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UBC Theses and Dissertations

The white dwarf initial-final mass relation : ultramassive white dwarfs ejected from young open star clusters Miller, David Ross


Intermediate mass stars either end their lives as a white dwarf (WD) or a neutron star, depending almost entirely on star’s mass. The mass limit between these two fates is critical for a number of astrophysical quantities, including galactic heavy element enrichment and compact object formation rates. Unfortunately, this mass limit is not well constrained, with different methodologies suggesting this limit could reasonably be anywhere from 8 to 12 M⊙. The mass limit for WD production can be constrained by developing the WD initial-final mass relation (IFMR). Determining the mass of a WD precursor requires identifying WDs that are members of young open star clusters. Extensive searches of open clusters have left a significant gap in the high mass region of the IFMR, this dearth may be the result of the WDs receiving a small velocity kick in the late stages of stellar evolution. In this work, we search the Gaia DR2 and EDR3 databases for ultramassive white dwarfs whose kinematics suggest they may have escaped from young open star clusters. Using a series of methods, we identified 13 candidate ultramassive WDs whose kinematics agreed with past cluster membership. Each of these candidates was followed up with spectroscopy to determine the WDs atmospheric parameters and better assess potential cluster membership. We determine that three of these candidates are high-confidence cluster members, four are questionable members, and the remaining six are non-members. The three high-confidence cluster member WDs are each more massive than any previous cluster WD known, with some of the most massive known progenitors. The most massive of these WDs has a progenitor of approximately 8.5 M⊙, supporting an increased mass limit for WD production.

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