On the White Dwarf Mass Problem of Cataclysmic Variables

TL;DR

This paper investigates why white dwarfs in cataclysmic variables are more massive than expected, suggesting unstable mass transfer and angular momentum loss as key factors in their evolution.

Contribution

The study introduces updated models of WD binary evolution, highlighting the role of unstable mass transfer and angular momentum loss in explaining the WD mass discrepancy.

Findings

Thermal timescale mass transfer does not significantly alter WD mass distribution.

Unstable mass transfer with efficient angular momentum loss likely explains the mass discrepancy.

Updated models support the importance of angular momentum loss mechanisms in WD binary evolution.

Abstract

Recent observations show that the white dwarfs (WDs) in cataclysmic Variables (CVs) have an average mass significantly higher than isolated WDs and WDs in post-common envelope binaries (PCEBs), which are thought to the progenitors of CVs. This suggests that either the WDs have grown in mass during the PCEB/CV evolution or the binaries with low-mass WDs are unable to evolve to be CVs. In this paper, we calculate the evolution of accreting WD binaries with updated hydrogen accumulation efficiency and angular momentum loss prescriptions. We show that thermal timescale mass transfer is not effective in changing the average WD mass distribution. The WD mass discrepancy is most likely related to unstable mass transfer in WD binaries in which an efficient mechanism of angular momentum loss is required.