Re: Perform differential photometry on an object moving across a field
Posted by
karenacollins on
Feb 23, 2016; 10:42am
URL: http://astroimagej.170.s1.nabble.com/Perform-differential-photometry-on-an-object-moving-across-a-field-tp240p355.html
Thanks Christophe,
I'll take all of this into account when I get time to work on this. To deal with interruptions in the image sequence, the algorithm I end up using will look at the time stamps in the header of each image and account for the amount of movement based on the amount
of time between each set of consecutive images.
It is not clear to me how to do proper photometry on a moving object automatically when it crosses another source in the field. If centroid is required, it will potential end up on the field star, and if the two sources are combined, the field source needs
to be subtracted. A smart enough algorithm could look back at the previous image and measure the field star brightness and attempt to remove that from the total measurement, but the two objects may be blended but both may not fall completely in the aperture.
I doubt that I will ever have the time to develop a foolproof totally automated moving object tracker and photometer.
Karen
On 2/22/2016 1:52 PM, chrismlt [via AstroImageJ] wrote:
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
To start a new topic under How to accomplish specific tasks in AstroImageJ, email
[hidden email]
To unsubscribe from AstroImageJ,
click here.
NAML