The detection efficiency for a double-line DWD where the two stars have similar flux contributions. Credit: arXiv (2024). DOI number: 10.48550/arxiv.2407.02594
An international team of astronomers reports the discovery of 34 rare double-lined white dwarf binary systems using the Intermediate-dispersion Spectrograph and Imaging System (ISIS) on the William Herschel Telescope (WHT). The finding was detailed in a research paper published on the preprint server arXiv.
Astronomers are interested in finding and studying double white dwarfs (DWDs) because their mergers are expected to produce new white dwarfs with higher masses. It is thought that some high-mass white dwarfs near the Sun could be DWD merger products.
To date, most binaries, including DWDs, have been detected by Doppler shifts in their spectral lines; hence, these systems are called spectroscopic binaries. Observations show that in some spectroscopic binaries, spectral lines from both stars are visible, and that these lines are alternately double and single. These systems are known as double-line spectroscopic binaries (SB2).
The number of known SB2 white dwarf systems with well-measured masses and orbital parameters is still relatively small. Finding new objects of this type could be crucial to increasing our knowledge of double white dwarfs in general.
A group of astronomers led by James Munday of the University of Warwick in the United Kingdom has examined 117 DWD binary star candidates using ISIS in the hope of confirming their SB2 DWD nature.
“Our study of 117 candidates randomly selected from a limited sample size of 399 yielded a detection efficiency of 29 percent, with 34 systems exhibiting a double line signature,” the researchers wrote in the paper.
The detected SB2 DWDs have masses ranging from 0.85 to 1.55 solar masses and orbital periods between 0.4 and 13.5 days. All of these systems are within 580 light-years of Earth, with the closest being only 83 light-years away.
The observations found that the masses of the hotter component in the reported binaries range from 0.4-0.75 solar masses with a median mass of about 0.53 solar masses. The colder companions have a median mass of about 0.45 solar masses.
The paper’s authors noted that the most massive of the detected double-lined DWDs, designated WDJ181058.67+311940.94, exceeds the so-called Chandrasekhar limit: the maximum mass of a stable white dwarf star, which is generally thought to be about 1.4 solar masses.
Therefore, this system, located about 160 light-years away, is expected to experience a Type Ia supernova explosion or merge into an ultra-massive white dwarf in the near future. However, further observations of this system are needed to make time estimates of its fate.
More information:
James Munday et al, The DBL Survey I: Discovery of 34 Double-Lined White Dwarf Binary Stars, arXiv (2024). DOI number: 10.48550/arxiv.2407.02594
Magazine information:
arXiv
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