1. Baldry, I. K., Bedding, T. R., Kurtz, D. W., 1998, MNRAS, in press.
2. Crawford D. L., 1979, AJ, 84, 1858
3. Deeming T. J., 1975, Ap&SS, 36, 137
4. Dolez N., Gough D. O., 1982,in Pulsations in Classical and Cataclysmic Variables, eds. J.P. Cox and C. J. Hansen, JILA, Boulder, p. 248
5. Dziembowski W., Goode P. R., 1984, Em. Soc. Aaron. Ital., 55, 185