7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Heavy element atomic datafor multi-messenger observations of neutron star mergers
Masaomi Tanaka1, Daiji Kato2,3, Gaigalas Gediminas4, Kyohei Kawaguchi5,6,Laima Kitovienė4, Pavel Rynkun4, Smaranika Banerjee7,1, Nanae Domoto1
1
Astronomical Institute, Tohoku University, Sendai, Japan
2
National Institute for Fusion Science, 322-6 Oroshi-cho, Toki, Japan
3
Interdisciplinary Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka,Japan
4
Institute of Theoretical Physics and Astronomy, Vilnius University, Vilnius, Lithuania
5Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Potsdam-Golm,
Germany
6
Institute for Cosmic Ray Research, The University of Tokyo, Kashiwa, Chiba , Japan
7
Stockholm University, Roslagstullsbacken 21, 114 21 Stockholm, Sweden
e-mail: masaomi.tanaka@astr.tohoku.ac.jp
Neutron star mergers are one of the most promising
spectral features of kilonovae. By using/constructing
sites for heavy element nucleosynthesis in the Universe.
atomic data with accurate transition wavelengths, weBy synthesizing heavy elements, they give rise toshow that the spectra of kilonovae tend to show
electromagnetic emission, so called kilonova, thermal
absorption features of Ca, Sr, La, and Ce [5,6]. Theseemission powered by radioactive decays of newly
elements are located at the left side of the periodic table,
synthesized r-process nuclei.
and they show a relatively simple atomic structure,Thanks to the “multi-messenger” observations of
causing the strong individual transitions. Decoding thesegravitational waves and electromagnetic waves in 2017,absorption features in kilonova spectra enables us toheavy element nucleosynthesis in the neutron starconfirm the presence of individual elements and tomergers has been directly confirmed. Observational
quantify the mass fraction of these elements in theproperties of kilonova are largely affected
ejected1374 byM. Tanaka
et al. material from neutron star mergers.
bound-bound opacities of heavy elements. Thus, it isessential to understand atomic properties of heavy
elements to link the observed signals with
nucleosynthesis of neutron star mergers.
Aiming at (1) evaluating the heavy element opacities inthe ejected material from neutron star mergers, and (2)extracting elemental information from the spectra ofkilonova, we have been constructing atomic data ofheavy elements through the collaboration between
astrophysicists and atomic physicists.
For the opacities, we have systematically calculated
atomic structure of heavy elements covering neutral
atoms up to triply ionized ions [1]. Our results show thatthe average opacities for lanthanides can be as Figure
high4. Planck
as mean opacities for all the elements. The opacities are calculated by assuming ρ = 1 × 10−13 g cm−3 , and t = 1 d after the merger. Bluelines present the opacities for T = 5000 and 10 000 K, respectively.
20-30 cm2 g-1 (Figure 1), which is higher than theredopacity
Figure 1: Planck mean opacities for all the heavyof Fe group elements by more than one order ofelements [1]. The opacities are calculated by assuming
magnitude. Such a high opacity nicely reproduces the
ρ=10-13 g cm-3, and t=1 day after the merger. Blue andproperties of the kilonova observed in 2017. Our datasets
red lines present the opacities for T = 5000 and 10 000 K,are publicly available through the “Japan-Lithuania
respectively.
Opacity Database for Kilonova” [2].
By extending these works, atomic data for highly
References
ionized heavy elements have also been constructed [3,4].
[1] Tanaka, M. et al. 2020, MNRAS, 496, 1369-1392
These results show that the opacity of highly ionized[2] Kato, D. et al. 2021,
lanthanides can be even higher by another order of
http://dpc.nifs.ac.jp/DB/Opacity-Database/magnitudes due to the complex atomic structure of two[3] Banerjee, S. et al. 2020, ApJ, 901, 29 (12pp)
open shells. This has an impact to the ultraviolet[4] Banerjee, S. et al. 2022, ApJ, 934, 117 (13pp)
emission from kilonova within a few hours after the[5] Domoto, N. et al. 2021, ApJ, 913, 26 (13pp)
merger.
[6] Domoto, N. et al. 2022, ApJ, 939, 8 (18pp)
Based on these new atomic data, we also study the