2022/10/11 by Kaustav K. Das, M. M. Kasliwal, Das, Kaustav K. +49 · 5 citations
Physics and Astronomy · #Gamma-ray bursts and supernovae #Astronomy and Astrophysical Research #Astro and Planetary Science
paper · pdf · doi:10.48550/arxiv.2210.05729
The fate of stars in the zero-age main-sequence (ZAMS) range ≈ 8-12 Msun is unclear. They could evolve to form white dwarfs or explode as electron-capture supernovae (SNe) or iron core-collapse SNe (CCSNe). Even though the initial mass function indicates that this mass range should account for over 40% of all CCSNe progenitors, few have been observationally confirmed, likely owing to the faintness and rapid evolution of these transients. In this paper, we present a sample of nine Ca-rich/O-poor Type IIb SNe detected by the Zwicky Transient Facility with progenitors likely in this mass range. We perform a holistic analysis of the spectroscopic and photometric properties of the sample. These sources have a flux ratio of [Ca II] λλ7291, 7324 to [O I] λλ6300, 6364 of \gtrsim 2 in their nebular spectra. Comparing the measured [O I] luminosity (\lesssim 1039 \mathrmerg s-1) and derived oxygen mass (\lesssim 0.1 Msun) with theoretical models, we infer that the progenitor ZAMS mass for these explosions is less than 12 Msun. These correspond to He-stars with core masses less than around 3 Msun. We find that the ejecta properties (Mej \lesssim 1 Msun) are also consistent with those expected for such low mass He-stars. The low ejecta mass of these sources indicates a class of strongly-stripped SNe that is a transition between the regular stripped-envelope SNe and ultra-stripped SNe. The progenitor could be stripped by a main sequence companion and result in the formation of a neutron star - main sequence binary. Such binaries have been suggested to be progenitors of neutron star - white dwarf systems that could merge within a Hubble time, and be detectable with LISA.
HostSubGP: Precise Galaxy Background Subtraction in Transient Spectroscopy with Gaussian Processes