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Pointing of HAGAR telescope mirrors
Gothe, K. S; Prabhu, T. P; Vishwanath, P. R; Acharya, B. S; Srinivasan, R; Chitnis, V. R; Kamath, P. U; Srinivasulu, G; Saleem, F; Kemkar, P. M. M; Mahesh, P. K; Gabriel, F; Manoharan, J; Dorji, N; Dorjai, T; Angchuk, D; D'souza, A. I; Duhan, S. K; Nagesh, B. K; Rao, S. K; Sharma, S. K; Singh, B. B; Sudersanan, P. V; Thsering, M. T; Upadhya, S. S; Anupama, G. C; Britto, R. J; Cowsik, R; Saha, L; Shukla, A
An array of seven atmospheric Cherenkov telescopes was commissioned at a high altitude site in Hanle in the Ladakh region of the Himalayas. The array called HAGAR has been designed to observe celestial γ-rays of energy >100 GeV. Each telescope is altitude-azimuth mounted and carries seven parabolic mirrors whose optic axes are co-aligned with the telescope axis. The telescopes point and track a celestial source using a PC-based drive control system. Two important issues in positioning of each HAGAR telescope are pointing accuracy of telescope axis and co-alignment of mirrors’ optic axes with the telescope axis. We have adopted a three pronged strategy to address these issues, namely use of pointing models to improve pointing accuracy of the telescopes, RA-DEC scan technique to measure the pointing offsets of the mirrors and mechanical fine-tuning of off-axis mirrors by sighting a distant stationary light source. This paper discusses our efforts in this regard as well as the current status of pointing and monitoring of HAGAR telescopes.
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The original publication is available at springerlink.com