Binaries discovered by the SPY project. IV. Five single-lined DA double white dwarfs

TL;DR

This paper reports the discovery and orbital analysis of five double white dwarf binaries from the SPY project, revealing their periods, companion types, and implications for white dwarf evolution.

Contribution

It provides new orbital solutions for five double white dwarf systems, including the first infrared evidence of a cool, helium-rich companion, advancing understanding of white dwarf binary formation.

Findings

Orbital periods range from 0.44 to 3.22 days.

No spectral lines from companions, indicating they are white dwarfs.

Infrared data suggests a cool, helium-rich white dwarf companion.

Abstract

We present results from our ongoing follow-up observations of double white dwarf binaries detected in the ESO SN Ia Progenitor SurveY (SPY). We discuss our observing strategy and data analysis and present the orbital solutions of five close double white dwarf binaries: HE0320-1917, HE1511-0448, WD0326-273, WD1013-010 and WD1210+140. Their periods range from 0.44 to 3.22 days. In none of these systems we find any spectral lines originating from the companion. This rules out main sequence companions and indicates that the companion white dwarfs are significantly older and cooler than the bright component. Infrared photometry suggests the presence of a cool, helium-rich white dwarf companion in the binary WD0326-273. We briefly discuss the consequences of our findings for our understanding of the formation and evolution of double white dwarfs.