CARMENES is the new optical/near-infrared spectrograph at Calar Alto observatory. The identification of the most promising targets for exoplanet hunting is a crucial first step to ensure an efficient use of the CARMENES guaranteed time. To achieve this, we obtained low-resolution (R ∼ 1500) spectra of 752 M (and late K) dwarfs, mostly fainter than J = 9 mag, using the CAFOS spectrograph of the 2.2 m telescope at Calar Alto observatory. We derived spectral types with 0.5 subtypes accuracy

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... ng the spectral indices technique and the best-fit & χ 2 matches. We also studied metallicity and surface gravity through spectral indices, and activity from the pseudo-equivalent width of the Hα line. We identified high-activity, low-metallicity and low-gravity stars, which should be discarded for exoplanet searches. Here we present preliminary results. 441 442 Low-resolution spectroscopy of M dwarfs 1 Istrument overview CARMENES 1 (Calar Alto high-Resolution for M dwarfs with Exoearths with Nea-infrarred and opticaí Echelle Spectrographs) is a next-generation instrument being built for the 3.5 m telescope at the Calar Alto observatory by a consortium of German and Spanish institutions. It consists of two separated spectrographs covering the wavelength ranges from 0.5 to 1.0 µm and from 1.0 to 1.7 µm with spectral resolutions R = 82,000, each of which shall perform high-accuracy radial-velocity measurements (∼1 m s −1) with long-term stability. The fundamental science objective of CARMENES is to carry out a survey of ∼300 late-type main-sequence stars with the goal of detecting low-mass planets in their habitable zones. We aim at being able to detect 2 M ⊕ planets in the habitable zone of M5 V stars. The CARMENES first light is expected to occur in Summer 2015 (Quirrenbach et al. 2014 [22])