E-CHONDRITES: SIGNIFICANCE OF THE PARTITION OF ELEMENTS BETWEEN ‘SILICATE’ AND ‘SULPHIDE’

Bulk chemical analyses of six E-chondrites (Daniel's kuil, Khairpur, Kota Kota, Saint-Sauveur, South Oman and St Mark's) are given, together with partial analyses of a further five (Blithfield, Hvittis, Indarch, Jajh deh Kot Lalu and Pillistfer). The distribution of some normally lithophile elements (Al, Ca, Cr, K, Mg, Na, P and Ti) between silicate and sulphide groups of minerals was determined using the selective attack by dry chlorine (350°C) on magnetically separated fractions. Subdivision of the E-chondrites into types I and II (Yavnel;, 1963; Anders, 1964) is accepted and it is shown using chemical data that St Mark's and Saint-Sauveur should be included in type I. Sulphides contribute an unexpectedly high proportion of several elements to the bulk: e.g. Ca (av. 88.5% type I, 66.3% type II); Ti(av. 77.1% type I, 84.8% type II) and P as phosphide (av. 44.4% type I, > 83.2% type II). The proportion of Ti contributed to the bulk composition by the sulphides in types I and II increases with increae in ‘thermal metamorphic effect’ (Easton, 1983b) within each type. There is marked variability in the relative abundances of metal, phosphide, silicate and sulphide among the members of each type in keeping with their aggregate nature. The chemical composition of the ‘silicate’ and ‘sulphide’ in type IE-chondrites differs from that in type II (e.g. CaO in the silicates, Mg in the bulk sulphides) which therefore precludes the isochemical evolution of all E-chondrites from a common parent material. Partition of Ti between silicate and sulphide groups of minerals indicates that types I and II E-chondrites originated in separate, chemically distinct bodies.     

Comment on ‘Where are the halo stars?’

We comment briefly on a recent paper by Fuhrmann which claims that about half of the sample of halo stars in the solar neighbourhood presented by Fuchs and Jahreiß [A&A 329 (1998) 81] are actually thick disc stars. By referring to star counts in the CADIS survey we argue that this is rather unlikely.     

Latitudinal UVR-PAR measurements in Argentina: extent of the ‘ozone hole’

The UVR-PAR Argentinean Monitoring Network started its operation in September 1994 recording ultraviolet (UVR) and Photosynthetic Available Radiation (PAR) at a frequency of once per minute, at four sites, throughout the entire year. Four spectroradiometers (GUV-511, Biospherical Instruments, Inc.) were installed at research centers separated by about 8–12 degrees of latitude, extending from the Subantarctic-Fueguian region to the Tropic of Capricorn. The instruments are located in populated areas ranging from 30,000 to 11 million people and with extremely different climate regimes and conditions of tropospheric pollution. Our ground-based data indicated that the irradiance increased steadily from south to north. This increase was also observed in the calculated daily doses of UV-B (280–320 nm); however, daily integrated values for UV-A (320–400 nm) and PAR (400–700 nm) were higher at mid-latitudes (Puerto Madryn, 42°47′S). A similar south-to-north increase was evident in the ratio of the energy at 305 nm and 340 nm wavelengths (with low 305/340 ratios indicating high total ozone column concentration), with low values at Ushuaia (55°01′S) and high values at Jujuy (24°10′S). However, the 305/340 ratios increased significantly over their normal spring values at two sites, Ushuaia and Puerto Madryn, for variable time periods during October-December. Our data suggest that the ozone hole was over South America extending to about 38°S for at least a week during October and about two weeks during November-December of the years of 1994 and 1995. However, it should be noted that the erythemal irradiance, in the area influenced by the ozone hole, was at all times lower than that in Buenos Aires and well below the value at Jujuy (tropical station). This study also indicates that when assessing the impact of solar UVR upon organisms, other variables such as cloud cover, solar zenith angle, day length, latitude, and atmospheric pollution should be considered in addition to total ozone column concentration.     

The polar substorm and electron ‘islands’ in the Earth's magnetic tail

The behaviour of energetic electrons in the distant magnetosphere near the midnight meridian during polar substorms has been studied for the period March 5th–April 4th, 1965, using data from two end window Geiger counters flown on the IMP 2 satellite (apogee 15.8 Earth radii) and magnetic records from a chain of auroral zone stations around the world at magnetic latitudes equivalent to L = 7.4 ± 2.0.

