Transparent Helium in Stripped Envelope Supernovae

TL;DR

This paper suggests that in some stripped envelope supernovae, helium becomes transparent due to low temperatures and velocities, complicating helium mass measurements from light curves and offering insights into supernova progenitors.

Contribution

It introduces a method to identify transparent helium in supernovae using light curve and velocity data, highlighting implications for understanding supernova progenitors.

Findings

Some SNe show signs of transparent helium due to low velocities and temperatures.

Helium transparency affects the interpretation of supernova light curves.

Differences between SNe Ib and Ic can be analyzed through velocity and opacity insights.

Abstract

Using simple arguments based on photometric light curves and velocity evolution, we propose that some stripped envelope supernovae (SNe) show signs that a significant fraction of their helium is effectively transparent. The main pieces of evidence are the relatively low velocities with little velocity evolution, as are expected deep inside an exploding star, along with temperatures that are too low to ionize helium. This means that the helium should not contribute to the shaping of the main SN light curve, and thus the total helium mass may be difficult to measure from simple light curve modeling. Conversely, such modeling may be more useful for constraining the mass of the carbon/oxygen core of the SN progenitor. Other stripped envelope SNe show higher velocities and larger velocity gradients, which require an additional opacity source (perhaps the mixing of heavier elements or radioactive nickel) to prevent the helium from being transparent. We discuss ways in which similar analysis can provide insights into the differences and similarities between SNe Ib and Ic, which will lead to a better understanding of their respective formation mechanisms.