Detection and characterisation of Asteroids with the 4m ILMT

A very unique strength of the Devasthal Observatory will be to combine the detection capability of optical transients by the 4m International Liquid Mirror Telescope (ILMT) with their follow up studies using the 1.3m Devasthal Fast Optical Telescope (DFOT) and/or the 3.6m Devasthal Optical Telescope (DOT), installed right next to the ILMT.

In this context, we have inspected 20 fields having an angular extent of 22’ in declination by 9x22’ in right ascension observed during October/November 2022 during 9 consecutive nights. All these fields were observed with the Sloan i’-band filter during the nights of 28, 29 and 30 October. Defining a transient as being a source appearing clearly on only one of the three i’-band frames and an asteroid candidate as consisting of three transients detected at the three different epochs, having similar angular separations while being properly oriented as a function of time, a total of more than 160 asteroid candidates have been visually identified. Furthermore, we report in these same fields 611 additional i’-band detections of transients which could be other known or new asteroids, highly variable stars, supernova candidates, etc.

Concentrating on just one of those 20 fields, the field with its R.A. (2022.8) starting at 04h32m, we have visually identified 25 known asteroids reported in the database of the Minor Planet Center. Making use of the image subtraction technique applied to the three g’-, r’- and i’-band CCD frames covering this same field (see ILMT poster by P. Kumar et al.), we could identify 10 additional known asteroids reported in the Minor Planet Center database. Furthermore, 142 additional transients have been identified on the basis of the g’-, r’- and i’-band CCD frames covering this unique field.

The conclusion is that in order to detect and characterize new supernovae, micro-lensing events, highly variable stars and quasars among the ILMT transients, we shall first have to identify all known and new asteroids. Thanks to its large diameter and short focal length (f/D ~2.4), the ILMT turns out to be an excellent hunter for asteroids.