Young stellar populations in the local group: an HST and GALEX comprehensive study

The study of the stellar constituents of star-forming sites in a wide variety of conditions yields the key to interpreting wide-field UV-optical imaging of extended nearby galaxies, and of distant galaxies. We obtained six-band imaging (from far-UV to I) with HST-WFPC2 of 67 sites of recent star formation in eight Local Group galaxies. HST pointings were selected from GALEX wide-field FUV imaging, which traces the young stellar populations. The HST observations were optimized to characterize the hottest, most massive stars in these regions. From the HST photometry, analyzed with stellar model colors, we derived the physical parameters of the massive stars in each field, and of the extinction by interstellar dust. The HST results are used to interpret GALEX UV measurements of SF across the entire galaxies. Our comprehensive photometric study at HST resolution (sub-pc scale in these galaxies) also provides an ideal selection of targets for follow-up spectroscopy with large ground-based telescopes, and in the UV with HST- or WSO-class telescopes, to clarify the influence of metallicity on the properties and the evolution of massive stars.     

Mediterranean Seagrass Growth and Demography Responses to Experimental Warming

We experimentally examined the effects of increased temperature on growth and demography of two Mediterranean seagrasses Posidonia oceanica and Cymodocea nodosa. Shoots of C. nodosa and seedlings and shoots of P. oceanica were kept in mesocosms for 3?months and exposed to temperatures between 25 and 32?°C encompassing the range of maximum summer seawater temperatures projected for the Mediterranean Sea during the twenty-first century. The response of P. oceanica seedlings to warming was evident with reduced growth rates, leaf formation rates and leaf biomass per shoot. Younger life stages of P. oceanica may therefore be particularly vulnerable to climate change and warming. Leaf formation rates in the shoots of P. oceanica declined with increasing temperature and the lowest population growth (?0.005?day^?1) was found at 32?°C. Temperature effects on C. nodosa were variable. Rhizome growth increased with warming (0.07?C0.09?cm?day^?1?°C of warming), whereas other indicators of plant performance (aboveground/belowground biomass, leaf biomass and population growth) appeared to be stimulated by increased temperature to a threshold temperature of around 29?C30?°C beyond which they declined. P. oceanica and C. nodosa are likely to be negatively impacted by the effects of global warming over the next century and climate change poses a significant challenge to seagrasses and may stress these key habitat-forming species that are already suffering losses from anthropogenic impacts.     

Book reviews

Deep Drilling in Crystalline Bedrock, Volumes 1 and 2 A. Bodén and K. G. Eriksson ( eds ), Springer-Verlag , 1988, Volume 1: The Deep Gas Drilling in the Siljan Impact Structure, Sweden, and Astroblemes, xiv + 364 pp, ISBN 3-540-18995-5, $83.50 (DM138); Volume 2: Review of Deep Drilling Projects, Technology, Sciences and Prospects for the Future, xii + 538 pp, ISBN 3-540-18996-3, $102 (DM168).
Seismic strong motion synthetics Ed. B. A. Bolt
GPS Techniques Applied to Geodesy and Surveying. Lecture Notes in Earth Sciences, Vol. 19 E. Groten and R. Strauss ( eds )
Interpretation of filtered gravity maps F. Steiner and L. Zilahi-Sebess
Surface Waves and Discontinuities P. Malischewsky     

Chondrule-like objects and brown glasses in howardites

Abstract— Chondrule-like objects and brown glasses were analyzed in the howardites, Bununu, Malvern, Monticello, Pavlovka, and Yamato 7308. The objects are very similar to chondrules in ordinary and carbonaceous chondrites. Like the brown glasses the chondrule-like objects could have been produced by impact melting that left some crystalline nuclei, followed by a slower cooling rate than for the glasses. Alternatively, these objects are chondrules implanted from chondrite impactors. They are, however, without rims or any adhering matrix. The brown glasses appear to represent melting of average regolithic surface material, except for Monticello and Y7308, both of which have some siliceous glasses. The siliceous glasses could not have been produced by vapor fractionation but by melting of differentiated lithologies such as fayalitic granites. Impact mechanics indicates that howardites with abundant brown glasses came from an asteroid larger than Vesta (>400 km radius), upon which impacts occurred at relative velocities of up to 5 km/s. Howardites with little or no brown glasses came from a smaller parent body. We conclude that at least two parent bodies are likely sources for the basaltic achondrites.     

