Solar Elemental Abundances Research Articles

Studies of intermediate-mass stellar models using eclipsing binaries

Evolutionary computations for intermediate-mass stars are analyzed using observed parameters for eclipsing SB2 binaries and theoretical parameters based on evolutionary tracks. Modern observations cannot be used to distinguish between models with and without convective overshooting for stars in the vicinity of the main sequence. Statistically significant discrepancies between the observed and computed stellar parameters are associated with systematic errors in photometric effective temperatures. After taking into account systematic effects, the theoretical computations fit the observational data uniformly well throughout the entire mass interval studied. Empirical and semiempirical (i.e., reduced to the ZAMS and with solar elemental abundances) formulas for the mass-luminosity, mass-effective temperature, and mass-radius relations are proposed.

Ionization and Cooling of a Hot Plasma with Temperature Fluctuations

Cooling functions for a stationary plasma are calculated in a wide temperature range from 5·103 K to 108 K, both for a plasma with the solar abundances of elements and for a plasma with an anomalous chemical composition typical of Wolf—Rayet stars. The HILYS project is described, with the aim of calculating cross sections and rates of excitation by electron collision of atoms and ions with a charge Z ≤ 26 and principal electron quantum numbers n ≤ 10, needed to calculate the ionization and thermal states of a plasma and the development of methods of calculating the plasma's spectrum in the visible, UV, and x-ray ranges. The results of a calculation of cross sections and effective collision strengths obtained within the framework of the project are given. The influence of temperature fluctuations (δT/T ≤ 0.16) on the relative ion abundances and the total cooling function is studied. It is shown that the presence of such fluctuations considerably increases the temperature range in which the abundances of ions of a given degree of ionization are not negligible, while the cooling function can differ considerably from that calculated for a one-temperature plasma. The contribution of dielectronic recombination to the total cooling function is investigated, and it proves to be significant only for a plasma with high abundances of heavy elements. The x-ray spectrum of the bright supergiant ζ Pup is analyzed.

シリカ鉱物 そのいん石と惑星における産状と惑星科学的意義

Silica minerals are poorly encountered in meteorites and the terrestrial planets. Especially, primitive meteorites, except enstatite chondrites, rarely contain silica minerals. This mainly reflects the solar elemental abundance that Mg is more abundant than Si. Unless the extensive magmatic fractionation took place for long time, silica minerals did not become common minerals in the planets. In spite of their rare occurrences, the polymorphs of silica minerals are significant to estimate the physical conditions of the formation processes of meteorites and planetary rocks.

Improved Laboratory Transition Parameters for Euiiand Application to the Solar Europium Elemental and Isotopic Composition

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.

A synthesis of data from fundamental plane and surface brightness fluctuation surveys

We perform a series of comparisons between distance-independent photometric and spectroscopic properties used in the surface brightness fluctuation (SBF) and fundamental plane (FP) methods of early-type galaxy distance estimation. The data are taken from two recent surveys: the SBF Survey of Galaxy Distances and the Streaming Motions of Abell Clusters (SMAC) FP survey. We derive a relation between colour and Mg2 index using nearly 200 galaxies and discuss implications for Galactic extinction estimates and early-type galaxy stellar populations. We find that the reddenings from Schlegel et al. for galaxies with appear to be overestimated by per cent, but we do not find significant evidence for large-scale dipole errors in the extinction map. In comparison with stellar population models having solar elemental abundance ratios, the galaxies in our sample are generally too blue at a given Mg2; we ascribe this to the well-known enhancement of the α-elements in luminous early-type galaxies. We confirm a tight relation between stellar velocity dispersion σ and the SBF ‘fluctuation count’ parameter N¯, which is a luminosity-weighted measure of the total number of stars in a galaxy. The correlation between N¯ and σ is even tighter than that between Mg2 and σ. Finally, we derive FP photometric parameters for 280 galaxies from the SBF survey data set. Comparisons with external sources allow us to estimate the errors on these parameters and derive the correction necessary to bring them on to the SMAC system. The data are used in a forthcoming paper, which compares the distances derived from the FP and SBF methods.

