Hidden Helium in the Type Ic Supernova 1994I

Supernovae (SNe) whose photospheric spectra lack Hydrogen and Helium features are classified as SNe Ic. However in the last decade, the question of hidden Helium (i.e. Helium present in the SN ejecta that does not produce noticeable spectral features) has arisen and been much debated. It has been shown that Helium is particularly sensitive to non-thermal effects of fast electrons produced by gamma rays originating from ⁵⁶Ni decay, so low ⁵⁶Ni mixing in the SN ejecta allows for He in the outer layers that does not produce spectral features. Multiple theoretical efforts have been devoted to understanding the hidden Helium question for SNe Ic using hydrodynamical and radiative transfer simulations of progenitor system evolution through explosion, but there is a severe lack of dedicated modeling applied to observed SNe Ic spectra. In this work, we use the fast, 1D radiative transfer code TARDIS in order to conduct the first systematic modeling investigation of hidden Helium in the well-observed SN Ic 1994I. We determine an upper bound for the mass of a potential outer Helium shell for the SN1994I ejecta, and moreover, we show that the pseudo equivalent width of the He I 20851 feature in our synthetic spectra correlates with the outer He shell mass. We discuss the importance of near infra-red spectral observations of future SNe Ic and how TARDIS can be used to model a statistical sample of observed SNe Ic in order to yield new insights into the hidden Helium question.