The 4-m International Liquid Mirror Telescope project

Abstract: The International Liquid Mirror Telescope (ILMT) project is a scientific collaboration in observational astrophysics between the Liège Institute of Astrophysics and Geophysics (Liège University, Belgium), the Aryabatta Research Institute of Observational Science (ARIES, Nainital, India) and several Canadian universities (British Columbia, Laval, Montréal, Toronto, Victoria and York). Meanwhile, several other institutes have joined the project: the Royal Observatory of Belgium, the National University of Uzbekistan and the Ulugh Beg Astronomical Institute (Uzbekistan) and the Poznan Observatory (Poland).
The Liège company AMOS (Advanced Mechanical and Optical Systems) has fabricated the telescope structure that has been erected on the ARIES site in Devasthal (Uttarakhand, India). It is the first liquid mirror telescope being dedicated to astronomical observations.
First light has been obtained on 29 April 2022 and commissioning is going on at the present time.
In this poster, we describe and illustrate the different components of the ILMT and their functions.
Taking advantage of the best seeing conditions and atmospheric absorption towards the zenith, the ILMT performs a deep survey and high S/N photometric and astrometric observations in the SDSS g’, r’ or i’ spectral bands of a narrow strip of sky (22’ in declination) passing over the zenith. In combination with a highly efficient 4kx4k CCD camera and a dedicated optical corrector, the images are being secured at the prime focus of the telescope using the Time Delayed Integration (TDI) technique. The singly scanned CCD frames correspond to an integration time of 102 sec, corresponding to the time an object’s image remains within the active area of the detector. The ILMT presently reaches 21 mag (g-band) in a single scan but this limiting magnitude can be further improved by co-adding the nightly images.
The uniqueness of good cadence (one day) and deeper imaging with the ILMT make it possible to detect and characterize artificial satellites and space debris (see Hickson et al.’s ILMT poster, hereafter ILMTP), solar system (see Pospieszalska et al.’s ILMTP), galactic (see Grewal et al.’s ILMTP) and extra-galactic objects (see Akhunov et al. + Sun et al. + B. Kumar et al.’s ILMTPs).
The fast f/D ~2.4 ratio of this telescope is particularly well adapted to the detection and characterization of low surface brightness objects (see Fu et al.’s ILMTP). Several examples of very extended and faint galactic nebulae observed with the ILMT are presented.
An image subtraction technique is also being applied to the nightly recorded observations in order to detect transients, objects exhibiting variations in flux or position (see P. Kumar et al.’s ILMTP).
Science data acquired during the fall of 2022 are being made freely available to the scientific community (see Misra et al.’s ILMTP).