[vsnet-alert 9908] re DA55 aka QSO B0133 +47 - arithmetic correction

[da55 at Safe-mail.net]

> V=r'-0.60(J-Ks)-0.03

that's wrong, it's

V=r'+0.60(J-Ks)-0.03

Sorry about that, the brain, it leaks.



[CMC14 goes from -30 to +50 declination, carries standard deviations for multiple photometric solution observations, and is examinable via VizieR.  loneos.phot is of course courtesy Brian Skiff, and also available via VizieR.  2MASS too.

There's no excuse nowadays for anyone not having a sequence with objects good to plus or minus 0.1 V between about V 9.5 and 14.5, possibly even 15.5, between these declinations, consequently.

As loneos.phot can be downloaded from CDS ftp, and matched against CMC14 at one arcsec resolution (because Brian Skiff took a great deal of effort in the astrometric referencing of loneos.phot) folk can readily generate their own relation for V-r' versus J-Ks and via that derive their own transformations if preferred.

Yer get the "global" standard deviation aspect by taking said listed loneos.phot V values and their difference from all the via r', J and Ks derived ones, for thousands to tens of thousands of objects, and taking the standard deviation on that.

Or just use the above anywhere where CMC14 stuff exists, trying not to use anything red, and hopefully using stuff with small errors in r' and J and Ks, and accepting that safe faint limit for J is about 15.5, for Ks about 14.5 and for r' about 15.5 or so, although it can be pushed further, but don't expect too much, but still preferable to using USNO A2.0.

For Galactic fields |b| < 5 r' from IPHAS and J and K from UKIDSS will be increasingly usable too, except former isn't yet formally calibrated and has a bit of an offset it seems, and coverage for latter is still small in the publicly available arena.  Basic V from SDSS g' and r' formulae work just as well as fancy ones, and usually agree well with CMC14 where they overlap (in terms of both coverage and magnitude range), and in some test cases I've checked, V from these two latter always compare well against Henden photometry for CV fields, all usually within 0.1 of each other.  SDSS dr5 photometric catalogue is also available via VizieR.

A lot of stuff hasn't been a problem for a long time, but folk are stubborn, and pick the wrong stuff to trust based on whatever logic they use, no matter how untested and unassessed it really is (or just can't be bothered if they've to do a bit of arithmetic by hand).  Like V from YB6 for one example, which is V from photographic survey plates, so isn't going to improve greatly over using V from POSS survey plates, although is a bit better than those].

John