Reprocessing of X-rays in the outer accretion disc of the black hole binary XTE J1817−330     

Marek Gierli&#;ski  Chris Done  Kim Page 《Monthly notices of the Royal Astronomical Society》2009,392(3):1106-1114

We build a simple model of the optical/ultraviolet (UV) emission from irradiation of the outer disc by the inner disc and coronal emission in black hole binaries. We apply this to the broad-band Swift data from the outburst of the black hole binary XTE J1817−330 to confirm previous results that the optical/UV emission in the soft state is consistent with a reprocessing a constant fraction of the bolometric X-ray luminosity. However, this is very surprising as the disc temperature drops by more than a factor of 3 in the soft state, which should produce a marked change in the reprocessing efficiency. The easiest way to match the observed constant reprocessed fraction is for the disc skin to be highly ionized (as suggested 30 yr ago by van Paradijs), so that the bulk of the disc flux is reflected and only the hardest X-rays heat the disc. The constant reprocessed fraction also favours direct illumination of the disc over a scattering origin as the optical depth/solid angle of any scattering material (wind/corona) over the disc should decrease as the source luminosity declines. By contrast, the reprocessed fraction increases very significantly (by a factor of ∼6) as the source enters the hard state. This dramatic change is not evident from X-ray/UV flux correlations as it is masked by bandpass effects. However, it does not necessarily signal a change in emission, for example, the emergence of the jet dominating the optical/UV flux as the reflection albedo must change with the dramatic change in spectral shape.  相似文献   

The link between SCUBA and Spitzer: cold galaxies at z≲ 1     

M. Symeonidis  M. J. Page  N. Seymour  T. Dwelly  K. Coppin  I. McHardy  G. H. Rieke  M. Huynh 《Monthly notices of the Royal Astronomical Society》2009,397(4):1728-1738

We show that the far-IR properties of distant Luminous and UltraLuminous InfraRed Galaxies (LIRGs and ULIRGs, respectively) are on average divergent from analogous sources in the local Universe. Our analysis is based on Spitzer Multiband Imaging Photometer (MIPS) and Infrared Array Camera (IRAC) data of   L _IR > 10¹⁰ L_⊙, 70 μm  selected objects in the  0.1 < z < 2  redshift range and supported by a comparison with the IRAS Bright Galaxy Sample. The majority of the objects in our sample are described by spectral energy distributions (SEDs) which peak at longer wavelengths than local sources of equivalent total infrared luminosity. This shift in SED peak wavelength implies a noticeable change in the dust and/or star-forming properties from   z ∼ 0  to the early Universe, tending towards lower dust temperatures, indicative of strong evolution in the cold dust, 'cirrus', component. We show that these objects are potentially the missing link between the well-studied local IR-luminous galaxies, Spitzer IR populations and SCUBA sources – the   z < 1  counterparts of the cold   z > 1  SubMillimetre Galaxies (SMGs) discovered in blank-field submillimetre surveys. The Herschel Space Observatory is well placed to fully characterize the nature of these objects, as its coverage extends over a major part of the far-IR/sub-mm SED for a wide redshift range.  相似文献   

The star formation history of the Universe as revealed by deep radio observations     

N. Seymour  T. Dwelly  D. Moss  I. McHardy  A. Zoghbi  G. Rieke  M. Page  A. Hopkins  N. Loaring 《Monthly notices of the Royal Astronomical Society》2008,386(3):1695-1708

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Quantification of Metals and Semimetals in Carbon‐Rich Rocks: A New Sequential Protocol Including Extraction from Humic Substances          下载免费PDF全文

Renato Henrique‐Pinto  Sarah‐Jane Barnes  Dany Savard  Sadia Mehdi 《Geostandards and Geoanalytical Research》2017,41(1):41-62

