Ce II-IV emission in kilonovae with R-matrix collision strengths and distorted wave recombination rates
Year: 2026
Type: preprint
Abstract: We provide transition probabilities and Maxwellian-averaged collision-strengths for the electron-impact excitation of Ce {\sc ii} - {\sc iv}. These ions are potentially abundant in kilonovae (KNe) and feature both forbidden and allowed transitions in the infrared. These atomic data are obtained using the {\sc grasp}$^0$ atomic structure code, interfaced with the non-perturbative {\sc darc} R-matrix close-coupling codes. We additionally use {\sc autostructure} to produce dielectronic and radiative recombination rate coefficients for Ce {\sc ii} - {\sc vi}. Using this data, we calculate an approximate ionization balance including non-thermal ionization rates with deposition rates from realistic models. We find Ce {\sc ii} - {\sc iv} to be of roughly equal abundance, subject to ejecta conditions. We find that generally we need $\gtrsim$ 10$^{-3}$ M$_{\odot}$ of Ce in total to produce emission of comparable luminosity to the features in the spectrum of AT2023vfi. In particular, it is found that [Ce {\sc iv}] 4.5 $μ$m requires both strong ionization and weak recombination, as well as a production of Ce considerably stronger than that of the solar abundance in order to have luminosity comparable to the apparent emission in this wavelength vicinity in \grb. %which is seemingly incompatible with the current understanding of the bulk composition of KNe. With such strict requirements on individual element masses, the detection of individual lanthanides on a line-by-line basis in the nebular phase seems unlikely - but lanthanides may remain important for cooling and early time analyses.
Source: arXiv (Cornell University)
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
Funders: U.S. Department of Energy, Auburn University, UK Research and Innovation, National Energy Research Scientific Computing Center, University of Leicester, European Commission, Queen's University Belfast, Queen's University, Office of Science, Engineering and Physical Sciences Research Council, Science and Technology Facilities Council
Awards: G1332530600, G1995055815, G271529020
OpenAlex ID: W7213297335