When the satellite was in the distant radiation zone or in the plasma sheet which extends down the Earth's magnetic tail, sudden decreases in the horizontal magnetic field component at ground stations near the midnight meridian (negative magnetic bays) were followed by sudden increases in 40 keV electron fluxes (electron islands) at the satellite. When the satellite was at high latitudes in the magnetic tail ‘bays’ often were not followed by ‘islands.’ When the satellite was near the centre of the plasma sheet, energetic electron fluxes were observed even during magnetically quiet periods. The time delay between the sharp onset of magnetic bays in the auroral zone and the corresponding rapid increase in energetic electron intensity at the satellite, typically some tens of minutes, was least when the satellite was close to the Earth and increased with its increasing radial distance from the Earth. The delay was also a function of distance of the satellite from the centre of the plasma sheet, and of the magnitude of the intensity increase (smaller delays for larger intensity increases). We deduce that the disturbance producing the magnetic bays and associated particle acceleration originates fairly deep in the magnetosphere and propagates outward to higher L values, and down the plasma sheet in the Earth's magnetic tail on the dark side of the Earth. It is unlikely that the accelerated electrons are themselves drifting away from the Earth, because the apparent velocity with which the islands move away from the Earth decreases with increasing distance from the Earth.

It is suggested that the polar substorm and the associated particle acceleration are part of an impulsive ejection mechanism of magnetospheric energy into the ionosphere, rather than an impulsive injection mechanism of solar wind energy into the magnetosphere.     

The central region of NGC 3077: ground‐based photometry and age of bright ‘starlike’ objects

We present UBVI_C photometry of starlike objects in the central region of NGC 3077. The colour‐colour and colour‐magnitude diagrams of the objects are discussed. Many of the objects under consideration, starlike from the ground, are probably dense young star clusters (super star clusters, SSC). Ages spreading over ∼4 to ∼150 Myr are estimated for most of these objects. Sakai and Madore (2001) found enhanced star formation ∼30–125 Myr ago also in the halo of this galaxy; thus, high star forming activity has occurred within the entire galaxy (centre and halo) since ∼130…150 Myr. Having ended in the outer regions about 30 Myr ago, it is going on near the centre with full vigour. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Fundamental Plane of E Galaxies in Compact Groups

We present a study focusing on the nature of compact groups through the study of their elliptical galaxies. We determine central velocity dispersions (σ_o) for 18 bright elliptical galaxies located in the core of Hickson compact groups and a control sample of 12 brightbona fide ellipticals located in the field or very loose groups. Several tests are carried out to avoid systematic effects in σ measurements. We use these velocity dispersions to compare the position of 11 compact group galaxies in the Fundamental Plane to that of a large and homogeneous sample of elliptical galaxies (Burstein et al., 1987).We find that little or no significant difference exists, as far as the Fundamental Plane is concerned, between ellipticals in compact groups and their counterparts in other environments. This revised version was published online in July 2006 with corrections to the Cover Date.     

The brown dwarf desert as a consequence of orbital migration

We show that the dearth of brown dwarfs in short-period orbits around Solar-mass stars – the brown dwarf desert – can be understood as a consequence of inward migration within an evolving protoplanetary disc. Brown dwarf secondaries forming at the same time as the primary star have masses which are comparable to the initial mass of the protoplanetary disc. Subsequent disc evolution leads to inward migration, and destruction of the brown dwarf, via merger with the star. This is in contrast with massive planets, which avoid this fate by forming at a later epoch when the disc is close to being dispersed. Within this model, a brown dwarf desert arises because the mass at the hydrogen-burning limit is coincidentally comparable to the initial disc mass for a Solar mass star. Brown dwarfs should be found in close binaries around very low mass stars, around other brown dwarfs, and around Solar-type stars during the earliest phases of star formation.     

On the ‘Divergence Problem’ in Northern Forests: A review of the tree-ring evidence and possible causes

