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

Medler, K, Mazzali, PA, Ashall, C, Teffs, J, Shahbandeh, M and Shappee, B (2022) Flat-topped NIR profiles originating from an unmixed helium shell in the Type IIb SN 2020acat. Monthly Notices of the Royal Astronomical Society: Letters, 518 (1). L40-L44. ISSN 1745-3925

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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 μm 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.

Item Type: Article
Additional Information: This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2022 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
Uncontrolled Keywords: 0201 Astronomical and Space Sciences
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: Oxford University Press (OUP)
SWORD Depositor: A Symplectic
Date Deposited: 31 Oct 2022 15:29
Last Modified: 15 Nov 2022 13:00
DOI or ID number: 10.1093/mnrasl/slac127
URI: https://researchonline.ljmu.ac.uk/id/eprint/17976
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