The ATLAS All-Sky Stellar Reference Catalog

TL;DR

The paper presents the creation of an all-sky stellar reference catalog, ATLAS Refcat2, combining multiple data sources to improve photometric calibration for sky surveys, achieving high completeness and low systematic errors.

Contribution

It introduces ATLAS Refcat2, a comprehensive all-sky star catalog that enhances photometric calibration accuracy for sky surveys by integrating diverse data sources.

Findings

Achieves at least 99% completeness to magnitude 19.

Systematic errors are no larger than 5 millimag RMS.

Errors can reach 20 millimag near the galactic plane.

Abstract

The Asteroid Terrestrial-impact Last Alert System (ATLAS) observes most of the sky every night in search of dangerous asteroids. Its data are also used to search for photometric variability, where sensitivity to variability is limited by photometric accuracy. Since each exposure spans 7.6 deg corner to corner, variations in atmospheric transparency in excess of 0.01 mag are common, and 0.01 mag photometry cannot be achieved by using a constant flat field calibration image. We therefore have assembled an all-sky reference catalog of approximately one billion stars to m~19 from a variety of sources to calibrate each exposure's astrometry and photometry. Gaia DR2 is the source of astrometry for this ATLAS Refcat2. The sources of g, r, i, z photometry include Pan-STARRS DR1, the ATLAS Pathfinder photometry project, ATLAS re-flattened APASS data, SkyMapper DR1, APASS DR9, the Tycho-2 catalog, and the Yale Bright Star Catalog. We have attempted to make this catalog at least 99% complete to m<19, including the brightest stars in the sky. We believe that the systematic errors are no larger than 5 millimag RMS, although errors are as large as 20 millimag in small patches near the galactic plane.