C. J. Zeippen

Bio: C. J. Zeippen is an academic researcher from University of Paris. The author has contributed to research in topics: Configuration interaction & Ground state. The author has an hindex of 16, co-authored 54 publications receiving 1212 citations. Previous affiliations of C. J. Zeippen include PSL Research University & Ohio State University.

Up-dated opacities from the Opacity Project

Abstract: Using the code AUTOSTRUCTURE, extensive calculations of inner-shell atomic data have been made for the chemical elements He, C, N, O, Ne, Na, Mg, Al, Si, S, Ar, Ca, Cr, Mn, Fe and Ni. The results are used to obtain up-dated opacities from the Opacity Project, OP. A number of other improvements on earlier work have also been included. Rosseland-mean opacities from OP are compared with those from OPAL. Differences of 5 to 10% occur. OP gives the `Z-bump', at log(T)=5.2, to be shifted to slightly higher temperatures. The opacities from OP, as functions of temperature and density, are smoother than those from OPAL. Extensive tests show that the numerical accuracy of the OP opacities following integration over frequency mesh and interpolation on temperature-density mesh is better than 1%. Prior to a number of recent investigations which have indicated a need for a downward revision in the solar abundances of oxygen and other elements, there was good agreement between properties of the sun deduced from helioseismology and from stellar evolution models calculated using OPAL opacities. The revisions in abundances destroy that agreement. In a recent paper Bahcall et al argue that the agreement would be restored if opacities for the regions of the sun between 0.7 and 0.4 solar radii were larger than those given by OPAL by about 10%. In the region concerned, the present results from OP do not differ from those of OPAL by more than 2.5%.

Atomic data from the IRON project - LVIII. Electron impact excitation of Fe XII

Abstract: A new calculation of rate coefficients for electron collisional excitation of Fe XII is presented and compared to earlier calculations Significant differences are found with all earlier work due to the inclusion of resonance processes that have not previously been considered and to the use of the intermediate coupling frame transformation method The resulting dataset of collision strengths is shown to resolve many of the outstanding discrepancies between theory and solar observations In particular, density sensitive line ratios in Fe XII now indicate electron densities close to those derived from other ions of comparable ionization potential

Atomic data from the IRON Project. XXIX. Radiative rates for transitions within the N = 2 complex in ions of the boron isoelectronic sequence

Abstract: As part of the IRON Project, radiative rates have been calculated for the E1, E2 and M1 transitions within the complex in ions of the boron isoelectronic sequence (). The computations have been carried out with the atomic structure code superstructure which facilitates the generation of extended radiative datasets including configuration interaction, Breit–Pauli relativistic contributions and semi-empirical term-energy corrections. By means of extensive comparisons with the available datasets for this sequence, with detailed single-ion calculations and recent experiments, we have been able to assign accuracy ratings to the present A -values. We find that in general the spin-allowed and spin-forbidden E1 transitions are accurate to 10% and 20%, respectively, except for a few transitions in ions with that are perturbed by admixture with low-lying states (e.g. 2s) and for those affected by the avoided crossing of the 2s2pS1/2 and P1/2 which takes place at . It is concluded that, statistically, the present dataset is the most accurate to date for this astrophysically relevant sequence.

A Decade with VAMDC: Results and Ambitions

Abstract: This paper presents an overview of the current status of the Virtual Atomic and Molecular Data Centre (VAMDC) e-infrastructure, including the current status of the VAMDC-connected (or to be connected) databases, updates on the latest technological development within the infrastructure and a presentation of some application tools that make use of the VAMDC e-infrastructure. We analyse the past 10 years of VAMDC development and operation, and assess their impact both on the field of atomic and molecular (A&M) physics itself and on heterogeneous data management in international cooperation. The highly sophisticated VAMDC infrastructure and the related databases developed over this long term make them a perfect resource of sustainable data for future applications in many fields of research. However, we also discuss the current limitations that prevent VAMDC from becoming the main publishing platform and the main source of A&M data for user communities, and present possible solutions under investigation by the consortium. Several user application examples are presented, illustrating the benefits of VAMDC in current research applications, which often need the A&M data from more than one database. Finally, we present our vision for the future of VAMDC.

Atomic data from the IRON Project LI. Electron impact excitation of Fe IX

Abstract: We calculate collision strengths and thermally averaged collision strengths for electron excitation between the one hundred and forty energetically lowest levels of Fe 8+ . The scattering target is more elaborate than in any earlier work and large increases are found in the excitation rates among the levels of the 3s 2 3p 5 3d electron configuration due to resonance series that have not been considered previously. The implications for solar and stellar spectroscopy have been discussed elsewhere (Storey & Zeippen 2001). We correct some errors that were made in generating the figures given in that paper and present corrected versions.

The Chemical Composition of the Sun

Abstract: The solar chemical composition is an important ingredient in our understanding of the formation, structure, and evolution of both the Sun and our Solar System. Furthermore, it is an essential refer ...

