The evolved B[e] star HD 87643: observations and a radiation-driven disc wind model for B[e] stars

New high-resolution spectroscopic and medium-resolution spectropolarimetric data of the B[e] star HD 87643 are presented, complemented with optical broad- and narrow-band imaging. The spectrum of HD 87643 exhibits the hybrid characteristics well known to be representative of the group of B[e] stars; a fast wind with an expansion velocity in excess of 1000 km s⁻¹ is measured in the hydrogen and helium lines, while a slower component is traced by lower excitation lines and forbidden lines. Clues to the geometry of the rapidly expanding circumstellar shell are provided by the startling polarization changes across Hα. Comparison with published schematic calculations indicates that the polarizing material is located in a slowly rotating, expanding disc structure. A hydrodynamical model is then presented, the results of which are consistent with the original two-wind concept for B[e] stars, and which exhibits kinematic properties that may well explain the observed spectral features in HD 87643. The model calculations use as input a B star undergoing mass loss, surrounded by an optically thick disc. The resulting configuration consists of a fast polar wind from the star and a slowly expanding disc wind. The model also predicts that the stellar wind at intermediate latitudes is slower and denser than in the polar region.     

Kinetics of the Gas-Phase Reactions of OH and NO3 Radicals and O3 with the Monoterpene Reaction Products Pinonaldehyde, Caronaldehyde, and Sabinaketone

Using a relative rate method, rate constants have been measured for the gas-phase reactions of OH and NO3 radicals with pinonaldehyde, caronaldehyde and sabinaketone at 296 ± 2 K. The OH radical reaction rate constants obtained are (in units of 10–12 cm3 molecule–1 s–1): pinonaldehyde, 48 ± 8; caronaldehyde, 48 ± 8; and sabinaketone, 5.1 ± 1.4, and the NO3 radical reaction rate constants are (in units of 10–14 cm3 molecule–1 s–1): pinonaldehyde, 2.0 ± 0.9; caronaldehyde, 2.5 ± 1.1; and sabinaketone, 0.036 ± 0.023, where the error limits include the estimated overall uncertainties in the rate constants for the reference compounds. Upper limits to the O3 reaction rate constants were also obtained, of <2 × 10–20 cm3 molecule–1 s–1 for pinonaldehyde and caronaldehyde, and <5 × 10–20 cm3 molecule–1 s–1 for sabinaketone. These reaction rate constants are combined with estimated ambient tropospheric concentrations of OH radicals, NO3 radicals and O3 to calculate tropospheric lifetimes and dominant transformation process(es) of these and other monoterpene reaction products.     

Natural organics as fluorescent tracers of river-sea mixing

The use of dissolved organic matter fluorescence as a tracer of river-sea mixing was examined in two South Carolina estuaries. Fluorescence declined linearly with seawater dilution in laboratory mixing studies, and also behaved conservatively in an estuary where a single river emptied into a bay. Fluorescence-salinity relationships were also studied in another estuary where a piedmont river (high suspended sediment, low fluorescence) and a coastal plains river (low sediment, high fluorescence) mixed with ocean water. The factor of 2 or greater difference in fluorescence between the two rivers allowed their relative contribution to the estuarine water mass to be distinguished. Petroleum hydrocarbons, measured in estuarine water at 0·7-1·8 μg l⁻¹ concentrations, contributed negligibly to water fluorescence.     

Impact of Climate Change on <Emphasis Type="Italic">Vibrio vulnificus</Emphasis> Abundance and Exposure Risk

Vibrio species are marine bacteria that occur in estuaries worldwide; many are virulent human pathogens with high levels of antibiotic resistance. The average annual incidence of all Vibrio infections has increased by 41% between 1996 and 2005. V. vulnificus (Vv), a species associated with shellfish and occurring in the US Southeast, has ranges of temperature (16–33 °C) and salinity (5–20 ppt) dependencies for optimal growth. Increased water temperatures caused by atmospheric warming and increased salinity gradients caused by sea level rise raise concerns for the effect of climate change on the geographic range of Vv and the potential for increased exposure risk. This research combined monthly field sampling, laboratory analysis, and modeling to identify the current occurrence of Vv in the Winyah Bay estuary (South Carolina, USA) and assess the possible effects of climate change on future geographic range and exposure risk in the estuary. Vv concentrations ranged from 0 to 58 colony forming units (CFU)/mL, salinities ranged from 0 to 28 ppt, and temperature from 18 to 31 °C. A significant empirical relationship was found between Vv concentration and salinity and temperature that fit well with published optimal ranges for growth for these environmental parameters. These results, when coupled with an existing model of future specific conductance, indicated that sea level rise has a greater impact on exposure risk than temperature increases in the estuary. Risk increased by as much as four times compared to current conditions with the largest temporally widespread increase at the most upriver site where currently there is minimal risk.     

