Re: Analyzing Data

["Robert Creager" <robert_creager@logicalchaos.org>]

Andrew,

Will this help? http://star-www.st-and.ac.uk/starlink/stardocs/sc6.htx/node32.html

Sorry,
Rob

Andrew Bennett <andrew.bennett@ns.sympatico.ca> wrote ..
> On Sun, 4 Aug 2002 17:29:22 -0400, Michael Richmond wrote:
> 
> >
> >  Doug wrote:
> >
> >> I suspect that a very successful minor modification to the
> >> WS statistic would be for it to calculate residuals from a
> >> given night's mean magnitude instead of a global mean magnitude.
> >> This would get rid of the effects of zero-point changes which
> >> aren't currently calibrated out.
> >
> >  Doug, can you clarify that last statement?  The current pipeline
> >gives each image a zero-point value based on the instrumental magnitudes
> >of Tycho stars in the frame.  If two frames cover the same patch
> >of sky on two nights, they should share the same Tycho stars.
> >I don't see how large zero-point offsets could remain; perhaps I'm
> >looking at it the wrong way.
> >
> >                                    Michael
> 
> A long time ago, before I quit on TASS in favour of
> pruning grape vines, I was beating my head against just
> this problem in DS20.
> 
> The basic problem seems to be that two frames on different
> nights don't cover the same patch of sky, don't share the 
> same Tycho stars and do manage to have unexpectedly large
> zero-point offsets. What is worse is that these offsets
> seem to manage to afflict individual stars without
> affecting all nearby stars in the same way ...
> 
> I spent several months trying to get ensemble correction
> to work using a selected area smaller than the whole
> image and, as programmed be me, it did damn all good.
> 
> In order to look for tree branches and roofs in the data,
> one needs to convert from celestial back to local
> coordinates e.g. HA & elevation. Could somebody remind
> me of the right way to do this?
> 
> Andrew Bennett, Avondale Vineyard