So, the reason the -log likelihood wasn't being calculated correctly dealt with the step size in the isochone. The difference between one isochrone point and the next on the main sequence can be several tenths of a magnitude and larger than the photometric error. Therefore this influences the probability. Getting stars near isochrone points is just as important as getting stars on the general shape of the isochrone.In order to combat this problem, I linearly interpolated between neighboring points to create two new points at one third intervals between the original points. This hopefully will not introduce too much error because of the small range over which I am performing the calculation. I checked the Y2 isochrones, and they had an even worse grid. I may still search for another, better isochrone source.
While it now centers around the predicted age, an actual peak doens't really exist. Seems like there is a minimum -log likelihood value, that cuts of under. This is my next problem to fix.
And congratulations to Mary on a beautiful presentation :)
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