A 7000 yr perspective on volcanic ash clouds affecting northern Europe

The ash cloud resulting from the 2010 eruption of Eyjafjöll caused severe disruption to air travel across Europe but as a geological event, it is not unprecedented. Analysis of peat and lake sediments from northern Europe has revealed the presence of microscopic layers of Icelandic volcanic ash (tephra). These sedimentary records, together with historical records of Holocene ash falls, demonstrate that Icelandic volcanoes have generated substantial ash clouds that reached northern Europe many times. Here we present the first comprehensive compilation of sedimentary and historical records of ash-fall events in northern Europe, spanning the last 7000 years. Within this period ten tephra layers have been identified in the Faroe Islands, 14 in Great Britain, 11 in Germany, 38 in Scandinavia and 33 in Ireland. Seven ash fall events have been historically documented prior to the Eyjafjöll 2010 event. Ash fall events appear to be more frequent in the last 1500 years, but it is unclear whether this reflects a true increase in eruption frequency or dispersal, or is an artefact of the records themselves or the way they have been generated. In the last 1,000 years, volcanic ash clouds reached Northern Europe with a mean return interval of 53 ± 8 years (the range of return intervals is between 6 and 112 years). Modelling using the ash records for the last millennium indicates that for any 10 year period there is a 17% probability of tephra fallout event in Northern Europe. These values must be considered as conservative estimates due to the nature of tephra capture and preservation in the sedimentary record.

A puzzling periodicity in the pulsating DA white dwarf G 117-B15A

We present time-resolved optical spectrophotometry of the pulsating hydrogen atmosphere (DA) white dwarf G 117-B15A. We find three periodicities in the pulsation spectrum (215 s, 272 s, and 304 s) all of which have been found in earlier studies. By comparing the fractional wavelength dependence of the pulsation amplitudes ( chromatic amplitudes) with models, we confirm a previous report that the strongest mode, at 215 s, has l = 1. The chromatic amplitude for the 272 s mode is very puzzling, showing an increase in fractional amplitude with wavelength that cannot be reproduced by the models for any ` at optical wavelengths. Based on archival HST data, we show that while the behaviour of the 215 s mode at ultra-violet wavelengths is as expected from models, the weird behaviour of the 272 s periodicity is not restricted to optical wavelengths in that it fails to show the expected increase in fractional amplitude towards shorter wavelengths. We discuss possible causes for the discrepancies found for the 272 s variation, but find that all are lacking, and conclude that the nature of this periodicity remains unclear.

Time-resolved optical spectroscopy of the pulsating DA white dwarf HS0507+0434B - New constraints on mode identification and pulsation properties

We present a detailed analysis of time-resolved optical spectra of the ZZ Ceti white dwarf, HS 0507+0434B. Using the wavelength dependence of observed mode amplitudes, we deduce the spherical degree, l, of the modes, most of which have l = 1. The presence of a large number of combination frequencies (linear sums or differences of the real modes) enabled us not only to test theoretical predictions but also to indirectly infer spherical and azimuthal degrees of real modes that had no observed splittings. In addition to the above, we measure line-of-sight velocities from our spectra. We find only marginal evidence for periodic modulation associated with the pulsation modes: at the frequency of the strongest mode in the lightcurve, we measure an amplitude of 2.6 +/- 1.0 kms(-1), which has a probability of 2% of being due to chance; for the other modes, we find lower values. Our velocity amplitudes and upper limits are smaller by a factor of two compared to the amplitudes found in ZZ Psc. We find that this is consistent with expectations based on the position of HS 0507+0434B in the instability strip. Combining all the available information from data such as ours is a first step towards constraining atmospheric properties in a convectionally unstable environment from an observational perspective.

Forensic examination of multilayer white paint by lateral scanning Raman spectroscopy

Multilayer samples of white architectural paint potentially have very high evidential value in forensic casework, because the probability that two unrelated samples will have the same sequence of layers is extremely low. However, discrimination between the different layers using optical microscopy is often difficult or impossible. Here, lateral scanning Raman spectroscopy has been used to chemically map the cross-sections of multilayer white paint chips. It was found that the spectra did allow the different layers to be delineated on the basis of their spectral features. The boundaries between different layers were not as sharp as expected, with transitions occurring over length scales of > 20 µm, even with laser spot diameters <4 µm. However, the blurring of the boundaries was not so large as to prevent recording and identification of spectra from each of the layers in the samples. This method clearly provides excellent discrimination between different multilayer white paint samples and can readily be incorporated into existing procedures for examination of paint transfer evidence.

