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 ...

The Chemical Composition of the Sun

Solar photospheric and meteoritic CI chondrite abundance determinations for all elements are summarized and the best currently available photospheric abundances are selected. The meteoritic and solar abundances of a few elements (e.g., noble gases, beryllium, boron, phosphorous, sulfur) are discussed in detail. The photospheric abundances give mass fractions of hydrogen (X ¼ 0:7491), helium (Y ¼ 0:2377), and heavy elements (Z ¼ 0:0133), leading to Z=X ¼ 0:0177, which is lower than the widely used Z=X ¼ 0:0245 from previous compilations. Recent results from standard solar models considering helium and heavy-element settling imply that photospheric abundances and mass fractions are not equal to protosolar abundances (representative of solar system abundances). Protosolar elemental and isotopic abundances are derived from photospheric abundances by considering settling effects. Derived protosolar mass fractions are X0 ¼ 0:7110, Y0 ¼ 0:2741, and Z0 ¼ 0:0149. The solar system and photospheric abundance tables are used to compute self-consistent sets of condensation temperatures for all elements. Subject headings: astrochemistry — meteors, meteoroids — solar system: formation — Sun: abundances — Sun: photosphere

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Solar System Abundances and Condensation Temperatures of the Elements

We review the current status of our knowledge of the chemical composition of the Sun, essentially derived from the analysis of the solar photospheric spectrum. The comparison of solar and meteoritic abundances confirms that there is a very good agreement between the two sets of abundances. They are used to construct a Standard Abundance Distribution.

Standard Solar Composition

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.

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

New radiative lifetime measurements using time-resolved laser-induced fluorescence are reported for the lowest six even-parity levels of Eu II. Branching fractions, measured from Fourier transform spectra, are combined with these lifetimes to determine atomic transition probabilities for the strongest blue-UV lines and additional yellow-red lines of Eu II. These results are compared with published data, and generally good agreement is found. Recommended hyperfine structure constants and isotopic shifts for these lines are also assembled from the literature and supplemented, as needed, using results from nonlinear least-squares fits of line profiles in Fourier transform spectra. These laboratory data are applied in a new determination of the solar Eu elemental abundance, yielding log10 e(Eu) = 0.52 ± 0.01, with ±0.04 estimated for each of internal (scatter) and external (systematic) uncertainties. From analysis of the profiles of three Eu II lines, primarily λ4129, isotopic fractions of 151Eu and 153Eu are shown to be consistent with their values in meteoritic material.

https://iopscience.iop.org/article/10.1086/323407/pdf

Improved Laboratory Transition Parameters forEu II and Application to the Solar Europium Elemental and Isotopic Composition

Radiative lifetimes, accurate to � 5%, have been measured for 168 odd-parity levels of Nd ii using laser-induced fluorescence. The lifetimes are combined with branching fractions measured using Fouriertransform spectrometry to determine transition probabilities for over 700 lines of Nd ii. This work is the largest-scale laboratory study to date of Nd ii transition probabilities using modern methods. This improved data set is used to determine Nd abundances for the Sun and three metal-poor giant stars with neutroncapture enhancement: CS 22892� 052, HD 115444, and BD +17 � 3248. In all four stars the line-to-line scatter is considerably reduced from earlier published results. The solar photospheric abundance is determined to be log � ðNd Þ¼ 1:45 � 0:01ð� ¼ 0:05Þ, which is in excellent agreement with meteoric data. The ratio of Nd/Eu is virtually identical in all three metal-poor Galactic halo stars. Furthermore, the newly determined stellar Nd abundances, in comparison with other heavy neutron-capture elements, are consistent with an r-process–only origin early in the history of the Galaxy. These more accurate Nd abundance determinations might help to constrain the predicted solar system r-process abundances, and suggest other elements for further neutron-capture abundance studies. Subject headings: atomic data — stars: abundances — Sun: abundances On-line material: machine-readable tables

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IMPROVED LABORATORY TRANSITION PROBABILITIES FOR Nd ii AND APPLICATION TO THE NEODYMIUM ABUNDANCES OF THE SUN AND THREE METAL-POOR STARS