Abundances and charge states of particles in the solar wind

The Sun is the only star from which matter can be collected in order to investigate its elemental and isotopic composition. Solar elemental abundances provide the most important benchmark for the chemical evolution of the galaxy. They can be derived from photospheric observations, from in situ investigations of the solar wind, and from solar energetic particles. Solar isotopic abundances provide an important reference for the galactic evolution and if available with sufficient precision, also for the chemical and physical evolution of the solar system. The abundances of isotopes in the solar atmosphere can only be inferred from in situ observations of solar particles. This review makes an attempt to summarize current knowledge about the composition of the solar wind and shows how the elemental, isotopic, and charge state composition of solar wind particles is shaped as the solar corona expands throughout the heliosphere.

Elemental abundance analyses with DAO spectrograms -- XXI. The hot metallic-lined stars 60 Leonis and 6 Lyrae

ABSTRA C T Elemental abundances of the hot metallic-lined (Am) stars 60 Leo and 6 Lyr, with modest rotational velocities, are derived consistently with other studies in this series of papers. Both stars are found to show the Am phenomenon strongly, with nearly solar abundances of the light elements, overabundances of most Fe peak elements, and considerable overabundances of SrYZr, Ba and some rare earths. Ca is underabundant, while Sc is very underabundant.

Supernova Grains: The Source of Cosmic-Ray Metals

We show that the Be abundances in old halo stars formed in the early Galaxy strongly suggest that the refractory cosmic-ray metals, in both the early Galaxy and the present epoch, are accelerated from fresh supernova ejecta rather than from the interstellar medium, as proposed in most current models. To resolve this problem, we suggest that the high-velocity grains formed in supernova ejecta are the injection source for these cosmic rays, including C and O. We show how this cosmic-ray injection source can refute previous arguments against cosmic-ray acceleration from fresh supernova ejecta: the enrichment of the highly refractory elements relative to the volatiles and the similarity of the refractory cosmic-ray source and solar elemental and isotopic abundance ratios. We also show that the cosmic-ray source O abundance may be the direct consequence of the condensation of O as refractory oxides and that the problematic cosmic-ray C-to-O ratio may be understood if a large fraction of the C in the ejecta is in graphite grains. We further show that if the refractory metals are accelerated from fresh ejecta, the cosmic-ray source -->54Fe/ -->56Fe should be higher than the corresponding solar value. Such a difference is apparent in some recent cosmic-ray measurements, but forthcoming Advanced Composition Explorer results are needed to confirm this finding.

Quasi-Equilibrium Density Distributions of Small Dust Aggregations in the Solar Nebula

The rotational velocity of a fluid element around the midplane of the solar nebula increased as dust settled toward the midplane. The Kelvin and Helmholtz instability due to velocity difference of a dust-rich region and a dust-poor region should have occurred and the dust layer became turbulent when the Richardson number decreased below the critical value. Then, dust aggregations stirred up due to turbulent diffusion and were prevented to settle further. In this paper, the sizes of dust aggregations are assumed to be equal to or smaller than the typical radius of chondrules (∼0.3 mm). In this case, even very weak turbulence stirs up dust aggregations. Therefore a dust density distribution is considered to be self regulated so that the Richardson number is nearly equal to the critical value. The quasi-equilibrium dust density distribution is derived analytically by assuming that the Richardson number is equal to the critical value. The derived dust density at the midplane is much smaller than the critical density of the gravitational stability, if the solar composition of dust to gas ratio is assumed. On the other hand, the dust aggregations concentrate around the midplane and the dust layer becomes gravitationally unstable, if more than 97% (at 1 AU from the Sun) of the gaseous components have been dissipated from the nebula, leaving dusty components. Two alternative scenarios of planetesimal formation are proposed: planetesimals were formed by (1) mutual sticking of dust aggregations by nongravitational forces or by (2) gravitational instabilities in the nebula where the dust to gas ratio is much larger than the ratio with solar elemental abundance. Case (2) might be realized due to dissipation of the nebular gas and/or addition of dust by the bipolar outflow. In case (1), chondrule sizes do not indicate the maximum size of dust aggregations in the solar nebula.

