Spectral modelling of kilonovae (KNe)requireslarge amounts of collisional excitation and photoionization atomic data for lowly ionized (neutral,singly, and doubly ionized)species of heavy elements. Much of the data currently used is calculated using approximate hydrogenic results or adoptssemi-empirical formulae. We present atomic data forions of tellurium (Te) computed using the well-known R-matrix method. Results will also be presented for radiative and thermal collisions of Te iv and v, for which the required atomic data are also typically limited in the literature. The Multi-Configuration-Dirac- Hartree-Fock method is used to produce model atomic structures and radiative rates. These modelstructures are then used to calculate electron-impact-excitation and photoionization cross-sections. The resulting excitation and radiative rates are further used in a collisional radiative model to produce synthetic spectra, which are compared with observations. We also investigate the possibility of Te iv contributing to the 1.08 mu m emission feature in the mid-epochs of AT2017gfo alongside the established P-Cygni feature of Sr ii.

High abundances of various lead (Pb) species have been identified in the spectra of many asymptotic giant branch stars and O- and B-type subdwarfs (sdO/B). Additional atomic data relating to Pb, and in particular photoionization cross-sections, are needed to allow a greater understanding of the origin of these observed Pb abundances, and hence discern the evolutionary pathway of these stars. We have calculated level-resolved photoionization cross-sections for Pb iii, iv, v, and vi. Four new target structures have been developed with the General Relativistic Atomic Structure Package (grasp(0)), whose corresponding energy levels, Einstein A-coefficients, and oscillator strengths have been found to be in good agreement with previous experimental and theoretical sources. The photoionization cross-sections calculated using the Dirac Atomic R-matrix Codes (darc) are available in topbase format, and follow the trends expected for an isonuclear series. These new Pb data sets will now allow for the modelling of Pb abundances and line opacities under non-local thermodynamic equilibrium (non-LTE) conditions. Using the helium-rich hot subdwarf EC 22536-5304 as a test case, we show that there are noticeable differences in the Pb line profiles across the ultraviolet and optical wavelength regions under LTE and non-LTE conditions. There is both depletion and enrichment of individual Pb species. This highlights the importance of applying non-LTE conditions when modelling EC 22536-5304, as well as other O/B-type stars.

A large number of $\bf{R}$-matrix calculations of electron-impact excitation for heavy elements ($Z\gt 70$) have been performed in recent years for applications in fusion and astrophysics research. With the expanding interest in heavy ions due to kilonova (KN) events such as AT2017gfo and AT2023vfi, these new data can be utilized for the diagnosis and study of observed KN spectra. In this work, recently computed electron-impact excitation effective collision strengths are used, for the first three ionization stages of tungsten (W, $Z=74$), platinum (Pt, $Z=78$), and gold (Au, $Z=79$), to construct basic collisional radiative models tailored for the late stage nebular phases of KN. Line luminosities are calculated at a range of electron temperatures and densities and the strengths of these lines for a representative ion mass are compared. For the case of W iii, these optically thin intensities are additionally used to constrain the mass of this ion in both AT2017gfo and AT2023vfi. Comparing with theoretical predictions of nucleosynthesis yields from neutron star merger simulations, broad agreement with the inferred ion masses of W is found. Furthermore, we highlight the value of W measurements by showing that the abundance of other groups of elements and outflow properties are constrained by exploiting theoretically motivated correlations between the abundance of W and that of lanthanides or third r-process peak elements. Based on simple estimates, we also show that constraints on the distribution of tungsten in the ejecta may be accessible through the line shape, which may also yield information on the neutron star merger remnant evolution.

The Axelrod approximation is widely used in astrophysical modelling codes to evaluate electron-impact excitation effective collision strengths for forbidden transitions. Approximate methods such as this are a necessity for many heavy elements with open shells where collisional data is either non existent or sparse as the use of more robust methods prove prohibitively expensive. Atomic data for such forbidden transitions are essential for producing full collisional radiative models that do not assume Local-Thermodynamic-Equilibrium (LTE). In this short work we present the re-optimization the simple Axelrod formula for a large number of R-matrix data sets, ranging from Fe and Ni to the first r-process peak elements of Sr, Y and Zr, to higher Z systems Te, W, Pt and Au. We show that the approximate treatment of forbidden transitions can be a significant source of inaccuracy in such collisional radiative models. We find a large variance of the optimized coefficients for differing systems and charge states, although some general trends can be seen based on the orbital structure of the ground-state-configurations. These trends could potentially inform better estimates for future calculations for elements where R-matrix data is not available.

