URANIUM DISTRIBUTION and “EXCESSIVE” U-He AGES IN IRON METEORITIC TROILITE

Uranium was measured by fission track analysis in meteoritic troilite and graphite. The distribution is extremely heterogeneous, with a few high-U grains dominating the total abundances. U/He ages cannot be estimated from such a distribution pattern, and therefore previously reported excessive ages are not valid.     

Are natural hazards temporally random?

The paper employs statistical hypothesis tests to explore the question of whether natural hazards (hail and tornadoes being considered here) are or are not intertemporally random. The answer to this question, at least for these two hazards, is surprising and has important policy implications: hazards appear to be more likely in year t if an event was experienced in year t?1: hence, apparent ‘Gambler's Fallacy’ behaviour on the part of farmers and others may indeed be rational. Should this result hold for a full range of climate-related hazard types. as we suspect, hundreds of millions of dollars of crop loss and other damages may be preventable (e.g., rotating to frost-resistant crops if past events suggest greater than usual likelihood of early or late frost). The degree of positive serial correlation is also seen to vary a great deal regionally, with individuals in some states being unable to benefit from knowledge of prior hazard occurrence.     

Properties of star formation in the spiral arms of barred galaxies

It is assumed that the two-fold disc-wide symmetry of spirals is caused by density waves, but also the potential of a bar component may have a significant influence on structural properties. The strength of the bar component appears to be anti-correlated with the degree of symmetry of star-forming regions in the spiral arms (Rozas et al., 1998). We present new results of R and Hα surface photometry of a sample of bright barred spirals. A photometric decompositon of the galaxy components is carried out in order to make a more accurate measurement of the strength of the bar and its interrelation to gas and stars in the disc. This revised version was published online in August 2006 with corrections to the Cover Date.     

Isobaric cooling and anti-clockwise P–T paths in the Variscan Odenwald Crystalline Complex, Germany

Mineral assemblages in Al₂O₃‐rich, SiO₂‐ and K₂O‐poor metapelitic rocks from the western Odenwald Crystalline Complex (Variscan Mid‐German Crystalline Rise, southern Germany) include corundum, spinel, cordierite, sillimanite, garnet and staurolite. Quartz is absent from almost all samples. Therefore, the applicability of conventional geothermobarometry is very limited or even impossible. Detailed petrographic investigation on selected samples permits inference of the sequence of appearance and disappearance of several mineral assemblages. The recognition of such partial re‐equilibration stages and their associated mineral assemblages, together with mineral stabilities predicted from KFMASH pseudosections, enables the determination of the pressure‐temperature (P–T) trajectories experienced by these rocks during the Variscan metamorphism. The rocks were metamorphosed under low‐P/high‐T conditions and underwent an anti‐clockwise P–T evolution. A pressure increase from about 2 kbar to 4 ± 0.5 kbar was accompanied by heating. Peak metamorphic conditions were reached at pressures of 4 ± 0.5 kbar and temperatures of at least 640 °C, probably even higher. The retrograde evolution is characterised by near‐isobaric cooling from ≥ 640 °C to approximately 550 °C. The rocks underwent the anti‐clockwise evolution in a subduction‐related magmatic arc setting. The close spatial association of the low‐P/high‐T rocks with recently discovered metabasic eclogites in the eastern part of the Odenwald Crystalline Complex may indicate a fossil paired metamorphic belt in the Central European Variscides.     

The host galaxies of active galactic nuclei

We examine the properties of the host galaxies of 22 623 narrow-line active galactic nuclei (AGN) with  0.02 < z < 0.3  selected from a complete sample of 122 808 galaxies from the Sloan Digital Sky Survey. We focus on the luminosity of the [O  iii ]λ5007 emission line as a tracer of the strength of activity in the nucleus. We study how AGN host properties compare with those of normal galaxies and how they depend on L [O  iii ]. We find that AGN of all luminosities reside almost exclusively in massive galaxies and have distributions of sizes, stellar surface mass densities and concentrations that are similar to those of ordinary early-type galaxies in our sample. The host galaxies of low-luminosity AGN have stellar populations similar to normal early types. The hosts of high-luminosity AGN have much younger mean stellar ages. The young stars are not preferentially located near the nucleus of the galaxy, but are spread out over scales of at least several kiloparsecs. A significant fraction of high-luminosity AGN have strong Hδ absorption-line equivalent widths, indicating that they experienced a burst of star formation in the recent past. We have also examined the stellar populations of the host galaxies of a sample of broad-line AGN. We conclude that there is no significant difference in stellar content between type 2 Seyfert hosts and quasars (QSOs) with the same [O  iii ] luminosity and redshift. This establishes that a young stellar population is a general property of AGN with high [O  iii ] luminosities.     

