J. Winkler

HERMES: a high-resolution fibre-fed spectrograph for the Mercator telescope

The HERMES high-resolution spectrograph project aims at exploiting the specific potential of small but flexible telescopes in observational astrophysics. The optimised optical design of the spectrograph is based on the well-proven concept of white-pupil beam folding for high-resolution spectroscopy. In this contribution we present the complete project, including the spectrograph design and procurement details, the telescope adaptor and calibration unit, the detector system, as well as the optimised data-reduction pipeline. We present a detailed performance analysis to show that the spectrograph performs as specified both in optical quality and in total efficiency. With a spectral resolution of 85 000 (63 000 for the low-resolution fibre), a spectral coverage from 377 to 900 nm in a single exposure and a peak efficiency of 28%, HERMES proves to be an ideal instrument for building up time series of high-quality data of variable (stellar) phenomena.

Two Fabry-Pérots and two calibration units for CARMENES

The wavelength calibration and nightly drift measurements for CARMENES (Calar Alto high-Resolution search for M dwarfs with Exoearths with Near-infrared and optical Echelle Spectrographs) are provided by a combination of hollow cathode lamps and two Fabry-Pérot units. CARMENES consists of two spectrograph, one for the visible part of the spectrum (520 -960 nm) and one for the near infrared (960 - 1710 nm). Each spectrograph has its own calibration unit and its own Fabry-Pérot. The calibration units are equipped with Th-Ne, U-Ar and U-Ne hollow cathode lamps as well as a flat field lamp. The Fabry-Pérots are optimized for the wavelength ranges of the spectrographs and use halogen-tungsten lamps as light sources. The Fabry-Pérots have a free spectral range of 15 GHz for the visible and 12.2 GHz for the near infrared which translates to 17,900 useful emission lines for the visible spectrograph and 9,700 for the infrared. These lines are used to compute the wavelength solution, and to monitor the instrumental drift during the night. The Fabry-Pérot units are temperature and pressure stabilized and designed to reach an internal stability of better than 10 cm/s per night. Here, we present the designs of both Fabry-Pérot units and the calibration units.