Chromium and phosphorus enrichment in the metal of type II (C2) carbonaceous chondrites

Electron microprobe analyses of metal grains in nine C2 meteorites show consistently high Cr and P contents, with large grain to grain variations within individual meteorites. Cr ranges from 0.16 to 1.0 wt.% (average 0.6 per cent for 43 analyses). P ranges from 0.00 to 3.2 wt.% (average 0.42 per cent). In addition, metal grains in seven C3 meteorites show a lesser enrichment of Cr, 0.00 to 0.7 per cent (average 0.13 per cent for 59 analyses), with no P present. Both of these elements, Cr and P, are generally below detection in the metal of other chondrite groups, equilibrated and unequilibrated. C2 metal grains occur typically as spherical to ovate blebs contained within single, euhedral forsterite crystals or crystal fragments that are either isolated in the black C2 matrix or are in clusters making up white inclusions. Metal is rare within true chondrules. Calculations of the expected Cr contents in metal condensing directly from a solar nebular gas agree remarkably well with the observed values. Unfortunately, no calculation is possible for P because of insufficient data at the present time. The composition and the textural relationships indicate this Cr, P rich metal, and the enclosing forsterite are direct condensates from a cooling solar nebula. Cr and P, in the quantities reported here, characterize C2 metal.     

Embryo aberrations in sea ice amphipod Gammarus wilkitzkii exposed to water soluble fraction of oil

Offshore oil and gas activities have gained momentum in the European Arctic, raising concerns of the potential impact of oil-related chemicals on the polar marine ecosystem, notably on sea ice communities. Herein, malformations on embryos of the Arctic sea ice amphipod Gammaruswilkitzkii exposed to the water soluble fraction of oil were studied. The females ranged from development stage three to nine. No differences in reproductive stage were observed among the different treatments after 30 days of exposure. Frequency of embryo aberrations was significantly higher in the high-dose compared to controls, indicating that the embryos of G. wilkitzkiii were affected by oil.     

Determining kinematic order and relative age of faulting via flexural‐kinematic restoration: A case study in far western Nepal

Forward modeled, balanced cross sections that account for the flexural response to thrust loading and erosional unloading can verify and refine the kinematic sequence of deformation in fold‐thrust belts as well as help assess the validity of a balanced cross section. Results from flexural‐kinematic reconstructions that indicate either the cross section, the kinematic order or both are invalid include: (a) a predicted final topography that is dramatically different from the actual topography; (b) large normal fault or thrust fault bounded synorogenic basins that are not present in the mapped geology; and/or (c) an exhumation history that is not consistent with provenance records in the basin or measured thermochronometers. Where detailed measured foreland basin sections exist, flexural‐kinematic modeling of fold‐thrust belt deformation, including out‐of‐sequence (OOS) faults can predict a foreland basin evolution that can be compared to measured data. The modeling process creates a “pseudostratigraphy” in the modeled foreland. The pseudostratigraphy and predicted provenance of each modeled stratigraphic increment can be directly compared to measured stratigraphic sections. We present a case study using two cross sections through the Himalaya of far western Nepal (Api and Simikot) to assess the validity of the section geometries and the resulting kinematic histories, displacement rates, flexural wave response and predicted provenance for both sections. Insights from combining the flexural‐kinematic models with existing stratigraphic data include: (a) Changing the order of proposed OOS and normal faults to earlier in the evolution of the fold‐thrust belt was necessary to reproduce the foreland provenance data. We argue that OOS thrust and normal faults in the Api section occurred between 11 and 4 Ma. (b) Published shortening estimates for the Simikot cross section are too high (>50 km), resulting in unrealistic shortening rates up to 80 mm/yr between 25 and 20 Ma. (c) Flexural forward models with and without an additional sediment loading modeling step indicate that while sediment loading does not have a measurable effect on the magnitude and location of erosion within the fold‐thrust belt, it does have a small effect on accumulation rates and thus the predicted age of stratigraphic boundaries when compared to measured stratigraphic thicknesses and age. Thickness difference range from 0.2 to 0.5 km and can result in predicted age differences of ca. 1 Ma. Accounting for both flexural isostacy and erosion can eliminate unviable kinematic sequences and when combined with provenance data from measured stratigraphic sections, can provide insight into the order, age and rate of deformation.     

Composite lightcurve of asteroid Moskva (787)

89 CCD frames of the asteroid Moskva (787) were obtained over six nights. Lightcurves have been acquired for each night. We suggest a possible composite lightcurve with a corresponding rotational period of 0.4 days. This is to the knowledge of the authors the first lightcurve of Moskva(787) to be published.