A New Merging Double Degenerate Binary in the Solar Neighborhood

TL;DR

This paper reports the discovery and detailed characterization of WD 1242-105, a nearby double white dwarf binary system with a short orbital period, providing insights into local space density and gravitational wave sources.

Contribution

It presents the first detailed analysis of WD 1242-105 as a double-line spectroscopic binary, including its fundamental parameters and gravitational wave implications.

Findings

Binary system at 39 pc distance

Total mass of 0.95 M$_\\odot$ and 2.85-hour orbit

Predicted merger in 740 million years

Abstract

Characterizing the local space density of double degenerate binary systems is a complementary approach to broad sky surveys of double degenerates to determine the expected rates of white dwarf binary mergers, in particular those that may evolve into other observable phenomena such as extreme helium stars, Am CVn systems, and supernovae Ia. However, there have been few such systems detected in local space. We report here the discovery that WD 1242$-$105, a nearby bright WD, is a double-line spectroscopic binary consisting of two degenerate DA white dwarfs of similar mass and temperature, despite it previously having been spectroscopically characterized as a single degenerate. Follow-up photometry, spectroscopy, and trigonometric parallax have been obtained in an effort to determine the fundamental parameters of each component of this system. The binary has a mass ratio of 0.7 and a trigonometric parallax of 25.5 mas, placing it at a distance of 39 pc. The system's total mass is 0.95 M$_\odot$ and has an orbital period of 2.85 hours, making it the strongest known gravitational wave source ($\log h = -20.78$) in the mHz regime. Because of its orbital period and total mass, WD 1242$-$105 is predicted to merge via gravitational radiation on a timescale of 740 Myr, which will most likely not result in a catastrophic explosion.