# Duplicate entries in Tycho-2 main and supplement 1

When checking the internal consistency of the Tycho-2 catalogue, I came across 254 entries in the main catalogue file that are also present in supplement 1 (the Hipparcos/Tycho-1 stars not included in Tycho-2). These entries have the same TYC1/2/3 identifiers, and the same HIP number, but they refer to different CCDM components. For all but a few cases, the A component is found in the main catalog file, while the B component is found in supplement 1. From the description Tycho-2 catalogue guide, I would expect these stars to have at least a different TYC3 identifier. Does anybody know why these stars were not given a unique TYC identifier?

Brightest example: HIP 84606 (TYC 2604-1775-1)

I loaded the Tycho-2 catalogue into a MySQL database, the following query selects all the duplicate entries, ordered by increasing magnitude:

SELECT tyc, MIN(HIP) AS hip, MIN(VTmag) AS mag FROM
(
SELECT CONCAT(TYC1, '-', TYC2, '-', TYC3) AS tyc, HIP, VTmag FROM tyc2
UNION ALL
SELECT CONCAT(TYC1, '-', TYC2, '-', TYC3) AS tyc, HIP, VTmag FROM suppl_1
UNION ALL
SELECT CONCAT(TYC1, '-', TYC2, '-', TYC3) AS tyc, HIP, VTmag FROM suppl_2
) AS t1
GROUP BY tyc HAVING COUNT(tyc)>1 ORDER BY mag ASC

• Could you confirm your source is cdsarc.u-strasbg.fr/cats/I/259 – user21 Jan 11 '17 at 14:18
• That's indeed where I retrieved the Tycho-2 catalogue from. To be sure nothing fishy happened when I converted the raw data files to my database, I checked that the files themselves do indeed contain the duplicates as well. – Roel Zinkstok Jan 12 '17 at 10:05