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Signatures of r-process elements in kilonova spectra

Published online by Cambridge University Press:  27 February 2023

Nanae Domoto Open the ORCID record for Nanae Domoto [Opens in a new window] ,
Masaomi Tanaka Open the ORCID record for Masaomi Tanaka [Opens in a new window] ,
Shinya Wanajo  and
Kyohei Kawaguchi
Nanae Domoto
Affiliation:
Astronomical Institute, Tohoku University, Aoba, Sendai 980-8578, Japan email: n.domoto@astr.tohoku.ac.jp
Masaomi Tanaka
Affiliation:
Astronomical Institute, Tohoku University, Aoba, Sendai 980-8578, Japan email: n.domoto@astr.tohoku.ac.jp
Shinya Wanajo
Affiliation:
Max-Planck-Institut für Gravitationsphysik (Albert-Einstein-Institut), Am Mühlenberg 1, D-14476 Potsdam-Golm, Germany Interdisciplinary Theoretical and Mathematical Sciences Program (iTHEMS), RIKEN, Wako, Saitama 351-0198, Japan
Kyohei Kawaguchi
Affiliation:
Institute for Cosmic Ray Research, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8582, Japan Center for Gravitational Physics, Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto, 606-8502, Japan
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Abstract

Binary neutron star (NS) mergers have been expected to synthesize r-process elements and cause electromagnetic radiation called kilonovae. Although r-process nucleosynthesis was confirmed by the observations of GW170817/AT2017gfo, individual elements have not been identified except for strontium. Toward identification of elements in kilonova spectra, we perform radiative transfer simulations in NS merger ejecta. We find that Sr II triplet lines appear in the spectrum, which is consistent with the absorption feature observed in GW170817/AT2017gfo. The synthetic spectrum also shows the strong Ca II triplet lines. Absence of the Ca II line features in GW170817/AT2017gfo implies that the Ca/Sr ratio is < 0.002 in mass fraction, which is consistent with nucleosynthesis for electron fraction ≥ 0.40 and entropy per nucleon (in units of Boltzmann constant) ≥ 25. Identification of absorption lines in near-infrared wavelengths which have not yet been decoded may lead to clarify the abundances synthesized in NS merger ejecta.

Keywords

stars: neutronradiative transferline: identification
Type
Contributed Paper
Information
Proceedings of the International Astronomical Union , Volume 16 , Symposium S363: Neutron Star Astrophysics at the Crossroads: Magnetars and the Multimessenger Revolution , June 2020 , pp. 237 - 240
Copyright
© The Author(s), 2023. Published by Cambridge University Press on behalf of International Astronomical Union

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