Stable nickel production in type Ia supernovae: A smoking gun for the progenitor mass?

Blondin, Stéphane; Bravo, Eduardo; Timmes, Frank; Dessart, Luc; Hillier, D. John

doi:10.1051/0004-6361/202142323

Stable nickel production in type Ia supernovae: A smoking gun for the progenitor mass?

Stéphane Blondin
(
- Marseille, Lab. Astrophys. and
- Pontificia U. Catol. Chile, Santiago
)
,
Eduardo Bravo
(
- Barcelona, Polytechnic U.
)
,
Frank Timmes
(
- Arizona State U., Tempe and
- Michigan State U., JINA
)
,
Luc Dessart
(
- Paris, Inst. Astrophys.
)
,
D. John Hillier
(
- Pittsburgh U.
)

Sep 28, 2021

19 pages

Published in:

Astron.Astrophys. 660 (2022) A96

Published: Apr 1, 2022

e-Print:

2109.13840 [astro-ph.SR]

DOI:

10.1051/0004-6361/202142323

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Abstract: (EDP Sciences)

Context. At present, there are strong indications that white dwarf (WD) stars with masses well below the Chandrasekhar limit (MCh ≈ 1.4 M⊙) contribute a significant fraction of SN Ia progenitors. The relative fraction of stable iron-group elements synthesized in the explosion has been suggested as a possible discriminant between MCh and sub-MCh events. In particular, it is thought that the higher-density ejecta of MCh WDs, which favours the synthesis of stable isotopes of nickel, results in prominent [Ni II] lines in late-time spectra (≳150 d past explosion).Aims. We study the explosive nucleosynthesis of stable nickel in SNe Ia resulting from MCh and sub-MCh progenitors. We explore the potential for lines of [Ni II] in the optical an near-infrared (at 7378 Å and 1.94 μm) in late-time spectra to serve as a diagnostic of the exploding WD mass.Methods. We reviewed stable Ni yields across a large variety of published SN Ia models. Using 1D MCh delayed-detonation and sub-MCh detonation models, we studied the synthesis of stable Ni isotopes (in particular, 58Ni) and investigated the formation of [Ni II] lines using non-local thermodynamic equilibrium radiative-transfer simulations with the CMFGEN code.Results. We confirm that stable Ni production is generally more efficient in MCh explosions at solar metallicity (typically 0.02–0.08 M⊙ for the 58Ni isotope), but we note that the 58Ni yield in sub-MCh events systematically exceeds 0.01 M⊙ for WDs that are more massive than one solar mass. We find that the radiative proton-capture reaction 57Co(p, γ)58Ni is the dominant production mode for 58Ni in both MCh and sub-MCh models, while the α-capture reaction on 54Fe has a negligible impact on the final 58Ni yield. More importantly, we demonstrate that the lack of [Ni II] lines in late-time spectra of sub-MCh events is not always due to an under-abundance of stable Ni; rather, it results from the higher ionization of Ni in the inner ejecta. Conversely, the strong [Ni II] lines predicted in our 1D MCh models are completely suppressed when 56Ni is sufficiently mixed with the innermost layers, which are rich in stable iron-group elements.Conclusions. [Ni II] lines in late-time SN Ia spectra have a complex dependency on the abundance of stable Ni, which limits their use in distinguishing among MCh and sub-MCh progenitors. However, we argue that a low-luminosity SN Ia displaying strong [Ni II] lines would most likely result from a Chandrasekhar-mass progenitor.Key words: supernovae: general / nuclear reactions, nucleosynthesis, abundances / supernovae: individual: SN 2017bzc / radiative transfer

Note:

Accepted for publication in A&A, replaced with accepted version (+ corrected a typo in the conclusions: "overabundance" replaced with "over abundance"). 20 pages, 10 figures. Model spectra available at https://zenodo.org/record/5528088

supernovae: general
nuclear reactions, nucleosynthesis, abundances
supernovae: individual: SN 2017bzc
radiative transfer

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Figures(14)