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A Unique Liquid-Mirror Telescope sees First Light in the Indian Himalayas

Astronomers in India, Belgium and Canada have a new tool with which to view the cosmos with the commissioning of the International Liquid Mirror Telescope (ILMT). This novel instrument employs a 4-metre-diameter rotating mirror made up of a thin film of liquid mercury, to collect and focus light. The telescope is designed to survey the strip of sky passing overhead each night, allowing it to identify transient or variable objects such as supernovae, gravitational lenses, space debris, asteroids, etc. It is located at an altitude of 2450 metre at the Devasthal Observatory campus of Aryabhatta Research Institute of observational sciencES (ARIES), an autonomous institute under the Department of Science and Technology (DST), Govt. of India in Nainital district, Uttarakhand.

Figure 1: A panoramic view of the Devasthal Observatory campus of ARIES at Nainital, Uttarakhand.

Liquid-mirror telescopes take advantage of the fact that the surface of a rotating liquid naturally takes on a parabolic shape, which is ideal for focusing light. A thin transparent film of mylar protects the mercury from wind. The reflected light passes through a sophisticated multi-lens optical corrector that produces sharp images over a wide field of view. A large-format electronic camera, located at the focus, records the images. Prof. Paul Hickson (University of British Columbia, Canada), an expert on liquid mirror technology, added that “the rotation of the earth causes the images to drift across the camera, but this motion is compensated electronically by the camera. This mode of operation increases observing efficiency, and makes the telescope particularly sensitive to faint and diffuse objects.”

Figure 2: Top view of the ILMT located at the Devasthal Observatory of ARIES showing the liquid mercury mirror covered by a thin mylar film.

“ILMT is the first liquid-mirror telescope designed exclusively for astronomical observations installed at the Devasthal Observatory of ARIES” says Prof. Dipankar Banerjee, Director, ARIES. Prof. Banerjee mentioned that Devasthal Observatory now hosts two four-metre class telescopes – the ILMT and the Devasthal Optical Telescope (DOT). Both are the largest aperture telescopes available in the country. Prof. Banerjee is also enthusiastic about the application of Big Data and Artificial Intelligence/Machine Learning (AI/ML) algorithms that will be implemented for classifying the objects observed with the ILMT. He stated “I am hopeful that this project will attract and motivate several young minds from scientific and engineering backgrounds to take up challenging problems.”

“The wealth of data generated with the ILMT survey will be exemplary. In future several young researchers will be working on different science programs utilizing the ILMT data" said Dr. Kuntal Misra who is the Project Investigator of ILMT at ARIES. “When regular science operations begin later this year, the ILMT will produce about 10 GB of data every night, which will be quickly analyzed to reveal variable and transient stellar sources” said Dr. Brajesh Kumar, ILMT Project Scientist at ARIES. The 3.6 metre DOT, with the availability of sophisticated back end instruments, will allow rapid follow-up observations of the newly-detected transient sources with the adjacent ILMT. 

“The data collected from ILMT will be ideally suited to perform a deep photometric and astrometric variability survey over a period of typically 5 years” notes Project Director Prof. Jean Surdej (University of Liège, Belgium and University of Poznan, Poland).

Figure 3: A colour composite photograph of a small portion of the sky observed with the ILMT through the g, r and i Sloan filters. NGC 4274 Galaxy can be seen in the top right corner.

The ILMT collaboration includes researchers from ARIES in India, the University of Liège and the Royal Observatory of Belgium in Belgium, Poznan Observatory in Poland, the Ulugh Beg Astronomical Institute of the Uzbek Academy of Sciences and National University of Uzbekistan in Uzbekistan, the University of British Columbia, Laval University, the University of Montreal, the University of Toronto, York University and the University of Victoria in Canada. The telescope was designed and built by the Advanced Mechanical and Optical Systems (AMOS) Corporation and the Centre Spatial de Liège in Belgium.

This story is also available on DST website.