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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.

Jupiter-family comets are ephemeral small bodies injected into the inner solar system from the Kuiper Belt, doomed to either sublimate all their volatiles and become inert or violently shatter from the activity. We investigate two target candidates of the ESA Rosetta mission, comets 46P/Wirtanen and 67P/Churyumov-Gerasimenko, which had favorable apparitions for Earth-based observations in 2018–2019 and 2021, respectively. Using the Hubble Space Telescope STIS and COS instruments, we observed OH and CS emissions to characterize production rates of H2O and CS, established Af ρ values, and placed upper limits on the production rate of C2 and its parent. We find CS/H2O relative abundances that are significantly (5σ–7σ) larger than previous remote near-UV (NUV) measurements of 46P and 67P at similar heliocentric distances and CS/H2O values larger than those obtained via contemporaneous submillimeter observations for the same apparitions. We also find that for 67P the remote derivations of CS2/H2O ratios are substantially (∼50×) higher than the values measured by the ROSINA mass spectrometer on board the Rosetta spacecraft for all NUV-derived CS2 production rates. The discrepancy points toward an unidentified CS parent or parents with contributing factors from uncertainties with the fluorescence efficiencies of the CS (0,0) band of the A 1Π–X 1Σ+ system around 2580 Å. Given the significance of understanding the chemistry and dissociation physics of sulfur-bearing molecules in comets for tracing planetesimal formation environments, as well as the limited studies in this area, we propose several hypotheses to explain this discrepancy and outline future studies to address these issues.

In astronomy emission spectroscopy is widely used technique to study various objects. Although emission spectra of individual compounds are quite well known so composition of the studied body can be analysed the information on processes active in distant object can be encoded in the determined spectra as well. To decode such information the individual elementary processes need to be well understood. For example, in case of comets which are simple leftovers from the beginning of the Solar System understanding the connection between the coma and the comet’s nucleus is critical because observations rarely detect the nucleus directly, and its properties must often be inferred from measurements of the coma. As measurements of the coma do not necessarily represent the characteristics of the nucleus due to spatial, temporal and chemical evolution of the emitted material, projecting the coma observations back to the nucleus requires understanding of the processes in the coma. Within the Rosetta various instruments were used for spectroscopy. OSIRIS was equipped with several band filters that are commonly used in ground-based studies (Farnham et al. 2000). The spectroscopic measurements done within the Rosetta mission led to conclusion that electron-molecule processes play much more significant role than it used to be suspected in the past (Bodewits et al. 2016). This fact can be utilized to remotely study the plasma-chemical reactions active in distant objects. For example, the formation of excited OH by electron impact on H2O has an electron temperature threshold of 9.1 eV; H Ly-a has a threshold of 15.4 eV; and the production of OI 130.4 nm emission requires electron temperatures above 23.5 eV (Beenakker et al. 1974; Morgan & Mentall 1974). At electron temperatures below 10 eV, collisions with water molecules result in ro-vibrational excitation and energy is emitted in the IR range (Itikawa & Mason 2005). Electron impact emission thus provides a sensitive diagnostic probe for studying coma (Bodewits et al. 2019). The presence of spectral structures depends on reaching the threshold electron energy for specific transition. Emission cross sections that have thresholds of 10-100 eV – typical for the coma (Broiles et al. 2016) – depend strongly on electron impact energy. Knowledge of emission spectra and cross sections for electron-molecule reactions is critical for evaluation of physical-chemical properties of cometary coma based on spectroscopic observations. For thorough analysis of such studies a reliable database of reference spectra and emission cross sections must be available. Especially the availability of cross section data the Achilles’ heel since most of the values were determined only for a few individual energies but for successful application in models of atmospheres or comas they need to be known for wider range of energies. Such data can be provided by laboratory experiments studying individual electron-molecule interactions in various experimental configurations such as crossed beams of electrons and molecules. The example of the apparatus scheme aimed at studying electron induced excitation reactions is shown in the figure. The electron beam generated by trochoidal electron monochromator collides perpendicularly with molecular beam created by effusive capillary. Photons emitted by excited reaction products are guided out of the vacuum chamber into the spectrometer equipped by CCD or photomultiplier detectors. The details of the experimental system were described elsewhere (Orszagh et al. 2017). Fig. 1. Scheme of the experimental apparatus. The main result of the experiment are the emission spectra (see second figure as an example) and emission cross section curves determined in precisely defined conditions. The shape of the spectrum given by population of individual ro-vibrational states and presence of individual spectral features depends strongly on excitation source and its energy (Bodewits et al. 2019). Fig. 2. Emission spectrum of hydrogen induced by 50 eV electrons impact. From the relative cross section curves it is possible to determine the lowest kinetic energy (threshold energy) of the electrons necessary to create a specific excited product and after calibration to absolute values we get series of cross sections for individual electron impact energies. Below the threshold the spectral line or band will not be present in the spectrum. The third figure shows relative emission cross section of oxygen where two thresholds correspond to different processes generating excited oxygen atom. Fig. 3. Relative emission cross section curve for oxygen atom. By putting spectral and relative cross sections information together by measuring emission spectra at several electron impact energies we can get a surface formed by emission cross section values within selected range of wavelengths and electron energies (see the last figure). Fig. 4. 3D spectral map of emission induced by electron impact on pyridine. Such complex information on the kinetics of electron-molecule excitation reactions is unfortunately rare mostly due to the technically demanding experiment but they provide valuable reference for analysis of astronomical spectroscopic data. Electron-molecule reactions in environment such as cometary comas or atmospheres can serve as a remote probe for characterization of local conditions if reference laboratory data on their kinetics are available. Acknowledgments This project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No 871149. This research was supported by Slovak grant agency VEGA within the projects nr. 1/0489/21 and 1/0553/22, by Slovak Research and Development Agency within project nr. APVV-19-0386, and by NASA ROSES project nr. NNH18ZDA001N-RDAP. Beenakker, C.I.M. et al., 1974. Chemical Physics, 6(3), pp.445–454. Bodewits, D. et al. 2016. Astronomical J., 152, 130. Bodewits, D. et al., 2019. Astrophys. J., 885(167), p. 16. Broiles, T.W. et al., 2016. Journal of Geophysical Research: Space Physics, 121 (8), pp.7407–7422. Farnham, T.L., Schleicher, D.G. & A'Hearn, M.F., 2000. Icarus, 147, p.180. Itikawa, Y. & Mason, N., 2005. Journal of Physical and Chemical Reference Data, 34(1), pp.1–22. Morgan, H. D. & Mentall, J.E., 1974. Journal of Chemical Physics, Volume 60, Issue 12, pp. 4734-4739. Orszagh, J. et al. 2017, Astrophys. J., 841(17).

