Performance report on FEROS, the new fiber-linked echelle spectrograph at the ESO 1.52-m telescope

FEROS is a new fiber-fed bench-mounted prism-crossdispersed echelle spectrograph which has been recently commissioned at the ESO 1.52-m telescope at La Silla. The opto-mechanical concept and performance predictions have been presented by Kaufer & Pasquini.(1) In this contribution we present the test results as obtained during two commissioning runs in October and December 1998. Special emphasis is given to the measured performances in efficiency, spectral resolution, straylight contamination, and spectral stability. The definite highlight of the FEROS instrument performance is the high peak detection quantum efficiency of 17% at 550nm (1%@360nm, 16%@440nm, 11%@790nm, 6%@900nm). These measured numbers include the a-mirror telescope, the fiber link, the instrument, and the detector while the whole wavelength range is covered by a single exposure on a thinned EEV 2kx4k 15 micron pixel CCD and a constant resolving power of R = 48.000. In addition the FEROS instrument proved its high spectral stability by radial-velocity observations as carried out on the known radial-velocity standard star tau Ceti over a time base of 2 months. By recording a calibration-lamp spectrum in parallel with the object spectrum and by the use of a simple cross-correlation technique, a rms of 21 m/s has been obtained for a data set of 130 individual measurements. FEROS has been made available to the ESO community in January 1999.