Hydrogen safety Progress report no. 7 1 Jul. - 30 Sep. 1965

Performance characteristics of two console-type hydrogen gas detectors sampling by diffusion and convectio

Hydrogen safety Progress report no. 6, 1 Apr. - 30 Jun. 1965

Hydrogen safety hazards, storage, and handling - Hydrogen plume studies to determine quantity-distance criteria and guidelines for optimum placement of hydrogen detector

Hydrogen Flare Stack Diffusion Flames - Low and High Flow Instabilities, Burning Rates, Dilution Limits, Temperatures, and Wind Effects

Combustion characteristics and safety factors for hydrogen diffusion flames in flare stack operation

Extended atomic data for oxygen abundance analyses

As the most abundant element in the universe after hydrogen and helium, oxygen plays a key role in planetary, stellar, and galactic astrophysics. Its abundance is especially influential on stellar structure and evolution, and as the dominant opacity contributor at the base of the Sun's convection zone it is central to the discussion around the solar modelling problem. However, abundance analyses require complete and reliable sets of atomic data. We present extensive atomic data for O I, by using the multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction methods. Lifetimes and transition probabilities for radiative electric dipole transitions are given and compared with results from previous calculations and available measurements. The accuracy of the computed transition rates is evaluated by the differences between the transition rates in Babushkin and Coulomb gauges, as well as by a cancellation factor analysis. Out of the 989 computed transitions in this work, 205 are assigned to the accuracy classes AA-B, that is, with uncertainties less than 10%, following the criteria defined by the National Institute of Standards and Technology Atomic Spectra Database. We discuss the influence of the new log(gf) values on the solar oxygen abundance and ultimately advocate $\log\epsilon_{\mathrm{O}}=8.70\pm0.04$.Comment: 13 pages, 5 figures; Accepted for publication in Astronomy & Astrophysic

NLTE Spectra of Kilonovae [Correction to vol 526, pg 5220, 2023]

The electromagnetic transient following a binary neutron star merger is knownas a kilonova (KN). Owing to rapid expansion velocities and small ejectamasses, KNe rapidly transition into the Non-Local Thermodynamic Equilibrium(NLTE) regime. In this study, we present synthetic NLTE spectra of KNe from 5to 20 days after merger using the \texttt{SUMO} spectral synthesis code. Westudy three homogeneous composition, 1D multi-zone models with characteristicelectron fractions of $Y_e \sim 0.35, 0.25$ and $0.15$. We find that emissionfeatures in the spectra tend to emerge in windows of reduced line blocking, asthe ejecta are still only partially transparent even at 20 days. For the $Y_e\sim 0.35$ (lanthanide-free) ejecta, we find that the neutral and singlyionised species of Rb, Sr, Y and Zr dominate the spectra, all with goodpotential for identification. We directly test and confirm an impact of Sr onthe 10000 angstrom spectral region in lanthanide-free ejecta, but also see thatits signatures may be complex. We suggest the Rb I $\rm{5p^{1}}$- $\rm{5s^{1}}$7900 angstrom transition as a candidate for the $\lambda_0 \sim$ 7500--7900angstrom P-Cygni feature in AT2017gfo. For the $Y_e \sim 0.25$ and $0.15$compositions, lanthanides are dominant in the spectral formation, in particularNd, Sm, and Dy. We identify key processes in KN spectral formation, notablythat scattering and fluorescence play important roles even up to 20 days aftermerger, implying that the KN ejecta are not yet optically thin at this time.<br

Titanium abundances in late-type stars I. 1D non-LTE modelling in benchmark dwarfs and giants

