[Aavso-photometry] Differential vs. absolute magnitudes

[Jeff Hopkins]

Hi Gianluca,

I looked at the AAAVSO web site regarding this and it is confusing. 
They talk about absolute photometry, but then also absolute 
magnitude. I think what they mean by absolute photometry is the 
extraterrestrial instrumental magnitude which would include the 
extinction correction, transformation correction and zero point, all 
this for each band.

I find it strange that the do not recommend differential photometry. 
Perhaps I misunderstand this, but it is a fact differential 
photometry is not only much easier, it also is more accurate.

Personally I think this could be handle better differently. Common 
things like the program star name, comparison star names and notes 
need not be repeated. Just enter the MJD or MHDJ with the filter, 
differential mag,  # of observations averaged, Standard Deviation. 
Does anyone really care what the air mass was or chart used? There is 
a large amount of redundant data they way it is now. And again the 
reference to absolute magnitude is very unprofessional.

Just my opinion.

Jeff


At 13:53 -0700 03/09/2008, gianlucaros at gmail.com wrote:
>I still have some confusion about differential vs. absolute
>magnitudes. If I have understood properly transformation coefficients
>improves the accuracy of the measurements and zero point is necessary
>only for all sky photometry. Concerning the new AAVSO format that asks
>to specify differential vs. absolute magnitudes, does this request
>mean to specify that magnitudes are obtained with either differential
>or absolute photometry? Is the latter possible only if you have the
>standardized magnitude of your comp star? Can I find information about
>standardized magnitudes for comp stars in the photometric table of the
>VSP or shall I calculate myself? I apolologize for asking something
>that perhaps has been already addressed by some of you.
>Gianluca

-- 
Jeff Hopkins
HPO SOFT
Counting Photons
http://www.hposoft.com/Astro/astro.html
Hopkins Phoenix Observatory
7812 West Clayton Drive
Phoenix, Arizona 85033-2439 U.S.A.
(623)849-5889
(623) 247-1190 (Fax)
www.hposoft.com