There are 3 essential steps to follow to make light curves of variables objects

Image registration

  The goal of image registration is to re-map each image on the same grid. The reference system, or common grid is usually one of the image. The output of this procedure will be a FITS image interpolated on the reference grid.

This procedure involve 2 steps:

- Getting the astrometric transform, X=f(x_ref,y_ref )

- Making image interpolation (Bicubic Splines)

Image Subtraction

This is the main program, and the core of the new method presented in the 2 papers.  Before you run the code, you need to make a good reference image by stacking some of your best images.  Then you can use the image subtraction code to adjust the reference image to the seeing of each individual image (which have been previously registered and interpolated).

The image subtraction code can process the whole frame by small pieces, it is especially useful in case of large images which can be processed with limited memory ressources.

The code has 2 level of rejection for variable objects:

- Checking that each individual star does not show flux variations

- Checking the chi-square for each individual star

The final output of the code will a subtracted image of the flux variation beween the individualimage and the reference frame.


This package will make photometry of variable objects by using the subtracted images. The flux of the variable will be calculated using profile fitting photometry at fixed position. As for the image subtraction code, the frame can be also treated by small pieces. The profile of each frame is calculated by making median stacking of a few reference stars.