Infrared spectral signatures of light r-process elements in kilonovae

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Jerkstrand, Anders and Pognan, Quentin and Banerjee, Smaranika and Sterling, N C and Grumer, Jon and Ferguson, Niamh and Butler, Keith and Gillanders, James and Smartt, Stephen and Kawaguchi, Kyohei and Vilagos, Blanka (2026) Infrared spectral signatures of light r-process elements in kilonovae. Monthly Notices of the Royal Astronomical Society, 548 (4). stag733. ISSN 1365-2966 (https://doi.org/10.1093/mnras/stag733)

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Abstract

A central question regarding neutron star (NS) mergers is whether they are able to produce all the r-process elements, from first to third peak. We here study theoretical infrared signatures of first-peak elements with spectral synthesis modelling. By combining state-of-the-art non-local thermodynamic equilibrium physics with new radiative and collisional data for these elements, we identify several promising diagnostic lines from Ge, As, Se, Br, Kr, and Zr. The models give self-consistent line luminosities and indicate specific features that probe emission volumes at early phases (10 d), the product of ion mass and electron density in late phases (75 d), and in some cases direct ionic masses at intermediate phases. Emission by [Se i] 5.03 m + [Se iii] 4.55 m is the only candidate from the first r-process peak that could explain the Spitzer photometry of AT2017gfo. However, the models show consistently that with a Kr/Te and Se/Te ratio following the solar r-process pattern, Kr + Se emission is dominant over Te for the feature at 2.1 m observed in both AT2017gfo and AT2023vfi. The somewhat better line profile fit with [Te iii] may suggest that both AT2017gfo and AT2023vfi had a strongly subsolar production of the light r-process elements. An alternative scenario could be that Kr + Se in an asymmetric morphological distribution generates the feature. Further James Webb Space Telescope spectral observations hold promise to determine the light r-process production of kilonovae, and in particular whether the light elements are made in a slow disc outflow or in a fast proto-NS wind. We identify specific needs for further atomic data for elements.

  • Item type:Article
    ID code:96075
    Dates:
    Date
    Event
    1 June 2026
    Published
    20 April 2026
    Published Online
    16 April 2026
    Accepted
    Subjects:Science > Astronomy
    Department:Faculty of Science > Physics
    Depositing user: Pure Administrator
    Date deposited:22 Apr 2026 15:02
    Last modified:02 Jun 2026 07:12
    URI:https://strathprints.strath.ac.uk/id/eprint/96075
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