Zirconium Abundances Research Articles

Abundances of Heavy Elements in the B8 Mn Star HD 110073

The synthesis of several spectral intervals in the optical range allows the determination of LTE abundances of strontium, yttrium, zirconium, barium, praseodymium, neodymium, platinum and mercury for this B8 Mn star. Compared to the solar abundances, strontium, yttrium, barium, praseodymium and mercury are found to be overabundant by factors of 2.5, 130, 10, 150 and 60,000. Only upper limits could be determined for zirconium and platinum. The lines of Nd iii are blended with lines of more abundant elements which precludes the determination of the abundance of neodymium. The abundance of manganese, derived from the Mn ii line at 3986.59 Å is about 100 times larger than in the Sun.

A newly discovered southern HgMn star: HD 4065A

Evidence is presented that HD 4065A is a newly discovered HgMn star. The Hg ii line at 3983.93 Å is present in two spectra acquired with the High Resolution Spectrograph mounted behind the South African Large Telescope and separated by about 2 months and 25 days. The lines on the second spectrum are redshifted reflecting the orbital motion of HD 4065A around the center of mass of a binary system. The far-ultraviolet spectrum, SWP 20399 collected with IUE, shows a strong resonance line of Ga ii usually conspicuous in the far-ultraviolet spectra of HgMn star. A first spectrum synthesis of the spectral range from 3900 up to 4000 Å yields estimates of the abundances of calcium (0.10 solar), zirconium (25 solar) and mercury (50,000 solar).

Abundance of zirconium in the globular cluster 47 Tucanae: a possible Zr–Na correlation?

We determined abundances of Na and Zr in the atmospheres of 237 RGB stars in Galactic globular cluster (GGC) 47 Tuc (NGC 104), with a primary objective of investigating possible differences between the abundances of Zr in the first generation (1P) and second generation (2P) stars. For the abundance analysis, we used archival UVES/GIRAFFE spectra obtained during three different observing programmes. Abundances were determined from two Na I and three Zr I lines, using 1D hydrostatic ATLAS9 model atmospheres. The target stars for the abundance analysis were limited to those with 4200 ≤ Teff ≤ 4800 K. This is the largest sample of GGC stars in which Na and Zr abundances have been studied so far. While our mean [Na/Fe] and [Zr/Fe] ratios agree well with those determined in the earlier studies, we find a weak but statistically significant correlation in the [Zr/Fe] – [Na/Fe] plane. A comparison of the mean [Zr/Fe] abundance ratios in the 1P and 2P stars suggests a small but statistically significant Zr over-abundance in the 2P stars, ∆[Zr/Fe]2P−1P ≈ +0.06 dex. Also, our analysis shows that stars enriched in both Zr and Na are more centrally concentrated. However, we find no correlation between their distance from the cluster centre and their full spatial velocity, as indicated by the velocity dispersions at different mean values of [Zr/Fe] and [Na/Fe]. While there may be some influence of CN line blends on the determined Zr abundances, it seems very unlikely that the detected Zr–Na correlation, for the slightly higher Zr abundances in the 2P stars, would be caused by the CN blending alone. The obtained results indicate that, in 47 Tuc, some amount of Zr should have been synthesised by the same polluters that enriched 2P stars with the light elements. While sizeable amounts of Zr may be synthesised by both AGB stars (M ~ 1.5–5 M⊙) and massive rotating stars (M ~ 12–25 M⊙, υrot > 150 km s−1), our data alone do not allow us to distinguish which of the two scenarios, or whether or not a combination of both, could have operated in this GGC.

