The GraF instrument for Imaging Spectroscopy with the Adaptive Optics

The GraF instrument using a Fabry-Perot interferometer cross-dispersed with a grating was one of the first integral-field and long-slit spectrographs built for and used with an adaptive optics system. We describe its concept, design, optimal observational procedures and the measured performances. The instrument was used in 1997–2001 at the ESO3.6 m telescope equipped with ADONIS adaptive optics and SHARPII+camera. The operating spectral range was 1.2–2.5 μm. We used the spectral resolution from 500 to 10 000 combined with the angular resolution of 0.1″–0.2″. The quality of GraF data is illustrated by the integral field spectroscopy of the complex0.9″ × 0.9″ central region of η Car in the1.7 μm spectral range at the limit of spectral and angular resolutions.