Yttrium abundance in the sun.
Solar abundance of Y derived from Y II lines by computing transition probabilities and oscillator strength involving several configurations
Aller, L. H.↗
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Recurrent 3he-Rich Solar Energetic Particle Injections Observed By Solar Orbiter at ∼0.5 Au
We report Solar Orbiter observations of six recurrent solar energetic particle injections in 2022 March 3−6 at ∼0.5 au. All but one were associated with jets emanating from a plage near a large sunspot in active region 12 957. We saw large jets in injections with high 3He and Fe enrichments and minor jets in injections with no or lower enrichments. Furthermore, the event with the highest enrichment showed a more compact configuration of the underlying photospheric magnetic field. The higher fluences as well as harder spectra were seen in the event with a simultaneous jet and wider eruption. However, in this case, the energy buildup time in the source might be required to produce such spectra. Extreme-ultraviolet images from Solar Orbiter revealed a number of intersecting loops at the base of jets not seen from 1 au that might be a precondition for the recurrent events.
Sun: particle emission↗
The abundance of iron in the sun and the meteorites.
Fe abundance in sun and meteorites, noting discrepancies for photosphere and corona and probable causes
Cameron, A. G. W.↗
Helium abundance of the sun.
Critical review of the four methods that have been used to estimate the ratio of helium to hydrogen in the sun - the solar neutrino flux, spectral intensity of helium lines in prominences and the chromosphere, elemental abundance of solar cosmic rays, and variations of solar wind He/H. At present the measured value for the neutrino flux cannot be explained by any of the theoretical models of the sun, and thus the neutrino measurements cannot yield an estimate of He/H. Helium line intensity measurements give the most accurate values for He/H now available - i.e., 5 to 8% helium by number. However, these results refer to the chromosphere and prominences only, and questions of spatial and temporal variations of the observed quantities and of the inferred helium abundances have not yet been dealt with adequately.
Hirshberg, J.↗
Element Abundance Ratios in the Quiet Sun Transition Region
Element abundance ratios of magnesium to neon (Mg/Ne) and neon to oxygen (Ne/O) in the transition region of the quiet Sun have been derived by re-assessing previously published data from the Coronal Diagnostic Spectrometer on board the Solar and Heliospheric Observatory in the light of new atomic data. The quiet Sun Mg/Ne ratio is important for assessing the effect of magnetic activity on the mechanism of the first ionization potential (FIP) effect, while the Ne/O ratio can be used to infer the solar photospheric abundance of neon, which cannot be measured directly. The average Mg/Ne ratio is found to be 0.52+/-0.11, which applies over the temperature region 0.2-0.7MK, and is consistent with the earlier study. The Ne/O ratio is, however, about 40%larger, taking the value 0.24+/-0.05 that applies to the temperature range 0.08-0.40MK. The increase is mostly due to changes in ionization and recombination rates that affect the equilibrium ionization balance. If the Ne/O ratio is interpreted as reflecting the photospheric ratio, then the photospheric neon abundance is 8.08+/-0.09 or 8.15+/-0.10 (on a logarithmic scale for which hydrogen is 12), according to whether the oxygen abundances of M.Asplund et al. or E.Caffau et al. are used. The updated photospheric neon abundance implies a Mg/Ne FIP bias for the quiet Sun of 1.6+/-0.6.
transition region↗
On krypton isotopic abundances in the sun and in the solar wind
The Kr isotopic systematics in the meteorite Pesyanoe which is known to contain solar-type gases, are reported. Discrepancies in the isotopic data of fractions released at stepwise increasing temperatures cannot be reconciled with spallation Kr components, although spallation effects are significant. Fractionation mechanisms on the parent body and in the solar wind source region are considered and the implications for solar abundances discussed.
Marti, K.↗
Element Abundance Variations in the Sun and Heliosphere; Meeting E2.1 of the COSPAR Scientific Assembly, 30th, Hamburg, Germany, July 11-21, 1994
A conference on advances in space research related to element abundance variations in the sun and heliosphere produced related papers. The areas addressed in these papers included abundance variations in the solar wind, element abundances in the solar corona, iron abundance in the solar photosphere and corona, iron and calcium abundances during solar flares, helium abundance in the solar corona, element abundances in the solar interior, energetic particle abundances, fluxes of low-energy ions, and solar models. The primary source of data was space-based measurements.