Abundance of zirconium in the red giants of Galactic globular cluster 47 Tuc

Abundance of zirconium in the red giants of Galactic globular cluster 47 Tuc

Shear-Hosted Uranium Deposits: A Review

A group of uranium deposits is described that is hosted within polyphase shear zones. The group is economically significant, collectively containing over 500,000 tonnes of uranium and several examples have been or are being mined. Over a hundred individual deposits are known widely spread over many countries. It is proposed that this group be assigned to a new shear-hosted uranium deposit category. Uranium deposition was superimposed upon intense and extensive feldspathic alteration formed during ductile deformation. This intense alteration has led to the alternative albitite-type or metasomatite-type nomenclature. The evidence is clear that in most cases uranium mineralization postdates regionally extensive feldspar alteration and is associated with a range of alteration assemblages which overprint early albite or K-feldspar dominant alteration. Abundance of hydrothermal zirconium and phosphate minerals is a common characteristic of this group which implies high activity of F and P during mineralisation, but the source of hydrothermal fluids remains uncertain. Also uncertain is the geodynamic setting of uranium mineralisation which is a consequence of absolute mineralisation age being poorly defined. Data from three of the four major districts are suggestive that mineralisation was a consequence of fluid migration along shears during regional compression. This paper reviews key aspects of the group in a mineral systems context, focussing on the four major districts of Kropyvnytskyi (Ukraine), Lagoa Real (Brazil), Mount Isa (Australia) and the Central Mineral Belt (Canada).

Abundance of zirconium in the atmospheres of red giants in Galactic globular cluster 47 Tuc

AbstractWe determined zirconium abundance in the atmospheres of 327 red giant branch (RGB) stars in the globular cluster 47 Tuc. The 1D LTE abundances were obtained from the archival VLT GIRAFFE spectra, using 1D hydrostaticATLAS9 stellar model atmospheres and synthetic Zr I line profiles computed with theSYNTHE package. The average zirconium abundance determined in the sample of RGB stars, 〈[Zr/Fe]〉 = +0.38 ± 0.12, agrees well with zirconium abundances obtained at this metallicity in the Galactic field stars, as well as with those observed in other Galactic globular clusters.

Rubidium and zirconium abundances in massive Galactic asymptotic giant branch stars revisited

Luminous Galactic OH/IR stars have been identified as massive (>4-5 M_s) AGB stars experiencing HBB and Li production. Their Rb abundances and [Rb/Zr] ratios derived from hydrostatic model atmospheres, are significantly higher than predictions from AGB nucleosynthesis models, posing a problem to our understanding of AGB evolution and nucleosynthesis. We report new Rb and Zr abundances in the full sample of massive Galactic AGB stars, previously studied with hydrostatic models, by using more realistic extended model atmospheres. We use a modified version of the spectral synthesis code Turbospectrum and consider the presence of a circumstellar envelope and radial wind. The Rb and Zr abundances are determined from the 7800 A Rb I resonant line and the 6474 A ZrO bandhead, respectively, and we explore the sensitivity of the derived abundances to variations of the stellar (Teff) and wind (M_loss, beta and vexp) parameters in the extended models. The Rb and Zr abundances derived from the best spectral fits are compared with the most recent AGB nucleosynthesis theoretical models. The new Rb abundances are much lower (even 1-2 dex) than those derived with the hydrostatic models, while the Zr abundances are similar. The Rb I line profile and Rb abundance are very sensitive to the M_loss rate but much less sensitive to variations of the wind velocity-law and the vexp(OH). We confirm the earlier preliminary results based on a smaller sample of massive O-rich AGB stars, that the use of extended atmosphere models can solve the discrepancy between the AGB nucleosynthesis theoretical models and the observations of Galactic massive AGB stars. The Rb abundances, however, are still strongly dependent of the M_loss, which is unknown in these AGB stars. Accurate M_loss rates in these massive Galactic AGB stars are needed in order to break the models degeneracy and get reliable Rb abundances in these stars.

