The orbital period changes for novae

TL;DR

This paper models how different mass loss mechanisms during nova eruptions affect the orbital period changes in cataclysmic variables, explaining observed short-term variations that conflict with standard long-term evolution theories.

Contribution

It introduces a model considering three mass loss mechanisms during nova eruptions, showing binary-driven mass loss explains most observed orbital period changes in CVs.

Findings

Binary-driven mass loss explains most short-term orbital period variations.

Frank jet may be relevant for long-period CVs with evolved companions.

Standard theory cannot account for observed positive and negative period changes.

Abstract

Cataclysmic variable (CVs) are close interacting binaries in which a white dwarf accretes materials from a low mass main sequence companion. CVs can experience nova eruptions due to low mass transfer rates. In the standard theory of CV evolution, the ejected materials during nova eruptions are assumed to leave the system in the form of fast, isotropic, optically thick winds, which predicts that novae only result in positive variation (expansion) of orbital period (i.e. positive $\Delta P$). In addition, the angular momentum losses (magnetic braking and gravitational radiation) only predicts a steady long-term decay in the orbital period of CVs, i.e. $\dot P$ is negative. Interestingly, an observation lasting over 30 years reveals positive and negative values for both $\Delta P$ and $\dot P$ in CVs, strongly conflicting with the standard evolutionary patterns. However, it cannot be excluded that these observations originate from short-term phenomena caused by nova eruptions because of a short timescale of observations. In this paper, we model the effect of instantaneous nova eruptions on the evolution of CVs, considering three mechanisms associated with mass loss in nova eruptions, including fast wind, Frank jet and binary-driven mass loss. By assuming that the observed $\Delta P$ and $\dot P$ are dominated by short-term phenomena, our results show that the binary-driven mass loss can explain almost all of the observations of normal CVs. However, the Frank jet may be needed for some of long-period CVs with evolved companions.