Re: Data reduction methodology for V-I colors

[Chris Albertson <chrisalbertson90278@yahoo.com>]

Could it be that the zero point is really a function of
(x,y) on the frame and that using one "zero point" for the
entire frame is only a gross approximation of the true
"zero function".  It seems unlikely to me that the atmosphere
really is equally transparent over a degrees wide field.

Professionals may  have been using zero points for years but
how many of them use wide feild images?

One experiment might be to plot the difference between
instrumental and catalogged magnitutes and see if the differences
"clump" togeter.  If there were a cloud blocking
half the frame you would see it.  But more subtle effects
might also be detectable.

If the transpaarency does vary across a frame at the few percent
level then maybe you will have to compute some kind of "zero
function".

The "gradient" Tom talked about seems like it might headed in 
this direction.  "gradient" is a kind of fuction (a first order
one.) but I supect a tilted plain will not fit much better then
our current zeroth order function.  The physical atmosphere is
likey bumpy with sharp discontinuities.




--- Thomas Droege <tdroege2@earthlink.net> wrote:

> I will leave this for Michael.  I have just looked at data sets as a
> whole.
> Why not join in the fun?  There is lots of data.  Andrew, Michael and
> I
> have been working on this.   There is room for more clever minds to
> puzzle
> over the data.  As always, I stand willing to copy CDs for anyone
> willing
> to compute on the data.  
> 
> Tom Droege
> 
> 
> > [Original Message]
> > From: Michael Koppelman <lolife@bitstream.net>
> > To: <tdroege2@earthlink.net>
> > Cc: tass <tass@listserv.wwa.com>
> > Date: 8/31/2004 12:24:00 PM
> > Subject: Re: Data reduction methodology for V-I colors
> >
> > But aren't you getting a different zeropoint solution for every
> frame? 
> > Why not use a single zeropoint for the entire night?
> >
> > On Aug 31, 2004, at 12:20 PM, Thomas Droege wrote:
> >
> 
> 
> 
> 


=====
Chris Albertson
  Home:   310-376-1029  chrisalbertson90278@yahoo.com
  Cell:   310-990-7550
  Office: 310-336-5189  Christopher.J.Albertson@aero.org
  KG6OMK


		
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