S.Gennari (1) and L.Vanzi (2)
(1) Osservatorio Astrofisico di Arcetri, Largo E.Fermi 5, 50125 Firenze, Italy
(2) Università degli Studi di Firenze - Dipartimento di Astronomia, Largo E.Fermi 5, 50125 Firenze, Italy
We present a new cooled grating near infra-red spectrometer designed to acquire spectra at the TIRGO telescope in the 0.9-2.5 micron region with a resolving power of 1000, equiped with a Rockwell NICMOS 3 detector.
keywords: Infrared Spectroscopy :: NICMOS 3 :: TIRGO
The spectrometer has a spectral resolution in the range $300/div4000$, an angular resolution of 1.73 arcsec/pix on a field of 70 arcsec and it operates in the near infrared ($0.9/div2.5/mu m$).
The detector is a Rockwell $256/times 256$ NICMOS3 engineering grade array of which is used a subsection of $70/times40$ pixel is used.
The optical design of the spectrometer is presented in fig.1: The lens B is a field lens. The mirros D and E are a cassegrain system (f/20) that collimates the optical beam coming from the telescope. The collimated beam is reflected on the grating G by the plane mirrow F. Finally the camera of the spectrometer (mirrors H and I), focalize the radiation on the detector L.
All the mirrors are gold coated. The grating has 150 grooves per mm and a blaze of 8.6 degree (2 micron at the first order) and is used in the Littrow configuration, the back side is a plane mirror that can be used to obtain images of faint sources.
The grating motion is assured by an external motor via a ferrofluidic feedthrough, two internal stepper motors allow the selection of slits and filters in the positions A and C.
A little amount of active charcoal is present in order to maintain the value of the pressure required (10e-4 mb) for a sufficiently long time (more than 20 days):.
The cooling and heating times are shorter than 7 hours and the rate of evaporation of the nitrogen from the main reservoir allows about 19 hours of operation in working conditions.
S.Gennari, L.Vanzi (1993) - Mem.S.A.It. (in press)
S.Gennari (1993) - Technical Report of Astrophysical Observatory of Arcetri 6/1993