Strontium (Sr) emissions have been observed across a wide range of astrophysical phenomena, from kilonovae (KNe) events to white dwarf (WD) stars. Precise and extensive atomic data for low ionization stages of Sr is required for accurate theoretical modelling and to improve our understanding of evolutionary pathways. We calculated energy levels, Einstein A coefficients and electron-impact excitation collision strengths for Sr i, Sr iii, Sr iv, and Sr v at the temperature and density ranges of interest in KNe and WD research. We developed new target structures using the grasp(0) and autostructure packages. The energies and A-values arising from the new structures were found to be in good agreement with experimental and theoretical equivalents reported in the literature. Maxwellian averaged electron impact collision strengths were calculated using the R-matrix approach, as applied through the darc and rmbp coding packages. These are presented in adf04 file format. The new data sets allowed us to construct synthetic spectra for the first five ionization stages of Sr and probe possible density and temperature diagnostic lines. The synthetic spectra within the KNe regime revealed possible Sr iv and Sr v candidate lines at 1027.69 and 1203.35 nm, respectively. These may provide useful benchmarks for determining the extent of Sr ionization that can be reached in an evolving KNe event. Additional diagnostic lines were found to be poor across the Sr ion stages for both KNe and WD regimes due to most levels being in either coronal or local thermodynamic equilibrium (LTE) conditions.

To better understand plasma wall interactions involving tungsten, accurate atomic structure and electron-impact driven collisional processes for near-neutral ion stages of tungsten are required. Complementing existing work on neutral and singly ionised tungsten, atomic structure and collisional calculations for W2+ electron-impact excitation have been completed. These excitation calculations are an important component of S/XB coefficients for near-neutral charge states, which may be used to spectroscopically infer re-deposition of tungsten at the plasma-solid boundary of fusion relevant devices. With W2+ in particular having emission lines that can be observed at ultraviolet (UV) wavelengths, while higher charge states of tungsten are unlikely to have lines possible to observe outside of the vacuum UV range. The atomic structure was generated using the General-purpose Relativistic Atomic Structure Package (GRASP(0)), implementing the Multi-configuration Dirac Fock approach. This structure was the basis for a subsequent Dirac R-matrix electron-impact excitation calculation to provide Maxwellian averaged rate coefficients. A synthetic spectrum was generated from this data using a collisional-radiative model to predict the strongest W III spectral lines and these lines were compared to emission from the Compact Toroidal Hybrid (CTH) plasma device. Several of the strongest W III lines are observed in CTH and agree well with the modelled line wavelengths and intensities, a table of these lines is provided that could be observed in other devices.

We estimate the coronal density of Capella using the O vii and Fe xvii line systems in the soft X-ray regime that have been observed over the course of the Chandra mission. Our analysis combines measures of error due to uncertainty in the underlying atomic data with statistical errors in the Chandra data to derive meaningful overall uncertainties on the plasma density of the coronae of Capella. We consider two Bayesian frameworks. First, the so-called pragmatic Bayesian approach considers the atomic data and their uncertainties as fully specified and uncorrectable. The fully Bayesian approach, on the other hand, allows the observed spectral data to update the atomic data and their uncertainties, thereby reducing the overall errors on the inferred parameters. To incorporate atomic data uncertainties, we obtain a set of atomic data replicates, the distribution of which captures their uncertainty. A principal component analysis of these replicates allows us to represent the atomic uncertainty with a lower-dimensional multivariate Gaussian distribution. A t -distribution approximation of the uncertainties of a subset of plasma parameters including a priori temperature information, obtained from the temperature-sensitive-only Fe xvii spectral line analysis, is carried forward into the density- and temperature-sensitive O vii spectral line analysis. Markov Chain Monte Carlo based model fitting is implemented including Multi-step Monte Carlo Gibbs Sampler and Hamiltonian Monte Carlo. Our analysis recovers an isothermally approximated coronal plasma temperature of ≈5 MK and a coronal plasma density of ≈10 ^10 cm ^−3 , with uncertainties of 0.1 and 0.2 dex, respectively.

