Astronomy Tea Talk

Speaker: Chang Liu

Title: What Do Rare Weirdos Tell Us About the Broader Population? An Examination of the Progenitor Systems of Type Ia Supernovae

Abstract: While there is a broad consensus that Type Ia supernovae (SNe Ia) arise from white dwarf (WD) explosions, the traditional scenario involving a Chandrasekhar-mass (M_Ch) WD cannot fully account for the observed diversity of thermonuclear WD explosions. Thus, the nature of SN Ia progenitors remains unresolved. Observations at early (~days post-explosion) and late times (>200 days after peak) uniquely probe the outermost and innermost ejecta, respectively. The synergy of these two phases is essential for a complete picture of SN Ia demographics, but to date no experiment has been designed to systematically probe both these phases. Here, I will present observational evidence that some SNe Ia come from sub-M_Ch WDs that explode via helium-shell double detonations. At early times, their unusual color evolution and prominent continuous absorption in the near-ultraviolet reveal Fe-group elements formed in the shell detonation; whereas at late times, the absence of [Ni II] emission in the nebular-phase suggests a low central density in the progenitor, consistent with a sub-M_Ch explosion. I will conclude with a summary of our on-going experiment to jointly analyze the early- and late-time behavior of SNe Ia. To date we have observed ~40 ZTF SNe Ia with both very early-time light curves and nebular-phase spectra. Leveraging a new and novel host-galaxy subtraction technique, we are — for the first time — able to include SNe embedded in high-background galaxy environments. This has yielded the most host-unbiased sample of nebular-phase spectra to date, enabling an unprecedented investigation into SN Ia progenitor demographics.

For more information, please contact Mandy Chen or Kaitlyn Shin by email at [email protected], [email protected].