Distribution Of Heavy Elements Research Articles

The Electron Temperature Gradient in the Galactic Disk

We derive the electron temperature gradient in the Galactic disk using a sample of HII regions that spans Galactocentric distances 0--17 kpc. The electron temperature was calculated using high precision radio recombination line and continuum observations for more than 100 HII regions. Nebular Galactocentric distances were calculated in a consistent manner using the radial velocities measured by our radio recombination line survey. The large number of nebulae widely distributed over the Galactic disk together with the uniformity of our data provide a secure estimate of the present electron temperature gradient in the Milky Way. Because metals are the main coolants in the photoionized gas, the electron temperature along the Galactic disk should be directly related to the distribution of heavy elements in the Milky Way. Our best estimate of the electron temperature gradient is derived from a sample of 76 sources for which we have the highest quality data. The present gradient in electron temperature has a minimum at the Galactic Center and rises at a rate of 287 +/- 46 K/kpc. There are no significant variations in the value of the gradient as a function of Galactocentric radius or azimuth. The scatter we find in the HII region electron temperatures at a given Galactocentric radius is not due to observational error, but rather to intrinsic fluctuations in these temperatures which are almost certainly due to fluctuations in the nebular heavy element abundances. Comparing the HII region gradient with the much steeper gradient found for planetary nebulae suggests that the electron temperature gradient evolves with time, becoming flatter as a consequence of the chemical evolution of the Milky Way's disk.

Chandra and XMM Observations of Galaxy Groups: The Influence of Central AGN at the Low End of the Cluster Mass Scale

AbstractChandra and XMM, offering between them high angular resolution, substantial collecting area, and spatially-resolved spectroscopy at good spectral resolution, have given us the means to discover hitherto unanticipated phenomena, in groups as in clusters, and to explore a new set of issues that bring us closer to understanding the formation and evolution of groups and their constituent galaxies: the distribution of heavy elements, the presence of X-ray cavities and their relation to radio observations, the nature of cooling cores, and X-ray signatures of recent galaxy interactions. We here show Chandra and XMM data selected to illustrate recent results regarding some of these themes.

Spiral stellar density waves and the flattening of abundance gradients in the warm gas component of spiral galaxies

Motivated by recent observations of plateaus and minima in the radial abundance distributions of heavy elements in the Milky Way and some other spiral galaxies, we propose a dynamical mechanism for the formation of such features around corotation. Our numerical simulations show that the non-axisymmetric gravitational field of spiral density waves generates cyclone and anticylone gas flows in the vicinity of corotation. The anticyclones flatten the pre-existing negative abundance gradients by exporting many more atoms of heavy elements outside corotation than importing inside it. This process is very efficient and forms plateaus of several kiloparsec in size around corotation after two revolution periods of a galaxy. The strength of anticyclones and, consequently, the sizes of plateaus depend on the pitch angle of spiral arms and are expected to increase along the Hubble sequence.

Heavy metal and trace element distributions in groundwater in natural slopes and highly urbanized spaces in Mid-Levels area, Hong Kong

The lower slope of the Mid-Levels area, Hong Kong, is one the most heavily urbanized coastal areas in the world. A comprehensive groundwater heavy metal and trace element study was conducted in the Mid-Levels area aiming to investigate the impacts of urbanization on the aqueous distributions of these chemicals. Groundwater samples were collected in the upper natural slopes and the lower highly urbanized spaces in the area in different seasons, and analyzed for heavy metal and trace element contents. Compared to the results from natural slopes, groundwater samples in the developed spaces did not exhibit significant elevated levels in Zn, Cr, Cu, Cd, Pb and Fe, which are commonly found in stormwater. On the other hand, the samples were found to have elevated contents in Mn, V, Co and Mo, minor stormwater-related heavy metals, suggesting that stormwater drains may be leaking to some extent. However, the results suggested that the vadose zone could remove many of the heavy metals, protecting groundwater from being contaminated seriously. Statistical analysis suggested that a certain amount of Mn and Co was likely to be re-mobilized from natural soils due to the changes in local redox conditions, while Mn, V, Co and Mo may also be derived from steel corrosion as a result of prolonged submergence. Besides, the average B concentration in the developed spaces was about eight times higher than that in the natural slopes, indicating the presence of sewage. The mean Se concentration in the developed spaces was about 100 times higher than that in the natural slopes. About 40% of samples in the developed spaces contained Se level higher than the drinking water guideline value proposed by the World Health Organization. Se was found to be positively correlated with B and SO 4 2− ( R=0.534 and 0.631, respectively), suggesting that Se may also be related to leakage from sewage pipes. Part of the Sr may come from leakage of flushing water and/or sewage as Sr was strongly correlated with Cl − ( R=0.929). According to the measured results, deep groundwater samples collected from piezometers (>10 m in depth) in the urbanized spaces appeared to be virtually free from any anthropogenic contaminations. This study may shed important light on the identification and evaluation of leakage from service pipes in a particular area based on aqueous distributions of heavy metals and trace elements. Moreover, the above findings may be instructional for other coastal cities with a similar level of urban development to understand the potential threats to their groundwater resources.

