The peculiar Ca-rich SN 2019ehk: Evidence for a Type IIb core-collapse supernova from a low mass stripped progenitor

Understand

The nature of the peculiar `Ca-rich' SN 2019ehk in the nearby galaxy M100 remains unclear.

• Its origin has been debated as either a stripped core-collapse supernova or a thermonuclear helium detonation event.
• Here, we present very late-time photometry of the transient obtained with the Keck I telescope at $\approx280$ days from peak light.
• Using the photometry to perform accurate flux calibration of a contemporaneous nebular phase spectrum, we measure an [O I] luminosity of $(0.19-1.08)\times10^{38}$ erg s$^{-1}$ and [Ca II] luminosity of $(2.7-15.6)\times10^{38}$ erg s$^{-1}$ over the range of the uncertain extinction along the line of sight.