Dr. Yossef Zenati, Johns Hopkins University

Thermonuclear Transient: The origins of Calcium-rich supernovae

Calcium-rich explosions are very faint (MB ∼ −15.5), type I supernovae (SNe) showing strong Ca-lines, mostly observed in old stellar environments. Several models for such SNe had been explored and debated, but none were able to consistently reproduce the observed properties of Ca-rich SNe, nor their rates and host-galaxy distributions. Here we show that the disruptions of low-mass carbon-oxygen (CO) white dwarfs (WDs) by hybrid Helium-CO (HeCO) WDs during their merger could explain the origin and properties of such SNe. We make use of detailed multi-dimensional hydrodynamical-thermonuclear (FLASH) simulations to characterize such explosions. We find that the accretion of CO material onto a HeCO-WD heats its He-shell and eventually leads to its "weak" detonation and ejection and the production of a sub-energetic ∼ 1049erg Ca-rich SN, while leaving the CO core of the HeCO-WD intact as a hot remnant WD, possibly giving rise to X-ray emission as it cools down. We model the detailed light-curve and spectra of such explosions to find an excellent agreement with observations of Ia/c Ca-rich might potentially also Ib Ca-rich SNe. We thereby provide a viable, consistent model for the origins of Ca-rich. These findings can shed new light on the role of Ca-rich in the chemical evolution of galaxies and the intra-cluster medium, and their contribution to the observed 511 keV signal in the Galaxy originating from positrons produced from 44Ti decay. Finally, the origins of such SNe point to the key role of HeCO WDs as SN progenitors and their potential role as progenitors of other thermonuclear SNe including normal Ia.

URL: https://uconn-cmr.webex.com/uconn-cmr/j.php?MTID=m153210cf8a5dbd0dec15adb42e84ea45