Mixed crystalline precursor complexes of the type [Ba(C 2H 6O 2) 4][Ti 1− xSn x(C 2H 4O 2) 3] ( [formula omitted]) for BaTi 1− xSn xO 3 ceramics: Synthesis, structure and calcination

The synthesis of [Ba(C 2H 6O 2) 4][Ti(C 2H 4O 2) 3], its crystal structure and thermal decomposition is described. This 1,2-ethanediolato complex forms with the isotypic tin compound [Ba(C 2H 6O 2) 4][Sn(C 2H 4O 2) 3] solid solutions [Ba(C 2H 6O 2) 4][Ti 1− x Sn x (C 2H 4O 2) 3] in any ratio. Corresponding mixed crystalline samples are suitable precursor complexes for BaTi 1− x Sn x O 3 ceramics with the feature of a heavy element distribution in molecular scale matching the element distribution of the final ceramics.

V453 Oph: a s-process enriched, but carbon-deficient RV Tauri star of low intrinsic metallicity

This paper reports the detection of a heavy element enriched RV Tauri variable with an abundance pattern that differs significantly from a standard s-process enriched object: V453 Oph. Based on optical high-resolution spectra, we determined that this object of low intrinsic metallicity ([Fe/H] = -2.2) has a mild, but significant, enrichment ([s/Fe] ∼ +0.5) of heavy elements for which the distribution points to slow neutron capture nucleosynthesis. This result is strengthened by a comparative analysis to the non-enriched RV Tauri star DS Aqr ([s/Fe] = 0.0). Although V453 Oph is the first RV Tauri star showing a strong s-process signature, it is not accompanied by C enhancement, challenging our current nucleosynthetic models of post-AGB stars that predict a simultaneous enrichment in C and s-process elements. The low N abundance excludes CN cycling as being responsible for the low C abundance. We explore three different scenarios to explain the heavy element distribution in this evolved object: an enrichment of the parental cloud, an accretion scenario in which the chemical patterns were acquired by mass transfer in a binary system and an intrinsic enrichment by dredge-up.

Supporting the Josephson Interpretation of Low Energy Nuclear Reactions and Stabilization of Nuclear Waste

Brian Josephson appealed at the meeting of the Nobel Laureates July 2004 against the ignorance of physicist to the phenomenon of cold fusion. Though there are good reasons against many publications on this topic but not for all what was reported. It seems to be indicated to summarize the following serious, reproducible and confirmed observations on the reactions of protons or deuterons incorporated in host metals such as palladium, nickel and other metals. We underline the confusing discovery by Cockroft and Oliphant with the anomalous low energy for nuclear reactions which was hundred times lower than in the usual cases when smashing nuclei against their Coulomb potential. A similar unexpected result was that of Otto Hahn’s-the chemist!-Discovery of fission that had changed the world. A significant result of cold fusion was seen in gaseous atmosphere or discharges between palladium targets, rather significant and fully reproducible, e.g. From the “life after death” heat production of such high values per host atom that only nuclear reactions can be involved. This supports the earlier evaluation of neutron generation in fully reversible experiments with gas discharges hinting that a reasonable screening effect-preferably in the swimming electron layer-may lead to reactions at nuclear distances d of picometers with reaction probability times U off about mega seconds similar to the K-shell capture radioactivity. Further electrolytic experiments led to Low Energy Nuclear Reactions (LENR) where the involvement of pollution could be excluded from the generation of very seldom rare earth elements. A basically new theory for DD cross sections is used to confirm the picometer-mega second reactions of cold fusion. Other theoretical aspects are given from measured heavy element distributions similar to the standard abundance distribution, SAD, in the Universe with consequences on endothermic heavy nucleus generation, magic numbers and to quark-gluon plasmas. One application may be the elimination of long lived nuclear waste by transmutation into stable nuclei.

