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Most stars become white dwarfs after they have exhausted their nuclear fuel (the Sun will be one such). Between one-quarter and one-half of white dwarfs have elements heavier than helium in their atmospheres, even though these elements ought to sink rapidly into the stellar interiors (unless they are occasionally replenished). The abundance ratios of heavy elements in the atmospheres of white dwarfs are similar to the ratios in rocky bodies in the Solar System. This fact, together with the existence of warm, dusty debris disks surrounding about four per cent of white dwarfs, suggests that rocky debris from the planetary systems of white-dwarf progenitors occasionally pollutes the atmospheres of the stars. The total accreted mass of this debris is sometimes comparable to the mass of large asteroids in the Solar System. However, rocky, disintegrating bodies around a white dwarf have not yet been observed. Here we report observations of a white dwarf-WD 1145+017-being transited by at least one, and probably several, disintegrating planetesimals, with periods ranging from 4.5 hours to 4.9 hours. The strongest transit signals occur every 4.5 hours and exhibit varying depths (blocking up to 40 per cent of the star's brightness) and asymmetric profiles, indicative of a small object with a cometary tail of dusty effluent material. The star has a dusty debris disk, and the star's spectrum shows prominent lines from heavy elements such as magnesium, aluminium, silicon, calcium, iron, and nickel. This system provides further evidence that the pollution of white dwarfs by heavy elements might originate from disrupted rocky bodies such as asteroids and minor planets. [ABSTRACT FROM AUTHOR]

The first stars in the Universe were probably quite different from those born today. Composed almost entirely of hydrogen and helium (plus a tiny trace of lithium), they lacked the heavier elements that determine the formation and evolution of younger stars. Although we cannot observe the very first stars — they died long ago in supernovae explosions — they created heavy elements that were incorporated into the next generation. Here we describe how observations of heavy elements in the oldest surviving stars in our Galaxy's halo help us understand the nature of the first stars — those responsible for the chemical enrichment of our Galaxy and Universe. [ABSTRACT FROM AUTHOR]

Vega, the second brightest star in the northern hemisphere, serves as a primary spectral type standard. Although its spectrum is dominated by broad hydrogen lines, the narrower lines of the heavy elements suggested slow to moderate rotation, giving confidence that the ground-based calibration of its visible spectrum could be safely extrapolated into the ultraviolet and near-infrared (through atmosphere models), where it also serves as the primary photometric calibrator. But there have been problems: the star is too bright compared to its peers and it has unusually shaped absorption line profiles, leading some to suggest that it is a distorted, rapidly rotating star seen pole-on. Here we report optical interferometric observations that show that Vega has the asymmetric brightness distribution of the bright, slightly offset polar axis of a star rotating at 93 per cent of its breakup speed. In addition to explaining the unusual brightness and line shape peculiarities, this result leads to the prediction of an excess of near-infrared emission compared to the visible, in agreement with observations. The large temperature differences predicted across its surface call into question composition determinations, adding uncertainty to Vega's age and opening the possibility that its debris disk could be substantially older than previously thought. [ABSTRACT FROM AUTHOR]

Investigates the chemical separation and characterization of only seven detected atoms of hassium in the fusion reaction between magnesium and curium. Enthalpy of adsorption; Chemical properties of hassium; Seven nuclear decay chains originating from hassium isotopes; Thermochromatogram of hassium oxide and osmium oxide.

Shows that the heavy rare-earth elements in abyssal clinopyroxenes that are moderately incompatible are highly correlated with the Cr/(Cr+Al) ratios of coexisting spinels. Indication that this correlation deteriorates only for the most highly incompatible elements; Development of a quantitative melting indicator for mantle residues from electron-and ion-microprobe data from residual abyssal peridotites collected on the central Indian ridge.

The chemical properties of an element are primarily governed by the configuration of electrons in the valence shell. Relativistic effects influence the electronic structure of heavy elements in the sixth row of the periodic table, and these effects increase dramatically in the seventh row-including the actinides-even affecting ground-state configurations. Atomic s and p1/2 orbitals are stabilized by relativistic effects, whereas p3/2, d and f orbitals are destabilized, so that ground-state configurations of heavy elements may differ from those of lighter elements in the same group. The first ionization potential (IP1) is a measure of the energy required to remove one valence electron from a neutral atom, and is an atomic property that reflects the outermost electronic configuration. Precise and accurate experimental determination of IP1 gives information on the binding energy of valence electrons, and also, therefore, on the degree of relativistic stabilization. However, such measurements are hampered by the difficulty in obtaining the heaviest elements on scales of more than one atom at a time. Here we report that the experimentally obtained IP1 of the heaviest actinide, lawrencium (Lr, atomic number 103), is electronvolts. The IP1 of Lr was measured with 256Lr (half-life 27 seconds) using an efficient surface ion-source and a radioisotope detection system coupled to a mass separator. The measured IP1 is in excellent agreement with the value of 4.963(15) electronvolts predicted here by state-of-the-art relativistic calculations. The present work provides a reliable benchmark for theoretical calculations and also opens the way for IP1 measurements of superheavy elements (that is, transactinides) on an atom-at-a-time scale. [ABSTRACT FROM AUTHOR]

