Re: Optimum usage of AstroImageJ for diffuse objects such as comets

Posted by GordonMcKay on Jan 05, 2022; 5:50pm
URL: http://astroimagej.170.s1.nabble.com/Optimum-usage-of-AstroImageJ-for-diffuse-objects-such-as-comets-tp1630p1722.html

After much work and testing of newly written post-processing software I believe AstroImageJ can be used in a highly effective way for the photometric analysis of diffuse objects such as comets. The methodology is relatively simple although a thorough knowledge of how AIJ computes target and reference flux in both the object field itself and the background annuli is required so that once the standard AIJ measurements table is exported it can be post-processed to provide a significantly enhanced flux/magnitude estimation of the diffuse object (in my case a comet). I am using a multi aperture scenario (MAP) choosing a range of ever widening apertures so that a profile of flux values is obtained. 2 sigma cleaning of background in AIJ is extremely effective for point sources but does not readily apply to diffuse objects. A quick comparison of the excellent seeing profiles in AIJ shows up the "noise" issue quickly. Once the standard MAP exercise is completed the measurements table is exported to an external tool custom written for the task. Only the availability of detailed parameter values and how they are derived in AIJ makes this possible. The background flux around the target object is re-computed from the reference fields. This effectively nulls out attendant noise. Using the best reference star G magnitudes available from GAIA EDR3 data the cometary coma profiling results are encouraging. It seems possible that a software enhancement in AIJ could accommodate this methodology but it is appreciated that no software enhancement is ever simple!! If anyone wishes to discuss this methodolgy please message me here.