Recent radiative lifetime measurements accurate to ±5% using laser-induced fluorescence (LIF) on 43 even-parity and 15 odd-parity levels of Ce II have been combined with new branching fractions measured using a Fourier transform spectrometer (FTS) to determine transition probabilities for 921 lines of Ce II. This improved laboratory data set has been used to determine a new solar photospheric Ce abundance, log e = 1.61 ± 0.01 (σ = 0.06 from 45 lines), a value in excellent agreement with the recommended meteoritic abundance, log e = 1.61 ± 0.02. Revised Ce abundances have also been derived for the r-process-rich metal-poor giant stars BD+17°3248, CS 22892-052, CS 31082-001, HD 115444, and HD 221170. Between 26 and 40 lines were used for determining the Ce abundance in these five stars, yielding a small statistical uncertainty of ±0.01 dex similar to the solar result. The relative abundances in the metal-poor stars of Ce and Eu, a nearly pure r-process element in the Sun, matches r-process-only model predictions for solar system material. This consistent match with small scatter over a wide range of stellar metallicities lends support to these predictions of elemental fractions. A companion paper includes an interpretation of these new precision abundance results for Ce as well as new abundance results and interpretation for Pr, Dy, and Tm.

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Improved Laboratory Transition Probabilities for Ce II, Application to the Cerium Abundances of the Sun and Five R-Process-Rich, Metal-Poor Stars, and Rare Earth Lab Data Summary

Recent radiative lifetime measurements accurate to +/- 5% using laser-induced fluorescence (LIF) on 43 even-parity and 15 odd-parity levels of Ce II have been combined with new branching fractions measured using a Fourier transform spectrometer (FTS) to determine transition probabilities for 921 lines of Ce II. This improved laboratory data set has been used to determine a new solar photospheric Ce abundance, log epsilon = 1.61 +/- 0.01 (sigma = 0.06 from 45 lines), a value in excellent agreement with the recommended meteoritic abundance, log epsilon = 1.61 +/- 0.02. Revised Ce abundances have also been derived for the r-process-rich metal-poor giant stars BD+17 3248, CS 22892-052, CS 31082-001, HD 115444 and HD 221170. Between 26 and 40 lines were used for determining the Ce abundance in these five stars, yielding a small statistical uncertainty of 0.01 dex similar to the Solar result. The relative abundances in the metal-poor stars of Ce and Eu, a nearly pure r-process element in the Sun, matches r-process only model predictions for Solar System material. This consistent match with small scatter over a wide range of stellar metallicities lends support to these predictions of elemental fractions. A companion paper includes an interpretation of these new precision abundance results for Ce as well as new abundance results and interpretations for Pr, Dy and Tm.

/pdf/improved-laboratory-transition-probabilities-for-ce-ii-4i2kkqcuzg.pdf

Improved Laboratory Transition Probabilities for Ce II, Application to the Cerium Abundances of the Sun and Five r-process Rich, Metal-Poor Stars, and Rare Earth Lab Data

Various laser diagnostics are used to study the cathode-fall and negative-glow regions of a He glow discharge with a cold Al cathode. The electric field and absolute metastable densities are mapped and the gas temperature is measured over a range of current densities from a near-normal (173 V) to a highly abnormal (600 V) cathode fall. These measurements are analyzed to yield the current balance at the cathode surface, the ionization rate in the cathode-fall region, and the metastable production rate in the cathode-fall and negative-glow regions. The experimental results compare favorably with the results of Monte Carlo simulations. The density and temperature of the low-energy electron gas in the negative glow is determined by combining information from the experiments and Monte Carlo simulations.

E. A. Den Hartog

Papers

Improved Laboratory Transition Parameters forEu II and Application to the Solar Europium Elemental and Isotopic Composition

IMPROVED LABORATORY TRANSITION PROBABILITIES FOR Nd ii AND APPLICATION TO THE NEODYMIUM ABUNDANCES OF THE SUN AND THREE METAL-POOR STARS

Improved Laboratory Transition Probabilities for Ce II, Application to the Cerium Abundances of the Sun and Five R-Process-Rich, Metal-Poor Stars, and Rare Earth Lab Data Summary

Improved Laboratory Transition Probabilities for Ce II, Application to the Cerium Abundances of the Sun and Five r-process Rich, Metal-Poor Stars, and Rare Earth Lab Data

Laser optogalvanic and fluorescence studies of the cathode region of a glow discharge