Quasar catalogue for the astrometric calibration of the forthcoming ILMT survey
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J. Astrophys. Astr. (2020) 41:22 https://doi.org/10.1007/s12036-020-09642-x
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Quasar catalogue for the astrometric calibration of the forthcoming ILMT survey AMIT KUMAR MANDAL1,4,*, BIKRAM PRADHAN2, JEAN SURDEJ3, C. S. STALIN4,
RAM SAGAR4 and BLESSON MATHEW1 1
Department of Physics, CHRIST (Deemed to be University), Hosur Road, Bangalore 560 029, India. Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital 263 001, India. 3 Space Science, Technologies and Astrophysics Research (STAR) Institute, Universite´ de Lie`ge, Alle´e du 6 Aouˆt 19c, 4000 Lie`ge, Belgium. 4 Indian Institute of Astrophysics, Block II, Koramangala, Bangalore 560 034, India. E-mail: [email protected] 2
MS received 27 May 2020; accepted 13 July 2020 Abstract. Quasars are ideal targets to use for astrometric calibration of large scale astronomical surveys as they have negligible proper motion and parallax. The forthcoming 4-m International Liquid Mirror Telescope (ILMT) will survey the sky that covers a width of about 270 . To carry out astrometric calibration of the ILMT observations, we aimed to compile a list of quasars with accurate equatorial coordinates and falling in the ILMT stripe. Towards this, we cross-correlated all the quasars that are known till the present date with the sources in the Gaia-DR2 catalogue, as the Gaia-DR2 sources have position uncertainties as small as a few milli arcsec (mas). We present here the results of this cross-correlation which is a catalogue of 6738 quasars that is suitable for astrometric calibration of the ILMT fields. In this work, we present this quasar catalogue. This catalogue of quasars can also be used to study quasar variability over diverse time scales when the ILMT starts its observations. While preparing this catalogue, we also confirmed that quasars in the ILMT stripe have proper motion and parallax lesser than 20 mas yr1 and 10 mas, respectively. Keywords. Quasars—parallaxes—proper motions—ILMT—astrometry.
1. Introduction The 4-m International Liquid Mirror Telescope (ILMT) which will observe in the Time Delayed Integration (TDI) mode is expected to be commissioned soon on the Aryabhatta Research Institute of Observational Sciences (ARIES) site in Devasthal, India (Surdej et al. 2018). The ILMT will be repeatedly scanning the sky within a narrow stripe of width 270 . The positions of the celestial objects in the sky change with time as the sky moves across the fixed detector surface due to the rotation of the Earth around the polar axis. The TDI mode of the charge couple device (CCD) mounted at the ILMT helps to track the
stars by registering the electronic charges with the rate at which the target source drifts across the detector (Surdej et al. 2018) and the positions of each object in the observed image come out in pixel units. To convert the observations from the pixel coordinate system to the world coordinate system (a, d) we need to carry out astrometric calibration of the ILMT fields. For that, we
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