Common Proper Motion Wide White Dwarf Binaries Selected From The Sloan Digital Sky Survey

TL;DR

This study identifies and confirms new wide white dwarf binary systems using SDSS data, expanding the known sample and providing valuable data for testing stellar evolution theories.

Contribution

The paper introduces a method to find wide white dwarf binaries in SDSS data, significantly increasing the known sample, especially at low proper motions and large separations.

Findings

Nine new high-probability wide WDWDs identified

Three previously known candidates confirmed

Total known wide WDWDs increased to 45

Abstract

Wide binaries made up of two white dwarfs (WDs) receive far less attention than their tight counterparts. However, our tests using the binary population synthesis code {\tt StarTrack} indicate that, for any set of reasonable initial conditions, there exists a significant observable population of double white dwarfs (WDWDs) with orbital separations of 10$^2$ to 10$^5$ AU. We adapt the technique of Dhital et al.\ to search for candidate common proper motion WD companions separated by $<10\amin$ around the $>$12,000 spectroscopically confirmed hydrogen-atmosphere WDs recently identified in the Sloan Digital Sky Survey. Using two techniques to separate random alignments from high-confidence pairs, we find nine new high-probability wide WDWDs and confirm three previously identified candidate wide WDWDs. This brings the number of known wide WDWDs to 45; our new pairs are a significant addition to the sample, especially at small proper motions ($<$200 mas/yr) and large angular separations ($>$10\asec). Spectroscopic follow-up and an extension of this method to a larger, photometrically selected set of SDSS WDs may eventually produce a large enough dataset for WDWDs to realize their full potential as testbeds for theories of stellar evolution.