Abundance stratification in Type Ia supernovae – VIII. The 03fg-like SN 2012dn: a double-degenerate merger interpretation

Aouad, CJ; Mazzali, PA; Hachinger, S; Ashall, C

Abundance stratification in Type Ia supernovae – VIII. The 03fg-like SN 2012dn: a double-degenerate merger interpretation

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Aouad, CJ ORCID: 0000-0001-6063-0344, Mazzali, PA ORCID: 0000-0001-6876-8284, Hachinger, S and Ashall, C (2026) Abundance stratification in Type Ia supernovae – VIII. The 03fg-like SN 2012dn: a double-degenerate merger interpretation. Monthly Notices of the Royal Astronomical Society, 552 (4). ISSN 0035-8711

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Publisher URL: https://doi.org/10.1093/mnras/stag1699

Abstract

A detailed study using abundance tomography of SN 2012dn, a peculiar Type Ia supernova, is presented. Despite exhibiting a normal peak luminosity, it retains early-phase super-Chandrasekhar (03fg-like) characteristics: weak Fe iii, narrow intermediate-mass element, persistent carbon, and the absence of high-velocity Ca ii features. Its nebular spectrum is unusually faint due to grey dimming beginning (Formula presented) 60 d after maximum and shows [O i] emission, rare in Type Ia supernovae. While a Chandrasekhar-mass density profile reproduces the photospheric phase, it fails at late times. The [O i] emission requires additional low-velocity mass, implying a total ejecta mass of 1.66 (Formula presented), including 0.33 (Formula presented) of oxygen (with 0.1 (Formula presented) in the core). The (Formula presented) Ni mass is estimated to be 0.45–0.49 (Formula presented), a range set by uncertainties in the grey-extinction correction applied at the nebular phase, and is insufficient on its own to account for the peak luminosity. Stable iron is confined to intermediate layers and absent from both the core and outer ejecta, the latter indicating subsolar progenitor metallicity. Silicon and sulfur span the full ejecta, while carbon extends down to (Formula presented) km s(Formula presented). These properties favour a double-degenerate CO–CO white dwarf merger scenario. The remaining luminosity deficit may be explained by additional energy input from a weak interaction with a low-mass, carbon-rich circumstellar shell.

Item Type:	Article
Uncontrolled Keywords:	astro-ph.HE; astro-ph.HE; 5101 Astronomical Sciences; 51 Physical Sciences; 0201 Astronomical and Space Sciences; Astronomy & Astrophysics; 5101 Astronomical sciences; 5107 Particle and high energy physics; 5109 Space sciences
Subjects:	Q Science > QB Astronomy Q Science > QC Physics
Divisions:	Astrophysics Research Institute
Publisher:	Oxford University Press
Date of acceptance:	4 September 2026
Date of first compliant Open Access:	21 October 2026
Date Deposited:	21 Oct 2026 13:35
Last Modified:	21 Oct 2026 13:35
DOI or ID number:	10.1093/mnras/stag1699
URI:	https://researchonline.ljmu.ac.uk/id/eprint/29724

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