MAXIPOL: a balloon-borne experiment for measuring the polarization anisotropy of the cosmic microwave background radiation

We discuss MAXIPOL, a bolometric balloon-borne experiment designed to measure the E-mode polarization anisotropy of the cosmic microwave background radiation (CMB) on angular scales of 10^′ to 2°. MAXIPOL is the first CMB experiment to collect data with a polarimeter that utilizes a rotating half-wave plate and fixed wire-grid polarizer. We present the instrument design, elaborate on the polarimeter strategy and show the instrument performance during flight with some time domain data. Our primary dataset was collected during a 26 h turnaround flight that was launched from the National Scientific Ballooning Facility in Ft. Sumner, New Mexico in May 2003. During this flight five regions of the sky were mapped. Data analysis is in progress.     

HH 111 STIS Observations and their Analysis using Analytical and Numerical Models

The internal structure of stellar jets arising from young stellar objects is characterized by a series of `knots' or condensations which have highly supersonic proper motions. These structures, we believe, are the result of a variable ejection from the source, which leads to the formation of internal working surfaces or small bowshock within the jet beam. In this paper we present a long-slit spectrum of Herbig-Haro object HH 111 obtained with STIS and an interpretation of this observation in terms of an ejection velocity variability model.     

Rapid vegetation change during the early Holocene in the Faroe Islands detected in terrestrial and aquatic ecosystems

High‐resolution pollen, plant macrofossil and sedimentary analyses from early Holocene lacustrine sediments on the Faroe Islands have detected a significant vegetation perturbation suggesting a rapid change in climate between ca. 10 380 cal. yr BP and the Saksunarvatn ash (10 240±60 cal. yr BP). This episode may be synchronous with the decline in δ¹⁸O values in the Greenland ice‐cores. It also correlates with a short, cold event detected in marine cores from the North Atlantic that has been ascribed to a weakening of thermohaline circulation associated with the sudden drainage of Lake Agassiz into the northwest Atlantic, or, alternatively, a period with distinctly decreased solar forcing. The vegetation sequence begins at ca. 10 500 cal. yr BP with a succession from tundra to shrub‐tundra and increasing lake productivity. Rapid population increases of aquatic plants suggest high summer temperatures between 10 450 and 10 380 cal. yr BP. High pollen percentages, concentrations and influx of Betula, Juniperus and Salix together with macrofossil leaves indicate shrub growth around the site during the initial phases of vegetation colonisation. Unstable conditions followed ca. 10 380 cal. yr BP that changed both the upland vegetation and the aquatic plant communities. A decrease in percentage values of shrub pollen is recorded, with replacement of both aquatics and herbaceous plants by pioneer plant communities. An increase in total pollen accumulation rates not seen in the concentration data suggests increased sediment delivery. The catchment changes are consistent with less seasonal, moister conditions. Subsequent climatic amelioration reinitiated a warmth‐driven succession and catchment stabilisation, but retained high precipitation levels influencing the composition of the post‐event communities. Copyright © 2003 John Wiley & Sons, Ltd.     

The Morávka meteorite fall: 1. Description of the events and determination of the fireball trajectory and orbit from video records

Abstract— The Morávka (Czech Republic) meteorite fall occurred on May 6, 2000, 11:52 UT, during the daytime. Six H5–6 ordinary chondrites with a total mass of 1.4 kg were recovered. The corresponding fireball was witnessed by thousands of people and also videotaped by 3 casual witnesses. Sonic booms were recorded by 16 seismic stations in the Czech Republic and Poland and by one infrasonic station in Germany. A total of 2.5% of the fireball eyewitnesses reported electrophonic sounds. Satellites in Earth orbit detected part of the fireball light curve. In this first paper from a series of 4 papers devoted to the Morávka meteorite fall, we describe the circumstances of the fall and determine the fireball trajectory and orbit from calibrated video records. Morávka becomes one of only 6 meteorites with a known orbit. The slope of the trajectory was 20.4° to the horizontal, the initial velocity was 22.5 km/s, and the terminal height of the fireball was 21 km. The semimajor axis of the orbit was 1.85 AU, the perihelion distance was 0.982 AU, and the inclination was 32.2°. The fireball reached an absolute visual magnitude of ?20 at a height of 33 km.