The Age of White Dwarf Companions

TL;DR

This study investigates the ages of white dwarf pairs in binary systems using spectroscopic data, suggesting unstable mass transfer is common in their evolution, with most pairs having age differences less than 0.5 billion years.

Contribution

It provides new constraints on the binary evolution of white dwarf systems by analyzing their cooling ages and inferring mass transfer stability.

Findings

Most systems have age differences under 0.5 Gyr.

Unstable mass transfer likely occurred in most double degenerate systems.

Stable first mass transfer phase remains possible but less certain.

Abstract

We carried out a spectroscopic investigation of single lined white dwarfs (WDs) in double degenerate (DD) systems and discuss their binary evolution. Simulated spectra of the Halpha region are used to derive upper limits on the temperature of the invisible component and thus lower limits on the cooling age. This is done for a range of hypothetical secondary masses and a minimum cooling age deduced. Results are compared with the well known parameters of the visible primary, which allows us to determine a lower limit for the cooling age difference of both WDs. Most of the ten systems in our sample have a minimum age difference of not larger than 0.5Gyr and their small orbital separation is highly suggestive of at least one unstable mass transfer phase. However, a stable first mass transfer phase is feasible as the age difference is less then 1Gyr. The results imply that unstable mass transfer is the most likely final contact binary scenario to have occurred in DD systems but the first mass transfer phase is not constrained.