PIXE determination of element distribution in Fomes fomentarius

AbstractThe element distribution in the fruit body of a wood‐rotting fungus was studied. Samples of Fomes fomentarius were collected in nature, together with bark and a piece of substrate wood. For PIXE analysis, slices were cut from the fruit body. The slices were analyzed using a proton beam at many points from the fruit body surface to the core, or across the fruit–substrate interface. The analysis was performed with an external proton beam in a low‐pressure nitrogen atmosphere; 9–12 elements heavier than silicon were found above the limit of quantitation. Manganese showed interesting systematic behavior. The suitability and usefulness of PIXE analysis for studying the distribution of heavy elements in fruit bodies of wood‐rotting fungi are discussed. Copyright © 2005 John Wiley & Sons, Ltd.

Is HE 0107−5240 A Primordial Star? The Characteristics of Extremely Metal‐Poor Carbon‐Rich Stars

We discuss the origin of HE 0107-5240, which, with a metallicity of [Fe/H] = -5.3, is the most iron-poor star yet observed. Its discovery has an important bearing on the question of the observability of first-generation stars in our universe. In common with other stars of very small metallicity (-4 [Fe/H] -2.5), HE 0107-5240 shows a peculiar abundance pattern, including large enhancements of C, N, and O, and a more modest enhancement of Na. The observed abundance pattern can be explained by nucleosynthesis and mass transfer in a first-generation binary star, which, after birth, accretes matter from a primordial cloud mixed with the ejectum of a supernova. We elaborate the binary scenario on the basis of our current understanding of the evolution and nucleosynthesis of extremely metal-poor, low-mass model stars and discuss the possibility of discriminating this scenario from others. In our picture, iron-peak elements arise in surface layers of the component stars by accretion of gas from the polluted primordial cloud, pollution occurring after the birth of the binary. To explain the observed C, N, O, and Na enhancements, as well as the 12C/ 13C ratio, we suppose that the currently observed star, once the secondary in a binary, accreted matter from a chemically evolved companion, which is now a white dwarf. To estimate the abundances in the matter transferred in the binary, we rely on the results of computations of model stars constructed with up-to-date input physics. Nucleosynthesis in a helium-flash-driven convective zone into which hydrogen has been injected is followed, allowing us to explain the origin in the primary of the observed O and Na enrichments and to discuss the abundances of s-process elements. From the observed abundances, we conclude that HE 0107-5240 has evolved from a wide binary (of initial separation ~20 AU) with a primary of initial mass in the range 1.2-3 M☉. On the assumption that the system now consists of a white dwarf and a red giant, the present binary separation and period are estimated at 34 AU and a period of 150 yr, respectively. We also conclude that the abundance distribution of heavy s-process elements may hold the key to a satisfactory understanding of the origin of HE 0107-5240. An enhancement of [Pb/Fe] 1-2 should be observed if HE 0107-5240 is a second-generation star, formed from gas already polluted with iron-group elements. If the enhancement of main-line s-process elements is not detected, HE 0107-5240 may be a first-generation secondary in a binary system with a primary of mass less than 2.5 M☉, born from gas of primordial composition, produced in the big bang, and subsequently subjected to surface pollution by accretion of gas from the parent cloud metal-enriched by mixing with the ejectum of a supernova.

