Problem with imexamine & phot
rachel wrote on Jul 12, 2006
Hi,
I am trying to remove stars from an image in order to do photometric analysis on a galaxy. I am running the killall task, created by Buta and McCall (see Buta R.J. & McCall M.L. 1999, ApJ, 124, 33). It locates the stars using daofind and measures the magnitudes using phot. The problem I am having is that there are discrepancies between the output list of stars' measured magnitudes and the magnitudes for the same stars measured in imexamine. They differ by almost 10 magnitudes.
I have tried changing different parameters in both tasks, but I cannot seem to figure out what the difference is caused by. If anyone could offer some insight to this problem and into the tasks of phot and imexamine, it would be much appreciated.
Thank you.
-rachel
I am trying to remove stars from an image in order to do photometric analysis on a galaxy. I am running the killall task, created by Buta and McCall (see Buta R.J. & McCall M.L. 1999, ApJ, 124, 33). It locates the stars using daofind and measures the magnitudes using phot. The problem I am having is that there are discrepancies between the output list of stars' measured magnitudes and the magnitudes for the same stars measured in imexamine. They differ by almost 10 magnitudes.
I have tried changing different parameters in both tasks, but I cannot seem to figure out what the difference is caused by. If anyone could offer some insight to this problem and into the tasks of phot and imexamine, it would be much appreciated.
Thank you.
-rachel
Mike Fitzpatrick wrote on Jul 12, 2006
Quick guess: the 'magzero' parameter?
-Mike
-Mike
rachel wrote on Jul 12, 2006
No, that's not the problem. It's set to 25 under imexamine ("rimexam") and zmag=25 in phot. That was my initial thought as well.
When I look at the mag file output from phot, the flux given is 165386 counts. I calculate the mag to be 11.95, where in imexamine it is 11.90 (reasonable), but the magnitude output in phot is 18.147. It seems like it is not acknowledging the zmag I've entered. Also, the itime=1 so that doesn't seem to be the issue either.
-rachel
When I look at the mag file output from phot, the flux given is 165386 counts. I calculate the mag to be 11.95, where in imexamine it is 11.90 (reasonable), but the magnitude output in phot is 18.147. It seems like it is not acknowledging the zmag I've entered. Also, the itime=1 so that doesn't seem to be the issue either.
-rachel
Mike Fitzpatrick wrote on Jul 12, 2006
Have you also checked the aperture radius? In PHOTPARS these default to '3' times the 'scale' parameter in DATAPARS, but in IMEXAM it defaults to a value of 5 and might be adjusted based on the number of iterations. The magnitude difference corresponds to an itime of about 300, does that sound familiar?
Beyond that, and even up to now, I'd just be guessing. It wouldn't hurt to unlearn all of the task parameters and psets or reinitialize your uparm directory in case the KILLALL script isn't resetting something critical.
-Mike
Beyond that, and even up to now, I'd just be guessing. It wouldn't hurt to unlearn all of the task parameters and psets or reinitialize your uparm directory in case the KILLALL script isn't resetting something critical.
-Mike
Last post on Jul 12, 2006