The space density of magnetic and non-magnetic cataclysmic variables, and implications for CV evolution

TL;DR

This study constrains the space densities of magnetic and non-magnetic cataclysmic variables, revealing implications for their evolution, faintness in X-rays, and their contribution to Galactic X-ray sources.

Contribution

It provides new constraints on CV space densities and discusses their evolutionary pathways and magnetic properties based on observational data.

Findings

High non-magnetic CV space density implies most are X-ray faint.

Long-period IPs evolve into polars, explaining short-period polar population.

Sufficient IP density accounts for Galactic Centre X-ray sources.

Abstract

We present constraints on the space densities of both non-magnetic and magnetic cataclysmic variables, and discuss some implications for models of the evolution of CVs. The high predicted non-magnetic CV space density is only consistent with observations if the majority of these systems are extremely faint in X-rays. The data are consistent with the very simple model where long-period IPs evolve into polars and account for the whole short-period polar population. The fraction of WDs that are strongly magnetic is not significantly higher for CV primaries than for isolated WDs. Finally, the space density of IPs is sufficiently high to explain the bright, hard X-ray Galactic Centre source population.