def METHOD_NAME(self, star):
    """Update the star to have the current interpolated fit parameters according to the
    current PSF model.
    :param star:        Star instance to update.
    :returns:           Star instance with its fit parameters updated.
    """
    if 'chipnum' not in star.data.properties:
        raise ValueError("SingleChip requires the star to have a chipnum property")
    chipnum = star['chipnum']
    return self.psf_by_chip[chipnum].METHOD_NAME(star)