An anomalous reduction in forest growth indices and temperature sensitivity has been detected in tree-ring width and density records from many circumpolar northern latitude sites since around the middle 20th century. This phenomenon, also known as the “divergence problem”, is expressed as an offset between warmer instrumental temperatures and their underestimation in reconstruction models based on tree rings. The divergence problem has potentially significant implications for large-scale patterns of forest growth, the development of paleoclimatic reconstructions based on tree-ring records from northern forests, and the global carbon cycle. Herein we review the current literature published on the divergence problem to date, and assess its possible causes and implications. The causes, however, are not well understood and are difficult to test due to the existence of a number of covarying environmental factors that may potentially impact recent tree growth. These possible causes include temperature-induced drought stress, nonlinear thresholds or time-dependent responses to recent warming, delayed snowmelt and related changes in seasonality, and differential growth/climate relationships inferred for maximum, minimum and mean temperatures. Another possible cause of the divergence described briefly herein is ‘global dimming’, a phenomenon that has appeared, in recent decades, to decrease the amount of solar radiation available for photosynthesis and plant growth on a large scale. It is theorized that the dimming phenomenon should have a relatively greater impact on tree growth at higher northern latitudes, consistent with what has been observed from the tree-ring record. Additional potential causes include “end effects” and other methodological issues that can emerge in standardization and chronology development, and biases in instrumental target data and its modeling. Although limited evidence suggests that the divergence may be anthropogenic in nature and restricted to the recent decades of the 20th century, more research is needed to confirm these observations.     

The lack of thermical equilibrium as a consequence on the universe expansion

The time-asymmetry of the universe is essentially produced by its low-entropy, unstable states. Using quantitative arguments Paul Davies has demonstrated that the expansion of the universe coupled with nuclear reaction within the stars may produce a decrease in entropy, thereby explaining its low entropy states. This idea is implemented in a qualitative way in a simple homogeneous model. Some rough coincidence with observational data is found.     

Measurement of Na and I recoil discrimination and detection efficiency in a cooled ‘UVIS’ NaI crystal for dark matter searches

The UVIS dark matter detector, proposed by Spooner and Smith (Phys. Lett. B 314 (1993) 430), consists of < 1000 ppm Tl doped NaI scintillator operated at 100-200 K, with measurement of UV and visible scintillation components used to discriminate between electrons (gammas) and Na or I recoils. Presented here are results of measurements of the gamma/nuclear recoil discrimination power of a Kyropolous NaI (0.5 ppm Tl) UVIS test detector operated at 160 K, with monoenergetic neutrons used to induce nuclear recoils via elastic scattering. Defining the statistical gain factor for N events as , the coefficient C_m was measured as a function of photoelectron pulse height. At 40 photoelectrons C_m was found to be 0.5 (corresponding to 90% rejection of gammas with 20% loss of neutron events). The scintillation efficiency for Na and I recoils relative to electrons was also measured at 160 K and found to be 35 ± 5% for Na recoils and 10 ± 2% for iodine.     

Virial oscillations of celestial bodies IV: The Lyapunov stability of motion

It is shown that with a virial approach to the solution of the many-body problem the integral characteristics of a system (Jacobi's function and total energy), being present in Jacobi's equation, are immanent to its own integrals. Estimating the Lyapunov stability of motion of a system they play the role of Lyapunov functions.Studying Lyapunov stability of the virial oscillations of celestial bodies we used the Duboshin criterion applicable when permanent perturbations are present. In the case of conservative systems the potential energy of the system plays the role of such a perturbation. Thus, the nature of the virial oscillations can be understood as an effect of non-linear resonance between the kinetic and the potential energies.It is shown that the stability of virial oscillations of conservative systems relative to variations of the form-factors product is only a necessary condition in the proof of the hypothesis that =const. for celestial bodies. The sufficient condition for the proof of this equality consists of the given direct derivation of the equation of virial oscillations of celestial bodies from Einstein's equation, as well as of the equivalence of Schwarzschild's solution and the solution of Jacobi's equation at .The stability of virial oscillations for dissipative systems is studied. It is shown that the stability is limited by the period of time of its bifurcation.     

Virial oscillations of celestial bodies: V. The structure of the potential and kinetic energies of a celestial body as a record of its creation history

The physical meaning of the terms of the potential and kinetic energy expressions, expanded by means of the density variation function for a nonuniform self-gravitating sphere, is discussed. The terms of the expansions represent the energy and the moment of inertia of the uniform sphere, the energy and the moment of inertia of the nonuniformities interacting with the uniform sphere, and the energy of the nonuniformities interacting with each other. It follows from the physical meaning of the above components of the energy structure, and also from the observational fact of the expansion of the Universe that the phase transition, notably, fusion of particles and nuclei and condensation of liquid and solid phases of the expanded matter accompanied by release of energy, must be the physical cause of initial thermal and gravitational instability of the matter. The released kinetic energy being constrained by the general motion of the expansion, develops regional and local turbulent (cyclonic) motion of the matter, which should be the second physical effect responsible for the creation of celestial bodies and their rotation.