A Brief History of Star Formation and Chemical Enrichment in the Bulge of the Milky way

Observations of the stellar content of the bulge of the Milky Way can provide critical guidelines for the interpretation of observations of distant galaxies, in particular for understanding their stellar content and evolution. In this brief overview I will first highlight some recent work directed towards measuring the history of star formation and the chemical composition of the central few parsecs of the Galaxy. These observations point to an episodic history of star formation in the central region with several bursts having occurred over the past few 100 Myr (e.g. Blum et al., 1996b). High resolution spectroscopic observations by Ramírez et al. (1998) of luminous M stars in this region yield a near solar value for [Fe/H] from direct measurements of iron lines. Then I will present some results from an ongoing program by my colleagues and myself the objective of which is the delineation of the star formation and chemical enrichment histories of the central 100 parsecs of the Galaxy, the `inner bulge'. From new photometric data we have concluded that there is a small increase in mean [Fe/H] from Baade's Window to the Galactic Center and deduce a near solar value for stars in the central region. For radial distances greater than 1^° from the Galactic Center we fail to find a measurable population of stars that are significantly younger than those in Baade's Window. Within 1^° we find a number of luminous M giants that most likely are the result of a star formation episode not more than one or two Gyr ago. This revised version was published online in July 2006 with corrections to the Cover Date.     

Elasticity of antigorite,seismic detection of serpentinites,and anisotropy in subduction zones

Serpentinization of the mantle wedge is an important process that influences the seismic and mechanical properties in subduction zones. Seismic detection of serpentines relies on the knowledge of elastic properties of serpentinites, which thus far has not been possible in the absence of single-crystal elastic properties of antigorite. The elastic constants of antigorite, the dominant serpentine at high-pressure in subduction zones, were measured using Brillouin spectroscopy under ambient conditions. In addition, antigorite lattice preferred orientations (LPO) were determined using an electron back-scattering diffraction (EBSD) technique. Isotropic aggregate velocities are significantly lower than those of peridotites to allow seismic detection of serpentinites from tomography. The isotropic V_P/V_S ratio is 1.76 in the Voigt–Reuss–Hill average, not very different from that of 1.73 in peridotite, but may vary between 1.70 and 1.86 between the Voigt and Reuss bonds. Antigorite and deformed serpentinites have a very high seismic anisotropy and remarkably low velocities along particular directions. V_P varies between 8.9 km s^? 1 and 5.6 km s^? 1 (46% anisotropy), and 8.3 km s^? 1 and 5.8 km s^? 1 (37%), and V_S between 5.1 km s^? 1 and 2.5 km s^? 1 (66%), and 4.7 km s^? 1 and 2.9 km s^? 1 (50%) for the single-crystal and aggregate, respectively. The V_P/V_S ratio and shear wave splitting also vary with orientation between 1.2 and 3.4, and 1.3 and 2.8 for the single-crystal and aggregate, respectively. Thus deformed serpentinites can present seismic velocities similar to peridotites for wave propagation parallel to the foliation or lower than crustal rocks for wave propagation perpendicular to the foliation. These properties can be used to detect serpentinite, quantify the amount of serpentinization, and to discuss relationships between seismic anisotropy and deformation in the mantle wedge. Regions of high V_P/V_S ratios and extremely low velocities in the mantle wedge of subduction zones (down to about 6 and 3 km.s^?1 for V_P and V_S, respectively) are difficult to explain without strong preferred orientation of serpentine. Local variations of anisotropy may result from kilometer-scale folding of serpentinites. Shear wave splittings up to 1–1.5 s can be explained with moderately thick (10–20 km) serpentinite bodies.     

Spatial analysis of linguistic data with GIS functions

Abstract

During the 1980s techniques for analysis of geographical patterns have been refined to the point that they may be applied to data from many fields. Quantitative spatial analysis and existing functions available in geographical information systems (GIS) enable computerized implementations of these spatial analysis methods. This paper describes the application of quantitative spatial analysis and GIS functions to analysis of language data, using the extensive files of the Linguistic Atlas of the Middle and South Atlantic States (LAMSAS). A brief review of recent development of using quantitative and statistical methods for analysing linguistic data is also included.     

