Calibrated lanthanide atomic data for kilonova radiative transfer: Atomic structure and opacities

The early spectra of the kilonova AT2017gfo following the binary neutron star merger GW170817 exhibit numerous features shaped by r-process nucleosynthesis products. Although a few species were tentatively detected, no third-peak elements were unambiguously identified, as the amount of atomic data required for radiative transfer modeling is immense. Although comprehensive atomic data, including atomic opacities, is now available for many elements, wavelength-calibrated data remain limited to a few selected ions. To examine the atomic opacities of all singly and doubly ionized lanthanides, from La ( <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"> <a:mrow> <a:mi>Z</a:mi> <a:mo>=</a:mo> <a:mn>57</a:mn> </a:mrow> </a:math> ) to Yb ( <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" display="inline"> <c:mi>Z</c:mi> <c:mo>=</c:mo> <c:mn>70</c:mn> </c:math> ), we perform atomic structure calculations using the code. Our calculations incorporate an innovative optimization of the local central potential and the number of configurations considered, alongside a calibration technique aimed at enhancing agreement between theoretical and experimental atomic energy levels. We assess the accuracy of the computed data, including energy levels and electric dipole (E1) transition strengths, as well as their impact on kilonova opacities. We find that strong transitions [ <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" display="inline"> <e:mi>log</e:mi> <e:mo stretchy="false">(</e:mo> <e:mi>g</e:mi> <e:mi>f</e:mi> <e:mo stretchy="false">)</e:mo> <e:mo>&gt;</e:mo> <e:mo>−</e:mo> <e:mn>1</e:mn> </e:math> ] are in good agreement with both experiments and semiempirical calculations. For ions with substantial experimental data, the computed opacities exhibit good agreement with prior calculations. By calibrating low-lying energy levels with experimental data, we have identified 66 722 transitions with experimentally calibrated wavelength information, rendering future lanthanide line identifications through radiative transfer modeling feasible. In total, our calculations encompass 28 ions, yielding 146 849 energy levels below the ionization threshold and 29 337 507 transitions among these levels.