Determination Of Solar Abundances Research Articles

The Sun as a probe of Fundamental Physics and Cosmology

The high quality data provided by helioseismology, solar neutrino flux measurements, spectral determination of solar abundances, nuclear reactions rates coefficients among other experimental data, leads to the highly accurate prediction of the internal structure of the present Sun - the standard solar model. In this talk, I have discussed how the standard solar model, the best representation of the real Sun, can be used to study the properties of dark matter, for which two complementary approaches have been developed: - to limit the number of theoretical candidates proposed as the dark matter particles, this analysis complements the experimental search of dark matter, and - as a template for the study of the impact of dark matter in the evolution of stars, which possibly occurs for stellar populations formed in regions of high density of dark matter, such as stars formed in the centre of galaxies and the first generations of stars.

ON USING THE COLOR-MAGNITUDE DIAGRAM MORPHOLOGY OF M67 TO TEST SOLAR ABUNDANCES

The open cluster M67 has solar metallicity and an age of about 4 Gyr. The turnoff (TO) mass is close to the minimum mass for which solar metallicity stars develop a convective core during main sequence evolution as a result of the development of hydrogen burning through the CNO cycle. The morphology of the color–magnitude diagram (CMD) of M67 around the TO shows a clear hook-like feature, a direct sign that stars close to the TO have convective cores. VandenBerg et al. investigated the possibility of using the morphology of the M67 TO to put constraints on the solar metallicity, particularly CNO elements, for which solar abundances have been revised downward by more than 30% over the last few years. Here, we extend their work, filling the gaps in their analysis. To this aim, we compute isochrones appropriate for M67 using new (low metallicity) and old (high metallicity) solar abundances and study whether the characteristic TO in the CMD of M67 can be reproduced or not. We also study the importance of other constitutive physics on determining the presence of such a hook, particularly element diffusion, overshooting and nuclear reaction rates. We find that using the new solar abundance determinations, with low CNO abundances, makes it more difficult to reproduce the characteristic CMD of M67. This result is in agreement with results by VandenBerg et al. However, changes in the constitutive physics of the models, particularly overshooting, can influence and alter this result to the extent that isochrones constructed with models using low CNO solar abundances can also reproduce the TO morphology in M67. We conclude that only if all factors affecting the TO morphology are completely under control (and this is not the case), M67 could be used to put constraints on solar abundances.

New results on standard solar models

We describe the current status of solar modelling and focus on the problems originated with the introduction of solar abundance determinations with low CNO abundance values. We use models computed with solar abundance compilations obtained during the last decade, including the newest published abundances by Asplund and collaborators. Results presented here make focus both on helioseismic properties and the models as well as in the neutrino fluxes predictions. We also discuss changes in radiative opacities to restore agreement between helioseismology, solar models, and solar abundances and show the effect of such modifications on solar neutrino fluxes.

NEW SOLAR COMPOSITION: THE PROBLEM WITH SOLAR MODELS REVISITED

We construct updated solar models with different sets of solar abundances, including the most recent determinations by Asplund et al. (2009). The latter work predicts a larger ($\sim 10%$) solar metallicity compared to previous measurements by the same authors but significantly lower ($\sim 25%$) than the recommended value from a decade ago by Grevesse & Sauval (1998). We compare the results of our models with determinations of the solar structure inferred through helioseismology measurements. The model that uses the most recent solar abundance determinations predicts the base of the solar convective envelope to be located at $R_{\rm CZ}= 0.724{\rm R_\odot}$ and a surface helium mass fraction of $Y_{\rm surf}=0.231$. These results are in conflict with helioseismology data ($R_{\rm CZ}= 0.713\pm0.001{\rm R_\odot}$ and $Y_{\rm surf}=0.2485\pm0.0035$) at 5$-\sigma$ and 11$-\sigma$ levels respectively. Using the new solar abundances, we calculate the magnitude by which radiative opacities should be modified in order to restore agreement with helioseismology. We find that a maximum change of $\sim 15%$ at the base of the convective zone is required with a smooth decrease towards the core, where the change needed is $\sim 5%$. The required change at the base of the convective envelope is about half the value estimated previously. We also present the solar neutrino fluxes predicted by the new models. The most important changes brought about by the new solar abundances are the increase by $\sim 10%$ in the predicted $^{13}$N and $^{15}$O fluxes that arise mostly due to the increase in the C and N abundances in the newly determined solar composition.

Standard solar model calculation of the neutrino fluxes

I summarize the current status of solar neutrino fluxes predictions in the framework of the Standard Solar Model (SSM). I discuss the effects that using the most recent solar abundance determination in the solar modelling has on neutrino fluxes predictions and helioseismology quantities.

