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.     

A ‘superoutburst’ in XTEJ1118+480

I propose that the properties of the two outbursts observed in the X‐ray transient XTEJ1118+480 in 2000 are akin to superoutbursts of SU UMa stars. In these systems a ‘normal’ outburst immediately precedes a 5–10 times longer (‘super’) outburst. The optical light curve of the outbursts of XTEJ1118+480 is remarkably similar to that seen in some SU UMa stars, such as UVPer and TLeo, where the precursor outburst is distinct from the superoutburst, but the time scales are a factor of ∼15 different. The first outburst of XTEJ1118+480 was relatively short (∼1 month) while the second outburst was ∼5 times longer. During the second outburst superhumps were seen, a feature characteristic for superoutbursts. The gap of about a month between the two outbursts is longer in X‐rays with respect to the optical, a feature not previously recognized for X‐ray transients. Also in SU UMa stars the precursor outburst becomes more distinct at shorter wavelengths. Finally, I show that the time of appearance of the superhumps in XTEJ1118+480 is consistent with the expected superhump growth time, if the superhump mechanism was triggered during the first outburst. I conclude that the similarity in outburst behaviour in the two types of systems provides further support that a common mechanism is at work to start the long (‘super’) outbursts.     

Power spectra from ‘spotted’ accretion discs

We are carrying out a project to calculate power spectra of variability, assuming a model of a ‘spotted’ accretion disc near a black hole. We consider relativistic effects that change photon energy and produce light‐bending and time‐delays acting on the X‐ray signal received by an observer. We assume that the life‐time and the intrinsic emissivity of individual.aring events are described in terms of a simple stochastic process. This allows us to give approximate analytical formulae and compare them with numerical computations. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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 DEFINITION OF A HOWARDITE

Delaney et al. (1983) propose to redefine howardites as basaltic achondrites containing more than 10% of magnesian orthopyroxenite (diogenite) component. Since the 10% requirement is arbitrary and of no genetic significance this redefinition should be rejected and the earlier definition of Score et al. (1982) “Howardites are polymict pyroxene-plagioclase achondrites containing magnesian orthopyroxene” — in any amount — should be retained.     

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 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)     

Low frequency radio emission from the &;#x2018;quiet&;#x2019; Sun

We present observations of the ‘quiet’ Sun close to the recent solar minimum (Cycle 22), with the Gauribidanur radioheliograph. Our main conclusion is that coronal streamers also influence the observed radio brightness temperature.     

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.     

Elemental abundance analyses with DAO spectrograms: XXX. The middle B through early A stars ξ2 Ceti (B9 III), 21 Aquilae (B8 II‐III), ι Aquilae (B5 III), and ι Delphini (A2V)

This series of high quality elemental abundance analyses of mostly main‐sequence band normal and peculiar B, A, and F stars defines their properties and provides data for the comparison with the analyses of somewhat similar stars and with theoretical predictions. Most use high dispersion and high S/N (≥ 200) spectrograms obtained with CCD detectors at the long camera of the Coudé spectrograph of the 1.22‐m Dominion Astrophysical Observatory telescope. Here we reanalyze 21 Aql with better quality spectra and increase the number of stars consistently analyzed in the spectral range B5 to A2 by analyzing three new stars for this series. In the early A stars the normal and non‐mCP stars have abundances with overlapping ranges. But more stars are needed especially in the B5 to B9 range. ξ² Cet on average has a solar composition with a few abundances outside the solar range while both 21 Aql and ι Aql have abundances marginally less than solar. The abundances of ι Del are greater than solar with a few elements such as Ca being less than solar. It is an Am star (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Elemental abundance analyses with DAO spectrograms: XXXIII. β UMa (A0mA1 IV‐V), α Dra (A0 III), π Dra (A2 IIIs), and κ Cep (B9 III)

This paper presents extended analyses of β UMa (A0mA1 IV‐V), α Dra (A0 III), π Dra (A2 IIIs), and κ Cep (B9 III) which have previously been studied in this series. α Dra is a metal‐poor star while κ Cep has solar abundances. Both β UMa and π Dra are Am stars. Whenever possible, more accurate and precise gf values replace older values. High S/N (200+) and high dispersion Dominion Astrophysical Observatory spectrograms to the red of previously obtained spectra supplement the observations. The derived rotational velocities are 45, 25, 26, and 23 km s^–1, respectively. These LTE fine analyses use the ATLAS9 and the WIDTH9 programs of R. L. Kurucz. The results of the extended and the previous analyses are in good agreement. Thus in the past decade a significant improvement in the system of gf values has not been achieved although for many lines there have been changes. The use of additional regions has increased the quality of some results (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

A PRELIMINARY SORTING-OUT OF “NESS COUNTY” METEORITES

With the exception of a distinctive olivine-bronzite chondrite recognized by H. H. Nininger: “Ness County (1938)”, most of the numerous stony meteorites found in Ness County, Kansas, have been lumped together under the designation “Ness County (1894)”. It is the purpose of this paper to show that at least three separate falls are covered by this name     

Empirical transformations from U.T. to E.T. for the period 1800–1988 (Astronomisches Rechen-Institut — Mitteilungen Serie B)

Approximation formulae describing the long-term changes in the rotation of the Earth are evaluated. The time scale reduction from Universal to Ephemeris Time can be accomplished by a 12th degree polynomial with a mean error of less than one second for the entire time span 1800–1988. The maximum residuals of least squares fits of the 19th and 20th century data, respectively, can be limited to this accuracy by even simpler expressions.