The titanium abundances of late-type stars are important tracers of Galactic formation history. However, abundances inferred from Ti I and Ti II lines can be in stark disagreement in very metal-poor giants. Departures from local thermodynamic equilibrium (LTE) have a large impact on the minority neutral species and thus influences the ionisation imbalance, but satisfactory non-LTE modelling for both dwarfs and giants has not been achieved in previous literature. The reliability of titanium abundances is reassessed in benchmark dwarfs and giants using a new non-LTE model and one-dimensional (1D) model atmospheres. A comprehensive model atom was compiled with a more extended level structure and newly published data for inelastic collisions between Ti I and neutral hydrogen. In 1D LTE, the Ti I and Ti II lines agree to within $0.06$ dex for the Sun, Arcturus, and the very metal-poor stars HD84937 and HD140283. For the very metal-poor giant HD122563, the Ti I lines give an abundance that is $0.47$ dex lower than that from Ti II. The 1D non-LTE corrections can reach $+0.4$ dex for individual Ti I lines and $+0.1$ dex for individual Ti II lines, and reduce the overall ionisation imbalance to $-0.17$ dex for HD122563. However, it also increases the imbalance for the very metal-poor dwarf and sub-giant to around $0.2$ dex. Using 1D non-LTE reduces the ionisation imbalance in very metal-poor giants but breaks the balance of other very metal-poor stars, consistent with the conclusions in earlier literature. To make further progress, consistent 3D non-LTE models are needed.Comment: 9 pages plus appendix, 6 figures; accepted for publication in Astronomy & Astrophysic

Excitation and charge transfer in low-energy hydrogen atom collisions with neutral manganese and titanium

Data for inelastic processes due to hydrogen atom collisions with manganese and titanium are needed for accurate modeling of the corresponding spectra in late-type stars. In this work excitation and charge transfer in low-energy Mn+H and Ti+H collisions have been studied theoretically using a method based on an asymptotic two-electron linear combination of an atomic orbitals model of ionic-covalent interactions in the neutral atom-hydrogen-atom system, together with the multichannel Landau-Zener model to treat the dynamics. Extensive calculations of charge transfer (mutual neutralization, ion-pair production), excitation and de-excitation processes in the two collisional systems are carried out for all transitions between covalent states dissociating to energies below the first ionic limit and the dominating ionic states. Rate coefficients are determined for temperatures in the range 1000–20 000 K in steps of 1000 K. Like for earlier studies of other atomic species, charge transfer processes are found to lead to much larger rate coefficients than excitation processes

Carbon monoxide formation and cooling in supernovae

Context. The inclusion of molecular physics is an important piece that tends to be missing from the puzzle when modeling the spectra of supernovae (SNe). Molecules have both a direct impact on the spectra, particularly in the infrared, and an indirect one as a result of their influence on certain physical conditions, such as temperature. Aims. In this paper, we aim to investigate molecular formation and non-local thermodynamic equilibrium (NLTE) cooling, with a particular focus on CO, the most commonly detected molecule in supernovae. We also aim to determine the dependency of supernova chemistry on physical parameters and the relative sensitivity to rate uncertainties. Methods. We implemented a chemical kinetic description of the destruction and formation of molecules into the SN spectral synthesis code SUM

Excitation and charge transfer in low-energy hydrogen atom collisions with neutral manganese and titanium

Data for inelastic processes due to hydrogen atom collisions with manganese and titanium are needed for accurate modeling of the corresponding spectra in late-type stars. In this work excitation and charge transfer in low-energy Mn+H and Ti+H collisions have been studied theoretically using a method based on an asymptotic two-electron linear combination of an atomic orbitals model of ionic-covalent interactions in the neutral atom-hydrogen-atom system, together with the multichannel Landau-Zener model to treat the dynamics. Extensive calculations of charge transfer (mutual neutralization, ion-pair production), excitation and de-excitation processes in the two collisional systems are carried out for all transitions between covalent states dissociating to energies below the first ionic limit and the dominating ionic states. Rate coefficients are determined for temperatures in the range 1000–20 000 K in steps of 1000 K. Like for earlier studies of other atomic species, charge transfer processes are found to lead to much larger rate coefficients than excitation processes.</jats:p