Bely-Dubau, F.↗
Radiative lifetimes for some resonance transitions of Fe I and Fe II in the region between 2300 A and 3050 A, and the application to iron abundance determinations in the sun and in the QSO PHL 938.
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Assousa, G. E.↗
He-3 and other lunar volatiles
Constraints are considered and estimates are given for the abundances of He-3, other noble gases, and chemically reactive volatiles (e.g., H, C, N, S, F, Cl) on the Moon. For the case of surface inventories, solar wind particles implanted into grains on the surface of the Moon provide an accessible, though not necessarily abundant, source of H, C, N and the noble gases. Solar wind implanted species are concentrated in the infest grain sized, and are only found in the upper few meters of the regolith, where there are grains that have been directly exposed to the Sun. Elemental abundances in surface soils are typically 10s of mg/g, and vary according to the exposure history of the soil. The abundance of the rare, but possibly economically important, isotope He-3 is typically a few mg/g. The largest uncertainty in estimates of the total lunar abundance of solar wind implanted species comes from the lack of knowledge of their distribution with depth below the upper meter or two. For the case of bulk inventories, constraints resulting from lunar sample analyses and from physical chemical models of volatile behavior during the hypothesized giant impact origin of the Moon is used to give estimated abundances.
Fegley, B., Jr.↗
The γ -process nucleosynthesis in core-collapse supernovae
The γ-process nucleosynthesis in core-collapse supernovae is generally accepted as a feasible process for the synthesis of neutron-deficient isotopes beyond iron. However, crucial discrepancies between theory and observations still exist: the average yields of γ-process nucleosynthesis from massive stars are still insufficient to reproduce the solar distribution in galactic chemical evolution calculations, and the yields of the Mo and Ru isotopes are a factor of ten lower than the yields of the other γ-process nuclei. We investigate the γ-process in five sets of core-collapse supernova models published in the literature with initial masses of 15, 20, and 25 M ⊙ at solar metallicity. We compared the γ-process overproduction factors from the different models. To highlight the possible effect of nuclear physics input, we also considered 23 ratios of two isotopes close to each other in mass relative to their solar values. Further, we investigated the contribution of C–O shell mergers in the supernova progenitors as an additional site of the γ-process. Our analysis shows that a large scatter among the different models exists for both the γ-process integrated yields and the isotopic ratios. We find only ten ratios that agree with their solar values, all the others differ by at least a factor of three from the solar values in all the considered sets of models. The γ-process within C–O shell mergers mostly influences the isotopic ratios that involve intermediate and heavy proton-rich isotopes with A > 100. We conclude that there are large discrepancies both among the different data sets and between the model predictions and the solar abundance distribution. More calculations are needed; particularly updating the nuclear network, because the majority of the models considered in this work do not use the latest reaction rates for the γ-process nucleosynthesis. Moreover, the role of C–O shell mergers requires further investigation.
79 ASTRONOMY AND ASTROPHYSICS↗
Nanoflares, Spicules, and Other Small-Scale Dynamic Phenomena on the Sun
There is abundant evidence of highly dynamic phenomena occurring on very small scales in the solar atmosphere. For example, the observed pr operties of many coronal loops can only be explained if the loops are bundles of unresolved strands that are heated impulsively by nanoflares. Type II spicules recently discovered by Hinode are an example of small-scale impulsive events occurring in the chromosphere. The exist ence of these and other small-scale phenomena is not surprising given the highly structured nature of the magnetic field that is revealed by photospheric observations. Dynamic phenomena also occur on much lar ger scales, including coronal jets, flares, and CMEs. It is tempting to suggest that these different phenomena are all closely related and represent a continuous distribution of sizes and energies. However, this is a dangerous over simplification in my opinion. While it is tru e that the phenomena all involve "magnetic reconnection" (the changin g of field line connectivity) in some form, how this occurs depends s trongly on the magnetic geometry. A nanoflare resulting from the interaction of tangled magnetic strands within a confined coronal loop is much different from a major flare occurring at the current sheet form ed when a CME rips open an active region. I will review the evidence for ubiquitous small-scale dynamic phenomena on the Sun and discuss wh y different phenomena are not all fundamentally the same.
