The 3,6 m Indo-Belgian Devasthal Optical Telescope : General description

Abstract

In 2007, AMOS SA signed a contract for the design and building of a 4M class telescope with ARIES (Aryabhatta Research Institute of Observational Sciences) India. Today the telescope is constructed and ready to be shipped in India. The telescope will be installed at Devasthal, in the Himalayan range, 2500m above the sea; 350 km North of Delhi. The optical combination is a Ritchey-Chrétien type with a Cassegrain focus where the light beam can be directed toward a main port designed for interfacing an instrument with a mass up to 2 tons or toward two side ports for smaller instruments. The primary mirror unit is an active system that controls the mirror figure to keep the telescope wavefront error in the specification for any operational conditions. The mount type is an alt-azimuth. The Telescope design was presented 4 years ago at Marseille; since then it has been fully assembled and tested at sub-system and system levels in AMOS assembly hall. This paper starts with a reminding of the specifications and the optical design. Then an overview of the as built telescope and a presentation of the tests made in factory are given.