SOIL,SUBSOIL, AND FOREST COMPOSITION IN SOUTH-CENTRAL MICHIGAN,USA

Although soil texture is an important predictor of upland forest composition in southern Michigan, the relationship in some areas is weak and other environmental factors may exert stronger control on species composition. One of these may be concealed subsoil lithology where coarse-textured glaciofluvial sediments are buried beneath finer-textured till. Samples of forest composition, soil, and subsoil characteristics from 48 less-disturbed woodlots in the south-central Lower Peninsula reveal that upland oaks and hickories are predominant where the till veneer is thin and sand and gravel are relatively near the surface. Where till is relatively thick and outwash is deeply buried, woodlot composition is sugar maple-beech. In each of these cases, soil texture is unrelated to stand composition. The likely effect of buried near-surface glaciofluvial sediments is moisture stress such that xeric species dominate these drier sites. The influence of subsoil on forest geography is a significant new finding with regard to southern Michigan and has possible application elsewhere in glaciated eastern North America.     

Application of the Ti-in-quartz thermobarometer to rutile-free systems. Reply to: a comment on: ‘TitaniQ under pressure: the effect of pressure and temperature on the solubility of Ti in quartz’ by Thomas et al.

The premise of the Wilson et al. comment is that the Ti-in-quartz solubility calibration (Thomas et al. in Contrib Mineral Petrol 160:743–759, 2010) is fundamentally flawed. They reach this conclusion because P–T estimates using the Ti-in-quartz calibration differ from their previous interpretations for crystallization conditions of the Bishop and Oruanui rhyolites. If correct, this assertion has far-reaching implications, so a careful assessment of the Wilson et al. reasoning is warranted. Application of the Ti-in-quartz calibration as a thermobarometer in rutile-free rocks requires an estimation of TiO₂ activity in the liquid ( (liquid–rutile); referenced to rutile saturation) and an independent constraint on either P or T to obtain the crystallization temperature or pressure, respectively. The foundation of Wilson et al.’s argument is that temperature estimates obtained from Fe–Ti oxide thermometry accurately reflect crystallization conditions of quartz in the two rhyolites discussed. We maintain that our experimental approach is sound, the thermodynamic basis of the Ti-in-quartz calibration is fundamentally correct, and our experimental results are robust and reproducible. We suggest that the reason Wilson et al. obtain implausible pressure estimates is because estimates for T and they used as input values for the Ti-in-quartz calibration are demonstrably too high. Numerous studies show that Fe–Ti oxide temperature estimates of some rhyolites are substantially higher than those predicted by well-constrained phase equilibria. In this reply, we show that when reasonable input values for T and (liquid–rutile) are used, pressure estimates obtained from the Ti-in-quartz calibration are well aligned with phase equilibria and essentially identical to melt inclusion volatile saturation pressures.     

Overview and Assessment of Antarctic Ice-Sheet Mass Balance Estimates: 1992�C2009

Mass balance estimates for the Antarctic Ice Sheet (AIS) in the 2007 report by the Intergovernmental Panel on Climate Change and in more recent reports lie between approximately +50 to ?250 Gt/year for 1992 to 2009. The 300 Gt/year range is approximately 15% of the annual mass input and 0.8 mm/year Sea Level Equivalent (SLE). Two estimates from radar altimeter measurements of elevation change by European Remote-sensing Satellites (ERS) (+28 and ?31 Gt/year) lie in the upper part, whereas estimates from the Input-minus-Output Method (IOM) and the Gravity Recovery and Climate Experiment (GRACE) lie in the lower part (?40 to ?246 Gt/year). We compare the various estimates, discuss the methodology used, and critically assess the results. We also modify the IOM estimate using (1) an alternate extrapolation to estimate the discharge from the non-observed 15% of the periphery, and (2) substitution of input from a field data compilation for input from an atmospheric model in 6% of area. The modified IOM estimate reduces the loss from 136 Gt/year to 13 Gt/year. Two ERS-based estimates, the modified IOM, and a GRACE-based estimate for observations within 1992?C2005 lie in a narrowed range of +27 to ?40 Gt/year, which is about 3% of the annual mass input and only 0.2 mm/year SLE. Our preferred estimate for 1992?C2001 is ?47 Gt/year for West Antarctica, +16 Gt/year for East Antarctica, and ?31 Gt/year overall (+0.1 mm/year SLE), not including part of the Antarctic Peninsula (1.07% of the AIS area). Although recent reports of large and increasing rates of mass loss with time from GRACE-based studies cite agreement with IOM results, our evaluation does not support that conclusion.