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Re: brief note on astrometry of Mark IV comatic images
On Thu, 01 Jun 2000 00:47:13 +0100, Andrew Bennett <andrew.bennett@ns.sympatico.ca> wrote:
*>On Sun, 28 May 2000 19:34:29 -0500, you wrote:
*>
*>>I find that I am getting 6000 or so stars per medium star density image=20
*>>when I set things to detect to mag 15 or so. This is 600+ pixels per=20
*>>star. On these images it is hard to find star pairs where it might be a=
*>=20
*>>problem to separate them. I am waiting patiently to get an image in =
*>the=20
*>>milky way to look at. It looks (by eye) pretty easy to separate stars 5=
*>=20
*>>pixels apart.
*>
*>Confusion errors are insidious. They don't show
*>up on image to image comparisons unless you change
*>the PSF i.e buy a bigger telescope. I just got out=20
Tom, if you have a list of 6000 detections, how about sorting them by
location and see if any of them overlap? For instance, if your software
produces a list by pixel location, and uses an aperture of say five pixels;
would it "find" an overlapping pair as two candidates with positions that are
LESS than five pixels apart? (Make sure your software does not automatically
reject such candidates.)
Er, "sort" is a MS-DOS utility program. If you do this manually remember
to use root 2 times the aperture as the distance for each axis - in
my example that's 7 pixels or so. A QBASIC program could read a sorted
list and look if X (or Y) changes by less than 7, and print both lines.
If your list was in a database, or even a spreadsheet, I
imagine a proper query would find them. No doubt one of our colleagues
could take your list and do this work in less than a hour, given the
proper info and your list.
Herb Johnson
Herbert R. Johnson http://pluto.njcc.com/~hjohnson
hjohnson@pluto.njcc.com voice 609-771-1503, New Jersey USA
amateur astronomer and astro-tour guide
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