An eclipse of the X-ray flux from the dwarf nova OY Carinae in quiescence

We present a phase-resolved ROSAT HRI X-ray light curve of the dwarf nova OY Car in quiescence. The X-ray flux is eclipsed at the same time as the optical eclipse of the primary, and the region of X-ray emission is comparable in size to the white dwarf. We use subsequent optical observations to update the orbital ephemeris of the system.     

The granulitic impactite suite: Impact melts and metamorphic breccias of the early lunar crust

Abstract— An important and poorly understood group of rocks found in the ancient lunar highlands is called “feldspathic granulitic impactites.” Rocks of the granulite suite occur at most of the Apollo highlands sites as hand samples, rake samples, clasts in breccias, and soil fragments. Most lunar granulites contain 70–80% modal plagioclase, but they can range from anorthosite to troctolite and norite. Previous studies have led to different interpretations for the thermal history of these rocks, including formation as igneous plutons, long-duration metamorphism at high temperatures, and short-duration metamorphism at low temperatures. This paper reports on a study of 24 polished thin sections of lunar granulites from the Apollo 15, 16, and 17 missions. We identify three different textural types of granulitic breccias: poikilitic, granoblastic, and poikilitic-granoblastic breccias. These breccias have similar equilibration temperatures (1100 ± 50 °C), as well as common compositions. Crystal size distributions in two granoblastic breccias reveal that Ostwald ripening took place during metamorphism. Solid-state grain growth and diffusion calculations indicate relatively rapid cooling during metamorphism (0.5 to 50 °C/year), and thermal modeling shows that they cooled at relatively shallow depths (<200 m). In contrast, we conclude that the poikilitic rocks formed by impact melting, whereas the poikilitic-granoblastic rocks were metamorphosed and may have partially melted. These results indicate formation of lunar granulites in relatively small craters (30–90 km in diameter), physically associated with the impact-melt breccia pile, and possibly from fine-grained fragmental precursor lithologies.     

Linking hydrology and stream geochemistry in urban fringe watersheds

Urbanization represents a dramatic example of human interference with the hydrological cycle. Changes to ground cover affect both the hydrological and geochemical characteristics in a watershed. Ecosystem degradation also occurs in undisturbed watersheds at the “urban fringe” due to regional atmospheric deposition. These urban fringe catchments can also serve as an upstream source of various chemical constituents into downstream (urban) river systems. The current study focuses on the impacts of regional urbanization in the upper Arroyo Seco watershed located on the eastern edge of the Los Angeles basin, where estimates of dry deposition are considered some of the highest in North America. Collected hydrologic, geochemical and atmospheric data were assessed at seasonal time scales to evaluate current hydrochemical dynamics. Stream water chemical composition in the upper Arroyo Seco watershed exhibits significant seasonal variability, particularly for . Almost all study solutes show dilution behavior. However, hydrologically enhanced behavior was observed for with increased concentrations during the wet season. Seasonal stream concentration–discharge relationships were developed using a hyperbolic dilution model. The developed model was then used to predict concentrations for observational gaps in stream water chemical composition, allowing for seasonal and annual mass loadings to be estimated for the downstream urban stream. The hydrological signal in the resultant chemical loads is extremely strong, especially during the wet season. Both observations and model predictions indicate the watershed is a sink for atmospheric nitrate and a source for various cations.     

Diel patterns in coastal‐stream nitrate concentrations linked to evapotranspiration in the riparian zone of a low‐relief,agricultural catchment

Evapotranspiration (ET) can cause diel fluctuations in the elevation of the water table and the stage in adjacent streams. The diel fluctuations of water levels change head gradients throughout the day, causing specific discharge through near‐stream sediment to fluctuate at the same time scale. In a previous study, we showed that specific discharge controls the residence time of groundwater in streambed sediment that, in turn, exerted the primary control on removal from groundwater passing through the streambed. In this study, we examine the magnitude of diel specific discharge patterns through the streambed driven by ET in the riparian zone with a transient numerical saturated–unsaturated groundwater flow model. On the basis of a first‐order kinetic model for removal, we predicted diel fluctuations in stream concentrations. Model results indicated that ET drove a diel pattern in specific discharge through the streambed and riparian zone (the removal zones). Because specific discharge is inversely proportional to groundwater travel time through the removal zones and travel time determines the extent of removal, diel changes in ET can result in a diel pattern in concentration in the stream. The model predictions generally matched observations made during summertime base‐flow conditions in a small coastal plain stream in Virginia. A more complicated pattern was observed following a seasonal drawdown period, where source components to the stream changed during the receding limb of the hydrograph and resulted in diel fluctuations being superimposed over a multi‐day trend in concentrations. Copyright © 2013 John Wiley & Sons, Ltd.