2011-02-08 (MD): Fixed a bug that would give bogus V errors. Also, warning at this
point: the Ru magnitudes result from extrapolating 2MASS magnitudes.
Where those are missing or bad, the Ru magnitudes are bad, too.
2011-06-06 (MD): Silent update: 7836 objects had Ru magnitudes computed although at
least one 2MASS magnitude was NULL. In consequence, these objects had
large negative Ru magnitudes. These erroneous Ru magnitudes are now
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.