Stellar Yields and Chemical Evolution -- I. Abundance Ratios and Delayed Mixing in the Solar Neighbourhood

We analyse two recent computations of type II supernova nucleosynthesis by Woosley & Weaver (1995, WW95) and Thielemann, Nomoto, & Hashimoto (1996, TNH96), focusing on the ability to reproduce the observed [Mg/Fe]-ratios in various galaxy types. We show that the yields of oxygen and total metallicity are in good agreement. However, TNH96-models produce more magnesium in the intermediate and less iron in the upper mass range of type II supernovae than WW95-models. To investigate the significance of these discrepancies for chemical evolution, we calculate Simple Stellar Population-yields for both sets of models and different IMF slopes. We conclude that the Mg-yields of WW95 do not suffice to explain the [Mg/Fe] overabundance neither in giant elliptical galaxies and bulges nor in metal-poor stars in the solar neighbourhood and the galactic halo. Calculating the chemical evolution in the solar neighbourhood according to the standard infall-model (e.g. Matteucci & Greggio 1986; Timmes, Woosley, & Weaver 1995; Yoshii, Tsujimoto, & Nomoto 1995), we find that using WW95 and TNH96 nucleosynthesis, the solar magnesium abundance is underestimated by 29 and 7 per cent, respectively. We include the relaxation of the instantaneous mixing approximation in chemical evolution models by splitting the gas component into two different phases. In additional simulations of the chemical evolution in the solar neighbourhood, we discuss various timescales for the mixing of the stellar ejecta with the interstellar medium. We find that a delay of the order of $10^{8}$ years leads to a better fit of the observational data in the [Mg/Fe]-[Fe/H] diagram without destroying the agreement with solar element abundances and the age-metallicity relation.

Standard Solar Neutrinos

view Abstract Citations (66) References (102) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Standard Solar Neutrinos Dar, Arnon ; Shaviv, Giora Abstract We describe in detail an improved standard solar model that has been used to calculate the fluxes of standard solar neutrinos. It includes pre-main-sequence evolution, element diffusion, partial ionization effects, and all the possible nuclear reactions between the main elements. It uses updated values for the initial solar element abundances, the solar age, the solar luminosity, the nuclear reaction rates, and the radiative opacities. Neither nuclear equilibrium nor complete ionization are assumed. The calculated solar neutrino fluxes are compared with published results from the four solar neutrino experiments. The calculated 8B solar neutrino flux is consistent, within the theoretical and experimental uncertainties, with the solar neutrino observations at Homestake and Kamiokande. The observations suggest that the 7Be solar neutrino flux is much smaller than that predicted. However, conclusive evidence for the suppression of the 7Be solar neutrino flux will require experiments like BOREXINO and HELLAZ. If the Be solar neutrino flux is suppressed, it still can be due either to standard physics reasons or neutrino properties beyond the standard electroweak model. Only future neutrino experiments, such as SNO, Super-kamiokande, BOREXINO, and HELLAZ, will be able to show that the solar neutrino problem is a consequence of neutrino properties beyond the standard electroweak model. Publication: The Astrophysical Journal Pub Date: September 1996 DOI: 10.1086/177748 Bibcode: 1996ApJ...468..933D Keywords: ELEMENTARY PARTICLES; NUCLEAR REACTIONS; NUCLEOSYNTHESIS; ABUNDANCES; SUN: INTERIOR full text sources ADS |

