The Role of the Convective Kissing Instability in Cataclysmic Variable Evolution

Abstract The convective kissing instability (CKI) is postulated to occur in low mass stars around the fully convective transition. Non-equilibrium 3 He burning leads to the merging of core and envelope convective zones, which causes abrupt decreases in the stellar radius. It has been suggested by van Saders & Pinsonneault that these effects may be relevant for cataclysmic variables (CVs). We have performed stellar evolution modeling to study the role of the CKI in CV evolution. We find that the CKI has no effect on normal CVs which evolve via magnetic braking and gravitational radiation above the period gap. CKI cycles either do not occur or are abruptly halted once mass transfer begins. If only gravitational radiation is considered, the CKI does occur. The abrupt radius changes can cause detachment phases which produce small period gaps with widths of a few minutes. We describe how the size of the period gaps is controlled by the 3 He profiles of the secondaries. We also discuss how the results of this study apply to the evolution of strong field polars, where the magnetic field of the white dwarf is strong enough to suppress magnetic braking.