Coordinate file generated by daofind is empty
Arghya wrote on May 24, 2022
Hi ,
I am currently a beginner with IRAF and am trying to overplot the coordinate file generated by Daofind package , but unfortunately the file has no data , only the header names ,format and units. I have tried experimenting with different parameters but to no avail. Daofind works fine for my image in python so my image file is not the issue. Any help is appreciated.
Mike Fitzpatrick wrote on May 24, 2022
Without seeing the image or the parameters you used I can't offer any specific advice. An empty coordinate file usually means there was some kind of error in how the DATAPARS or FINDPARS parameters were set, e.g. a bad FWHM value or sky level, finding threshold set inappropriately, etc. You might have a look at pg 38-45 of the "Guide to Stellar CCD Photometry" (https://iraf.net/irafdocs/daophot2/) for info on how to set the parameters for DAOFIND.
I assume when you say "DAOFIND in python" you're referring to something like the astropy photutils tasks? I'm not familiar with those, but note there may be differences in how parameters are set (e.g. pixel sizes vs arcsec, are values in ADU, etc).
Arghya wrote on May 25, 2022
So i used daofind in interactive mode and used the curson option (spacebar) and that resulted in a coordinate file but its clearly not accurate. (see image) . Running daofind in non interactive mode gives empty coordinate file.
Arghya wrote on May 25, 2022
Mike Fitzpatrick wrote on May 26, 2022
The multiple detections in saturated features is usually seen when the parameters aren't set properly for the data (i.e. the DATAPARS pset) or the detection limits are off. The screenshot isn't clear enough for me to read the terminal, by "see the image" I meant I would need the actual FITS file as well as a dump of the parameters you used (e.g. "cl\$this-\$this->_split2($m[0])_split2($m[0]) dpar daofind", and same for datapars/findpars).
Also suspicious is the image name being "3.fits", in general numeric image name should be avoided since image extensions are sometimes removed to create other filenames which can get confused with a numeric value. Did you end up changing any of your initial parameter values after reading the documentation of how they should be set or were you pretty close already?
Last post on May 26, 2022