Astrometric and photometric standard candidates for the upcoming 4-m ILMT survey

TL;DR

This paper provides a catalog of astrometric and photometric standard candidates for the upcoming ILMT survey, leveraging Gaia EDR3, SDSS, and PanSTARRS-1 data, and reports initial positional offsets.

Contribution

It introduces a comprehensive catalog of calibration sources for the ILMT survey, combining Gaia, SDSS, and PanSTARRS-1 data, and assesses initial astrometric offsets.

Findings

Catalog of sources for astrometric calibration derived from Gaia EDR3.

Supplementary photometric catalog including white dwarfs from SDSS.

Reported positional offsets in the ILMT TDI frame compared to Gaia.

Abstract

The International Liquid Mirror Telescope (ILMT) is a 4-meter class survey telescope that has recently achieved first light and is expected to swing into full operations by 1st January 2023. It scans the sky in a fixed 22' wide strip centered at the declination of $+29^o21'41''$ and works in Time Delay Integration (TDI) mode. We present a full catalog of sources in the ILMT strip that can serve as astrometric calibrators. The characteristics of the sources for astrometric calibration are extracted from Gaia EDR3 as it provides a very precise measurement of astrometric properties such as RA ($\alpha$), Dec ($\delta$), parallax ($\pi$), and proper motions ($\mu_{\alpha^{*}}$ & $\mu_{\delta}$). We have crossmatched the Gaia EDR3 with SDSS DR17 and PanSTARRS-1 (PS1) and supplemented the catalog with apparent magnitudes of these sources in g, r, and i filters. We also present a catalog of spectroscopically confirmed white dwarfs with SDSS magnitudes that may serve as photometric calibrators. The catalogs generated are stored in a SQLite database for query-based access. We also report the offsets in equatorial positions compared to Gaia for an astrometrically calibrated TDI frame observed with the ILMT.