ZTF data from ZTF20aabowdt. On the left, the top panel shows the light curve, the middle panel shows the folded light curve (P = 25.92 minutes), and the final panel shows the periodogram. The median uncertainty in the ZTF measurements is 33% and is not shown for clarity. On the right, a zoom on the eclipse of the folded light curve. The smoothed light curve (using a Gaussian kernel) is overplotted. Legend: Data from bands g, r, i are displayed in green, red and blue. Credit: Khalil et al, 2023
By studying dwarf novae identified by the Zwicky Transient Facility (ZTF), astronomers discovered four binary systems. The objects turned out to be ultracompact eclipsing white dwarf binaries. The discovery was reported in a paper published Dec. 15 on the preprint server. arXiv.
Observations show that accreting ultracompact binaries are white dwarfs in the process of stable accretion of matter from a degenerate or semi-degenerate donor. Studying the evolution of such systems could help us deepen our knowledge of the final fate of white dwarf binary star mergers.
Now, a team of astronomers led by Jasmine M. Khalil of the University of Amsterdam, Netherlands, reports the detection of new such systems. Khalil’s team combed through the list of more than 4,000 dwarf novae obtained with ZTF. As a result, they identified four ultracompact eclipsing and accumulating binaries, one of which was found to have been reported by previous studies.
“We found four new ultracompact eclipsing and accreting binary systems with orbital periods between 25.9 and 56 minutes, one of which has already been published as an AM CVn (AM Canum Venaticorum type star), while the other three systems are new discoveries,” the researchers wrote. in the newspaper.
The binaries identified by astronomers are designated ZTF20aabowdt, ZTF18acgmwpt, ZTF19abugzba and ZTF21abbxnbm. ZTF18acgmwpt, located approximately 5,300 light years away, was first reported in 2021 and confirmed as an AM CV system with helium absorption lines in its spectrum.
As noted in the article, the four binaries have orbital periods between 25.92 and 56.16 minutes. In general, accreting ultracompact binaries have orbital periods less than 65 minutes, meaning that their orbital evolution is governed by gravitational wave radiation.
Observations revealed that ZTF20aabowdt, ZTF18acgmwpt, and ZTF21abbxnbm exhibit deep eclipses. However, when it comes to ZTF19abugzba, it has a shallow eclipse with a depth of only about 50%. It was noted that the ZTF20aabowdt also appears to exhibit a narrower eclipse than other systems.
Astronomers noted that ZTF21abbxnbm, which has the longest orbital period among the four binaries reported in the study, is unusual because it exhibits three superexplosions in three years. This suggests that it is a helium cataclysmic variable (CV) instead of a typical long-period AM CVn like the other three systems.
The researchers added that although accreting ultracompact binary systems are typically blue because the donor is cold and not visible in the near-infrared, ZTF19abugzba and ZTF21abbxnbm exhibit redder colors.
The paper’s authors propose high-speed photometric and spectroscopic follow-up observations to better characterize the reported systems, as many of their properties still remain unknown.
More information:
JM Khalil et al, Four new ultracompact eclipsing and accreting white dwarfs found with the Zwicky transient facility, arXiv (2023). DOI: 10.48550/arxiv.2312.09980
Journal information:
arXiv
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