Multi-purpose InSTRument for Astronomy at Low-resolution: MISTRAL@OHP

MISTRAL is the new Faint Object Spectroscopic Camera mounted at the foldedCassegrain focus of the 1.93m telescope of Haute-Provence Observatory. Wedescribe the design and components of the instrument and give some detailsabout its operation. We emphasise in particular the various observing modes andthe performances of the detector. A short description is also given about theworking environment. Various types of objects, including stars, nebulae,comets, novae, galaxies have been observed during various test phases toevaluate the performances of the instrument. The instrument covers the range of4000 to 8000A with the blue setting, or from 6000 to 10000A with the redsetting, at an average spectral resolution of 700. Its peak efficiency is about22a point source in one hour with a signal to noise of 3 in the continuum (andbetter if emission lines are present). In imaging mode, limiting magnitudes of20-21 can be obtained in 10-20mn (with average seing conditions of 2.5 arcsecat OHP). The instrument is very users-friendly and can be put into operationsin less than 15mn (rapid change-over from the other instrument in use) ifrequired by the science (like for Gamma-Rays Bursts). Some first scientificresults are described for various types of objects, and in particular for thefollow-up of GRBs. While some further improvements are still under way, inparticular to ease the switch from blue to red setting and add more grisms orfilters, MISTRAL is ready for the follow-up of transients and other variableobjects, in the soon-to-come era of e.g. the SVOM satellite and of the Rubintelescope.