Direct detection of gravitational waves (GWs) on 17 August 2017, propagating from a binary neutron star merger, or a “kilonova”, opened the era of multimessenger astronomy. The ejected material from neutron star mergers, or “kilonova”, is a good candidate for optical and near infrared follow-up observations after the detection of GWs. The kilonova from the ejecta of GW1780817 provided the first evidence for the astrophysical site of the synthesis of heavy nuclei through the rapid neutron capture process or r-process. Since properties of the emission are largely affected by opacities of the ejected material, enhancements in the available r-process data is important for neutron star merger modeling. However, given the complexity of the electronic structure of these heavy elements, considerable efforts are still needed to converge to a reliable set of atomic structure data. The aim of this work is to alleviate this situation for low charge state elements in the Os-like isoelectronic sequence. In this regard, the general-purpose relativistic atomic structure packages (GRASP0 and GRASP2K) were used to obtain energy levels and transition probabilities (E1 and M1). We provide line lists and expansion opacities for a range of r-process elements. We focus here on the Os isoelectronic sequence (Os I, Ir II, Pt III, Au IV, Hg V). The results are benchmarked against existing experimental data and prior calculations, and predictions of emission spectra relevant to kilonovae are provided. Fine-structure (M1) lines in the infrared potentially observable by the James Webb Space Telescope are highlighted.

The detection of iron and nickel vapours in a broad range of Solar System comets, and of nickel vapour in a comet from outside the Solar System, provides a glimpse into the organic chemistry of young planetary systems. Emission spectra of pure metal atoms detected in cometary comae.