Standard solar neutrinos

The predictions of an improved standard solar model are compared with the observations of the four solar neutrino experiments. The improved model includes premain sequence evolution, element diffusion, partial ionization effects, and all the possible nuclear reactions between the main elements. It uses updated values for the initial solar element abundances, the solar age, the solar luminosity, the nuclear reaction rates and the radiative opacities. Neither nuclear equilibrium, nor complete ionization are assumed. The calculated $^8$B solar neutrino flux is consistent, within the theoretical and experimental uncertainties, with the solar neutrino flux measured by Kamiokande. The results from the $^{37}$Cl and $^{71}$Ga radiochemical experiments seem to suggest that the terrestrial $^7$Be solar neutrino flux is much smaller than that predicted. However, the present terrestrial ``defecit'' of $^7$Be solar neutrinos may be due to the use of inaccurate theoretical neutrino absorption cross sections near threshold for extracting solar neutrino fluxes from production rates. Conclusive evidence for a real deficit of $^7$Be solar neutrinos will require experiments such as BOREXINO or HELLAZ. A real defecit of $^7$Be solar neutrinos can be due to either astrophysical reasons or neutrino properties beyond the standard electroweak model. Only future neutrino experiments, such as SNO, Superkamiokande, BOREXINO and HELLAZ, will be able to provide conclusive evidence that the solar neutrino problem is a consequence of neutrino properties beyond the standard electroweak model. Earlier indications may be provided by long baseline neutrino oscillation experiments.

Solar element abundances, non-LTE line formation in cool stars and atomic data

The composition of solar and meteoritic matter serves as a primary reference for cosmochemical studies. Element abundances in the Sun - and in cool stars in general - are usually determined by spectroscopy of a stellar atmosphere whose properties differ from most laboratory sources: (i) there are strong gradients of temperature and pressure, (ii) the main constituents are neutral hydrogen and helium, while the fractional abundance of electrons is only ≈10−4, (iii) the plasma is immersed in an intense, anisotropic radiation field, and is highly turbulent.The present contribution discusses meteoritic and solar abundances and their suitability as cosmic reference data. Also addressed are mayor diagnostic problems encountered in the analysis of the photospheric line spectrum of cool stars - in particular line broadening and deviations from LTE in neutral iron. This paper is an update of a review [1] given at the 1987 Meudon symposium on high-S/N stellar spectroscopy.

Composition and radiative properties of grains in molecular clouds and accretion disks

We define a model of the compositon and abundances of grains and gases in molecular cloud cores and accretion disks around young stars by employing a wide range of astronomical data and theory, the composition of primitive bodies in the solar system, and solar elemental abundances. In the coldest portions of these objects, we propose that the major grain species include olivine (Fe, Mg, 2SiO4), orthopyroxene (Fe, Mg, SiO3), volatile and refractory organics, water ice, troilite (FeS), and metallic iron. This compositional model differs from almost all previous models of the interstellar medium (ISM) by having organics as the major condensed C species, rather than graphite; by including troilite as a major grain species; and by specifying the mineralogical composition of the condensed silicates. Using a combination of laboratory measurements of optical constants and asymptotic theory, we derive values of the real and imaginary indices of refraction of these grain species over a wavelength range that runs from the vacuum ultraviolet (UV) to the radio domain. The above information on grain properties is used to estimate the Rosseland mean opacity of the grains and their monochromatic opacity.

Solar coronal abundances of elements with low first ionization potential: Chromium, calcium, and aluminum