We present results from a pilot study, using a laser-produced plasma, to identify new lines in the 350-1000 nm spectral region for the r-process element gold (Au), of relevance to studies of neutron star mergers. This was achieved via optical-IR spectroscopy of a laser-produced Au plasma, with an Au target of high purity (99.95%) and a low vacuum pressure to remove any air contamination from the experimental spectra. Our data were recorded with a spectrometer of 750 mm focal length and 1200 lines mm-1 grating, yielding a resolution of 0.04 nm. We find 54 lines not previously identified and which are not due to the impurities (principally copper (Cu) and silver (Ag)) in our Au sample. Of these 54 lines, we provisionally match 21 strong transitions to theoretical results from collisional-radiative models that include energy levels derived from atomic structure calculations up to the 6s level. Some of the remaining 33 unidentified lines in our spectra are also strong and may be due to transitions involving energy levels which are higher-lying than those in our plasma models. Nevertheless, our experiments demonstrate that laser-produced plasmas are well suited to the identification of transitions in r-process elements, with the method applicable to spectra ranging from UV to IR wavelengths.

R-matrix with pseudostates (RMPS) calculations have been carried out for photoionization of atomic sodium near threshold. The large RMPS atomic orbital and configuration basis allows for very accurate computations of low-energy photoionization cross sections up to approximate to 30 eV, the energy range for which the RMPS calculations were optimized. Consistency checks for accuracy include, first, the excellent agreement found between lengthand velocity-gauge theoretical results, a necessary but not sufficient requirement for having a converged wave function. A second accuracy quantification is the excellent prediction of the position of the Cooper minimum compared to experimental results. Particular attention is paid to the Cooper minimum occurring just above threshold, and the spin-orbit splitting of minima, resulting in a nonzero total cross section. Our RMPS results away from the minimum are found to be lower than the experimental data, and we make the case that the experimental magnitudes are an overestimate. A third important affirmation of the present accuracy is the continuity found between the 3s -> np bound-bound discrete oscillator strength density below threshold-see Wiese et al. [W. L. Wiese, M. W. Smith, and B. M. Miles, Atomic Transition Probabilities, Vol. 2: Sodium Through Calcium; A Critical Data Compilation (US Government Printing Office, Washington, DC, 1969)]-and the 3s -> cp bound-continuum RMPS oscillator strength density above threshold. These three somewhat independent tests of the accuracy of the computed cross sections add confidence to our recommending the present RMPS results as the most reliable extant data for low-energy Na photoionization (and the earlier Wiese et al. results for the discrete states).

Tellurium is a primary candidate for the identification of the 2.1 $\, \mu$m emission line in kilonovae (KNe) spectra AT2017gfo and GRB230307A. Despite this, there is currently an insufficient amount of atomic data available for this species. We calculate the required atomic structure and collisional data, particularly the data required for accurate non-local-thermodynamic-equilibrium (NLTE) modelling of the low temperatures and densities in KNe. We use a multiconfigurational Dirac-Hartree-Fock method to produce optimized one-electron orbitals for Te i-iii. As a result energy levels and Einstein A-coefficients for Te i-iii have been calculated. These orbitals are then employed within Dirac R-matrix collision calculations to provide electron-impact-excitation collision strengths that were subsequently averaged according to a thermal Maxwellian distribution. Subsequent tardis simulations using this new atomic data reveal no significant changes to the synthetic spectra due to the very minor contribution of Te at early epochs. NLTE simulations with the colradpy package reveal optically thin spectra consistent with the increasing prominence of the Te iii 2.1 $\, \mu$m line as the KNe ejecta cools. This is reinforced by the estimation of luminosities at nebular KNe conditions. New line ratios for both observation and laboratory benchmarks of the atomic data are proposed.

The spectra from singly ionized argon Ar II has significant diagnostic capability in the characterisation and modelling of both magnetically-confined fusion and astrophysical plasmas. The literature has several pre-existing data sets for Ar+ but this paper presents the results from 3 new atomic structure and electron-impact scattering models in order to better constrain the differences in atomic data and how they impact well-known plasma diagnostics. Several independent atomic structure methodologies are employed to calculate the energy levels and transition probabilities for each model. The first approach employs a relativistic Dirac-Coulomb Hamiltonian model, the second approach uses a semi-relativistic Breit–Pauli Hamiltonian with the mass-velocity, Darwin and spin–orbit corrections, and in a third case an ICFT approach. Three atomic structure models provide a foundation for Dirac R-matrix, a semi-relativistic ICFT (Intermediate Coupling Frame Transformation) and a Breit–Pauli R-Matrix with Pseudostates (BPRMPS) calculation. Synthetic spectra utilizing these three data sets are compared against measurements taken at the Compact Toroidal Hybrid (CTH) stellerator, and the total radiative power loss is also benchmarked against previous calculations.

