Modelling Type Ic Supernovae with TARDIS: Hidden Helium in SN1994I?

Abstract

Supernovae (SNe) with photospheric spectra devoid of Hydrogen and Helium features are generally classified as Type Ic SNe (SNe Ic). However, there is ongoing debate as to whether Helium can be hidden in the ejecta of SNe Ic (that is, Helium is present in the ejecta, but produces no obvious features in the spectra). We present the first application of the fast, 1-D radiative transfer code tardis to a SN Ic, and we investigate the question of how much Helium can be hidden in the outer layers of the SN Ic ejecta. We generate tardis models for the nearby, well-observed, and extensively modeled SN Ic 1994I, and we perform a code comparison to a different, well-established Monte Carlo based radiation transfer code. The code comparison shows that tardis produces consistent synthetic spectra for identical ejecta models of SN1994I. In addition, we perform a systematic experiment of adding outer He shells of varying masses to our SN1994I models. We find that an outer He shell of only 0.05M produces strong optical and NIR He spectral features for SN1994I which are not present in observations, thus indicating that the SN1994I ejecta is almost fully He deficient compared to the He masses of typical He-rich SN progenitors. Finally we show that the He I λ20851 line pseudo equivalent width of our modeled spectra for SN1994I could be used to infer the outer He shell mass which suggests that NIR spectral follow-up of SNe Ic will be critical for addressing the hidden helium question for a statistical sample of SNe Ic.

The double-peaked type Ic Supernova 2019cad: another SN 2005bf-like object

“…While both mechanisms are successful in explaining the absence of the hydrogen layer, removing the helium layer is still a challenge as it is found in denser ★ E-mail: claudia.gutierrez@utu.fi parts of the star. Given these complications, it has been proposed that some helium is possibly present in SNe Ic but it is not seen in the spectrum because it is not excited (Dessart et al 2012, but see Williamson et al 2020). On the other hand, recent observational evidence, such as the low progenitor masses inferred for SNe Ic from their light curves (Drout et al 2011;Lyman et al 2016;Taddia et al 2018b) and the relative SN Ic rate (Smith et al 2011), favour the the binary scenario.…”