Two papers recently reported the detection of gaseous nickel and iron in the comae of over 20 comets from observations collected over two decades, including interstellar comet 2I/Borisov. To evaluate the state of the laboratory data in support of these identifications, we re-analyzed archived spectra of comet C/1996 B2 (Hyakutake), one of the nearest and brightest comets of the last century, using a combined experimental and computational approach. We developed a new, many-level fluorescence model that indicates that the fluorescence emission of Fe I and Ni I vary greatly with heliocentric velocity. Combining this model with laboratory spectra of an Fe-Ni plasma, we identified 22 lines of Fe I and 14 lines of Ni I in the spectrum of Hyakutake. Using Haser models, we estimate the nickel and iron production rates as Q(Ni) = 2.6 - 4.1 x 10^22 s^-1 and Q(Fe) = 0.4 - 2.8 x 10^23 s^-1. From derived column densities, the Ni/Fe abundance ratio log10[Ni/Fe] = -0.15 +/- 0.07 deviates significantly from solar abundance ratios, and it is consistent with the ratios observed in solar system comets. Possible production and emission mechanisms are analyzed in context of existing laboratory measurements. Based on the observed spatial distributions, excellent fluorescence model agreement, and Ni/Fe ratio, our findings support an origin consisting of a short-lived unknown parent followed by fluorescence emission. Our models suggest that the strong heliocentric velocity dependence of the fluorescence efficiencies can provide a meaningful test of the physical process responsible for the Fe I and Ni I emission., 23 pages, 11 figures

Far ultraviolet observations of comets yield information about the energetic processes that dissociate the sublimated gases from their primitive surfaces. Understanding which emission processes are dominant, their effects on the observed cometary spectrum, and how to properly invert the spectrum back to composition of the presumably pristine surface ices of a comet nuclei are all critical components for proper interpretation and analysis of comets. The close approach of comet 46P/Wirtanen in 2018-2019 provided a unique opportunity to study the inner most parts of a cometary coma with the Hubble Space Telescope Cosmic Origins Spectrograph, rarely accessible with remote observations, at length scales (100's of km) and wavelengths (900-1430 Angstroms) previously probed only by the European Space Agency's Rosetta spacecraft. Our observations show a complex picture for the inner coma; atomic production rates for H and O that show water is the dominant source of both, an abundance of atomic sulfur that is difficult to explain with the lifetimes of common sulfur parent molecules, and a density distribution that is poorly fit with both Haser and vectorial models., Comment: 16 pages, 9 figures. Accepted in A'Hearn Special Issue of Planetary Science Journal

The 4 files contained in "N2_supp.tar.gz" contain our measured cross sections for the reactions: A+ + N2 -> A (A = He, Ne, Ar, Kr)

Using conductive and non-conductive source materials, an ion deflector plate was fabricated by fused filament fabrication. The fully vacuum-compatible design was tested by measuring the voltage-dependent deflection of Rb+ ions, and the results, which are ion energy dependent, are consistent with predicted kinematics for the ions. The results also compare well with a metal plate of similar dimensions and with an ion trajectory simulation.

Charge transfer of an electron from a neutral atom to an ion is a fundamental interaction thatplays a dominant role in the energy balance of atmospheric and astrophysical plasmas. The presentinvestigation measured the charge exchange cross sections of noble gas ions (He+, Ne+, Ar+, Kr+) withN2 in the intermediate energy range 0.2&ndash, 5.0 keV. The systems were chosen because there remains a lackof consensus amongst previous measurements and regions where there were no previous measurements.A description of the mechanical design for an electrically floated gas cell is described herein.

A gas cell apparatus to measure charge exchange cross sections for charge state- and energy-resolved ion beams with neutrals is described. The design features a short well-defined interaction region required for beams of multicharged ions with high cross sections. Our method includes measuring the beam transmission at four different neutral pressures and extracting the cross section from the slope of a beam loss vs pressure plot. The design and procedure were tested for Ar+ interacting with neutral Ar gas over the incident ion energy range of 1.0-5.0 keV. The charge exchange cross sections agree well with previous complementary measurement techniques.