view Abstract Citations (10) References (36) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Solar Coronal Abundances of Elements with Low First Ionization Potential: Chromium, Calcium, and Aluminum McKenzie, D. L. ; Feldman, U. Abstract We have used X-ray spectra obtained by the SOLEX spectrometers on the P78-1 satellite to study coronal abundances of three elements with low first ionization potential (FIP): Cr, Ca, and Al. The Cr/O abundance ratio was determined from the ratio of the Cr XV 2p6 (1)S0-2p5 3d (1)P1 line to the O VIII 1s (2)S-2p (2)P unresolved doublet, a ratio that is almost independent of temperture. In a scenario in which the ratio of an element's coronal to its photospheric abundance is largely determined by its FIP, the Cr/O ratio should be reflective of the absolute Cr abundance, because the FIPs of O and H are nearly equal. We find that the Cr/O abundance ratio in coronal active regions varies by a factor of 2.7 and is probably always enhanced by at least a factor of 3 over the photospheric ratio. The Ca/O abundance ratio was determined from the ratio of a blend of Ca XV lines at around 22.75 A to the O VIII 1s (2)S-2P (2)P doublet. Because this ratio is temperature dependent, only lower limits are derived for the Ca/O abundance ratio. The lower limits range from 3.0 to 9.7 times the photospheric ratio. Hence, it is likely that both Ca and Cr are always enriched by at least a factor of 3 in coronal active regions and flares. The Al/Mg abundance ratio determination was based on the line ratio (Al XII 1 S2 (i)S0-s2p (1)P1/(Mg XI 1s2 (1)S0-1s 3p (1)P1). Because this ratio is temperature sensitive and we have only six Al/Mg spectra, the results of this study are somewhat equivocal. The evidence indicates that Al is enriched in coronal active regions, but it is uncertain whether, as expected, it is enriched as much as is Ca, which has a slightly higher FIP. In order to account for these observations, as well as previously reported determinations of the Fe/O, O/Ne, and Fe/Mg coronal abundance ratios, in terms of a mechanism that moves ions much more easily than neutrals form the chromosphere to the corona, we have calculated the fraction of ionization for the abundant elelments in the chromosphere. Photoionization by blackbody radiaiton from just below the temperature minimum region, by locally produced Ly alpha radiation, and by line and continuum radiation emitted at high temperatures play and important role in determining the chromospheric ionization structure. In particular, photoionization of O I by EUV radiation from above must be invoked to account for variations in the coronal O/Ne abundance ratio. Because H I strongly absorbs this radiation, O is unionized at chromospheric depths of more than a few hundred kilometers. The ionization pattern, as a function of FIP, in the part of the upper chromosphere where the temperature is in the range 6000-8000 K, may account for the observed coronal abundance variations and enrichments. A mechanism that imparts a few tens of eV to ions, but not to neutrals, in this region could be responsible for the coronal enrichment of low-FIP elements. Publication: The Astrophysical Journal Pub Date: January 1994 DOI: 10.1086/173613 Bibcode: 1994ApJ...420..892M Keywords: Abundance; Aluminum; Calcium; Chromium; Ionization Potentials; Photosphere; Solar Corona; Black Body Radiation; Gamma Ray Astronomy; Lyman Alpha Radiation; Photoionization; Temperature Gradients; X Ray Spectra; Solar Physics; SUN: ABUNDANCES; SUN: CORONA; SUN: X-RAYS; GAMMA RAYS full text sources ADS |

New f-values in C I and the CNO abundances in the sun

In an attempt to refine our knowledge of the solar abundances of the CNO elements, we discuss in this paper the implications of a new accurate set of oscillator strengths recently calculated in intermediate coupling for the 2p( 2 P o )nl-2p( 2 P o )n'l' E1 transitions of astrophysical interest in C I and also for the forbidden transitions within the 2p 2 ground configuration. As with previous analyses devoted to nitrogen and oxygen, configuration interaction effects have been considered in the calculations in a detailed way and empirical adjustments have been introduced in the diagonal Hamiltonian matrix elements in order to improve the agreement between theoretical eigenvalues and experimental energy differences

