The ELM Survey. VII. Orbital Properties of Low Mass White Dwarf Binaries

TL;DR

This paper reports the discovery and analysis of 15 extremely low mass white dwarf candidates, including 9 in ultra-compact binaries, revealing their orbital properties, mass distributions, and potential evolutionary outcomes.

Contribution

It provides a detailed characterization of low mass white dwarf binaries, including their orbital period distribution, mass ratios, and merger predictions, expanding understanding of their evolution.

Findings

Median orbital period of 5.4 hours

Binary companions have a mean mass of 0.76 Msun

95% of binaries have total mass below Chandrasekhar limit

Abstract

We present the discovery of 15 extremely low mass (5 < log{g} < 7) white dwarf candidates, 9 of which are in ultra-compact double-degenerate binaries. Our targeted ELM Survey sample now includes 76 binaries. The sample has a lognormal distribution of orbital periods with a median period of 5.4 hr. The velocity amplitudes imply that the binary companions have a normal distribution of mass with 0.76 Msun mean and 0.25 Msun dispersion. Thus extremely low mass white dwarfs are found in binaries with a typical mass ratio of 1:4. Statistically speaking, 95% of the white dwarf binaries have a total mass below the Chandrasekhar mass and thus are not Type Ia supernova progenitors. Yet half of the observed binaries will merge in less than 6 Gyr due to gravitational wave radiation; probable outcomes include single massive white dwarfs and stable mass transfer AM CVn binaries.