Cataclysmic variable evolution: AM Her binaries and the period gap |
| |
| Authors: | R F Webbink D T Wickramasinghe |
| |
| Institution: | Department of Astronomy, University of Illinois at Urbana-Champaign, 1002 West Green Street, Urbana, IL 61801, USA; Department of Mathematics, School of Mathematical Sciences, Australian National University, Canberra, ACT 2601, Australia |
| |
| Abstract: | AM Her variables – synchronized magnetic cataclysmic variables (CVs) – exhibit a different period distribution from other CVs across the period gap. We show that non-AM Her systems may infiltrate the longer-period end of the period gap if they are metal-deficient, but that the position and width of the gap in orbital period are otherwise insensitive to other binary parameters (except for the normalization of the braking rate). In AM Her binaries, magnetic braking is reduced as the wind from the secondary star may be trapped within the magnetosphere of the white dwarf primary. This reduced braking fills the period gap from its short-period end as the dipole magnetic moment of the white dwarf increases. The consistency of these models with the observed distribution of CVs, of both AM Her and non-AM Her type, provides compelling evidence supporting magnetic braking as the agent of angular momentum loss among long-period CVs, and its disruption as the explanation of the 2–3 h period gap among non-magnetic CVs. |
| |
| Keywords: | stars: evolution stars: magnetic fields novae cataclysmic variables |
|
|
