This is the Henry Draper catalog (HD, Cannon & Pickering 1918-1924)
as distributed by the Astronomical Data Center in 1989 (Vizier
III/135A), with Gaia DR2 source_ids and positions added. The link to
modern Gaia DR2 was done through Fabricius et al's match between HD
and Tycho 2 (Vizier IV/25), TGAS to match Tycho 2 and Gaia DR1, and
Gaia DR2 to match against Gaia DR1.
HSOY is a catalog of 583'001'653 objects with precise astrometry based on
PPMXL and Gaia DR1. Typical formal errors at mean epoch in proper motion are
below 1 mas/yr for objects brighter than 10 mag, and about 5 mas/yr at the
faint end (about 20 mag). South of -30 degrees, astrometry is significantly
worse. HSOY also contains, where available, USNO-B, Gaia, and 2MASS
photometry. HSOY's positions and proper motions are given for epoch J2000.
The catalog becomes severely incomplete faintwards of 16 mag in the G-band.
The mean epochs are typically very close to Gaia's J2015.
HSOY still contains about 0.7% spurious close
"binaries" (non-matched stars) from the original USNO-B (marked with non-NULL
clone). Also, failed matches within Gaia DR1 contribute another 1.5% spurious
pairs (marked with non-NULL comp). In both cases, astrometry presumably is
sub-standard.
More information is available at http://dc.g-vo.org/hsoy.
A catalogue of 541 nearby (within 10pc of the sun) stars, brown
dwarfs, and confirmed exoplanets in 336 systems, as well 21
candidates, compiled from SIMBAD and several other sources. Where
available, astrometry and photometry from Gaia eDR3 has been inserted.
