LONGSP - THE GORNERGRAT LONGSLIT INFRARED SPECTROMETER

We present a near-infrared cooled grating spectrometer that has been d eveloped at the Arcetri Astrophysical Observatory for the 1.5 m Infrar ed Telescope at Gornergrat (TIRGO). The spectrometer is equipped with cooled reflective optics and a grating in Littrow configuration. The d etector is an engineering grade Rockwell NICMOS3 array (256 x 256 pixe ls of 40 mu m). The scale on the focal plane is 1.73 arcsec/pixel and the field of view along the slit is 70 arcsec. The accessible spectral range is 0.95 - 2.5 mu m with a dispersion, at first order, of about 11.5 Angstrom/pixel. This paper presents a complete description of the instrument, including its optics and cryo-mechanical system, along wi th astronomical results from test observations, started in 1994. Since January 1996, LonGSp is offered to TIRGO users and employed in severa l Galactic and extragalactic programs.