by The Zwicky Transient Facility (ZTF), a key tool for astronomers in their quest to unravel the mysteries of the universe, has made a groundbreaking discovery. By closely examining dwarf novae identified by the ZTF, scientists have identified four binary systems that turned out to be eclipsing accreting ultracompact white dwarf binaries. The finding is significant as the study of these systems could potentially shed light on the final fate of merging white dwarf binary stars. The research, led by Jasmine M. Khalil from the University of Amsterdam, was published on the pre-print server arXiv on December 15, providing valuable insights into the nature of these fascinating objects.
The team of astronomers meticulously analyzed a vast list of over 4,000 dwarf novae obtained with the ZTF, leading them to the identification of four eclipsing accreting ultracompact binaries. Notably, one of the systems had been previously reported by other studies, highlighting the success of the ZTF in confirming the existence of these intriguing objects. The four binaries, named ZTF20aabowdt, ZTF18acgmwpt, ZTF19abugzba, and ZTF21abbxnbm, showcased orbital periods ranging from 25.9 to 56 minutes.
Accreting ultracompact binaries are white dwarfs in the process of steadily accumulating material from a degenerate or semi-degenerate donor star. These systems are characterized by their exceptionally short orbital periods, typically below 65 minutes, which means their orbital evolution is largely governed by gravitational wave radiation. The new observations revealed important details about these binaries and their unique characteristics.
Among the four systems, ZTF18acgmwpt stood out as it had already been reported in 2021 and confirmed as an AM Canum Venaticorum-type star, featuring helium absorption lines in its spectrum. The team found that this system, located approximately 5,300 light years away, exhibited an orbital period of 25.92 minutes.
The other three systems, namely ZTF20aabowdt, ZTF19abugzba, and ZTF21abbxnbm, are new discoveries. They displayed deeper eclipses, except for ZTF19abugzba, which showed a shallower eclipse with a depth of only about 50%. Intriguingly, ZTF20aabowdt seemed to showcase a narrower eclipse compared to the other systems. These findings provide crucial insights into the distinctive characteristics of each binary system.
ZTF21abbxnbm, the system with the longest orbital period among the four binaries, exhibited an unusual feature. It displayed three super-outbursts within three years, suggesting that it is a helium cataclysmic variable (CV) rather than a typical long-period AM Canum Venaticorum-like system. This unexpected behavior adds to the intrigue surrounding these binaries and further highlights the importance of studying them to deepen our understanding of the cosmos.
The researchers also noted that ZTF19abugzba and ZTF21abbxnbm possess redder colors, which deviate from the typical blue hue of accreting ultracompact binaries. This divergence may provide additional clues about the nature of these systems and potentially open avenues for further investigations.
While this study has enriched our knowledge of accreting ultracompact binaries, many questions remain unanswered. To better understand these fascinating objects, the authors suggest conducting high-speed photometry and spectroscopic follow-up observations. These complementary techniques could unveil crucial information about the properties and behavior of these binary systems, paving the way for more exciting discoveries in the future. The Zwicky Transient Facility continues to push the boundaries of astronomical research, bringing us closer to unraveling the enigmas of the cosmos.
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Source: Coherent Market Insights, Public sources, Desk research
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