Hydraulic evolution of high-density turbidity currents from the Brushy Canyon Formation, Eddy County, New Mexico inferred by comparison to settling and sorting experiments

Hydraulic transformations in turbidity currents are commonly driven by or reflected in changes in suspended sediment concentrations, but changes preceding transformations can be difficult to diagnose because they do not produce qualitative changes in resultant deposits. This study integrates particle settling experiments and in situ detection of hydraulically contrasting particles in turbidites in order to infer changes in suspended sediment concentration during deposition of massive (Bouma Ta) sandstone divisions. Because grains of contrasting density are differentially sorted during hindered settling from dense suspensions, relative grading patterns can be used to estimate suspended sediment concentrations and interpret hydraulic evolution of the depositing turbidity currents.Differential settling of dense particles (aluminum ballotini) through suspensions of hydraulically coarser light particles (silica ballotini) with volumetric concentration, Cv, were studied in a thin vessel by using particle-image-velocimetry. At high Cv, aluminum particles were less retarded than co-sedimenting silica particles, and effectively settled as hydraulically coarser grains. This was because particles were entrained into clusters dominated by the settling behavior of the silica particles. Terminal settling velocities of both particles converged at Cv≥25%, and particle sorting was diminished.The results of settling experiments were applied to understand settling of analogous feldspar and zircon grains in natural turbidity flows. Distributions of light and heavy mineral grains in massive sandstones, Bouma Ta divisions, of turbidites from the Middle Permian Brushy Canyon Formation were observed in situ by X-ray fluorescence microscopy (μXRF). Hydraulic sorting of these grains resulted in characteristic patterns of zirconium abundance that decreased from base to top within Ta divisions. These profiles resulted from upward fining of zircon grains with respect to co-occurring feldspar grains. Although calculated settling velocity distributions for zircon grains in structureless sandstones were slower than those for feldspar grains at infinite dilution, calculated settling velocity distributions for zircon and feldspar grains in overlying black siltstone layers were identical. This evidence suggests that these sandstone divisions were deposited from hyperconcentrated suspensions where particle segregation was diminished and hydraulically fine grains were entrained with hydraulically coarse particles. Hydraulic fining of zircon grains during deposition implies that the suspended sediment concentration at the bases of turbidity currents increased even as the overall current evolved toward lower density as reflected by cessation of Ta deposition and by hydraulic equivalence of zircon and feldspar grains in overlying low-density turbiditic siltstones. This evolution likely resulted from volumetric collapse of the turbidity currents.

Determination of zirconium isotope composition and concentration for nuclear sample analysis using Thermal Ionization Mass Spectrometry

A new Thermal Ionization Mass Spectrometry (TIMS) analytical procedure was developed to measure with high accuracy the zirconium isotope abundance and concentration without molybdenum correction in nuclear samples. A zirconium selective separation using UTEVA column was used before the TIMS measurement in order to remove all possible isobaric interferences (Mo, Y, Nb and Ru) in the solution. The separated solution was then deposited onto a filament previously outgassed for 4h to reduce the molybdenum traces in the filament. Then, the filament was introduced into the TIMS source and was maintained for 4h at a current of 5A (ionization filament) and 1.2A (evaporation filament) in order to eliminate all molybdenum trace present in the filament and in the sample. This methodology allowed the zirconium isotope abundance determination without using the molybdenum interference correction equation. The analytical results obtained with a natural solution after separation is in good accordance with the reference values: bias lower than 0.16% for the 90Zr, 91Zr, 92Zr and 94Zr isotope abundance, and a bias of ∼0.8% for the minor isotope (96Zr) were observed. This zirconium abundance determination methodology was used on three nuclear samples. Then, the calibration of a 91Zr spike solution was performed by reverse isotope dilution using a SPEX standard zirconium solution. The zirconium concentration determination was then performed on the three nuclear samples by isotope dilution using the SPEX standard zirconium solution and the 91Zr spike solution. The final uncertainties were estimated to be lower than 1%.

Radioactive Clocks and Thermometer in S-type Stars

Direct probes of the temporal evolution of stars are rare. We derive the time spent by S-type stars since the onset of the first thermal pulse, from the 99 Tc – 99 Ru and 93 Zr – 93 Nb chronometers. Zirconium and niobium abundances constrain as well the nucleosynthesis temperature, supporting 13 C(α,n) 16 O as the s-process neutron source. Niobium abundances are used, for the first time, to efficiently separate stars with active nucleosynthesis from binary stars with fossil overabundances resulting from a previous mass transfer. The abundances of Tc, Nb, and Zr thus give access to the nucleosynthesis chronology and temperature, and provide a diagnostic of possible external pollution from a companion star.

