PPM-Extended (PPMX) is a catalogue of 18 088 919 stars on the ICRS system containing astrometric and photometric information. Its limiting magnitude is about 15.2 in the GSC photometric system. PPMX consists of three parts:
The typical accuracy of the proper motions is 2 mas/y for 66 percent of the survey stars (1) and the high-precision stars (2), and about 10 mas/y for all other stars. PPMX contains photometric information from ASCC-2.5 and 2MASS.
We performed a rigorous weighted least-squares adjustment of individual observations, spread over more than a century, to determine mean positions and proper motions. The stellar content of PPMX is taken from GSC 1.2 supplemented by catalogues like ARIHIP, PPM and Tycho-2 at the bright end. All observations have been weighted according to their individual accuracy. The catalogue has been screened towards rejecting false entries in the various source catalogues.