Revisiting Near-infrared Features of Kilonovae: The Importance of Gadolinium
The observation of the kilonova AT2017gfo and investigations of its light curves and spectra confirmed that neutron star mergers are sites of r -process nucleosynthesis. However, the identification of elements responsible for the spectral features is still challenging, particularly at the near-infra...
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2025-01-01
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| Series: | The Astrophysical Journal |
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| Online Access: | https://doi.org/10.3847/1538-4357/ada251 |
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| author | Salma Rahmouni Masaomi Tanaka Nanae Domoto Daiji Kato Kenta Hotokezaka Wako Aoki Teruyuki Hirano Takayuki Kotani Masayuki Kuzuhara Motohide Tamura |
| author_facet | Salma Rahmouni Masaomi Tanaka Nanae Domoto Daiji Kato Kenta Hotokezaka Wako Aoki Teruyuki Hirano Takayuki Kotani Masayuki Kuzuhara Motohide Tamura |
| author_sort | Salma Rahmouni |
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| description | The observation of the kilonova AT2017gfo and investigations of its light curves and spectra confirmed that neutron star mergers are sites of r -process nucleosynthesis. However, the identification of elements responsible for the spectral features is still challenging, particularly at the near-infrared wavelengths. In this study, we systematically searched for all possible near-infrared transitions of heavy elements using experimentally calibrated energy levels. Our analysis reveals that most candidate elements with strong absorption lines are lanthanides ( Z = 57–71) and actinides ( Z = 89–103). This is due to their complex structures leading to many low-lying energy levels, which results in strong transitions in the near-infrared range. N. Domoto et al. (2022) have shown that La iii and Ce iii can explain the absorption features at λ ∼ 12000–15000 Å. While our results confirm that these two elements show strong infrared features, we additionally identify Gd iii as the next most promising species. Due to its unique atomic structure involving the half-filled 4 f and the outer 5 d orbitals, Gd iii has one of the lowest-lying energy levels, between which relatively strong transitions occur. We also find absorption lines caused by Gd iii in the near-infrared spectrum of a chemically peculiar star HR 465, which supports their emergence in kilonova spectra. By performing radiative transfer simulations, we confirm that Gd iii lines affect the feature at ∼12000 Å previously attributed to La iii . Future space-based time-series observations of kilonova spectra will allow the identification of Gd iii lines. |
| format | Article |
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| institution | Kabale University |
| issn | 1538-4357 |
| language | English |
| publishDate | 2025-01-01 |
| publisher | IOP Publishing |
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| series | The Astrophysical Journal |
| spelling | doaj-art-76ce4d613e8a4d85bbcf677d1141fe4f2025-02-12T09:20:10ZengIOP PublishingThe Astrophysical Journal1538-43572025-01-0198014310.3847/1538-4357/ada251Revisiting Near-infrared Features of Kilonovae: The Importance of GadoliniumSalma Rahmouni0https://orcid.org/0009-0002-1232-243XMasaomi Tanaka1https://orcid.org/0000-0001-8253-6850Nanae Domoto2https://orcid.org/0000-0002-7415-7954Daiji Kato3https://orcid.org/0000-0002-5302-073XKenta Hotokezaka4https://orcid.org/0000-0002-2502-3730Wako Aoki5https://orcid.org/0000-0002-8975-6829Teruyuki Hirano6https://orcid.org/0000-0003-3618-7535Takayuki Kotani7https://orcid.org/0000-0001-6181-3142Masayuki Kuzuhara8https://orcid.org/0000-0002-4677-9182Motohide Tamura9https://orcid.org/0000-0002-6510-0681Astronomical Institute, Tohoku University , Aoba, Sendai 980-8578, Japan ; [email protected] Institute, Tohoku University , Aoba, Sendai 980-8578, Japan ; [email protected]; Division for the Establishment of Frontier Sciences, Organization for Advanced Studies, Tohoku University , Sendai 980-8577, JapanAstronomical Institute, Tohoku University , Aoba, Sendai 980-8578, Japan ; [email protected] Institute for Fusion Science , 322-6 Oroshi-cho, Toki 509-5292, Japan; Interdisciplinary Graduate School of Engineering Sciences, Kyushu University , Kasuga, Fukuoka 816-8580, JapanResearch Center for the Early Universe, Graduate School of Science, University of Tokyo , Bunkyo, Tokyo 113-0033, JapanNational Astronomical Observatory of Japan , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan; Astronomical Science Program, The Graduate University for Advanced Studies , SOKENDAI, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, JapanNational Astronomical Observatory of Japan , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan; Astronomical Science Program, The Graduate University for Advanced Studies , SOKENDAI, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan; Astrobiology Center , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, JapanNational Astronomical Observatory of Japan , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan; Astronomical Science Program, The Graduate University for Advanced Studies , SOKENDAI, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan; Astrobiology Center , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, JapanNational Astronomical Observatory of Japan , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan; Astrobiology Center , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, JapanNational Astronomical Observatory of Japan , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan; Astrobiology Center , 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan; Department of Astronomy, Graduate School of Science, The University of Tokyo , 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, JapanThe observation of the kilonova AT2017gfo and investigations of its light curves and spectra confirmed that neutron star mergers are sites of r -process nucleosynthesis. However, the identification of elements responsible for the spectral features is still challenging, particularly at the near-infrared wavelengths. In this study, we systematically searched for all possible near-infrared transitions of heavy elements using experimentally calibrated energy levels. Our analysis reveals that most candidate elements with strong absorption lines are lanthanides ( Z = 57–71) and actinides ( Z = 89–103). This is due to their complex structures leading to many low-lying energy levels, which results in strong transitions in the near-infrared range. N. Domoto et al. (2022) have shown that La iii and Ce iii can explain the absorption features at λ ∼ 12000–15000 Å. While our results confirm that these two elements show strong infrared features, we additionally identify Gd iii as the next most promising species. Due to its unique atomic structure involving the half-filled 4 f and the outer 5 d orbitals, Gd iii has one of the lowest-lying energy levels, between which relatively strong transitions occur. We also find absorption lines caused by Gd iii in the near-infrared spectrum of a chemically peculiar star HR 465, which supports their emergence in kilonova spectra. By performing radiative transfer simulations, we confirm that Gd iii lines affect the feature at ∼12000 Å previously attributed to La iii . Future space-based time-series observations of kilonova spectra will allow the identification of Gd iii lines.https://doi.org/10.3847/1538-4357/ada251Atomic dataRadiative transferSpectral line identificationNeutron stars |
| spellingShingle | Salma Rahmouni Masaomi Tanaka Nanae Domoto Daiji Kato Kenta Hotokezaka Wako Aoki Teruyuki Hirano Takayuki Kotani Masayuki Kuzuhara Motohide Tamura Revisiting Near-infrared Features of Kilonovae: The Importance of Gadolinium The Astrophysical Journal Atomic data Radiative transfer Spectral line identification Neutron stars |
| title | Revisiting Near-infrared Features of Kilonovae: The Importance of Gadolinium |
| title_full | Revisiting Near-infrared Features of Kilonovae: The Importance of Gadolinium |
| title_fullStr | Revisiting Near-infrared Features of Kilonovae: The Importance of Gadolinium |
| title_full_unstemmed | Revisiting Near-infrared Features of Kilonovae: The Importance of Gadolinium |
| title_short | Revisiting Near-infrared Features of Kilonovae: The Importance of Gadolinium |
| title_sort | revisiting near infrared features of kilonovae the importance of gadolinium |
| topic | Atomic data Radiative transfer Spectral line identification Neutron stars |
| url | https://doi.org/10.3847/1538-4357/ada251 |
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