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I have not tried this .edb version of the Tycho catalog but one explanation might be a mismatch in proper motion epochs. The .edb format does not contain the proper motion coefficients so the positions are fixed at some moment (hopefully the preparer of the .edb version moved all positions forward to the same moment) and then this moment is almost surely different than that of any other comparison catalogs.
Again, I have not had a chance to look at the .edb file under discussion, just wanted to toss out this possibility.
Happy holidays...
Elwood |