelle spectrograph.

It is designed to be a high resolution (R~48,000), high efficiency (20%), versatile spectrograph providing in a single spectrogram almost complete spectral coverage from ~350nm to ~920nm. The mechanical and thermal stability of FEROS allow for a precise wavelength calibration based on daytime calibrations and for most purposes additional calibrations during the night are not necessary, thus ensuring a high productivity in terms of scientific data produced. Although not intended as a `radial velocity machine', precise radial velocity work (accuracies of ~25m/s or better) is also possible, especially via the Object-Calibration mode. Extremely high precision Radial Velocity work (~1m/s) is better done using HARPS which also has higher resolution (R~115,000). Extremely high resolution work (upto R~235,000) is better done with CES.

FEROS is fed by two fibres providing simultaneous spectra of OBJECT plus either SKY or one of the two CALIBRATION lamps (wavelength calibration and flat-field). The fibres are illuminated via 2.0 arcsec apertures on the sky separated by 2.9 arcmins. A small amount of rotation of the telescope adapter is possible in the rare case that a field star by chance falls on the sky fibre. The resolving power of 48,000 achieved with a two-slice image slicer over the spectral range of ~350nm to ~920nm spread over 39 échelle orders. The detector is an EEV 2k×4k CCD.

A dedicated pipeline implemented as a MIDAS context provides, in almost realtime, extracted 1-dimensional, wavelength calibrated spectra which  can be used as a quicklook to check S/N etc. The core of the FEROS pipeline is included in the standard MIDAS distribution and together with the FEROS-DRS package can be used to re-reduce the data to obtain publication quality results.

Calibration lamp light is delivered to the SCIENCE fibres in the FEROS Fibre Head via the CALIBRATION fibres from the FEROS Calibration Unit.

Both FEROS and WFI are now permanently mounted at the MPG/ESO-2.20m telescope. Switching from one instrument to the other is a simple matter of moving the M3 and takes just 8 seconds.

In October of 2002 FEROS was transferred from the ESO-1.52m telescope to the MPG/ESO-2.20m telescope. In October-November of 2003 it was upgraded to full VLT-compliance (i.e. p2pp/OB controlled observing). In March of 2005, an Atmospheric Dispersion Corrector was installed and thus has been available since Period-75 onward.

Detailed information on FEROS is to be found in the FEROS web pages.

Spectral Coverage

FEROS provides almost complete spectral coverage from ~35