ABSTRACT The spectra of singly ionized Strontium and Yttrium (Sr ii and Y ii) have been proposed as identifications of certain spectral features in the AT2017gfo spectrum. With the growing demand for non-local-thermodynamic-equilibrium (NLTE) simulations of Kilonovae, there is an increasing need for atomic data for these and other r-process elements. Our goal is to expand upon the current set of atomic data for r-process elements, by presenting transition probabilities and Maxwellian-averaged effective collision strengths for Sr ii and Y ii. The Breit–Pauli and darcR-matrix codes are employed to calculate the appropriate collision strengths, which are thermally averaged according to a Maxwellian distribution to calculate excitation and de-excitation rates. The tardis and ColRadPy packages are subsequently used to perform local thermodynamic equilibrium (LTE) and NLTE modelling, respectively. A complete set of transition probabilities and effective collision strengths involving levels for Sr ii and Y ii have been calculated for temperature ranges compatible with kilonova plasma conditions. Forbidden transitions were found to disagree heavily with the Axelrod approximation, an approximation which is currently employed by other models within the literature. Theoretically important spectral lines are identified with both LTE and NLTE modelling codes. LTE simulations in tardis reveal no new significant changes to the full synthetic spectra. NLTE simulations in ColRadPy provide indications of which features are expected to be strong for a range of regimes, and we include luminosity estimates. Synthetic emission spectra over kilonova densities and temperatures reveal potentially interesting spectral lines in the NIR.

A selection of electron-impact excitation R-matrix calculations completed by the collision group at Queens University Belfast are discussed. The atomic data calculated are the foundation of applications in a variety of fields, a sample of which are presented here. They include an analysis of Fe ii emission in active galactic nuclei, the possible presence of Pt and Au in the spectra of binary neutron star mergers and the viability of W ions as a diagnostic tool in magnetically confined tokamak plasmas. The radiative atomic data were computed using the most recent version of the fully relativistic structure code grasp0 and the collision cross sections were evaluated using the recently developed pdarc R-matrix package.

The detection of a gravitational-wave signal and subsequent electromagnetic transient from a neutron star merger in 2017 is consistent with expectations of neutron star mergers as an r -process element production site. Within the first few days post-merger, the kilonova spectra are consistent with a blackbody illuminating a mix of heavy, r -process elements. With increasing time, the kilonova transitions to the non-LTE regime where the level populations and ionization balance are determined by both collisional and photoprocesses. Detailed cross section data for electron-impact processes involving the relevant species are often not available. In such circumstances, it is reasonable to use approximate methods as baseline data for use in spectral modeling, and it is useful to evaluate the accuracy of such methods against more sophisticated collision calculations when possible. We describe new calculations of the electron-impact excitation cross sections of Pt i – iIi using the DARC R -matrix codes. Using collisional-radiative models, we show that, at plasma conditions expected in kilonovae, the expressions of van Regemorter and Axelrod are insufficient for producing electron-impact excitation data for complex, heavy species such as the low charge states of Pt. Through comparisons with data generated with the relativistic distorted wave approach, as implemented in the Flexible Atomic Code, we show the distorted wave method produces cross section data that, when incorporated into spectral models, predicts strong spectral feature distributions similar in intensity to those from models built on data computed with the R -matrix approach for the considered ions and plasma conditions.

Tungsten is the material of choice for the divertors in ITER, SPARC and future fusion reactors. Accurate diagnosis of tungsten erosion and migration is important for first wall life time, slag production and core performance. The addition of a magnetic presheath requires time-dependent collisional radiative effects to be included for accurate neutral tungsten collisional radiative modeling. Gross erosion measurements could be modified by a factor of 10 due to the inclusion of time-dependent effects for ITER relevant divertor conditions. A simple sputtering model and sheath density model are developed to investigate time-dependent collisional radiative effects. Neutral tungsten spectral lines populated from different metastable levels depend on model parameters leading to potential spectroscopic diagnostics of plasma parameters. Electron temperatures inferred from spectroscopic line ratios are in agreement with Langmuir probe measurements in the Compact Toroidal Hybrid.

Aims: tungsten has been chosen for use as a plasma facing component in the divertor for the ITER experiment, and is currently being used on existing tokamaks such as JET. W+ plays an integral role in assessing the impurity influx from plasma facing component of tokamaks and subsequent redeposition. Together with previously calculated a neutral tungsten electron-impact dataset this study allows us to determine neighbouring spectral lines in the same wavelength window of the spectrometer, and detect if there is strong blending of overlapping lines between these two ion stages as well as providing ionisation per photon ratios for both species. The new data is to be used for tungsten erosion/redeposition diagnostics. Methods: a significantly modified version of the GRASP0 atomic structure code in conjunction with DARC (Dirac Atomic R-matrix Code) are used to calculate the Einstein A coefficients and collisional rates used to generate a synthetic W II spectrum. The W II spectrum is compared against tungsten spectral emission experiments. Results: this study is used to model the spectrum of W ii, providing the predictive capability of identifying spectral lines from recent experiments. These results provide an integral part of impurity influx and redeposition determination, as the ionisation rates may be used to calculate S/XB ratios.

