The 4 m International Liquid Mirror Telescope: Construction, operation, and science

¹ Institute of Astrophysics and Geophysics, Liège University, Allée du 6 Août 19c, 4000 Liège, Belgium
² Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital, 263001 Uttarakhand, India
³ Department of Physics and Astronomy, The University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada
⁴ Outer Space Institute, The University of British Columbia, 325-6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada
⁵ Deen Dayal Upadhyay Gorakhpur University, Civil Lines, Gorakhpur 273009, Uttar Pradesh, India
⁶ National University of Uzbekistan, Department of Astronomy and Astrophysics, 100174 Tashkent, Uzbekistan
⁷ Ulugh Beg Astronomical Institute of the Uzbek Academy of Sciences, Astronomicheskaya 33, 100052 Tashkent, Uzbekistan
⁸ Centre for Optics, Photonics and Lasers, Université Laval, 2375 rue de la Terrasse, Québec, Quebec G1V 0A6, Canada
⁹ Mahatma Jyotiba Phule Rohilkhand University, Pilibhit Bypass Road, Bareilly 243006, Uttar Pradesh, India
¹⁰ Research School of Astronomy & Astrophysics, Australian National University, Mt Stromlo Observatory, Cotter Road, Weston Creek 2611 ACT, Australia
¹¹ South-Western Institute for Astronomy Research, Yunnan University, Kunming 650500, Yunnan, P.R. China
¹² Inter-University Centre for Astronomy and Astrophysics (IUCAA), Post Bag 4, Ganeshkhind, Pune 411007, India
¹³ Indian Space Research Organization, Bengaluru, Karnataka, India
¹⁴ University of Calcutta, 87/1 College Street, Kolkata 700073, India
¹⁵ Instituto de Astrofísica, Pontificia Universidad Católica de Chile, Av. Vicuña Mackenna 4860, 7820436 Macul, Santiago, Chile
¹⁶ Department of Physics, Ashoka University Rai, Sonipat, Haryana 131029, India

^★ Corresponding author; jsurdej@uliege.be

Received: 18 October 2024
Accepted: 6 January 2025

Abstract

The International Liquid Mirror Telescope (ILMT) project was motivated by the need for an inexpensive 4 metre diameter optical telescope that could be devoted entirely to astronomical surveys. Its scientific programmes include the detection and study of transients, variable objects, asteroids, comets, space debris and low surface brightness galaxies. To this end, a collaboration was formed between the Institute of Astrophysics and Geophysics (Liège University, Belgium), several Canadian universities (University of British Columbia, Laval University, University of Montreal, University of Toronto, York University, University of Victoria) and the Aryabhatta Research Institute of Observational Sciences (ARIES, India). After several years of design work in Belgium and construction in India on the ARIES Devasthal site, the telescope saw its first light on 29 April 2022. Its commissioning phase lasted from May 2022 until June 2023 (beginning of the monsoon). The ILMT was inaugurated on 21 March 2023 and has been in regular operation since October 2023. The telescope continuously observes the sky passing at the zenith using the SDSS ɡ′, r′, and i′ filters. This paper describes the ILMT, its operation, performance and shows some initial results.