CLOUDY 90: Numerical Simulation of Plasmas and Their Spectra

Abstract: CLOUDY is a large‐scale spectral synthesis code designed to simulate fully physical conditions within an astronomical plasma and then predict the emitted spectrum. Here we describe version 90 (C90) of the code, paying particular attention to changes in the atomic database and numerical methods that have affected predictions since the last publicly available version, C84. The computational methods and uncertainties are outlined together with the direction future development will take. The code is freely available and is widely used in the analysis and interpretation of emission‐line spectra. Web access to the Fortran source for CLOUDY, its documentation Hazy, and an independent electronic form of the atomic database is also described.

A grid of MARCS model atmospheres for late-type stars. I. Methods and general properties

Abstract: Context. In analyses of stellar spectra and colours, and for the analysis of integrated light from galaxies, a homogeneous grid of model atmospheres of late-type stars and corresponding flux spectra is needed. Aims. We construct an extensive grid of spherically-symmetric models (supplemented with plane-parallel ones for the highest surface gravities), built on up-to-date atomic and molecular data, and make it available for public use. Methods. The most recent version of the MARCS program is used. Results. We present a grid of about 104 model atmospheres for stars with 2500K <= T-eff <= 8000 K, -1 <= log g = log (GM/R-2) <= 5 (cgs) with various masses and radii, -5 <= [Me/H] <= + 1, with [alpha/Fe] = 0.0 and 0.4 and different choices of C and N abundances. This includes "CN-cycled" models with C/N=4.07 (solar), 1.5 and 0.5, C/O ranging from 0.09 to (normally) 5.0 to also represent stars of spectral types R, S and N, and with 1.0 <= xi(t) = 5km s(-1). We also list thermodynamic quantities (T, P-g, P-e, rho, partial pressures of molecules, etc.) and provide them on the World Wide Web, as well as calculated fluxes in approximately 108 000 wavelength points. Underlying assumptions in addition to 1D stratification (spherical or plane-parallel) include hydrostatic equilibrium, mixing-length convection and local thermodynamic equilibrium. We discuss a number of general properties of the models, in particular in relation to the effects of changing abundances, of blanketing, and of sphericity. We illustrate positive and negative feedbacks between sphericity and molecular blanketing. We compare the models with those of other available grids and find excellent agreement with planeparallel models of Castelli & Kurucz (if convection is treated consistently) within the overlapping parameter range. Although there are considerable departures from the spherically-symmetric NextGen models, the agreement with more recent PHOENIX models is gratifying. Conclusions. The models of the grid show considerable regularities, but some interesting departures from general patterns occur for the coolest models due to the molecular opacities. We have tested a number of approximate "rules of thumb" concerning effects of blanketing and sphericity and often found them to be astonishingly accurate. Some interesting new phenomena have been discovered and explored, such as the intricate coupling between blanketing and sphericity, and the strong effects of carbon enhancement on metal-poor models. We give further details of line absorption data for molecules, as well as details of models and comparisons with observations in subsequent papers.

The Apache Point Observatory Galactic Evolution Experiment (APOGEE)

Abstract: National Science Foundation [AST-1109178, AST-1616636]; Gemini Observatory; Spanish Ministry of Economy and Competitiveness [AYA-2011-27754]; NASA [NNX12AE17G]; Hungarian Academy of Sciences; Hungarian NKFI of the Hungarian National Research, Development and Innovation Office [K-119517]; Alfred P. Sloan Foundation; National Science Foundation; U.S. Department of Energy Office of Science

Atomic Data for Resonance Absorption Lines. III. Wavelengths Longward of the Lyman Limit for the Elements Hydrogen to Gallium

Abstract: This compilation revises the 1991 listing of atomic data for the lighter elements from hydrogen to gallium. The tabulation emphasizes resonance lines, i.e., lines whose lower level is the ground state, or an excited fine-structure state of the ground term, and is restricted to wavelengths longward of the H I Lyman limit at 911.753 ?. All but the very weakest known and predicted electric-dipole transitions are included, but no forbidden lines. This paper has attempted to review all data published by the end of 2002.?????The tables contain the best data available to the author on ionization potentials, level designations, vacuum and air wavelengths, lower and upper energy levels, statistical weights, transition probabilities, natural damping constants (reciprocal lifetimes), oscillator strengths, and the often used combinations of log gf and log ?f. All ion stages with relevant classified lines are included. Individual components resulting from isotope shift and hyperfine structure are listed explicitly for certain species. The accompanying text provides references, explanations for the critical selection of data, and notes indicating where new measurements or calculations are needed.?????This compilation should be particularly useful in the analysis of interstellar and quasar absorption lines and other astrophysical sites where the density of particles and radiation is low enough to excite only the lowest atomic levels. The data also are relevant to the study of stellar atmospheres, and gaseous nebulae.?????An Appendix summarizes new data relevant to the similar compilation in Paper II for the elements germanium to uranium.