Radial-velocity measurements of the pulsating zirconium star: LS IV−14°116*

The helium-rich hot subdwarf LS IV -14 116 shows remarkably high surface abundances of zirconium, yttrium, strontium, and germanium, indicative of strong chemical stratification in the photosphere. It also shows photometric behaviour indicative of non-radial g-mode pulsations, despite having surface properties inconsistent with any known pulsational instability zone. We have conducted a search for radial velocity variability. This has demonstrated that at least one photometric period is observable in several absorption lines as a radial velocity variation with a semi-amplitude in excess of 5 km s$^{-1}$. A correlation between line strength and pulsation amplitude provides evidence that the photosphere pulsates differentially. The ratio of light to velocity amplitude is too small to permit the largest amplitude oscillation to be radial.

The solar photospheric abundance of zirconium

AbstractZirconium (Zr), together with strontium and yttrium, is an important element in the understanding of the Galactic nucleosynthesis. In fact, the triad Sr‐Y‐Zr constitutes the first peak of s‐process elements. Despite its general relevance not many studies of the solar abundance of Zr were conducted. We derive the zirconium abundance in the solar photosphere with the same CO5BOLD hydrodynamical model of the solar atmosphere that we previously used to investigate the abundances of C‐N‐O. We review the zirconium lines available in the observed solar spectra and select a sample of lines to determine the zirconium abundance, considering lines of neutral and singly ionised zirconium. We apply different line profile fitting strategies for a reliable analysis of Zr lines that are blended by lines of other elements. The abundance obtained from lines of neutral zirconium is very uncertain because these lines are commonly blended and weak in the solar spectrum. However, we believe that some lines of ionised zirconium are reliable abundance indicators. Restricting the set to Zr II lines, from the CO5BOLD 3D model atmosphere we derive A (Zr) = 2.62 ± 0.06, where the quoted error is the RMS line‐to‐line scatter (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Formation of Zr I and II lines under non-LTE conditions of stellar atmospheres

The formation of Zr I and Zr II lines in stellar atmospheres under non-LTE conditions has been considered for the first time. A model zirconium atom has been composed using 148 Zr I levels, 772 Zr II levels, and the ground Zr III state. Non-LTE calculations have been performed for model atmospheres with T eff = 5500 and 6000 K, log g = 2.0 and 4.0, [M/H] = −3, −2, −1, 0. In the entire investigated range of parameters, the Zr I levels are shown to be underpopulated relative to their LTE populations in the line formation region. In contrast, the excited Zr II levels are overpopulated, while the ground state and lower excited levels of Zr II retain their LTE populations. Since the non-LTE effects cause the Zr I and Zr II spectral lines being investigated to weaken, the non-LTE corrections to the abundance derived from Zr I and Zr II lines are positive. For Zr II lines, they increase with decreasing metallicity and surface gravity up to 0.34 dex for the model with T eff = 5500, log g = 2.0, and [M/H] = −2. The non-LTE effects depend weakly on temperature. The non-LTE corrections for Zr I lines reach 0.33 dex for solar-metallicity models. Zr I and Zr II lines in the solar spectrum have been analyzed. The non-LTE zirconium abundances derived from lines in the two ionization stages are shown to agree between themselves within the error limits, while the LTE abundance difference is 0.28 dex. The zirconium abundance in the solar atmosphere (averaged over Zr I and Zr II lines) is log ɛZr,⊙ = 2.63 ± 0.07.

