CARMENES, a next-generation instrument for the CAHA 3.5-m telescope

CARMENES is a study for a next-generation instrument for the 3.5m telescope at the Calar Alto Observatory that will be built by an international consortium. CARMENES stands for Calar Alto high-Resolution search for M dwarfs with Exo-Earths with a Near-infrared Echelle Spectrograph. Since M dwarfs have low effective temperatures (Teff < 4000 K), our spectrograph is designed to operate in the optical red and the near infrared, where they emit the bulk of their radiation. High thermal and mechanical stability and a suitable wavelength calibration strategy are needed to reach radial velocity accuracies of a few meters per second, which are necessary to detect exoplanets of only a few Earth masses within the habitable zones of such cool, low-mass stars. We also aim to search for gaseous planets in orbits around K giants and to use asteroseismology to refine the parameters of planet host stars. The target radial velocities will be monitored with a fibre-fed cross-dispersed echelle spectrograph with two channels that will provide almost full coverage of their respective wavelength ranges in one shot. The near infrared channel will cover the Y , J and H bands, have a spectral resolution R ~ 85 000 and be calibrated with ThAr lamps. We expect to reach a signal-to-noise ratio of 100 in 10 min of exposure time on a target with J = 8 mag. The visible channel, covering the spectral range from about 5 000 to 9 000 AA, will provide simultaneous monitoring of activity indicators (e.g. Halpha, Ca ii). In addition, there is a proposal for a secondary visible channel with lower resolution, restricted wavelength range and multiplex factor of about 12. We expect the instrument to start operations in 2013.