Fixing the Reference Frame for PPMXL Proper Motions Using Extragalactic Sources

TL;DR

This paper identifies and corrects systematic errors in PPMXL proper motions by using extragalactic sources, improving the accuracy of celestial reference frames especially in under-sampled regions.

Contribution

It introduces a new correction method for PPMXL proper motions using combined extragalactic sources from LAMOST and quasar catalogs, addressing regional sampling gaps.

Findings

Confirmed global proper motion shifts in PPMXL

Detected smaller-scale fluctuations in proper motion corrections

Provided a comprehensive correction table for 158,106 extragalactic objects

Abstract

We quantify and correct systematic errors in PPMXL proper motions using extragalactic sources from the first two LAMOST data releases and the Veron-Cetty & Veron Catalog of Quasars. Although the majority of the sources are from the Veron catalog, LAMOST makes important contributions in regions that are not well-sampled by previous catalogs, particularly at low Galactic latitudes and in the south Galactic cap. We show that quasars in PPMXL have measureable and significant proper motions, which reflect the systematic zero-point offsets present in the catalog. We confirm the global proper motion shifts seen by Wu, Ma, & Zhou (2011), and additionally find smaller-scale fluctuations of the QSO-derived corrections to an absolute frame. We average the proper motions of 158,106 extragalactic objects in bins of 3x3 degrees and present a table of proper motion corrections.