Speaker
Description
Although the highest possible mass for a white dwarf star (WD) is a well-established limit, known as the Chandrasekhar Mass (Mch = 1.4 M☉), the progenitor mass for such a white dwarf is much more contentious, as differences in the treatment of convection alone can create a variation in progenitor mass of ~2M☉. Furthermore, modeling a sequence through the end of the Super Asymptotic Giant Branch (SAGB) is extremely computationally expensive and requires overcoming several instabilities. Consequently, very few works have been dedicated to modeling the full evolution of ultramassive WDs. And yet, establishing an accurate initial-final mass relation and more fully understanding the characteristics of ultramassive white dwarfs remains imperative if we aim to better constrain the chemical evolution of the Galaxy, the rates for core-collapse supernovae events, and the very nature of type Ia supernovae. In this work, we use the stellar evolution code MESA, in version r24.08.1, to compute the evolution and final fate of stars with initial masses 6-9M☉ and metallicity Z=0.02, from the pre-ZAMS until low luminosities (L < 10^-4 L) in the white dwarf cooling curve. As a result, we find massive and ultramassive WDs with masses ranging from 0.927-1.313M, and either CO (Mwd 1.015M) or ONe (Mwd 1.088M) cores. The 7.5M sequence was the lowest mass explored to undergo carbon burning. At the lower end of our grid (Mwd 1.088M), our models are H-rich, while for masses larger than this, our models are more representative of H-deficient WDs. We discuss and detail each step of the progenitor’s evolution, providing core masses and ages at different stages, carbon ignition and thermal pulse characteristics, as well as crystallization temperatures and cooling ages. This is the first grid of UMWD that accounts for the evolution both during the TP-SAGB stage and post-AGB.