[vsnet-alert 10910] Re: re FWD ATEL 1892

[qso at Safe-mail.net]

The origin of the V mag in NOMAD is the unpublished YB6.

I mainly mention this because some people have a fascination with this catalogue, almost like ufology or something, this mystical catalogue that apparently has "Johnson B and V photometry" must be obtained, and much will be good.

Well, here YB6 says V is 13.3, ucac2 red sensitive instrumental says 13.6, ASAS3 V says 14.0, USNO A2.0 converted from A2.0 red and blue mags to V via Kato-san's conversion says 14.0, GSC 1.x/ACT says 13.9, NSVS red sensitive instrumental says 14.0, CMC14 r' says 13.8.

Using anything but YB6 V would be nearer, it seems.

Y means photographic survey plates with a yellow filter bunged in front of them.  B means blue plates, I don't know whether the Yale proper motion surveys used a blue filter with those or not.  That's the photometric context.  6 means 6th processing or edition or whatever via USNO NOFS PMM, primarily an astrometric exercise.

I've seen NOMAD used in papers for statistical assessment of common proper motion pairs, including some of its compilers in that paper's authors, which is logical for mixed pairs of bright and faint components.  I've seen NOMAD used for astrometry, albeit often with claims of superiority over its component parts despite the illogic of such claims, and I've seen it used photometrically in numerous places (I forgot to include GCN in the earlier list) and people seem eager to get at its YB6 V and B photometry.

Nope.

Cheers

John