Abstract
We argue that the period distribution of AM Herculis binaries in the enlarged sample incorporating results from the recent ROSAT X-ray survey differs significantly from that of other cataclysmic variables. In particular, there is no evidence for a pronounced period gap at 2—3 hr and the significance of the period spike at about 114 min is brought into question. We present an alternative evolutionary scenario for the AM Herculis binaries based on the hypothesis that magnetic braking by the stellar wind of the M star secondary either ceases or is severely curtailed when the rotation of the magnetic white dwarf becomes synchronised with the orbital motion, The orbital evolution of the AM Herculis binaries is thereafter driven mainly by angular momentum loss due to gravitational radiation. This scenario not only explains the higher proportion of AM Herculis binaries in the period gap when compared with other cataclysmic variables but also provides a natural explanation for the low mass transfer rates in these binaries and for the existence of an apparent upper limit for the surface magnetic fields of their white dwarfs.
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References
Bailey, J. and Cropper, M.: 1991,Monthly Not. Roy. Astr. Soc. 253, 27.
Bailey, J.et al.: 1993,Monthly Not. Roy. Astr. Soc. 261, 34P.
Beuermann, K. and Thomas, H.C.: 1993, COSPAR Symposium onRecent Results on X-Ray and EUV Astronomy, Washington DC (in press).
Buckley, D.A.H.: 1993,Proc. ASA (in press).
Buckley, D.A.H.et al.: 1993,Monthly Not. Roy. Astr. Soc. (in press).
Chanmugam, G. and Ray, A.: 1984,Astrophys. J. 285, 252.
Drissen, L.et al.: 1992,IAU Circ. 5609.
Faulkner, J.: 1971,Astrophys. J. 170, L99.
Hameury, J.M., King, A.R. and Lasota, J.P.: 1989a,Monthly Not. Roy. Astr. Soc. 237, 39.
Hameury, J.M., King, A.R. and Lasota, J.P.: 1989b,Monthly Not. Roy. Astr. Soc. 237, 845.
Hameury, J.M.,et al.: 1988,Monthly Not. Roy. Astr. Soc. 231, 535.
Lamb, D.Q. and Melia, F.: 1987,Astrophys. J. 321, L133.
Landau, L.D. and Lifshitz, E.M.: 1971,The Classical Theory of Fields, Pergamon Press, Oxford, p. 325.
Li, J.: 1992, D.Phil. Thesis, The University of Sussex.
Li, J.: 1993,Proc. ASA (in press).
Li, J., Wu, K. and Wickramasinghe, D.T.: 1993a,Monthly Not. Roy. Astr. Soc. (submitted).
Li, J., Wu, K. and Wickramasinghe, D.T.: 1993b, (in preparation).
Liebert, J. and Stockman, H.S.: 1985, in: D.Q. Lamb and Patterson, J. (eds.),Cataclysmic Variables and Low Mass X-Ray Binaries, D. Reidel Publ. Co., Dordrecht, p. 151.
Mestel, L.: 1968,Monthly Not. Roy. Astr. Soc. 138, 359.
Mestel, L. and Spruit, H.C.: 1987,Monthly Not. Roy. Astr. Soc. 226, 57.
Patterson, J.: 1984,Astrophys. J. Suppl. 54, 443.
Rappaport, S., Verbunt, F. and Joss, P.C.: 1983,Astrophys. J. 275, 713.
Ritter, H. and Kolb, U.: 1992,Astron. Astrophys. 259, 159.
Schmidt, G.: 1990, in: C. Mauche (ed.),Accretion-Powered Compact Binaries, Cambridge Univ. Press, Cambridge, p. 295.
Schmidt, G. and Stockman, H.S.: 1991,Astrophys. J. 371, 749.
Schwope, A.D., Thomas, H.C. and Beuermann, K.: 1993,Annals of the Israel Physical Society 10, 313.
Verbunt, F. and Zwaan, C.: 1981,Astron. Astrophys. 100, L7.
Warner, B. and Wickramasinghe, D.T.: 1991,Monthly Not. Roy. Astr. Soc. 248, 370.
Weber, E.J. and Davis, L.: 1967,Astrophys. J. 148, 271.
Wheatley, P.J.et al.: 1993,Annals of the Israel Physical Society, 10, 333.
Wickramasinghe, D.T. and Wu, K.: 1993,Monthly Not. Roy. Astr. Soc., (submitted).
Wickramasinghe, D.T., Wu, K. and Ferrario, L.: 1991,Monthly Not. Roy. Astr. Soc. 249, 460.
Wickramasinghe, D.T.et al.: 1993 (in press).
Wu, K. and Wickramasinghe, D.T.: 1993a,Annals of the Israel Physical Society, 10, 336.
Wu, K. and Wickramasinghe, D.T.: 1993b,Proc. ASA, (in press).
Wu, K. and Wickramasinghe, D.T.: 1993c,Monthly Not. Roy. Astr. Soc. (in press).
Zahn, J. P.: 1977,Astron. Astrophys. 57, 383.
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Wickramasinghe, D.T., Wu, K. The period gap and the AM Herculis type systems. Astrophys Space Sci 211, 61–70 (1994). https://doi.org/10.1007/BF00658043
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DOI: https://doi.org/10.1007/BF00658043