Hot star wind models with new solar abundances

We compare the hot star wind models calculated assuming older solar abundance determination with models calculated using the recently published values derived from 3D hydrodynamical model atmospheres. We show that the use of new abundances with lower metallicity improves the agreement between wind observation and theory in several aspects: (1) The predicted wind mass-loss rates are lower by a factor of 0.76. This leads to a better agreement with mass-loss rate determinations derived from observations with account of clumping. (2) As a result of the lowering of mass-loss rates, there is a better agreement between predicted modified wind momentum-luminosity relationship and that derived from observations with account of clumping. (3) Both the lower mass fraction of heavier elements and lower mass-loss rates lead to a decrease of the opacity in the X-ray region. This has influence on the prediction of the X-ray line profile shapes. (4) There is a better agreement between predicted PV ionization fractions and those derived from observations.

THE LOWER SOLAR ATMOSPHERE : RAPPORTEUR PAPER II

This “rapporteur” report discusses the solar photosphere and low chromosphere in the context of chemical composition studies. The highly dynamical nature of the photosphere does not seem to jeopardize precise determination of solar abundances in classical fashion. It is still an open question how the highly dynamical nature of the low chromosphere contributes to first ionization potential (FIP) fractionation.

Accurate oscillator strengths of astrophysical interest for neutral oxygen

A sample of 12 atomic O I allowed transitions is used to obtain an accurate scale of oscillator strengths for transitions of astrophysical interest. Configuration interaction effects are considered in detail, and the results are used to improve the solar abundance determination for oxygen. The new result is A(O) = 8.86 + or - 0.04.

Lifetimes of excited states in Pt I and IR I measured by the beam-sputtering technique

view Abstract Citations (14) References (12) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Lifetimes of excited states in Pt I and Ir I measured by the beam-sputtering technique. Ramanujam, P. S. ; Andersen, T. Abstract Radiative lifetimes for low-lying excited states in Pt I and Ir I have been determined by means of the beam-sputtering excitation method combined with the delayed-coincidence technique to test the reliability of recent solar-abundance determinations of Pt and Ir. The Ir abundance should be increased by a factor of 4 to log A(Ir) = 1.45 + 0.2, whereas the Pt abundance remains unchanged. The new solar Pt and Ir abundances are both in agreement with values derived from carbonaceous chondrites. Subject headings: atomic processes - laboratory spectra - transition probabilities Publication: The Astrophysical Journal Pub Date: December 1978 DOI: 10.1086/156694 Bibcode: 1978ApJ...226.1171R Keywords: Abundance; Atomic Excitations; Iridium; Platinum; Radiative Lifetime; Solar Spectra; Sputtering; Ion Beams; Light Emission; Line Spectra; Transition Probabilities; Atomic and Molecular Physics; Element Abundances:Sun; Laboratory Spectra; Transition Probabilities full text sources ADS |

Lifetimes of excited states in Y I, Y II, and Zr I by beam-foil and beam-sputtering excitation

view Abstract Citations (24) References (18) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Lifetimes of excited states in Y I, Y II, and Zr I by beam-foil and beam-sputtering excitation. Andersen, T. ; Ramanujam, P. S. ; Bahr, K. Abstract Radiative lifetimes have been determined by beam-foil and beam-sputtering excitation for some excited states in Y I, Y II, and Zr I to test the reliability of the transition probabilities used so far for solar abundance determinations of yttrium and zirconium. The yttrium abundance in the sun should be increased by a factor of about 2 to log A(Y) = 2.35 + or - 0.20 by using the new transition probabilities, whereas the zirconium abundance should remain unchanged. Publication: The Astrophysical Journal Pub Date: July 1978 DOI: 10.1086/156268 Bibcode: 1978ApJ...223..344A Keywords: Abundance; Atomic Excitations; Ion Beams; Photosphere; Radiative Lifetime; Sputtering; Transition Probabilities; Yttrium; Zirconium; Decay; Foils (Materials); Graphs (Charts); Line Spectra; Metal Ions; Solar Atmosphere; Wavelengths; Solar Physics; Transition Probabilities full text sources ADS |

Determinations of atomic lifetimes for the rare earth ions: Prii, Tmii, Luii, Ceiii

Radiative lifetimes have been determined by the beam-foil method for some excited states in the singly ionized rare earths Pr ii, Tm ii, and Lu ii, in order to test the reliability of the transition probabilities and oscillator strengths found by Corliss and Bozman and usually applied for solar abundance determinations. Correction factors of ∼4.5, ∼2.5, and ∼0.3 should be applied to Corliss and Bozman's values for Pr ii, Tm ii, and Lu ii, respectively. These corrections eliminate the discrepancies between the abundance in the solar photosphere and in meteorites for Pr and Tm. Radiative lifetimes for Ce iii are also reported.