Heliospheric filtration of interstellar heavy atoms: Sensitivity to hydrogen background

Heavy elements including He, C, N, O, Ne, and Ar are present in the interstellar medium surrounding the heliosphere. They form the most important source for heavy pickup ions and anomalous cosmic rays in the heliosphere. Kinetic numerical models are used to study the entrance and the heliospheric distribution of neutrals and singly charged ions of these six heavy element species as they interact through charge exchange with the neutral and ionized hydrogen of the heliosphere. Since the interstellar hydrogen parameters are not known precisely, three different representative hydrogen heliospheric models are used to study the heavy element distribution, and the sensitivity of key results, including filtration ratios of heavy elements and increased heavy neutral densities (walls), to the different hydrogen backgrounds is established. The key neutral heavy element results are largely insensitive to the specifics of the hydrogen background. The location and extent of neutral element features depends sensitively on the hydrogen background, as do all the heavy ion results.

Using X-ray absorption near edge structure (XANES) spectroscopy to determine selenium oxidation states in animal mineral supplements and feeds

Synchrotron-based X-ray absorption near edge structure (XANES) spectroscopy is a relatively new technique within the life sciences. XANES has been utilized to identify the location, oxidation state and spatial distribution of heavy metal elements in plants , neurons, blood and DNA, but has not been widely used in the animal sciences. Selenium content in animal feeds is monitored, as both selenium deficiencies and toxicities are associated with physiological disorders. Selenium is available as an animal feed in both inorganic and organic states. The bioavailability of selenium species has been tested in numerous animal trials; however, a simple, non-destructive test for selenium speciation is not available. The objective of this study was to determine whether XANES spectroscopy could be used to determine the selenium oxidation state found in various commercial animal feed products. A comparison of absorption spectra indicated that the animal mineral supplements contained an organoselenium or selenite. The processed animal feeds had a spectral profile similar to that of elemental selenium. Further experiments are necessary to determine the implication of selenium speciation on animal physiology. Key words: Selenium speciation, mineral supplements, ruminants, non-ruminants, synchrotron, XANES, X-ray

Implications of the central metal abundance peak in cooling core clusters of galaxies

Recent XMM-Newton observations of clusters of galaxies have provided detailed information on the distribution of heavy elements in the central regions of clusters with cooling cores providing strong evidence that most of these metals come from recent SN type Ia. In this paper we compile information on the cumulative mass profiles of iron, the most important metallicity tracer. We find that long enrichment times (≥5 Gyr) are necessary to produce the central abundance peaks. Classical cooling flows, a strongly convective intracluster medium, and a complete metal mixing by cluster mergers would destroy the observed abundance peaks too rapidly. Thus the observations set strong constraints on cluster evolution models requiring that the cooling cores in clusters are preserved over very long times. We further conclude from the observations that the innermost part of the intracluster medium is most probably dominated by gas originating predominantly from stellar mass loss of the cD galaxy.

Corotation, Stellar Wandering, and Fine Structure of the Galactic Abundance Pattern

We consider the effects of the corotation resonance of the Galactic spiral structure on the stellar orbits. It is shown that because of resonant interaction with the spiral gravitation field, stars can wander in the radial direction over a large part of the Galactic disk, moving over distances ~2-3 kpc in a short time, on the order of 1 billion years or even much less. This mechanism of radial stellar wandering is much faster than other stellar diffusion mechanisms that have been suggested in the literature. Corotation resonance also influences the Galactic distribution of heavy elements that are derived from old stellar-like objects. If at the initial time there is a simple linear distribution of metallicity in the disk, this is broken in ~3 billion years. In the framework of the model for the spiral density wave pattern with the corotation resonance close to the solar position (supposed to be 8.5 kpc from the center), the bimodal abundance pattern with a gradient in the inner part of the Galaxy (R ≤ 7.5 kpc) and a plateau for R between ~7.5 and about 10-11 kpc forms under the influence of the corotation resonance.

Abundance Distribution of Slow-Process Main Heavy Elements inAGB Stars

By re-analysing the results of the theoretical abundance of asymptoticgiant branch (AGB) stellarmodels and the observed abundances of 51 AGB samples, we find that theabundance distribution of s-process main heavy (SMH) elements of anyAGB star is similar to the scaled s-process main component of the solar system.This means that superposition of the SMH element abundance distributionsof AGB stars should be similar to the scaled solar s-process main component. Asa conclusion, the abundance pattern of the solar SMH elements isnot only an average result of a complex chemical evolution of galaxy,but also a typical one that can be used as a standard in abundanceinvestigation.