Klimchuk, James↗
The thermal structure of the sun
Thermal structure, element abundances, central density and temperature, and energy transfer in sun
Schocken, K.↗
A new solar carbon abundance based on non-LTE CN molecular spectra
A detailed non-LTE analysis of solar CN spectra strongly suggest a revised carbon abundance for the sun. We recommend a value of log carbon abundance = 8.35 plus or minus 0.15 which is significantly lower than the presently accepted value of log carbon abundance = 8.55. This revision may have important consequences in astrophysics.
Mount, G. H.↗
Neutron propagation and 2.2 MeV gamma-ray line production in the solar atmosphere
The 2.2 MeV gamma ray line intensity from the sun was calculated using a Monte Carlo method for neutron propagation in the solar atmosphere. Detailed results are provided on the total gamma ray yield per neutron and on the time profile of the 2.2 MeV line from an instantaneous and monoenergetic neutron source. The parameters which have the most significant effects on the line intensity are the energies of the neutrons, the position of the neutron source on the sun, and the abundance of He-3 in the photosphere. For an isotropic neutron source which is not too close to the limb of the sun, the gamma ray yield is between about 0.02 to 0.2 photons per neutron, provided that the neutron energies are in the range 1 to 100 MeV and the ratio He-3/H is less than about .00005.
Wang, H. T.↗
Neutron propagation and 2.2 MeV gamma-ray line production in the solar atmosphere
Calculation of the 2.2-MeV gamma-ray line intensity from the sun using a Monte Carlo method for neutron propagation in the solar atmosphere. Detailed results are provided concerning the total gamma-ray yield per neutron and the time profile of the 2.2-MeV line from an instantaneous and monoenergetic neutron source. The parameters which have the most significant effects on the line intensity are the energies of the neutrons, the position of the neutron source on the sun, and the abundance of He-3 in the photosphere. For an isotropic neutron source which is not too close to the limb of the sun, the gamma-ray yield is between about 0.02 to 0.2 photons per neutron, provided that the neutron energies are in the range from 1 to 100 MeV and the ratio He-3/H is less than about .00005.
Wang, H. T.↗
The evolution of the lithium abundances of solar-type stars. II - The Ursa Major Group
We draw upon a recent study of the membership of the Ursa Major Group (UMaG) to examine lithium among 0.3 Gyr old solar-type stars. For most G and K dwarfs, Li confirms the conclusions about membership in UMaG reached on the basis of kinematics and chromospheric activity. G and K dwarfs in UMaG have less Li than comparable stars in the Pleiades. This indicates that G and K dwarfs undergo Li depletion while they are on the main sequence, in addition to any pre-main-sequence depletion they may have experienced. Moreover, the Li abundances of the Pleiades K dwarfs cannot be attributed to main-sequence depletion alone, demonstrating that pre-main-sequence depletion of Li also takes place. The sun's Li abundance implies that the main-sequence mechanism becomes less effective with age. The hottest stars in UMaG have Li abundances like those of hot stars in the Pleiades and Hyades and in T Tauris, and the two genuine UMaG members with temperatures near Boesgaard's Li chasm have Li abundances consistent with that chasm developing fully by 0.3 Gyr for stars with UMaG's metallicity. We see differences in the abundance of Li between UMaG members of the same spectral types, indicating that a real spread in the lithium abundance exists within this group.
Soderblom, David R.↗
Silicon to iron abundances in solar cosmic rays and in the sun
Differential spectra of even charged nuclei between Si and Fe in the August 4, 1972 event were made in the energy region of 10 to 40 MeV/n-1 using rocket borne plastic detectors. The resulting relative abundances of elements and low energy enhancements are obtained and compared with spectroscopically determined photospheric abundances. The implications of the relative abundances on the acceleration mechanisms is discussed.
Vahia, M. N.↗