Effects of a Companion Star on Slow Nova Outbursts -- Transition from Static to Wind Evolutions

TL;DR

This paper proposes a new model for slow nova outbursts, where the transition from static to wind evolution is triggered by the companion star's effect, explaining different observed nova behaviors.

Contribution

It introduces a transition model from static to wind evolution in slow novae, emphasizing the companion star’s role in triggering this transition.

Findings

Transition occurs when the companion is embedded in the envelope

Close binaries trigger the transition, long-period binaries do not

Frictional energy deposition is negligible in most novae

Abstract

Two types of nova evolutions can be realized in low mass white dwarfs of ~0.5-0.7 M_sun, i.e., an evolution with optically thick winds like in usual classical novae, or an another type of evolution without them like in the symbiotic nova PU Vul. The latter type is characterized by spectra of no indication of strong winds as well as a long-lasted flat optical peak in its light curve. We propose a transition from no-optically-thick-wind evolution to usual evolution with optically thick winds as a new outburst model for slow novae that show a relatively long-lasted multipeak phase followed by a wind phase like in the slow novae V723 Cas, HR Del, and V5558 Sgr. We calculated nova envelopes with one-dimensional approximation of the companion's effects and found that when the companion star is deeply embedded in the extended nova envelope, the structure of static envelope approaches that of the optically thick wind solution. Thus, the transition from static to wind solution is triggered by the effect of the companion. The transition occurs in a close binary nova like V723 Cas, but is not triggered in a long period binary like PU Vul. We reconfirm our previous results that the frictional energy deposition is negligibly small in almost all of hydrogen/helium novae because of the low envelope density at the orbit.