Flat-topped NIR profiles originating from an unmixed helium shell in the Type 
IIb SN 2020acat

Medler, K.; Mazzali, P. A.; Ashall, C.; Teffs, J.; Shahbandeh, M.; Shappee, B.

doi:10.1093/mnrasl/slac127

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Flat-topped NIR profiles originating from an unmixed helium shell in the Type IIb SN 2020acat

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Mazzali, P. A.
Stellar Astrophysics, MPI for Astrophysics, Max Planck Society;

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Citation

Medler, K., Mazzali, P. A., Ashall, C., Teffs, J., Shahbandeh, M., & Shappee, B. (2023). Flat-topped NIR profiles originating from an unmixed helium shell in the Type IIb SN 2020acat. Monthly Notices of the Royal Astronomical Society, 518(1), L40-L44. doi:10.1093/mnrasl/slac127.

Cite as: https://hdl.handle.net/21.11116/0000-000D-1745-C

Abstract

The Near Infrared (NIR) spectra of the Type IIb supernova (SN IIb) SN 2020acat, obtained at various times throughout the optical follow-up campaign, are presented here. The dominant He i 1.0830 and 2.0581 μm features are seen to develop flat-topped P-Cygni profiles as the NIR spectra evolve towards the nebular phase. The nature of the NIR helium peaks imply that there was a lack of mixing between the helium shell and the heavier inner ejecta in SN 2020acat. Analysis of the flat-top features showed that the boundary of the lower velocity of the helium shell was ∼3 − 4 × 10³ km s⁻¹. The NIR spectra of SN 2020acat were compared to both SN 2008ax and SN 2011dh to determine the uniqueness of the flat-topped helium features. While SN 2011dh lacked a flat-topped NIR helium profile, SN 2008ax displayed NIR helium features that were very similar to those seen in SN 2020acat, suggesting that the flat-topped feature is not unique to SN 2020acat and may be the product of the progenitors structure.