Lithium and zirconium abundances in massive Galactic O-rich AGB stars

Lithium and zirconium abundances (the latter taken as representative for s-process enrichment) are determined for a large sample of massive Galactic O-rich AGB stars, for which high resolution optical spectroscopy has been obtained (R=40,000-50,000). This is done by computing synthetic spectra based on classical hydrostatic model atmospheres for cool stars using extensive line lists. The results obtained are discussed in the framework of hot bottom burning (HBB) and nucleosynthesis models. The complete sample is studied attending to various observational properties such as the position of the stars in the IRAS two-colour diagram ([12]-[25] vs [25]-[60]), Galactic distribution, expansion velocity (derived from the OH maser emission) and period of variability (when available). We conclude that a considerable fraction of the sources observed are actually massive AGB stars (M > 3-4 solar masses) experiencing HBB, as deduced from the strong Li overabundances found. A comparison of our results with similar studies carried out in the past for the Magellanic Clouds (MCs) reveals that, in contrast to MC AGB stars, our Galactic sample does not show any indication of s-process element enrichment. The differences observed are explained as a consequence of metallicity effects. Finally, we discuss the results obtained in the framework of stellar evolution by comparing our results with the data available in the literature for Galactic post-AGB stars and PNe.

New and improved experimental oscillator strengths in Zr II and the solar abundance of zirconium

Using the Fourier Transform Spectrometer at Lund Observatory, intensity calibrated spectra of singly ionized zirconium have been recorded and analyzed. Oscillator strengths for 263 Zr II spectral lines in the region 2500-5400 angstrom have been derived by combining new experimental branching fractions with previously measured radiative lifetimes. The transitions combine 34 odd parity levels with 29 low metastable levels between 0 and 2.4 eV. The experimental branching fractions have been compared with theoretical values and the oscillator strengths with previously published data when available. The oscillator strengths have been employed to derive the solar photospheric Zr abundance based on both 1D and 3D model atmospheres. Based on the seven best and least perturbed Zr II lines in the solar disk-center spectrum, we determine the solar Zr abundance to log epsilon(Zr) = 2.58 +/- 0.02 when using a 3D hydrodynamical solar model atmosphere. The new value is in excellent agreement with the meteoritic Zr abundance. (Less)

Hubble Space TelescopeObservations of Neutron‐Capture Elements in Very Metal Poor Stars

Using the Goddard High-Resolution Spectrograph (GHRS) of the Hubble Space Telescope (HST) we have detected the neutron-capture elements osmium, platinum, and lead in the very metal poor ([Fe/H] -2.8) Galactic halo star HD 115444. This star joins the metal-poor giant HD 126238 ([Fe/H] -1.7) as the second Galactic halo star for which neutron-capture elements have been detected. We have also determined upper limits on these same elements for the neutron-capture deficient star HD 122563 ([Fe/H] - 2.7). We have identified zirconium and germanium features in the HST spectra of all three stars; this marks the initial identification of the latter element in halo stars. We compare and contrast the spectra and abundances of the neutron-capture elements in these three stars. Combining the new HST observations of the third neutron-capture peak elements of HD 115444 with ground-based data, we find the stellar abundance distribution, over a wider atomic number range than ever before possible, is consistent with the solar system r-process abundance curve. Comparison of this star to the more metal-rich HD 126238 finds that the ratio of the third-peak element abundances to that of the pure r-process element europium is the same in both stars. Earlier ground-based studies have found that abundances of the lighter elements, such as barium and europium, in HD 115444 exceed those of HD 122563 by ~0.7 dex. Our osmium, platinum, and lead upper limits show a similar difference and are not inconsistent with either the scaled solar r-process or the solar total distribution. Thus, the second and third neutron-capture peak element (Z ≥ 56) abundances in all three stars are consistent with scaled solar system r-process abundances. However, the zirconium abundance is approximately the same in HD 122563 and HD 115444, so this element (near the first neutron-capture peak) is overabundant (somewhat) in HD 122563 and (slightly) in HD 115444 with respect to the solar r-process abundances. Germanium (synthesized in approximately equal amounts by the r- and the s-process in solar material) is underabundant in all three stars, but does seem to scale with metallicity—it is identical in HD 115444 and HD 126238, but significantly greater in the higher metallicity HD 126238. These new results support previous observations that demonstrate the operation of the r-process, including the synthesis of the heaviest such elements, early in the history of the Galaxy. Implications of these results for early Galactic chemical evolution are discussed.

