Rejecting neighbors in crowded star fields

[Guest]

On Thu, 29 Sep 2005 10:30:38 -0700
Steve Asztalos <asztalos1@llnl.gov> wrote:

>
> Hi,
>
> I've been running IRAF on some Gemini South image data taken in the
> R-band in May 20005. I'm interested in weak lensing and hence require
> uncontaminated, isolated objects for my analyses.
>
> My approach to this to date has been rather clumsy: I run daoedit and
> daofind on my images to construct and object list. Then, I manually
> inspect a bright subset of these stars using pstselect and psf,
> rejecting those stars whose psfs look visually contaminated.
>
> This procedure is not automated and hence not sustainable for the
> piepline analysis I had envisioned. At the least, it would be useful
> if stars rejected when running psf were excised from the .coo list
> automatically. Any thoughts or suggestions on how to to a better job
> of rejecting close neighbors?
>
> Sincerely,
>
> Steve - LSST

Hi Steve,

I apologize for the delayed reply; I was out of the office for the past
week.

Have you looked at pselect? You can use it to select a subset of the
records using various expressions/constraints (see 'phelp pselect').

Another task you can use is pexamine. This task is typically
interactive, though you could probably reduce (and maybe eliminate) the
interactive nature through the use of an image display cursor file or
graphics cursor file. From the documentation, this seems to write to
two files, one which is an accepted list, while the other is the
deletions list (though you need to specify the name in the
parameters). See 'phelp pexamine' for more details.

Once you have a good psf model, you can use substar to subtract the
close neighbors from the image. This is probably more 'manual' than
you would like, however.

Another suggestion is to take a look at the version of DAOPHOT written
by Peter Stetson (IRAF/NOAO's daophot is derived from an earlier
version). I'm not sure how useful it would be in pipelines, but it
may be worth a look. He's at DAO in Canada; his contact information
can be found at the following URL:

http://www.hia-iha.nrc-cnrc.gc.ca/staff/stetson_e.html

Finally, and in case you haven't read it already, there is a DAOPHOT
manual written by Lindsey Davis, which can be found at:

http://iraf.noao.edu/iraf/ftp/iraf/docs/daorefman.ps.Z

I hope that helps. Let me know if you have further questions.

Phillip


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