2026ApJ...996..134H

The separation of a binary system increases or decreases over time, governed by angular momentum (AM) changes. In cataclysmic variables (CVs), Roche-lobe overflow from the red dwarf (RD) to the white dwarf (WD) redistributes AM within the system through conservative mass transfer, modifying the separation. Moreover, angular momentum loss (AML) arises from magnetic braking by the RD and gravitational radiation from the binary's orbit. These three primary mechanisms have competing effects on the separation, which is correlated with the mass transfer rate. Long-term simulations show that the intereruption mass transfer rate gradually increases toward a nova eruption, and also evolves over the CV's lifetime, strongly depending on the RD mass. This work explores the limits of stellar mass combinations in CVs and derives theoretical (sometimes hypothetical) accretion rates at which the three mechanisms cancel each other out, yielding an equilibrium accretion rate that, if a given system were to reach it, would be maintained until the next nova eruption. These values are roughly 10^–11-10^–10M_⊙ yr^–1 for fully convective RDs (≲0.35M_⊙) independent of the WD mass and weakly dependent on the RD mass, while for RD masses of ≳0.35M_⊙the equilibrium accretion rate is at least ∼10^–9M_⊙ yr^–1 and dependent on the WD and RD masses-decreasing with the increase of the former and the decrease of the latter. The equilibrium accretion rate serves as a tool to calculate a lower limit to the system's recurrence period, based only on the WD mass and orbital period, which are typically determined observationally.