Re: Perform differential photometry on an object moving across a field

Posted by karenacollins on Jan 19, 2016; 12:57pm
URL: http://astroimagej.170.s1.nabble.com/Perform-differential-photometry-on-an-object-moving-across-a-field-tp240p320.html

Hi Pablo,

There is not currently a way to set the centroid radius separate from
the fixed aperture radius, if you require fixed aperture photometry.
However, if it is acceptable to use the variable aperture photometry
mode, then the the centroid and FWHM measurements will be made based on
the user supplied aperture radius settings, but the actual aperture
radius used to perform photometry is the user specified FWHM factor
times the measured FWHM in each image. So, in variable aperture mode,
the user specified aperture radius could be made large enough to
centroid on your moving object from image to image, and then the actual
aperture used to make the photometric measurement is typically smaller
(i.e. the factor you set x FWHM). I find that FWHM factors in the range
1-1.5 usually work well, depending on whether your images are defocused
or not.

I can see the usefulness of a separate centroid radius setting, so I am
adding that to the AIJ features to-do list. But, I don't expect I will
have time to implement that for at least another couple of months.

Karen