What is a UBV source for stars or stellar objects? I was using the V19(VizieR) catalog and the main identifier of the stars was in terms of an 'ID' number which they mentioned as being 'Star number in UBV source' I have no idea what that means. How would I find a more common identifier say  HD/HIP/HR number?
According to the associated paper (to get to this, click on the Bibcode link near the top right in VizieR), this refers to the source of the UBV photometry.
I believe the relevant references are the ones in the V/19/clusters table, e.g. for the second cluster (NGC 188) the reference is to Upgren, Mesrobian &amp; Kerridge (1972). This does provide cross-references, but only to another catalogue of the cluster by Sandage (1962). It isn't particularly surprising that there aren't cross-references to more general catalogues, as identifying which star is which in such crowded fields can be challenging depending on how accurately positions and stellar properties are given.
Tracking some of the other references down is challenging, this is not helped by the fact that the ADS seems to have Romanized several of the names in various different ways, and searching for one Romanization does not return results for the others (at least, nothing came back for &quot;Lavdovskij&quot;, although there are papers attributed to a &quot;V. V. Lavdovsky&quot; and &quot;V. V. Lavdovskii&quot;). I'm not sure how complete ADS coverage of Soviet publications (e.g. Izv. Glav. Astron. Obs. Pulkovo) is.