40 research outputs found
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 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 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 .Comment: 13 pages, 5 figures; Accepted for publication in Astronomy &
Astrophysic
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
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 dex lower than that from Ti II. The 1D non-LTE corrections can reach
dex for individual Ti I lines and dex for individual Ti II lines,
and reduce the overall ionisation imbalance to dex for HD122563.
However, it also increases the imbalance for the very metal-poor dwarf and
sub-giant to around 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
A spectral study of Te V from MCDHF calculations
State-of-the-art multiconfiguration Dirac-Hartree-Fock calculations for Te V have been performed and energies, LS-compositions, radiative lifetimes and Lande gJ-factors for 51 odd and even parity states are presented. In addition, predictions on transition rates and oscillator strengths for a multitude of transitions between these states are reported for the first time. To describe the atomic system accurately, by means of configuration interaction, valence and core-valence electron correlation effects were taken into account. Calculated energies and lifetimes of excited states agree very well with experimental data