Suggestions for future work

We find that the photometric method of mode discrimination works best if the widest possible wavelength range is used. The phase difference with respect to the u band increases with quite significantly towards longer wavelength. Most of the present attempts use observations in the b and y only. The photometry needs to be of extremely high quality to make use of such a short baseline. It would be more appropriate to use u and y or even u and I if two colours must be used. This choice must be weighted against the larger photometric scatter in the u band and the smaller amplitude in y and I. Obviously, better results are obtained when all colours can be combined in the way we have described.