We have developed a new sequential extraction technique that does not require complex procedures and is efficient in determining metal and semimetal contents of carbon‐rich rocks. Six geological reference materials (SBC‐1, SCHS‐1, SCo‐1, SDO‐1, SGR‐1b and SLg‐1) and an in‐house black shale (SH‐1) were selected to test the method, which consists of four main digestion steps involving: (a) dilute HCl acid; (b) NaOH; (c) aqua regia; and (d) hydrofluoric acid. Compared with traditional aqua regia + hydrofluoric acid attack, this new protocol recovers more of the moderately volatile elements during early extraction of humic substances. In addition when compared with reference values, those for most elements are in agreement within uncertainty. Furthermore, this new protocol reveals important information on the partitioning of elements; for instance, steps one and two indicate which elements are associated with carbonates and organic phases from fulvic and humic acid extractions, whereas step three provides results for which elements are associated with sulfide minerals and step four indicates which elements remained in the silicate and oxide phases.  相似文献   

Comparison between Nickel-Sulfur Fire Assay Te Co-precipitation and Isotope Dilution with High-Pressure Asher Acid Digestion for the Determination of Platinum-Group Elements,Rhenium and Gold     

Dany Savard  Sarah-Jane Barnes  Thomas Meisel 《Geostandards and Geoanalytical Research》2010,34(3):281-291

The accurate determination of platinum-group elements (PGE), rhenium and gold is important in both fundamental research and ore deposit studies. Questions have been raised by some authors as to whether the nickel-sulfur fire assay technique (NiS-FA) efficiently collects all the PGE. On the other hand, most isotope dilution (ID) techniques can only treat small test portion masses (2 g was used for high-pressure asher digestion; HPA) and this makes them more vulnerable to nugget effects. We determined PGE concentrations in ten reference materials with the aim of comparing the performance characteristics of the two methods. Both methods determine Ru, Pd, Os, Ir and Pt and we found that there were no significant systematic differences in the recovery. The advantages of NiS-FA were that: (a) it is capable of determining Rh and Au; (b) the relatively large test portion mass (15 g) reduces the nugget effect and (c) it is faster and less expensive than HPA-ID. The advantages of HPA-ID were that: (a) it determined Re and (b) it had low level blanks, lower detection limits and hence better precision in low-level homogeneous samples. Each technique had advantages and limitations; they should be considered as complementary rather than competing techniques.  相似文献   

Development and controlling factors of gullies and gully complexes,East Coast,New Zealand   总被引：1，自引：0，他引：1  

Thomas Parkner  Mike J. Page  Tomomi Marutani  Noel A. Trustrum 《地球表面变化过程与地形》2006,31(2):187-199

Sequential aerial photographs of a small headwater catchment in the Waiapu basin, East Coast Region, North Island, New Zealand, were interpreted to measure and analyse temporal changes in active area of gullies and gully complexes for a longer time span (1939–2003) and with higher temporal resolution compared to previous studies. We focus on the conditions leading to the development of gullies and gully complexes under pasture and forest by using topographic thresholds (slope–area relationships) of catchments for the initiation of gullies and gully complexes. In addition, the influence of two different lithologies as well as the occurrence of major rainfall events was related to gully activity. Twenty gullies and four gully complexes (occupying 62·5 ha or 12·5 per cent of the catchment area) occurred in the study catchment between 1939 and 2003. However, the majority of these were not active at all of the dates studied. Gullies developed in the sandstone‐dominated Tapuwaeroa Formation tended to attain their maximum size by 1957 with a mean catchment area of 2·1 ha. Gullies developed in mudstone of the Whangai Formation attained their maximum size in 1939 with a mean catchment area of 4·31 ha. Exceptions are gullies which developed into mass movement deposits or into an earth flow deposit as well as gullies developed under indigenous forest. Topographic threshold values for gullies under pasture and indigenous forest show that values for gullies under forest plot far above the threshold line of gullies under pasture, indicating that the topographical threshold for gully development under forest is higher compared to under pasture. A threshold value of 9·4 ha in catchment area is needed for the development of gully complexes under pasture, all located in the Whangai Formation and with the same orientation as the strike of the mudstones. Gully‐complex area and dominance of mass‐movement erosion increased with larger catchment area. A decreasing distance to the threshold line for gullies under pasture indicates a later development for gully complexes. No gully complexes developed under indigenous forest, indicating that the threshold value for gully‐complex development is higher than for gully complexes under pasture and was not reached in the study area. A model of shifting topographical threshold for gully development for a given catchment is developed which depends on land use. When a catchment has an indigenous forest cover the topographical threshold is very high. After conversion to pasture, threshold values decrease drastically. With the invasion of scrub, the threshold slowly increases and returns to a similar level to that under indigenous forest after reforestation. Development of gullies and gully complexes is a highly dynamic phenomenon, and phases of expansion and inactivity indicate that models describing only unidirectional advancing stages without periods of inactivity are not suitable. Therefore, this study adds more phases to models of gully and gully‐complex development in the East Coast Region. The threshold line for gully initiation under pasture and a value of 9·4 ha in catchment area for gully‐complex initiation permits one to predict which catchments, under similar environmental settings, develop gullies and gully complexes on a physical basis. This enables land managers to implement sustainable land‐use strategies to reduce erosion rates of gullies and gully complexes. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Effects of Flow Regulation in Flow Regime on the Murrumbidgee River,South Eastern Australia: an assessment using a daily estimation hydrological model     

