Equation of model

Hi

I have been trying to use the equation given from Vstar to overplot the data with the model light-curve using a programming language (for research purposes).

However, I find that using the given equation, with the dates of the data, often does not match the fit in the Vstar plot itself, there is a offset in the phase, such that the model curve (despite being correct in period and amplitude) does not fit the data. I have experimented with this but can see no obvious reason.

Any suggestions?

Many regards

Avon