The Perils of Pdot

TL;DR

This paper critiques the reliability of using binary period derivatives to infer the evolution of cataclysmic variables, highlighting potential pitfalls and exceptions like the young X-ray binary SN 2022jli.

Contribution

It emphasizes the limitations of using period derivative measurements for evolutionary constraints and clarifies when such measurements might be reliable.

Findings

Most $\dot P$ measurements are misleading for evolutionary inference.

SN 2022jli is a notable exception due to its high mass transfer rate.

Using $\dot P$ requires careful consideration of system specifics.

Abstract

Schaefer (2024) has recently published observations of binary period derivatives $\dot P$ for 52 cataclysmic variables, and concluded that these strongly conflict with all proposed evolutionary pictures for these systems. We point out once again that using measurements of $\dot P$ is likely in practice to produce misleading evolutionary constraints in almost every case. The one identified exception to this is probably the recently-born X-ray binary SN 2022jli, because of its extremely high mass transfer rate.