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

Posted by Pablo on Jan 20, 2016; 2:50pm
URL: http://astroimagej.170.s1.nabble.com/Perform-differential-photometry-on-an-object-moving-across-a-field-tp240p323.html

Hi Karen,

Thank you for your interest in solar system moving objects.

1) It is possible to find if the object is in the image (previously solving astrometrically, i.e. WCS included) using MPCORB.dat file from the Minor Planet Center web page http://www.minorplanetcenter.net/iau/MPCORB.html the problem with this is that this file must be updated to include the latest minor planet objects. It is also needed to compute the coordinates of the object for the given date (using the orbital elements included in MPCORB.dat) in order to find the object in the image. In summary, you should add your own ephemeris code or integrator.

2) It is also possible to get the proper motion of an object for a given date using MPC ephemeris http://www.minorplanetcenter.net/iau/MPEph/MPEph.html or JPL-HORIZONS system http://ssd.jpl.nasa.gov/horizons.cgi#top or any other ephemeris application. Usually the units for the proper motion of solar system objects are expressed in arcsec/hr or arcsec/min, but it is really easy (using the resolution of the image) to convert this speed to pixels/hr or pixels/min.

Of these two options the 1st one is the most difficult to program, but it would allow the automatic detection (and track) of the object in the (WCS solved) images. The 2nd one is the most direct to be programmed, but needs to identify the object and provide its proper motion. The 2nd one can be enough at this stage, and latter (with more time) perhaps you can think in adding the most automatic one.

The option you propose (click the moving object in 2 consecutive images to compute the proper motion in arcsecs or pixels) is also a good idea, but perhaps is easiest to program the 2nd option...any of these options added to the Multi-Aperture macro would be OK in order to do AIJ more useful for the minor planet community.

Thanks a lot Karen!