Synthetic photometry

In order to transform the theoretical quantities ( ) into magnitudes and colours, we first compute, by interpolation in the Ba Se L grid ( , , and the model spectrum at each point along the track or the isochrone, and then derive the synthetic photometry by convolving the resulting flux distribution with the filter transmission functions (as given in the following sections).

The Wolf-Rayet phases in the stellar tracks are excluded from this interpolation procedure because no physical model is available in the Ba Se L grid to accurately describe the atmosphere and the spectra of stars in these phases. For these reasons, in the files we assign an arbitrary value () to the magnitudes and the colours corresponding to these points. It has also to be pointed out that, because of some missing models in the Ba Se L set of models near K and , extrapolations in are necessary to compute the colours in this parameter range, leading to a few numerical approximations. As a consequence, the derived magnitudes and colours change more abruptly with than expected, and hence the shape of the stellar tracks do not appear very smooth in this region of the c-m diagram. For these peculiar points, we estimate our computed photometry to be accurate to about mag.