Mantle neon and atmospheric contamination

The apparent distinction between atmospheric and mantle 20Ne 22Ne ratios may provide a technique to quantify air contamination in mantle-derived materials. In the absence of mantle nuclear reactions, which produce either 20Ne or 22Ne in substantial quantities, it is likely that the entire mantle is characterized by a single, uniform 20Ne 22Ne ratio; a value of around 12.5 is suggested by analyses of MORBs, OIBs, diamonds and xenoliths. If this premise is correct, then any measured 20Ne 22Ne ratios in mantle samples that are lower than this must result from addition of an air component, with 20Ne 22Ne= 9.8 . This is most likely a syn- or post-eruptive contaminant. The degree of air contamination inferred from 20Ne 22Ne ratios is generally small for diamonds, but is increasingly significant for MORBs and OIBs; many OIB's may carry > 90% air neon. We calculated “air-neon corrected” 21Ne 22Ne and 40Ar 36Ar ratios for the highly degassed MORB mantle and for the less degassed (high 3He 4He ) “plume” reservoir. The inferred MORB composition is indistinguishable from measurements of some gas-rich glasses. The calculated plume composition is similar to the least air-like measurements from ocean islands, but is less air-like than has been proposed previously. This plume composition is not consistent with a completely undegassed reservoir. From these corrected mantle compositions, we calculated the relative time-integrated rare gas abundances in the mantle, using a simple evolutionary model, which simultaneously considers the isotopic compositions of He, Ne, Ar and Xe. The model shows that both MORB and plume reservoirs have evolved with nearly solar elemental abundances. This provides strong support to suggestions based on Ne isotopes that the Earth accreted with gases nearly solar in composition. Importantly, the inferred mantle Ne/Ar ratios are much higher than atmospheric, which is consistent with simultaneous fractionation of both the atmospheric neon isotope ratio and the Ne/Ar ratio by massive hydrodynamic escape. Mixing between MORB and plume reservoirs (with our calculated elemental and isotopic abundances), plus varying amounts of added air, can account for the rare gases in nearly all mantle-derived rocks.

Carbon and nitrogen abundances determined from transition layer lines

The possibility of determining relative carbon, nitrogen, and silicon abundances from the emission-line fluxes in the lower transition layers between stellar chromospheres and coronae is explored. Observations for main-sequence and luminosity class IV stars with presumably solar element abundances show that for the lower transition layers Em = BT<SUP>-gamma.</SUP> For a given carbon abundance the constants gamma and B in this relation can be determined from the C II and C IV emission-line fluxes. From the N V and S IV lines, the abundances of these elements relative to carbon can be determined from their surface emission-line fluxes. Ratios of N/C abundances determined in this way for some giants and supergiants agree within the limits of errors with those determined from molecular bands. For giants, an increase in the ratio of N/C at B-V of about 0.8 is found, as expected theoretically.

The near-maximum-light spectrum of the type IC supernova 1987M

An analysis of the near-maximum-light optical and near-UV spectrum of the Type Ic supernova 1987M is presented. In the spectrum, in addition to the fairly certain identifications of O I, Ca II, and optical Fe II lines, we identify a weak Hα line, a moderately weak Si II λ6355 doublet, and the He I λ5876 line. The near-UV region of the spectrum is found to result from a, blend of iron peak ion lines, with only solar abundances of the iron peak elements required in the supernova atmosphere. It is concluded that hydrogen is underabundant relative to solar composition in the supernova atmosphere by at least a factor of 10; no lower limit on hydrogen abundance has been determined. It is also concluded that a helium star model for Type Ic supernovae is adequate and slightly favored for explaining the analyzed spectrum. The implications of the spectrum analysis for explosion models of Types Ib and Ic supernovae are discussed.

惑星間塵の鉱物学

Interplanetary dust particles (IDPs), collected in the Earth's stratosphere, have been a subject of intense laboratory studies for the last ten years. A significant proportion of collected IDPs has a composition close to the solar (or chondritic) elemental abundance. This paper reviews results of mineralogical, petrological and chemical studies of the chondritic IDPs. Experimental studies on mineralogy, infrared absorption spectra, and isotopic properties of the chondritic IDPs have suggested that they are primitive and may contain records of the early solar system and possibly of events that predate it. Specific mineralogical and chemical features provide indications of processes including direct condensation from the solar nebula, hydrocarbon formation in the nebula, and aqueous alteration in water-rich parent bodies. Of particular interest are the mineralogical and chemical relationships between IDPs and carbonaceous chondrites. Data of both IDPs and carbonaceous chondrites have accumulated, and it is now possible to compare the mineralogies of the IDPs and the meteorites in considerable detail. Important points of information and their implications for the origin of IDPs are discussed. The current knowledge of mineralogy and chemistry of IDPs suggests that most hydrated IDPs were derived from asteroids and most anhydrous IDPs were derived from comets.