A Discussion on solar studies with special reference to space observations - Abundance of iron in the photosphere

About ten years ago astrophysics was haunted by a nightmare called non-local thermodynamic equilibrium (n.l.t.e.). Some astrophysicists, notably Pecker (1959) and R .N . Thomas, began to doubt whether the well-known formulae for thermal excitation and ionization could be applied with sufficient accuracy to, for example, the solar photosphere. If that contention had been true, it would have meant that all solar abundance determinations were affected by large errors. On the other hand, it would have been a hopeless enterprise to develop a purely statistical theory for the distribution of the atomic states, for example, of neutral iron under the influence of the complicated field of radiation in the photosphere together with all sorts of collisions. After preliminary studies (Unsold 1962) had made it probable that in reality deviations from local thermodynamic equilibrium (l.t.e) were quite negligible in the photosphere and the lower chromosphere (but probably not so in the higher chromosphere and certainly not in the corona), Holweger (1967) proceeded to construct an empirical model of the solar photosphere (and lower chromosphere) in l.t.e. Since it was known (Pagel 1959; Unsold 1962; Lambert & Pagel 1968) that the negative hydrogen ion in any case conformed to the laws of l.t.e., the continuous spectrum and its centre limb variation could be used for obtaining the temperature distribution T(r0) for about 0.05 < t0 < 2. Just extrapolating this temperature distribution towards smaller r 0—as many authors have done would lead to very serious errors. So T ( t0) out to t0 10-6 was obtained using the observed intensities within strong lines, where the line absorption coefficient is much larger than the continuous absorption coefficient.

Solar abundance determination

There is given a summary of observational and theoretical aspects dealt with in the solar abundance determination. The solar abundance of sixty-six chemical elements are known. The abundance of some of these elements are based on one spectral line only (Ga, Ge, Sn, Er, Yb, Lu, Au, and Th) and the results may be erroneous. For six elements (B, Cs, Hg, Tl, Bi, and U) are given only upper limits for the abundance. Lines of Ho and Tb are suspected in the solar spectrum, but so far the abundances of these elements are not determined.

Determination of Solar Abundances by a Method of Spectrum Synthesis

view Abstract Citations (26) References (8) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Determination of Solar Abundances by a Method of Spectrum Synthesis Ross, John ; Aller, Lawrence Abstract A procedure is described for obtaining the solar abundance, A, of an element, or more accurately gf A (where g is the statistical weight of the lower level and f is the oscillator strength). Instead of using the equivalent width of a line, one employs the entire profile. If the line falls in a crowded region of the spectrum where blending is severe, one attempts to reproduce the observed intensity distribution, I~(O,j~), over the relevant wavelength region by including all relevant bound-bound transitions. The cal- culation has been programmed for an IBM 360/75 computer. We assumed that when the parameters of the lines contributing to this region are adjusted so that the computed Ix(O,~~) distribution matches the observed Ix(O,~~) distribution, the correct values of the parameter gfA have been obtained. The method is useful for those elements which are represented only by lines falling in crowded regions of the solar spectrum. The adjustable parameters are gfA and the damping constant, I'. Depending on the basic physical data and the number of perturbing lines in the region, the value of gfA may be established to within 0.1 in the logarithm to the base 10. The damping constant, however, might be in error by a factor of 2 Publication: The Astrophysical Journal Pub Date: July 1968 DOI: 10.1086/149653 Bibcode: 1968ApJ...153..235R full text sources ADS |

Solar abundance determination from ultraviolet emission lines

The intensities of far ultraviolet emission lines from the solar corona are analyzed to determine relative coronal abundances for oxygen, silicon, and iron. Dielectronic recombination is included in the formulation of ionization equilibrium. Observations of solar radio emission are used to obtain abundances relative to hydrogen. The absolute coronal abundances appear to be in agreement with their respective photospheric values. General properties of the structure of the chromosphere and corona are deduced from the analysis of observed emission in the ultraviolet and radio wavelength regions.

On the determination of the solar chemical composition from a study of the ultraviolet resonance lines

On the assumption that the ultraviolet resonance lines are formed by collisional excitation followed by direct radiative transition of a quantum which eventually escapes from the atmosphere, it is shown how the chemical composition may be found. These assumptions are discussed, as is the accuracy of the determinations. The effects of non-radial inhomogeneities are also discussed. Finally the question of the determination of the hydrogen abundance is raised, for which purpose the solar radio observations are used.The results of this analysis are compared with other solar abundance determinations.