A discontinuity in mantle composition beneath the southwest Indian ridge.

The composition of mid-ocean-ridge basalt is known to correlate with attributes such as ridge topography and seismic velocity in the underlying mantle, and these correlations have been interpreted to reflect variations in the average extent and mean pressures of melting during mantle upwelling. In this respect, the eastern extremity of the southwest Indian ridge is of special interest, as its mean depth of 4.7 km (ref. 4), high upper-mantle seismic wave velocities and thin oceanic crust of 4-5 km (ref. 6) suggest the presence of unusually cold mantle beneath the region. Here we show that basaltic glasses dredged in this zone, when compared to other sections of the global mid-ocean-ridge system, have higher Na(8.0), Sr and Al2O3 compositions, very low CaO/Al2O3 ratios relative to TiO2 and depleted heavy rare-earth element distributions. This signature cannot simply be ascribed to low-degree melting of a typical mid-ocean-ridge source mantle, as different geochemical indicators of the extent of melting are mutually inconsistent. Instead, we propose that the mantle beneath approximately 1,000 km of the southwest Indian ridge axis has a complex history involving extensive earlier melting events and interaction with partial melts of a more fertile source.

A High‐Resolution Study of the Hydra A Cluster withChandra: Comparison of the Core Mass Distribution with Theoretical Predictions and Evidence for Feedback in the Cooling Flow

The cooling flow cluster Hydra A was observed during the orbital activation and calibration phase of the Chandra Observatory. While the X-ray image of the cluster exhibits complex structure in the central region as reported in McNamara et al., the large-scale X-ray morphology of the cluster is fairly smooth. A spectroscopic analysis of the ACIS data shows that the gas temperature in Hydra A increases outward, reaches a maximum temperature of 4 keV at 200 kpc, and then decreases slightly at larger radii. The distribution of heavy elements is nonuniform, with a factor of 2 increase in the Fe and Si abundances within the central 100 kpc. Beyond the central 100 kpc the Si-to-Fe abundance ratio is twice solar, while the Si-to-Fe ratio of the central excess is consistent with the solar value. One of the more surprising results is the lack of spectroscopic evidence for multiphase gas within the bulk of the cooling flow. Beyond the central 30 kpc, the ACIS spectra are adequately fitted with a single-temperature model. The addition of a cooling flow component does not significantly improve the fit. Only within the central 30 kpc (where the cooling time is less than 1 Gyr) is there spectroscopic evidence for multiphase gas. However, the spectroscopic mass deposition rate is more than a factor of 10 less than the morphologically derived mass accretion rate at 30 kpc. We propose that the cooling flow region is convectively unstable owing to heating by the central radio source, which significantly reduces the net accretion rate. In addition, we show that the mass distribution within the central 30-200 kpc region scales as ρd ∝ r-1.3, intermediate between an NFW and a Moore profile, but with a best-fit NFW concentration parameter (cNFW = 12) approximately 3 times greater than that found in numerical simulations. However, given the limited photon statistics, we cannot rule out the presence of a flat-density core with a core radius less than 30 kpc.

Feedback from Galaxy Formation: Escaping Ionizing Radiation from Galaxies at High Redshift

Several observational and theoretical arguments suggest that starburst galaxies may rival quasars as sources of metagalactic ionizing radiation at redshifts z > 3. Reionization of the intergalactic medium (IGM) at z > 5 may arise, in part, from the first luminous massive stars. To be an important source of radiative feedback from star formation, a substantial fraction (~1%-10%) of the ionizing photons must escape the gas layers of the galaxies. Using models of smoothly distributed gas confined by dark matter (DM) potentials, we estimate the fraction, ⟨fesc⟩ , of Lyman-continuum flux that escapes the halos of spherical galaxies as a function of their mass and virialization redshift. The gas density profile is found by solving the equation of hydrostatic equilibrium for the baryonic matter in the potential well of a DM halo with the density profile found by Navarro et al. We then perform a parametric study to understand the dependence of ⟨fesc⟩ on redshift, mass, baryonic fraction, star formation efficiency (SFE), stellar density distribution, and OB association luminosity function. We give useful analytical formulas for ⟨fesc(z,MDM)⟩. Using the Press-Schechter formalism, we find that stellar reionization at z ~ 7 is probably dominated by small galactic subunits, with MDM ≲ 107 M☉ and SFE ~ 10 times that in the Milky Way. This may affect the distribution of heavy elements throughout the intergalactic medium.