Paul Frazier  Ken Page  Arthur Read 《The Australian geographer》2005,36(3):301-314

In this paper, modelled hydrological data are used to quantify the effects of regulation on the flow regime of the lower Murrumbidgee River in the period 1970–1998. Although other studies report historical changes in flood frequency and duration, this study uses modelled natural daily flow data rather than pre-regulation records or aggregated modelled monthly data. The comparison of modelled natural and regulated daily flows shows the magnitude of changes to mean and seasonal flows, flood peaks and flow duration. At gauges upstream of major irrigation off-takes, mean flows have been increased by approximately 10 per cent, flood peaks have been reduced by 21–46 per cent, and there has been a seasonal redistribution such that flows in summer and autumn have been increased at the expense of those in winter and spring. At gauges downstream of the major irrigation off-takes, mean flows have been reduced by 8–46 per cent, flood peaks have been reduced by 16–61 per cent, and flows have been decreased in all seasons.  相似文献   

Major ion chemistry of the Yarlung Tsangpo-Brahmaputra river: Chemical weathering, erosion, and CO₂ consumption in the southern Tibetan plateau and eastern syntaxis of the Himalaya   总被引：1，自引：0，他引：1  

Michael T. Hren  C. Page Chamberlain  Peter M. Blisniuk 《Geochimica et cosmochimica acta》2007,71(12):2907-2935

The Yarlung Tsangpo-Brahmaputra river drains a large portion of the Himalaya and southern Tibetan plateau, including the eastern Himalayan syntaxis, one of the most tectonically active regions on the globe. We measured the solute chemistry of 161 streams and major tributaries of the Tsangpo-Brahmaputra to examine the effect of tectonic, climatic, and geologic factors on chemical weathering rates. Specifically, we quantify chemical weathering fluxes and CO₂ consumption by silicate weathering in southern Tibet and the eastern syntaxis of the Himalaya, examine the major chemical weathering reactions in the tributaries of the Tsangpo-Brahmaputra, and determine the total weathering flux from carbonate and silicate weathering processes in this region. We show that high precipitation, rapid tectonic uplift, steep channel slopes, and high stream power generate high rates of chemical weathering in the eastern syntaxis. The total dissolved solids (TDS) flux from the this area is greater than 520 tons km⁻² yr⁻¹ and the silicate cation flux more than 34 tons km⁻² yr⁻¹. In total, chemical weathering in this area consumes 15.2 × 10⁵ mol CO₂ km⁻² yr⁻¹, which is twice the Brahmaputra average. These data show that 15-20% of the total CO₂ consumption by silicate weathering in the Brahmaputra catchment is derived from only 4% of the total land area of the basin. Hot springs and evaporite weathering provide significant contributions to dissolved Na⁺ and Cl⁻ fluxes throughout southern Tibet, comprising more than 50% of all Na⁺ in some stream systems. Carbonate weathering generates 80-90% of all dissolved Ca²⁺ and Mg²⁺ cations in much of the Yarlung Tsangpo catchment.  相似文献   