ABSTRACT Neutron binary star mergers have long been proposed as sufficiently neutron rich environments that could support the synthesis of rapid neutron capture elements (r-process elements) such as gold. However, the literature reveals that beyond neutral and singly ionized systems, there is an incompleteness of atomic data for the remaining ion stages of importance for mergers. In this work, we report on relativistic atomic structure calculations for Au i–Au iii using the grasp0 codes. Comparisons to calculations using the Flexible Atomic Code suggest uncertainties on average of 9.2 per cent, 5.7 per cent, and 3.8 per cent for Au i–Au iii level energies. Agreement around ∼50 per cent is achieved between our computed A-values and those in the literature, where available. Using the grasp0 structure of Au i, we calculated electron-impact excitation rate coefficients and use a collisional-radiative model to explore the excitation dynamics and line ratio diagnostics possible in neutron star merger environments. We find that proper accounting of metastable populations is critical for extracting useful information from ultraviolet–visible line ratio diagnostics of Au i. As a test of our data, we applied our electron-impact data to study a gold hollow cathode spectrum in the literature and diagnosed the plasma conditions as Te = 3.1 ± 1.2 eV and $n_\textrm {e} = 2.7^{+1.3}_{-0.9}\times 10^{13}$ cm−3.

Energy levels, Einstein A-values, and oscillator strengths are calculated for doubly ionized germanium (GeIII). We have undertaken a study of the electron-impact excitation of GeIII and have also completed a study of the photoionization of GeII. GeIII target structures were generated using the relativisticgrasp0 package. Several scattering models were investigated to assess the uncertainty quantification of our results. Initially, the lowest lying 64 jj fine-structure levels were included in the close-coupling expansion resulting from 14 non-relativistic configurations. A second larger model was subsequently generated using the gasp package and incorporated the lowest 589 jj fine-structure levels from 17 non-relativistic configurations. Both the DARC (Dirac atomic R-matrix code) and Breit-Pauli parallel suite of R-matrix collision codes were utilized in the scattering calculations to generate the collision strengths for incident electron energies between 0 and 5 Rydbergs and subsequently the Maxwellian-averaged effective collision strengths for temperatures in the range of 1000-200000K. The photoionization calculations comprised of two studies, a DARC and a Breit-Pauli calculation incorporating the 250 lowest lying levels. Photoionization cross-sections for Geii are presented in the range of 0-5 Ryds. Due to the lack of data available in the literature, the present radiative data and electron-impact/photoionization cross-sections are compared between the models presented in this paper. To assess their significance for astrophysics, the data are incorporated into the stellar atmosphere package sterne. Test models for the heavy-metal subdwarf LSIV-14 degrees 116 are not affected by the new data, but models for cooler stars may be sensitive to them.

ABSTRACT Binary neutron star mergers are thought to be one of the dominant sites of production for rapid neutron capture elements, including platinum and gold. Since the discovery of the binary neutron star merger GW170817, and its associated kilonova AT2017gfo, numerous works have attempted to determine the composition of its outflowing material, but they have been hampered by the lack of complete atomic data. Here, we demonstrate how inclusion of new atomic data in synthetic spectra calculations can provide insights and constraints on the production of the heaviest elements. We employ theoretical atomic data (obtained using $\small {\rm GRASP}^{0}$) for neutral, singly and doubly ionized platinum and gold, to generate photospheric and simple nebular phase model spectra for kilonova-like ejecta properties. We make predictions for the locations of strong transitions, which could feasibly appear in the spectra of kilonovae that are rich in these species. We identify low-lying electric quadrupole and magnetic dipole transitions that may give rise to forbidden lines when the ejecta becomes optically thin. The strongest lines lie beyond 8000 Å, motivating high quality near-infrared spectroscopic follow-up of kilonova candidates. We compare our model spectra to the observed spectra of AT2017gfo, and conclude that no platinum or gold signatures are prominent in the ejecta. From our nebular phase modelling, we place tentative upper limits on the platinum and gold mass of ≲ a few 10−3 M⊙, and ≲ 10−2 M⊙, respectively. This work demonstrates how new atomic data of heavy elements can be included in radiative transfer calculations, and motivates future searches for elemental signatures.