Probing the Formation and Evolution of early-type galaxies: the SAURON project

We are conducting a systematic study of a carefully selected sampleof nearby E/S0 galaxies and Sa bulges using the unique panoramic integral-fieldspectrograph SAURON, mounted at the WHT. The goal of the SAURON projectis to fully map the gaseous/stellar kinematics and the stellar populations of a representative sample of 80 early-type galaxies up to 1 Re,probing different environments (clusters, field). These data, used in combination with existing ground-based and HST observations, and fed to the theoretical machinery we have developed, will allow to determine theintrinsic dynamical structure of the galaxies. We will also measure the masses of central black holes, relate the internal dynamics to the ageand metallicity of the stellar populations, and establish the historyof metal enrichment as a function of Hubble type and environment. Some brief results on two targets observed during the SAURON campaign will serve as an illustration of the unique and high quality data we are currently gathering. This revised version was published online in September 2006 with corrections to the Cover Date.     

A perturbation theory for Love waves in anelastic media

Summary. We give a systematic formulation and a rigorous justification of a perturbation technique for the computation of the eigenvalues and eigenfunctions of Love waves (and toroidal oscillations by an appropriate change for variables) in an anelastic medium with a constitutive law modelling geophysical media of current interest such as the Kelvin—Voigt Solid, the Maxwell Solid, the Standard Linear Solid, and the Standard Linear Solid with a continuous spectrum of relaxation times. We develop expressions relating the eigenvalues of eigenfunctions for Love waves in a continuously varying vertically stratified anelastic half-space to the corresponding elastic eigenvalues and eigenfunctions. Analytically, our correspondence principle has the form of a regular perturbation expansion in terms of a parameter for both the eigenvalues and eigenfunctions. The identification of ɛ is motivated by the dissipativity principle of viscoelasticity theory. Moreover, we show that our correspondence principle applies respectively only in the high and low frequency range for the Maxwell and Kelvin—Voigt Solids. Outside of the applicable range of frequencies, our correspondence principle yields no useful information. For the family of Standard Linear Solids it is uniformly applicable for all non-zero frequencies.
We also derive an explicit formula to estimate the radius of convergence of our perturbation expansions. This estimate of the radius of convergence for each eigenvalue and eigenfunction is functionally defined by the constitutive model for the anelastic medium. The estimate is frequency dependent and depends on the separation distance between the eigenvalue and the remainder of the spectrum of the corresponding elastic problem.     

Variations of Pb in a mine-impacted tropical river,Taxco, Mexico: Use of geochemical,isotopic and statistical tools

The potential environmental threat from Pb in Mexican rivers impacted by historic mining activities was studied using geochemical, isotopic and statistical methods. Lead geochemical fractionation and factor analysis of fractionated and total Pb indicate that anthropogenic sources have contributed significantly to Pb concentrations, while natural sources have contributed only small amounts. The analyses also indicate that two main processes are controlling the total Pb variation throughout the year in both rivers: erosion with discharge processes, and proportional dilution related to differences in grain-size distribution processes. Bio-available Pb in riverbed sediments was greater than 50% in 80% of the sampling stations indicating a high potential environmental risk, according to the risk assessment criteria (RAC). Nevertheless, based on the environmental chemistry of Pb and on multivariate statistical analysis, these criteria did not apply in this particular case. Significant differences (p < 0.05) in total Pb concentrations (from 50 to 5820 mg kg⁻¹) and in the geochemical fractionation were observed as a function of seasonality and location along the river flow path. In the Cacalotenango and Taxco rivers, the highest concentrations of total Pb were found at stations close to tailings during the rainy and post-rainy seasons. The geochemistry of Pb was mainly controlled, during the dry and post-rainy seasons by the organic matter and carbonate content, and in the rainy season by hydrological conditions (e.g., the increase in river flux), hydrological basin erosion, and the suspended solids concentration. Isotopic analyses of the ²¹⁰Pb/²¹⁴Pb ratio showed three processes in the Cacalotenango and Taxco rivers. First, the accumulation of atmospheric excess ²¹⁰Pb, favoured during calmer hydrodynamic conditions in the river basin commonly during dry periods, is recorded by a ²¹⁰Pb/²¹⁴Pb ratio of >1. In the case of the Cacalotenango river, ²¹⁰Pb did show preferential accumulation in sediments. Second, a ²¹⁰Pb/²¹⁴Pb ratio of <1 in some samples might be indicating (a) the presence of eroded material from weathered tailings with similar ²¹⁰Pb depletion (probably by secular disequilibrium caused by weathering or mining processes, which was observed in both rivers), or (b) preferential transport of Pb and sediments during high energy events (e.g., flow increase, as is the case of Taxco river). Third, no significant changes in the ²¹⁰Pb/²¹⁴Pb ratio might be reflecting a situation where mining material is not entering the system, or where hydrodynamic changes throughout the year of equal magnitude allow the system to reach a new equilibrium for the ²¹⁰Pb/²¹⁴Pb ratio. Finally, based on these results it is recommended that inhabitants of the studied area avoid using water from the Cacalotenango river in the rainy and post-rainy seasons, and to take precautions for its use in the dry season, such as allowing suspended material to settle before use, and that they should avoid use of Taxco river water at all times.     

