Differential Aperture Photometry


New member
Jan 5, 2017
Hi all,

I was pondering over a project for PixInsight and thought that it would be interesting to develop a Differential Aperture Photometry module. I have seen that there is an Aperture Photometry module already but this seems to go off and plate solve looking for a "known" magnitude star then work from that.

My experience is slightly different and does involve a little more research first but I have used this technique in developing target star light curves.

Basically the idea is to select the target star and determine the flux in an aperture surrounding the star to FWHM (full width half magnitude) radius and then subtract the background (sky) flux from an annulus around the star aperture. Secondary to this target a number of comparison stars are selected. The same calculations are done on these stars and then the target star is compared with the comparison stars to create relative flux data.

The key research step here is identifying comparison stars that have very small flux variations so that the relative flux is a consistent value.

A further step beyond this (which I didn't do) is to identify a reference star in the plate with known magnitude then a magnitude based light curve can be developed as well as the relative flux light curve.

So the question is where to start. I'm of a mind to look in the existing (plate solving) photometry routine and use this as a starting point??

Any pointers would be most welcome. particularly the calculations for flux in the aperture and annulus.

This is obviously going to be a bit of a long project because I need to climb the JavaScript learning curve first but I will try to keep this thread updated along the way. Perhaps dropping thoughts in for others to comment on??

Kindest Regards