Information on resource 'The Henry Draper Catalog with Gaia IDs'

This resource grew out of the realisation just how hard it is to do useful things with HD numbers in the VO. In provides the original Henry Draper catalog together with Gaia DR2 source ids for the stars identified in Fabricius et al's Tycho 2-HD match (2002A&A...386..709F)

It was generated as follows (cf. sources):

1. create a database table for the HD catalog with empty columns for the Gaia counterparts. While doing this, precess the B1900 positions to J2000. We haven't bothered with diffrences in the reference catalogs; at the 1 arcminute precision of the HD, this doesn't matter at all. All astrometry coming from HD is for debugging only.

2. Get a mapping from HD numbers to standard Tycho-2 ids from VizieR:

   select HD, n_HD, n_TYC,
     TYC1 || '-' || TYC2 || '-' || TYC3 as tycho_id
   from "IV/25/tyc2_hd"
   

3. Turn the Tycho 2 identifier to a Gaia DR2 source_id using the dr2_tycho_best_neighbour table. It does not exist on VizieR, so we used the ARI-Gaia service:

   select hd, n_hd, n_tyc, source_id
   from gaiadr2.tycho2_best_neighbour
   join TAP_UPLOAD.tyc
   on (tycho_id=original_ext_source_id)
   

   After this procedure, HD 45900, HD 260686, and HD 121169 did not have unique matches. It seemed excessive to complicate the data model just for these three objects. We have randomly dropped one possible match for each of them; in addition, HD 121169 should have had an second match, which did not work out in Gaia DR2. These doubtful cases can be identified by n_TYC=2.

4. Add a Gaia eDR3 source_id by matching the DR2 source_id gaiaedr3.dr2neighbourhood. This frequently has multiple eDR3 objects for a DR2 source_id. In this case, we blindly chose the brightest match, ignoring, for instance, component information that might be present in the DM number. Again, relatively close binaries may be trouble in this catalogue.

5. Complete the source_id, gaia_ra, gaia_dec, n_hd, and n_tyc columns of the table created in step (a) with the data obtained in steps (c) and (d) using the local edr3lite table.

Please report errors and problems to the site operators. Thanks.