Upgrading the AZT24 telescope at the Campo Imperatore high-altitude observatory: design and installation of a new, seeing-enhanced NIR imager

The AZT24 is a 1.1m telescope installed at the Campo Imperatore observing station, in Central Italy, at an elevation of 2200 m a.s.l. Since the 2nd half of 1990s, its focal plane has been equipped with SWIRCAM, a 1-2.5 micron camera based on an LN2-cooled, HgCdTe detector, able to exploit the excellent observing conditions offered by the site, especially at those wavelengths. After almost 30 years of operation, this system will now be upgraded with a new IR imager, based on an InGaAs detector, TEC-cooled at around -80 °C. Even with a reduced spectral coverage, the NIR imager will cover a wider field-of-view and will benefit from the seeing-enhancement capability produced by a devoted Tip-Tilt (TT) corrector. The overall project is presented in this paper, with emphasis on a commercial InGaAs detector for astronomical applications. The opto-mechanical layout is optimized to reduce the instrumental thermal background, while the TT-correction system produces a significant narrowing of the PSF, increasing the signal-to-noise ratio of the detected sources. Simulations of the expected performances are reported: they show that the upgraded system is suitable for a number of science cases, ranging from extragalactic Astronomy to stellar Astrophysics and Solar System studies. In addition, it represents an interesting testbench for some technological investigations, both in the field of Adaptive Optics and in that of data acquisition and processing techniques.