ASCA observations of two SNRs and NEI analysis

Based on the data from the ASCA observation of SNRs Kes79 and W49B, we present here the analysis of their X-ray spectra and morphologies. The Kes79 spectrum can be well fitted by a single NEI component, and the narrow-band images of that source show an inhomogeneous distribution of heavy elements. The heavy elements are richest in the positions S, SE and SW of Kes79, where there may exist interaction between shocks and molecular clouds implied by radio observations. For W49B we present here the non-equilibrium ionization (NEI) analysis based on its emission line diagnostics, and the spectral fit using two NEI components. The reverse shock in W49B may be still hot and we don't find evidence for a hotter blast wave in ASCA spectra.

Uranium-sensitive tomography with synchrotron radiation

Element-sensitive tomography produces quality information in the field of medical imaging. This method, also known as dichromatic tomography, can be useful to visualize the distribution of heavy elements, such as actinides, without destroying the sample. One of the problems is to obtain a monochromatic photon beam of sufficiently high energy; the other is to have a way of recording these high-energy photons with a good spatial resolution. Here, the results of a first experiment on uranium mapping with synchrotron radiation are reported. Various natural and artificial samples of a few centimetres in size with uranium concentration between 0.008 g cm−3 and 2 g cm−3 were scanned using photon beams around 115 keV and a specially designed camera. The data were then analysed using a conventional fast reconstruction technique. This yielded excellent results with spatial resolutions down to 50 µm. For the first time it was shown that element-sensitive tomography using synchrotron radiation could be extended to the heaviest natural element. Therefore, in principle, the spatial distribution of any element can now be reconstructed using synchrotron radiation. Extension of this technique to very heavy elements can be important for geology, health physics and nuclear waste storage.

The Distribution of Heavy Elements in Spiral and Elliptical Galaxies

ABSTRACTIn large disk and spheroidal galaxies, spatially resolved abundance information can be extracted by analysis of either emission lines, absorption lines, or both, depending on the situation. This review recaps significant results as they apply to nondwarf galaxies, including the Milky Way, spiral disks and bulges, and elliptical and lenticular galaxies. Methods for determining abundances are explained in appendices.Conclusions that span the galaxy types treated here are as follows. All galaxies, on average, have heavy‐element abundances (metallicities) that systematically decrease outward from their galactic centers while their global metallicities increase with galaxy mass. Abundance gradients are steepest in normal spirals and are seen to be progressively flatter going in order from barred spirals to lenticulars to ellipticals. The distribution of abundances N(Z) versus Z is strongly peaked compared with simple closed‐box model predictions of chemical enrichment in all galaxy types. That is, a “G dwarf problem,” commonly known in the solar cylinder, exists for all large galaxies.For spiral galaxies, local metallicity appears to be correlated with total (disk+bulge) surface density. Examination of N/O versus O/H in spiral disks indicates that production of N is dominated by primary processes at low metallicity and secondary processes at high metallicity. Carbon production increases with increasing metallicity. Abundance ratios Ne/O, S/O, and Ar/O appear to be universally constant and independent of metallicity, which argues either that the initial mass function (IMF) is universally constant or that these ratios are not sensitive to IMF variations. In the Milky Way, there is a rough age‐metallicity trend with much scatter, in the sense that older stars are more metal poor.In elliptical galaxies, nuclear abundances are in the range [Z/H] = 0.0–0.4, but the element mixture is not scaled‐solar. In large elliptical galaxies [Mg/Fe] is in the range 0.3–0.5, decreasing to ≈0 in smaller elliptical galaxies. Other light elements track the Mg enhancement, but the heavier Ca tracks Fe. Velocity dispersion appears to be a key parameter in the modulation of [Mg/Fe], but the cause of the connection is unclear.