The spatial distribution of Holocene cryptotephras in north-west Europe since 7 ka: implications for understanding ash fall events from Icelandic eruptions

We present distribution maps for all cryptotephras (distal volcanic ash layers) younger than 7 ka that have been reported from three or more lakes or peatlands in north-west Europe. All but one of the tephras originates from Iceland; the exception has been attributed to Jan Mayen. We find strong spatial patterning in tephra occurrence at the landscape scale; most, but not all of the tephra occurrences are significantly spatially clustered, which likely reflects atmospheric and weather patterns at the time of the eruptions. Contrary to expectations based on atmospheric modelling studies, tephras appear to be at least as abundant in Ireland and northern Scotland as in Scandinavia. Rhyolitic and other felsic tephras occur in lakes and peatlands throughout the study region, but andesitic and basaltic tephras are largely restricted to lake sites in the Faroe Islands and Ireland. Explanations of some of these patterns will require further research on the effects of different methodologies for locating and characterizing cryptotephras. These new maps will help to guide future investigations in tephrochronology and volcanic hazard analysis.

First record of greater white-toothed shrew Crocidura russula in Ireland

1. Skeletal remains of greater white-toothed shrew Crocidura russula were recovered from barn owl Tyto alba and kestrel Falco tinnunculus pellets collected at 15 locations in Counties Tipperary and Limerick in Ireland in September 2007 and March 2008. Seven greater white-toothed shrews were trapped at four locations in Tipperary in March 2008. This is the first Irish record of C. russula and compelling evidence that the species is established in Ireland.

Infrared spectrum of an extremely cool white-dwarf star

White dwarfs are the remnant cores of stars that initially had masses of less than 8 solar masses. They cool gradually over billions of years, and have been suggested(1,2) to make up much of the 'dark matter' in the halo of the Milky way. But extremely cool white dwarfs have proved difficult to detect, owing to both their faintness and their anticipated similarity in colour to other classes of dwarf stars. Recent improved models(3-5) indicate that white dwarfs are much more blue than previously supposed, suggesting that the earlier searches may have been looking for the wrong kinds of objects. Here we report an infrared spectrum of an extremely cool white dwarf that is consistent with the new models. We determine the star's temperature to be 3,500 +/- 200 K, making it the coolest known white dwarf. The kinematics of this star indicate that it is in the halo of the Milky Way, and the density of such objects implied by the serendipitous discovery of this star is consistent with white dwarfs dominating the dark matter in the halo.

On the parallax of WD 0346+246: a halo white dwarf candidate

We present a parallax measurement for the very cool degenerate WD 0346+246, the serendipitous discovery of which was reported by Hambly et al, We find an absolute parallax of 36 +/- 5 mas, yielding a distance estimate of 28 +/- 4pc. The resulting absolute visual magnitude of the object is M-V = 16.8 +/- 0.3, making it the second-lowest luminosity white dwarf currently known. We use the distance estimate and measured proper motion to show that the object has kinematics consistent with membership of the Galactic halo. WD 0346+246 is therefore by far the coolest and least luminous of only a handful of plausible halo white dwarf candidates. As such, the object has relevance to the ongoing debate concerning the results of microlensing experiments and the nature of any baryonic dark matter component to the Galactic halo residing in stellar remnants.

The 'Unhomely' White Women of Antillean Writing

While the field known as ‘Whiteness Studies’ has been thriving in Anglophone criticism and theory for over 25 years, it is almost unknown in France. This is partly due to epistemological and political differences, but also to demographic factors — in contrast with the post-plantation culture of the US, for example, whites in Martinique and Guadeloupe are a tiny minority of small island populations. Yet ‘whiteness’ remains a phantasized and a fetishized state in the Antillean imaginary, and is strongly inflected by gender. This article sketches the emergence of ‘white’ femininity during slavery, then examines its representation in the work of a number of major Antillean writers (Condé, Placoly, Confiant, Chamoiseau). In their work, a cluster of recurring images and leitmotifs convey the idealization or, more commonly, the pathologization, of the white woman; these images resonate strongly with Bhabha’s ‘unhomely’, and convey the disturbing imbrication of sex and race in Antillean history.