The PPMXL catalog of positions and proper motions on the ICRS. Combining USNO-B1.0 and 2MASS

TL;DR

The paper presents the creation of PPMXL, a comprehensive full-sky catalog combining USNO-B1.0 and 2MASS data to provide accurate positions and proper motions on the ICRS for about 900 million objects, enhancing astrometric resources.

Contribution

It introduces PPMXL, the largest ICRS proper motion catalog, by combining USNO-B1.0 and 2MASS data, and addresses previous limitations of other catalogs like UCAC3.

Findings

PPMXL contains about 900 million objects with proper motions.

Typical proper motion errors range from 4 to 10 mas/y.

Position errors at epoch 2000.0 are 80 to 300 mas.

Abstract

USNO-B1.0 and 2MASS are the most widely used full-sky surveys. However, 2MASS has no proper motions at all, and USNO-B1.0 published only relative, not absolute (i.e. on ICRS) proper motions. We performed a new determination of mean positions and proper motions on the ICRS system by combining USNO-B1.0 and 2MASS astrometry. This catalog is called PPMXL {VO-access to the catalog is possible via http://vo.uni-hd.de/ppmxl}, and it aims to be complete from the brightest stars down to about $V \approx 20$ full-sky. PPMXL contains about 900 million objects, some 410 million with 2MASS photometry, and is the largest collection of ICRS proper motions at present. As representative for the ICRS we chose PPMX. The recently released UCAC3 could not be used because we found plate-dependent distortions in its proper motion system north of -20$^\circ$ declination. UCAC3 served as an intermediate system for $\delta \leq -20^\circ$. The resulting typical individual mean errors of the proper motions range from 4 mas/y to more than 10 mas/y depending on observational history. The mean errors of positions at epoch 2000.0 are 80 to 120 mas, if 2MASS astrometry could be used, 150 to 300 mas else. We also give correction tables to convert USNO-B1.0 observations of e.g. minor planets to the ICRS system.