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28th of June 2023
ATNF Colloquium
Mergers of white dwarfs and the transients they make
Dr. Ashley Ruiter (UNSW, Canberra)
Abstract: For the last decade, mergers of double white dwarfs have been considered to be a likely, possibly even favoured, progenitor scenario for Type Ia supernovae. Though the Milky Way harbours ~100 million double white dwarf binaries, only a small fraction of these will actually merge in a Hubble time, let alone possess the "right" physical properties to lead to a Type Ia supernova if they do even merge. A different outcome of a white dwarf merger is the creation of another type of stellar transient: a hydrogen-deficient carbon (HdC) star. We know of ~130 of such ‘dusty’ HdC stars in the Galaxy - these are the R Coronae Borealis (RCB) stars, and they are thought to be the end result of a merger of a carbon-oxygen white dwarf and a helium-rich white dwarf, though their formation is not completely understood. In 2021, another type of hydrogen-deficient carbon star was found in great numbers: 27 ‘dustless’ HdC stars were spectroscopically confirmed in our own Milky Way, increasing the known number of this class from 4 (discovered >50 yrs ago) to 31. In 2022 we were granted time on the high-resolution (R~80,000) Veloce echelle spectrograph with the aim of disentangling the difference in evolutionary history between the long-known ‘dusty’ RCB stars and the newly-discovered plethora of ‘dustless’ HdC stars - both classes of objects presumed to be the result of double white dwarf mergers. Though we were mostly fully clouded out and we await new opportunities for obtaining and analysing observational data, I will discuss how different formation channels of white dwarf mergers may be plausibly linked to various transient phenomena such as Type Ia supernovae, dusty RCB stars, and dustless HdC stars. (Image created with Open AI tools)

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