Zirconium abundance in granulite-facies minerals, with implications for zircon geochronology in high-grade rocks

Zircon growth in high-grade metamorphic rocks may be triggered by net transfer reactions involving the breakdown of a phase bearing zirconium (Zr). We have measured the concentration of Zr in the major minerals in granulite-facies rocks of differing bulk composition. Both garnet and hornblende contain tens of parts per million Zr, and no other major phase contains significant Zr. Simple calculations show that reaction of either garnet or hornblende to form non–Zr-bearing phases will release sufficient Zr to account for at least some new zircon growth. U-Pb ages from new zircon, grown as a result of either hornblende or garnet breakdown, are not expected to record the time of peak metamorphism, but rather will record the time of particular metamorphic reactions, allowing direct correlation of zircon ages with petrologically derived pressure-temperature-time paths. This approach offers the potential for more rigorous interpretation of the metamorphic significance of zircon ages than has previously been possible.

A simple method of accounting for correlation effects in electron transitions and its application in finding oscillator strengths and the solar abundance of zirconium

A simple method of accounting for correlation effects in complex atoms and ions, having several open electronic shells, is described. It is based on the use of the so-called transformed radial orbitals to describe the admixed electronic configurations in the framework of the superposition-of-configurations method. The method has been applied to calculate the energy spectra and oscillator strengths of electric dipole transitions in neutral and singly ionized zirconium. On the basis of new values of oscillator strengths, the photospheric abundance of zirconium is found to be Azr= log (Nzr/NH) + 12.00 = 2.60 ±0.06 and, being in close agreement with the meteoritic abundance, illustrates the reasonable accuracy of the proposed method.

Disruption of the Mauna Loa Magma System by the 1868 Hawaiian Earthquake: Geochemical Evidence

To test whether a catastrophic earthquake could affect an active magma system, mean abundances (adjusted for "olivine control") of titanium, potassium, phosphorus, strontium, zirconium, and niobium of historic lavas erupted from Mauna Loa Volcano, Hawaii, after 1868 were analyzed and were found to decrease sharply relative to lavas erupted before 1868. This abrupt change in lava chemistry, accompanied by a halved lava-production rate for Mauna Loa after 1877, is interpreted to reflect the disruptive effects of a magnitude 7.5 earthquake in 1868. This interpretation represents a documentable case of changes in magmatic chemical variations initiated or accelerated by a major tectonic event.

Relative isotopic abundances of zirconium in R Cygni and V CANCRI

view Abstract Citations (14) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Relative isotopic abundances of zirconium in R Cygni and V Cancri. Zook, A. C. Abstract The relative abundances of the isotopes of Zr in the S stars R Cyg and V Cnc are calculated by determining isotopic splitting at the head of the 1Pi - 1Sigma (0, 1) band of ZrO in spectra obtained at resolution 30 pm on hypersensitized 127-O4 plates with a Varo tube on the 51-cm camera at the Coude focus of the 3-m telescope at Lick Observatory. The data reduction techniques and the fit to the model synthetic spectra of Kurucz (1970) are described, and the ratio (Zr-90):(Zr-91):(Zr-92):(Zr-93):(Zr-94):(Zr-96) is given as 47:10:17:6:20:00 percent. The presence of the long-lived unstable isotope Zr-93 is interpreted as evidence for recent nucleosynthesis, and the abundances found are shown to be consistent with s-process nucleosynthesis. Publication: The Astrophysical Journal Pub Date: February 1985 DOI: 10.1086/162895 Bibcode: 1985ApJ...289..356Z Keywords: S Stars; Stellar Composition; Zirconium Isotopes; Abundance; Cygnus Constellation; Nuclear Fusion; Spectrum Analysis; Stellar Spectra; Astrophysics full text sources ADS | data products SIMBAD (2)