[Aavso-photometry] transformations

[arne]

RICHARD MILES wrote:
> Arne,
> 
> I know your comments are largely directed at all-sky catalogues but can 
> you say something about the CMC-14 catalogue?
> 
> Roger Dymock, myself and John Greaves (yes, John, we've included your 
> name as you drew our attention to the possibility) are co-authors of a 
> paper which Roger and I have submitted to the BAA Journal on the subject 
> of using CMC-14/2MASS data to generate V magnitudes for stars.  You can 
> also use other conversion formulae to generate Rc magnitudes and 
> Sloan-r* mags.  The catalogue has virtually 100% coverage from -30 to 
> +50 Dec  (apart from a gap south of -15 Dec between 5.5-10.5 hours in 
> RA), and is photometrically useful from about 9th mag down to about 15th 
> mag.  BTW: I am currently helping in the development of software to 
> derive automatic plate solutions for V and R based on CMC-14 data, which 
> may be useful for VS observers working in these passbands.  Note that it 
> is primarily intended for observers working filtered or unfiltered on 
> asteroid photometry.  Hopefully the facility should be available shortly.
> 
CMC-14 is an excellent astrometric catalog and a decent photometric catalog.
However, like *every* one of these catalogs, it comes with a list of
caveats.  As you mention, it covers only part of the celestial sphere.
It also has a magnitude limit, r' bandpass that has to be transformed,
blending in crowded regions, etc.  For asteroid work, it is good since
it covers the ecliptic.  As I mentioned in my earlier posting, the
comparison star database uses a dozen catalogs to derive magnitudes,
and one of those is CMC-14.  John Greaves' relation is pretty good
on average for transformation, though there are a number of outliers.
I'm sure you have covered these issues in your article.
Arne