[News] Photometry QC's

[Dr. Mark Neeser]

Hi Ronald et al.,

some brief comments on your summary of photometric QC for AW:

> I)   Catalog creation:
>
>      1) Correctly identifying standard stars:
>
>         Depends on : proper astrometric calibration, quality of
>catalogued coordinates
>                      of standard stars.
>
>         Currently, the robustness of identification is improved by
>removing artifacts
>         from the catalog before association with the standard star
>catalog (hot pixels).
>         Also, whenever possible the catalogued coordinates of the
>standard stars are
>         also improved.


Regarding removing artifacts from the catalogues, I would argue that
they should not be there in the first place, and are indicative of
a failure in a previous QC.  Certainly hot pixels should be removed
from the images and not at the late stage of the catalogues.  Either
the bad pixel masks need to be improved (I thought, though, that they
worked fine), or your SExtractor -DETECT_MINAREA parameter is too
small.  Sex should not be detecting single pixels.


>       Suggestions for improvements/points of concern:
>
>          How to monitor and influence the quality of the aperture
>photometry ? Can any
>          meaningful QC scheme be defined for this ? Curves-of-growth ?
>It
>will involve
>          heavy manipulation of SExtractor. Suggestions are welcome.

I think that a curve of growth is the way to go.  A very good algorithm
is given by Stetson in:
http://adsabs.harvard.edu/cgi-bin/nph-bib_query?1990PASP..102..932S
It is also available in the DAOgrow algorithm (Stetson 1990), implemented in the
task mkapfile in digiphotx.photcalx (IRAF).


Cheers,

Mark




=====================================================
Dr. Mark J. Neeser

Institute for Astronomy and Astrophysics,       _/       _/     _/ _/_/  _/
Ludwig-Maximilians-Universitaet Muenchen       _/ _/  _/_/     _/ _/ _/	_/
                                              _/   _/  _/ _/  _/ _/  _/_/
Scheinerstrasse 1,                           _/       _/   _/_/ _/    _/
D-81679 Muenchen, Germany

Tel: +49-89-2180-5995
Fax: +49-89-2180-6003

email:  neeser at usm.uni-muenchen.de