Roughly half of the heavy elements (atomic mass greater than that of iron) are believed to be synthesized in the late evolutionary stages of stars with masses between 0.8 and 8 solar masses. Deep inside the star, nuclei (mainly iron) capture neutrons and progressively build up (through the slow-neutron-capture process, or s-process) heavier elements that are subsequently brought to the stellar surface by convection. Two neutron sources, activated at distinct temperatures, have been proposed: 13C and 22Ne, each releasing one neutron per α-particle (4He) captured. To explain the measured stellar abundances, stellar evolution models invoking the 13C neutron source (which operates at temperatures of about one hundred million kelvin) are favoured. Isotopic ratios in primitive meteorites, however, reflecting nucleosynthesis in the previous generations of stars that contributed material to the Solar System, point to higher temperatures (more than three hundred million kelvin), requiring at least a late activation of 22Ne (ref. 1). Here we report a determination of the s-process temperature directly in evolved low-mass giant stars, using zirconium and niobium abundances, independently of stellar evolution models. The derived temperature supports 13C as the s-process neutron source. The radioactive pair 93Zr-93Nb used to estimate the s-process temperature also provides, together with the pair 99Tc-99Ru, chronometric information on the time elapsed since the start of the s-process, which we determine to be one million to three million years. [ABSTRACT FROM AUTHOR]

Presents research which found that correlations exist between the work function and the extremal values of Poisson's ratio in cubic elemental metals. What Poisson's ratio is; Negative Poisson's ratio in thermodynamics and in crystalline solids; Negative Poisson's ratio in cubic elemental metals; Use of electron-gas model; Positive Poisson's ratios in cubic crystals; Applications for research.

The abundance of heavy elements (metallicity) in the photospheres of stars similar to the Sun provides a 'fossil' record of the chemical composition of the initial protoplanetary disk. Metal-rich stars are much more likely to harbour gas giant planets, supporting the model that planets form by accumulation of dust and ice particles. Recent ground-based surveys suggest that this correlation is weakened for Neptunian-sized planets. However, how the relationship between size and metallicity extends into the regime of terrestrial-sized exoplanets is unknown. Here we report spectroscopic metallicities of the host stars of 226 small exoplanet candidates discovered by NASA's Kepler mission, including objects that are comparable in size to the terrestrial planets in the Solar System. We find that planets with radii less than four Earth radii form around host stars with a wide range of metallicities (but on average a metallicity close to that of the Sun), whereas large planets preferentially form around stars with higher metallicities. This observation suggests that terrestrial planets may be widespread in the disk of the Galaxy, with no special requirement of enhanced metallicity for their formation. [ABSTRACT FROM AUTHOR]

The surface of hot neutron stars is covered by a thin atmosphere. If there is accretion after neutron-star formation, the atmosphere could be composed of light elements (H or He); if no accretion takes place or if thermonuclear reactions occur after accretion, heavy elements (for example, Fe) are expected. Despite detailed searches, observations have been unable to confirm the atmospheric composition of isolated neutron stars. Here we report an analysis of archival observations of the compact X-ray source in the centre of the Cassiopeia A supernova remnant. We show that a carbon atmosphere neutron star (with low magnetic field) produces a good fit to the spectrum. Our emission model, in contrast with others, implies an emission size consistent with theoretical predictions for the radius of neutron stars. This result suggests that there is nuclear burning in the surface layers and also identifies the compact source as a very young (∼330-year-old) neutron star. [ABSTRACT FROM AUTHOR]

Stellar explosions such as novae and supernovae produce most of the heavy elements in the Universe. The onset of a nova is well understood as driven by runaway thermonuclear fusion reactions on the surface of a white dwarf in a binary star system; but the structure, dynamics and mass of the ejecta are not well known. In rare cases, the white dwarf is embedded in the wind nebula of a red-giant companion, and the explosion products plough through the nebula and produce X-ray emission. Here we report X-ray observations of such an event, from the eruption of the recurrent nova RS Ophiuchi. The hard X-ray emission from RS Ophiuchi early in the eruption emanates from behind a blast wave, or outward-moving shock wave, that expanded freely for less than 2 days and then decelerated owing to interaction with the nebula. The X-rays faded rapidly, suggesting that the blast wave deviates from the standard spherical shell structure. The early onset of deceleration indicates that the ejected shell had a low mass, the white dwarf has a high mass, and that RS Ophiuchi is therefore a progenitor of the type of supernova (type Ia) integral to studies of the expansion of the Universe. [ABSTRACT FROM AUTHOR]

