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

Posted by chrismlt on Feb 22, 2016; 6:52pm
URL: http://astroimagej.170.s1.nabble.com/Perform-differential-photometry-on-an-object-moving-across-a-field-tp240p353.html

Karen,

About the possible algorithm I told you previously, of course, you're right : that will not work with poor tracking telescope. Indeed, you have to align the images sequence before running the algorithm. You can do this as usual with XY alignement, or better, you can WCS align the images ; when doing this, you finally will get all the elements needed to send a good MPC report with accurate  astrometry/photometry.

More on this : keeping an eye to the displacement of the target vs timing seems important. If, for some reason, there is an interruption in the sequence (technical issue with the instrument, clouds ...), and then the sequence resume, the algorithm will loose the target, because the centroid has moved more than expected from image to image. In this case, it seems better to use the target position in the first and last image vs time as a movement base, to find the centroid from image to image.

The algorithm you wrote about in your previous message should work properly in "clear" area ; in crowded field, just in case the moving target  cross a star, if centroids are at a same position for a while, the program could loose the target once more. Maybe the algorithm should have to look further before running (the next 3 or 4 images, maybe), in order to ascertain the target.

Well, just my two cents ;-)

Cheers,
Christophe