A Global Correction to PPMXL Proper Motions

TL;DR

This paper identifies and corrects systematic errors in the PPMXL proper motion catalog by modeling extragalactic sources' apparent motions, providing a magnitude-dependent correction applicable across the sky.

Contribution

It introduces a novel, all-sky, magnitude-dependent correction for PPMXL proper motions based on extragalactic sources, improving accuracy for celestial measurements.

Findings

Corrected proper motions show reduced systematic errors.

The correction is effective across different types of extragalactic sources.

Code for applying the correction is publicly available.

Abstract

In this paper we notice that extragalactic sources seem to have non-zero proper motions in the PPMXL proper motion catalog. We collect a large, all-sky sample of extragalactic objects and fit their reported PPMXL proper motions to an ensemble of spherical harmonics in magnitude shells. A magnitude dependent proper motion correction is thus constructed. This correction is applied to a set of fundamental radio sources, quasars, and is compared to similar corrections to assess its utility. We publish, along with this paper, code which may be used to correct proper motions in the PPMXL catalog over the full sky which have 2 Micron All Sky Survey photometry.