Amit Kashi

We conduct numerical simulations of multiple nova eruptions in detached, widely separated symbiotic systems that include an asymptotic giant branch (AGB) companion to investigate the impact of white dwarf (WD) mass and binary separation on the evolution of the system. The accretion rate is determined using the Bondi–Hoyle–Lyttleton method, incorporating orbital momentum loss caused by factors such as gravitational radiation, magnetic braking, and drag. The WD in such a system accretes matter coming from the strong wind of an AGB companion until it finishes shedding its envelope. This occurs on an evolutionary time-scale of ≈3 × 105 yr. Throughout all simulations, we use a consistent AGB model with an initial mass of 1.0 M⊙ while varying the WD mass and binary separation, as they are the critical factors influencing nova eruption behaviour. We find that the accretion rate fluctuates between high and low rates during the evolutionary period, significantly impacted by the AGB’s mass loss rate. We show that unlike novae in cataclysmic variables, the orbital period may either increase or decrease during evolution, depending on the model, while the separation consistently decreases. Furthermore, we have identified cases in which the WDs produce weak, non-ejective novae and experience mass gain. This suggests that provided the accretion efficiency can be achieved by a more massive WD and maintained for long enough, they could potentially serve as progenitors for type Ia supernovae.

We carry out a numerical experiment for ejecting winds in a massive colliding-wind binary system and quantify the accretion on to the secondary star under different primary mass-loss rates. We set a binary system comprising a luminous blue variable (LBV) as the primary and a Wolf–Rayet (WR) star as the secondary, and vary the mass-loss rate of the LBV to obtain different values of the wind momentum ratio η. Our simulations include two sets of cases: one in which the stars are stationary; and one that includes the orbital motion. As η decreases, the colliding-wind structure moves closer to the secondary. We find that for η ≲ 0.05, the accretion threshold is reached and clumps that originate from instabilities are accreted on to the secondary. For each value of η, we calculate the mass accretion rate and identify different regions in the $\dot{M} _{\rm acc}$ – η diagram. For 0.001 ≲ η ≲ 0.05, the accretion is sub-Bondi–Hoyle–Lyttleton (BHL), and the average accretion rate satisfies the power law $\dot{M}_{\rm acc} \propto \eta ^{-1.73}$ for static stars. The accretion is not continuous but rather changes from sporadic to a larger duty cycle as η decreases. For η ≲ 0.001, the accretion becomes continuous in time, and the accretion rate is BHL, up to a factor of 0.4–0.8. The simulations that include the orbital motion give qualitatively similar results, with the steeper power law $\dot{M}_{\rm acc} \propto \eta ^{-1.86}$ for the sub-BHL region and lower η as an accretion threshold.