Some heavy elements (with atomic number A > 69) are produced by the ‘rapid’ (r)-process of nucleosynthesis, where lighter elements are bombarded with a massive flux of neutrons. Although this is characteristic of supernovae and neutron star mergers, uncertainties in where the r-process occurs persist because stellar models are too crude to allow precise quantification of this phenomenon. As a result, there are many uncertainties and assumptions in the models used to calculate the production ratios of actinides (like uranium-238 and thorium-232). Current estimates of the U/Th production ratio range from ∼0.4 to 0.7. Here I show that the U/Th abundance ratio in meteorites can be used, in conjunction with observations of low-metallicity stars in the halo of the Milky Way, to determine the U/Th production ratio very precisely . This value can be used in future studies to constrain the possible nuclear mass formulae used in r-process calculations, to help determine the source of Galactic cosmic rays, and to date circumstellar grains. I also estimate the age of the Milky Way ( in a way that is independent of the uncertainties associated with fluctuations in the microwave background or models of stellar evolution. [ABSTRACT FROM AUTHOR]

Reports on research into cosmic explosions called supernovae with accelerator projects in nuclear physics to refine theoretical models. Details of the processes that produce exotic nuclei; How the neutron-drip line could provide the key to understanding the formation of heavy elements in type II supernovae; Capabilities of particle accelerator facilities, including EURISOL in Europe.

Questions on the number of stable elements with maximum atomic number z, which can be created, in light of the production of three superheavy elements in 1999. Identification of the laboratories where the elements were created; Graph showing the stable nuclei existing in nature compared with the age of the universe; Details on how the superheavy elements were produced; Information on the stability of nucleus. INSET: Box 1: The island of stability.

Discusses research which studied the origin of the Solar System's heavy elements. Origin in two different types of supernova; Previous research; Nuclear fusion reactions in the evolution of a star; Details about three basic nuclear processes that produce heavy elements, the s-, r-, and p-processes; Collapse of core of massive star.

Reports the chemical properties of element 106, seaborgium. Synthesis of heavy elements; Classification of seaborgium in the periodic table of elements; Comparison of its properties with those of other heavy elements.

The article discusses research by T. K. Sato and colleagues about the atomic properties of heavy element lawrencium. Topics mentioned include the ionization potential of lawrencium, relativistic quantum theory, spin-orbital interactions, relativistic effects, and momentum transfer during nuclear fusion.

The article discusses formation of stars by tiny galaxies which have heavier elements. Topics include lesser metallicity in smaller galaxies, presence of lower heavy elements such hydrogen and helium, and comparison to Milky Way and other large galaxies.

The article focuses on the report of C. Chiappini and colleagues regarding the measurement of heavy elements in first stars in NGC 6522 using a very large telescope from European Southern Observatory. It mentions that when strontium and yttrium elements were compared with iron, it was 10,000 times more effective in the stars to create elements. It adds that radioactive neons were generated in a cascade of nuclear reactions that also emit a high flux of neutron to create rare elements.

The article presents information on periodic oscillations that have been observed in exponential decay curves of two radioactive isotopes. According to observations, investigating ß-decays of highly positive ions of heavy elements can see a decay rate whose decline is not purely exponential. It states that modulation arises from the "mixing" of different types of neutrino, chargeless and almost massless particles produced in ß-decays. Moreover, it mentions that the modulations are due to the oscillation of neutrinos between two different mass states.

Discusses the reasons for difficulty in the fusion of two nuclei to produce a heavy element. Process that hinders the fusion; Significance of the consideration of microscopic effects in theoretical studies of nuclear collisions; Reference to a paper on the subject published in the April 2, 2003 issue of the periodical 'Nature.'

Focuses on the development of heavy elements, hassium atoms, that decay within seconds. Volatility of hassium tetroxide; Deviant behavior displayed by heavy elements; Interaction of electrons with other atoms and molecules.

Reports that element 106, seaborgium, has been placed firmly in group six on the periodic table of elements, under tungsten and molybdenum. The element's conventional behavior proving mysterious; Other heavy elements behaving in relativistic ways; Possibility of other elements being added to the table.

The article discusses the formative processes of stars in the Universe. The relative abundance patterns of certain heavy elements of stars has changed very little over billions of years. The abundance pattern of rare heavy elements in halo stars mirror those in our solar system. It implies that the formative processes for the elements are robust. The abundance patterns suggest more commonalities with neutron-capture element formation occurring early in the history of the Universe.

The article discusses various reports published within the issue, including one by Volker Springel and colleagues on how the growth of structure in the universe is a powerful way of comparing the predictions of the standard model with observations of clusters of galaxies and another by John Cowan and Chris Sneden on how patterns in the abundance of heavy elements in the oldest stars in the galaxy can infer what kinds of star preceded them.

Reports on the discovery of a star containing only insignificant amounts of heavy elements. Statement that such a star would be a relic of early galactic history, before star formation and evolution polluted the primordial gas with metals; Identification of the star, HE0107-5240, as being extremely metal-poor by a spectroscopic survey of the southern sky; Chemical composition of HE0107-5240; Possibility that the star originally formed as part of a binary pair.