Fast variability of BL Lacertae at 1 μm

We present the results of photometric observations of BL Lacertae at 1 μm performed during the strong outburst that occurred in the summer of 1997. Measurements were carried out using the F99 filter of the Arizona system. Simultaneous observations in the B V bands were made with other telescopes. Large and fast variations were observed on the night of August 2 when the brightness of BL Lacertae changed by ∼ 0.5 mag in about 2 h: the variation amplitude is greater at higher frequency. Some implications of these results for the origin of the fast variations are discussed. We also report the first F99 calibration for three reference stars in the BL Lac field.     

Measuring impact crater depth throughout the solar system

One important, almost ubiquitous, tool for understanding the surfaces of solid bodies throughout the solar system is the study of impact craters. While measuring a distribution of crater diameters and locations is an important tool for a wide variety of studies, so too is measuring a crater's “depth.” Depth can inform numerous studies including the strength of a surface and modification rates in the local environment. There is, however, no standard data set, definition, or technique to perform this data-gathering task, and the abundance of different definitions of “depth” and methods for estimating that quantity can lead to misunderstandings in and of the literature. In this review, we describe a wide variety of data sets and methods to analyze those data sets that have been, are currently, or could be used to derive different types of crater depth measurements. We also recommend certain nomenclature in doing so to help standardize practice in the field. We present a review section of all crater depths that have been published on different solar system bodies which shows how the field has evolved through time and how some common assumptions might not be wholly accurate. We conclude with several recommendations for researchers which could help different data sets to be more easily understood and compared.     

PDRS and Shocks in S106 IR and CEP a East

We present SWS grating scans of pure H2 rotational lines, as well as several infrared fine-structure lines for two embedded Young Stellar Objects, S106 IR and Cep A East. Excitation temperatures and masses were derived from the low-lying pure rotational levels of H2 and are 490 and 740 K and 0.04 and 0.007 M⊙ for S106 and Cep A, respectively. The observations were compared to theoretical models for PDRs and dissociative and non-dissociative shocks. The infrared spectrum of S106 IR is dominated by PDR emission while that of Cep A East has a large shock component. We suggest that the difference between these two objects could reflect an evolutionary trend. This revised version was published online in August 2006 with corrections to the Cover Date.     

Comparison of Fry strain ellipse and AMS ellipsoid trends to tectonic fabric trends in very low-strain sandstone of the Appalachian fold–thrust belt

In moderately to highly strained sandstones, both the long axis of the bedding-parallel finite-strain ellipse, as calculated by the normalized Fry method, and the projection of the long axis of the AMS ellipsoid on the plane of bedding, align well with local “structural grain” (trends of cleavage, folds, and faults). This relationship implies that results of both 2D Fry and AMS analyses represent the local layer-parallel tectonic strain component. Do both methods provide comparable results for very low-strain sandstone (e.g., <5%)? To address this question, Fry and AMS analyses were conducted in very low-strain sandstone from two localities in the Appalachian foreland fold–thrust belt: near Rosendale in New York and the Lackawanna synclinorium of Pennsylvania. We compared the map projections of both bedding-parallel Fry ellipses and AMS ellipsoids to the local structural grain. In both study areas, projections of the long axis of Fry strain ellipses do not cluster in a direction parallel to structural grain, whereas the projection of the long axes of AMS ellipsoids do cluster closely to structural grain. This observation implies that in very low-strain sandstone, AMS analysis provides a more sensitive “quick” indicator of tectonic fabric than does normalized Fry analysis.     

Grazing itineraries and forage selection of goats in the Al Jabal al Akhdar mountain range of northern Oman

In view of the repeatedly reported overstocking of the high-altitude pastures on Al Jabal al Akhdar, northern Oman, plant species abundance, cover and frequency, and herbaceous mass yield were studied in ungrazed versus heavily grazed areas of this mountain range. In addition, plant species selection by goats along a gradient of 1000–2000 m and spatial extent of pasture areas were investigated after abundant rainfall and a subsequent 6-months dry spell by means of manual observation and GPS/GIS tools.The substantially higher species diversity and herbaceous mass yield in the ungrazed area illustrate the production potential of these mountain pastures or, respectively, the biodiversity and productivity loss resulting from continuous grazing. The concentration of goats' selection on only a dozen herbaceous and ligneous species favours pasture encroachment with poisonous shrubs such as Nerium mascatense in the lower and Dodonaea viscosa in the higher altitudes. Given the spatially limited extent of pasture areas, these are exposed to high stocking rates. Therefore, grazing and feeding schemes need to be developed which reduce livestock pressure on the pastures, taking into account local property rights, herding skills and the recovery potential of the vegetation, which heavily depends on unpredictable rainfall events.