[vsnet-chat 2172] (fwd) Re: Supernovae estimates using USNO SA2.0

[Taichi Kato <tkato>]

(fwd) Re: [vsnet-chat 2171] Re: Supernovae estimates using USNO SA2.0

Subject: Re: [vsnet-chat 2171] Re: Supernovae estimates using USNO SA2.0 
Date: Sat, 24 Jul 1999 14:25:50 -0400
From: Stupendous Man <richmond@a188-l009.rit.edu>

  Kato-san,

  You and Arne are both right -- the two of you are talking about
two different situations.

  Arne's equation:

> >   Say that you have a sequence of reference (photographic) magnitudes
> > as well as the instrumental counts/magnitudes from your CCD system.
> > You can fit your data like
> >    Mref = a + b * Mccd
> >         = a + b * (-2.5 log (counts))
> >         = a + k * log(counts)

are appropriate when you are given two pieces of information:
     
       a. the magnitudes of some stars in a single passband from
                a photograpic plate, or catalog, etc.

       b. the magnitudes of the same stars in a single passband
                (which is presumably similar to the first passband)
                from some other instrument

  Your equations

>    Mref = a + Mccd + b * (color index)

add another degree of freedom, and will generally do a better job ...
but they require _three_ pieces of information

       a. the magnitudes of some stars in TWO passbands from a 
                photographic plate, or catalog, etc.

       b. the magnitudes of the same stars in a single passband
                from some other instrument


  One should try to use all the information one has in order to match
two magnitude systems as well as possible.  You just assume that there
is more information ...

-- 
-----                                      
Michael Richmond                   "This is the heart that broke my finger."
mwrsps@rit.edu                     http://stupendous.rit.edu/richmond/

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