We report on the XSTAR atomic database that contains a large quantity of atomic rates for use in spectral modeling of astrophysical plasmas. The database includes atomic energy levels, line wavelengths, radiative transition probabilities, electron impact excitation rates, photoionization cross section, recombination rate coefficients, electron impact ionization rates, and fluorescence and Auger yields. The species considered are all the ions of H, He, C, N, O, Ne, Mg, Si, S, Ar, Ca, Fe, and Ni. The database collects recent data from many sources including CHIANTI, TOPbase, ADAS, NIST, and the IRON Project. Two particular features of the database are the incorporation of photoionization cross sections from the Opacity Project for all levels of every ion, and state-specific recombination rates. State-specific collisional ionization and three-body recombination are also included. The collection of data is used to build excitation-ionization models of each ion for calculation of their spectra for electron densities of up to 1018 cm-3 and temperatures between 100 and 109 K. In addition, every ion model is designed to converge to LTE under appropriate conditions. These models and data are implemented in the photoionization modeling code XSTAR v.2.

https://iopscience.iop.org/article/10.1086/320363/pdf

The XSTAR Atomic Database

Anew air-radiationmodel is presented for the calculation of the radiative flux from lunar-return shock layers. For modeling atomic lines, the data from a variety of theoretical and experimental sources are compiled and reviewed. A line model is chosen that consists of oscillator strengths from the National Institute of Standards and Technology database and theOpacity Project (formany lines not listedby theNational Institute of Standards andTechnology), as well as Stark broadening widths obtained from the average of available values. Uncertainties for the oscillator strengths and Stark broadening widths are conservatively chosen from the reviewed data, and for the oscillator strengths, the chosen uncertainties are found to be larger than those listed in the National Institute of Standards and Technology database. This new atomic line model is compared with previous models for equilibrium constantproperty layers chosen to approximately represent a lunar-return shock layer. It is found that the new model increases the emission resulting from the 1–6-eV spectral range by up to 50%.This increase is due to both the increase in oscillator strengths for some important lines and to the addition of lines from the Opacity Project, which are not commonly treated in shock-layer radiation predictions. Detailed theoretical atomic bound–free cross sections obtained from the Opacity Project’s TOPbase are applied for nitrogen and oxygen. An efficient method of treating these detailed cross sections is presented.The emission fromnegative ions is considered and shown to contribute up to 10% to the total radiative flux. The modeling of the molecular-band systems using the smeared-rotational-band approach is reviewed. The validity of the smeared-rotational-band approach for both emitting and absorbing-band systems is shown through comparisons with the computationally intensive line-by-line approach. The absorbingband systems are shown to reduce the radiative flux by up to 10%, whereas the emitting-band systems are shown to contribute less than a 5% increase in the flux. The combined models chosen for the atomic line, atomic bound–free, negative-ion, and molecular-band components result in a computationally efficient model that is ideal for coupled solutions with a Navier–Stokes flowfield. It is recommended that the notable increases shown, relative to previous models, for the atomic line and negative-ion continuum should be included in future radiation predictions for lunarreturn vehicles.

Spectrum Modeling for Air Shock-Layer Radiation at Lunar-Return Conditions

The Virtual Atomic and Molecular Data Centre (VAMDC, http://www.vamdc.eu) is a European Union funded collaboration between groups involved in the generation, evaluation, and use of atomic and molecular data. VAMDC aims to build a secure, documented, flexible and interoperable e-science environment-based interface to existing atomic and molecular data. The project will cover establishing the core consortium, the development and deployment of the infrastructure and the development of interfaces to the existing atomic and molecular databases. It will also provide a forum for training potential users and dissemination of expertise worldwide. This review describes the scope of the VAMDC project; it provides a survey of the atomic and molecular data sets that will be included plus a discussion of how they will be integrated. Some applications of these data are also discussed.

/pdf/virtual-atomic-and-molecular-data-centre-2xlural9hh.pdf

Virtual Atomic and Molecular Data Centre

The measurement of stellar properties such as chemical compositions, masses and ages, through stellar spectra, is a fundamental problem in astrophysics. Progress in the understanding, calculation and measurement of atomic properties and processes relevant to the high-accuracy analysis of F-, G-, and K-type stellar spectra is reviewed, with particular emphasis on abundance analysis. This includes fundamental atomic data such as energy levels, wavelengths, and transition probabilities, as well as processes of photoionisation, collisional broadening and inelastic collisions. A recurring theme throughout the review is the interplay between theoretical atomic physics, laboratory measurements, and astrophysical modelling, all of which contribute to our understanding of atoms and atomic processes, as well as to modelling stellar spectra.

Accurate abundance analysis of late-type stars: advances in atomic physics

Using the coupled ablation and radiation capability recently included in the LAURA flowfield solver, this paper investigates the influence of ablation on the shock-layer radiative heating for Earth entry. The extension of the HARA radiation model, which provides the radiation predictions in LAURA, to treat a gas consisting of the elements C, H, O, and N is discussed. It is shown that the absorption coefficient of air is increased with the introduction of the C and H elements. A simplified shock layer model is studied to show the impact of temperature, as well as the abundance of C and H, on the net absorption or emission from an ablation contaminated boundary layer. It is found that the ablation species reduce the radiative flux in the vacuum ultraviolet, through increased absorption, for all temperatures. However, in the infrared region of the spectrum, the ablation species increase the radiative flux, through strong emission, for temperatures above 3,000 K. Thus, depending on the temperature and abundance of ablation species, the contaminated boundary layer may either provide a net increase or decrease in the radiative flux reaching the wall. To assess the validity of the coupled ablation and radiation LAURA analysis, a previously analyzed Mars-return case (15.24 km/s), which contains significant ablation and radiation coupling, is studied. Exceptional agreement with previous viscous shock-layer results is obtained. A 40% decrease in the radiative flux is predicted for ablation rates equal to 20% of the free-stream mass flux. The Apollo 4 peak-heating case (10.24 km/s) is also studied. For ablation rates up to 3.4% of the free-stream mass flux, the radiative heating is reduced by up to 19%, while the convective heating is reduced by up to 87%. Good agreement with the Apollo 4 radiometer data is obtained by considering absorption in the radiometer cavity. For both the Mars return and the Apollo 4 cases, coupled radiation alone is found to reduce the radiative heating by 30 60% and the convective heating by less than 5%.

Influence of Ablation on Radiative Heating for Earth Entry

TOPbase, the Opacity Project atomic database, has been set up at the Centre de Donnees Astronomiques de Strasbourg (CDS), France, for general access via Internet This database contains accurately calculated energy levels, f-values and photoionisation cross sections for astrophysically abundant ions We briefly describe the physical model and computational method used, the atomic data specifications, the database management system and the network access arrangements The new facility should be of value to the astronomical community

W. Cunto

Papers

TOPbases at the CDS