Zircons from kimberlite: New insights from oxygen isotopes, trace elements, and Ti in zircon thermometry   总被引：5，自引：0，他引：5  

F. Zeb Page  Bin Fu  John Fournelle  Daniel J. Schulze  Miguel A.S. Basei 《Geochimica et cosmochimica acta》2007,71(15):3887-3903

Zircons found in mantle-sourced kimberlite provide probes into the isotopic chemistry of the asthenosphere and subcontinental lithospheric mantle. However, little is known about the conditions of formation of these zircons. A suite of 88 zircons found in kimberlites from Africa, Siberia, Brazil, and the United States have been analyzed for their Ti concentration and selected zircons were analyzed for their Rare Earth Element (REE) concentrations by ion microprobe. In addition, precise and accurate laser-fluorination oxygen isotope data were obtained for zircons from Brazil (5.1 ± 0.3‰, 1SD) and the Midwest United States (5.3 ± 0.3‰), yielding mantle-like δ¹⁸O values similar to published data for Africa (5.2 ± 0.3‰) and Siberia (5.3 ± 0.2‰). Most megacrysts in this study preserve fine-scale, oscillatory zoning in CL and are generally homogenous in oxygen isotopic composition, consistent with preservation of primary compositions. A few zircons from Brazil show some evidence of chemical zoning due to recrystallization. The Ti content of mantle zircon is in general low with average compositions from each locality of 13 ± 8.4 ppm (1SD, Kaapvaal craton), 12 ± 8.7 ppm (Siberian platform), 18 ± 11 ppm (Brazil), and 4.8 ±4.3 ppm (United States). The recently calibrated Ti in zircon thermometer yields an average temperature of 744 ±62 °C (1SD) for the average of 13 ± 9 ppm Ti, with no correction for pressure, a_TiO2, or a_SiO2. The Ti content of zircons found within rutile nodules from the Orapa kimberlite (Kaapvaal craton) is almost indistinguishable from those with no constraint on a_TiO2, suggesting that reduced a_TiO2 is not responsible for lower than expected mantle temperatures. The average temperature in this study corresponds to ∼3 GPa on a 40 mW/m² cratonic geotherm. If correct, this would suggest that zircon megacrysts from all four cratons formed in the shallow lithospheric mantle. However, there are several possibly confounding effects to this thermometer, including: a pressure correction and disequilibrium zircon growth. Zircons from rutile nodules have REE contents that span the range of mantle zircon REE and are similar to both zircon megacrysts and zircons from metasomatic assemblages.  相似文献   

Preliminary investigation of the effects of purse seine size on estimates of density and species richness of estuarine fishes     

Mark A. Steele  Stephen C. Schroeter  Henry M. Page 《Estuaries and Coasts》2007,30(2):344-347

Small purse seines are well suited to sampling open water habitats in estuaries, yet little is known about how variation in their design affects estimates of density and species richness of estuarine fishes. We tested whether purse seine size (length and depth) affected estimates of density or species richness of fishes in San Dieguito Lagoon, southern California, U.S.A. Twenty-one species were captured, with the open water speciesAtherinops affinis dominating the catch. The larger net (36.4 m long × 3.6 m deep) produced higher estimates of density than the smaller net (18.2 m long × 2.4 m deep). The average number of species captured per sample was lower for the smaller net than the larger net, but species accumulation curves for the small and large nets were similar, indicating that the difference in the number of species per sample was primarily caused by the larger area sampled by the larger purse seine. Sampling with the larger purse seine was more time efficient than the smaller seine. We found small purse seines to be useful tools for sampling fishes in open water habitats in a small estuary, but we recommend that care be taken in selecting the size of a purse seine.  相似文献