Reflective aspherized grating spectrographs for the Haute-Provence,and Nanjing Observatories : MARLYs and CARELEC.

Several advantages achieved by spectrographs designed with all-reflective optics for high resolution spectroscopy, have incited us to develop new reflective mountings for low and medium resolution spectroscopy. Such systems must necessarily include corrective-gratings, thus reducing the number of optical surfaces to a minimum. The flat field anastigmat system has high throughput and achromatism extending into the UV and IR. The spectral coverage capability is much larger than actual CCDs and could be used in the IR up to 2.5 microns without modification of the optics. The first such instrument was designed for the prime focus of the Canada-France-Hawaii telescope. The presently described MARLY spectrographs of the Haute-Provence and Nanjing Observatories and CARELEC spectrograph of the 2 m telescope of the Haute-Provence Observatory are anastigmats with a flat-field external focus. Aspherical diffraction gratings were obtained by active optics and replication. Besides the achromatism of the mounting using a self-achromatic singlet lens as field flattener these instruments provide quasi-constant dispersions for each spectral coverage at the detector and are distortion free. These properties, basically due to reflective optics, are suitable for low dispersion faint object studies covering large spectral ranges, and also avoid data reduction problems due to the field distortion inherent in classical spectrograph designs.