RE: Data reduction methodology for V-I colors

[Richard Klappal <klappal@xnet.com>]

I think the biggest contribution to "scattered light" would be humidity
variation overnight, and the resulting backscatter of light pollution and
loss of sky transparency.  Those influences change continuously across the
night, pretty much negating any "one factor per night".

Rich


-----Original Message-----
From: owner-tass@listserv.wwa.com [mailto:owner-tass@listserv.wwa.com]On
Behalf Of Doug Welch
Sent: Tuesday, 31 August, 2004 14:02
To: Chris Albertson
Cc: tdroege2@earthlink.net; tass@listserv.wwa.com
Subject: Re: Data reduction methodology for V-I colors



If the correction is a function of magnitude, then scattered
light may be a factor. This may be scattered light in the
flat and not in an actual image.

Cheers,
Doug

On Tue, 31 Aug 2004, Chris Albertson wrote:

>
> 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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--
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 Douglas L Welch     | Res office/voicemail (905) 525-9140 x23186
 Physics & Astronomy | FAX                  (905) 546-1252
 McMaster University |
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