Molecular hydrogen line emission from the reflection nebula Parsamyan 18     

Ryder  Allen  Burton  Ashley  & Storey 《Monthly notices of the Royal Astronomical Society》1998,294(2):338-346

The newly commissioned University of New South Wales Infrared Fabry–Perot (UNSWIRF) has been used to image molecular hydrogen emission at 2.12 and 2.25 μm in the reflection nebula Parsamyan 18. P 18 is known to exhibit low values of the (1–0)/(2–1) S(1) ratio, suggestive of UV-pumped fluorescence rather than thermal excitation by shocks. Our line ratio mapping reveals the full extent of this fluorescent emission from extended arc-like features, as well as a more concentrated thermal component in regions closer to the central exciting star. We show that the emission morphology, line fluxes and gas density are consistent with the predictions of photodissociation region (PDR) theory. Those regions with the highest intrinsic 1–0 S(1) intensities also tend to show the highest (1–0)/(2–1) S(1) line ratios. Furthermore, variations in the line ratio can be attributed to intrinsic fluctuations in the incident radiation field and/or the gas density, through the self-shielding action of H₂. An isolated knot of emission discovered just outside P 18, and having both an unusually high (1–0)/(2–1) S(1) ratio and relative velocity, provides additional evidence for an outflow source associated with P 18.  相似文献   

The impact of cooling flows on the T_X–L_Bol relation for the most luminous clusters     

S. W. Allen  & A. C. Fabian 《Monthly notices of the Royal Astronomical Society》1998,297(3):L57-L62

We examine the effects of cooling flows on the T _X– L _Bol relation for a sample of the most X-ray luminous ( L _Bol > 10⁴⁵ erg s⁻¹) clusters of galaxies known. Using high-quality ASCA X-ray spectra and ROSAT images we explicitly account for the effects of cooling flows on the X-ray properties of the clusters and show that this reduces the previously noted dispersion in the T _X– L _Bol relationship. More importantly, the slope of the relationship is flattened from L _Bol ∝  T ³_X to approximately L _Bol ∝  T ²_X, in agreement with recent theoretical models which include the effects of shocks and pre-heating on the X-ray gas. We find no evidence for evolution in the T _X– L _Bol relation within z  ∼ 0.3. Our results demonstrate that the effects of cooling flows must be accounted for before cosmological parameters can be determined from X-ray observations of clusters. The results presented here should provide a reliable basis for modelling the T _X– L _Bol relation at high X-ray luminosities.  相似文献   

The relationship between cooling flows and metallicity measurements for X-ray-luminous clusters     

S. W. Allen  & A. C. Fabian 《Monthly notices of the Royal Astronomical Society》1998,297(3):L63-L68

We explore the relationship between the metallicity of the intracluster gas in clusters of galaxies, determined by X-ray spectroscopy, and the presence of cooling flows. Using ASCA spectra and ROSAT images, we demonstrate a clear segregation between the metallicities of clusters with and without cooling flows. On average, cooling-flow clusters have an emission-weighted metallicity a factor ∼ 1.8 times higher than that of non-cooling-flow systems. We suggest that this is caused by the presence of metallicity gradients in the cooling-flow clusters, coupled with the sharply peaked X-ray surface brightness profiles of these systems. Non-cooling-flow clusters have much flatter X-ray surface brightness distributions and are thought to have undergone recent merger events, which may have mixed the central high-metallicity gas with the surrounding less metal-rich material. We find no evidence for evolution in the emission-weighted metallicities of clusters within z  ∼ 0.3.  相似文献   

Welcoming remarks     

Clarence R. Allen 《Tectonophysics》1979,52(1-4)

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Electron microprobe study of a ‘mysterite’-bearing inclusion from the Krymka LL-chondrite     

Lawrence Grossman  John M. Allen  Glenn J. MacPherson 《Geochimica et cosmochimica acta》1980,44(2):211-216

The black inclusion from the Krymka LL3 chondrite previously found to contain ‘mysterite’ by Lewiset al. (1979) belongs to a hitherto unknown class of carbonaceous chondrites. Its olivine and pyroxene compositions. Fo 97–99 and En 96, respectively, are characteristic of carbonaceous chondrites and its plagioclase composition. An 100, is characteristic of C3's. It contains a peculiar group of Co-, Cr-rich metal grains whose compositions are similar, but not identical, to those in C2 chondrites and which also bear some similarities to those in Renazzo. Its weight ratios of total $\text{Fe}\text{SiO}{}_2$ and $\text{solSiO}{}_2\text{MgO}$ are 0.74 and 1.43, respectively, and its atomic ratio of $\text{Si}\text{Al}$ is 10.7, exactly the same as in carbonaceous chondrites. Its bulk chemical composition is very close to that of the Murchison C2 chondrite. The association of mysterite with a special type of carbonaceous chondrite material suggests that mysterite formed by low-temperature condensation in a different region of the nebula from other carbonaceous chondrites.  相似文献   

Scanning electron microscopy in the study of sediments,W. Brain Whalley (Ed.), Geo Abstracts,Norwich, England, 1978. No. of Pages: 414. Price: £12.75     

J. R. L. Allen 《地球表面变化过程与地形》1980,5(1):102-102

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How Good Are Estimates of Transmissivity from Slug Tests in Fractured Rock?   总被引：6，自引：1，他引：5  

Allen M. Shapiro  Paul A. Hsieh 《Ground water》1998,36(1):37-48

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Field meeting: The facies of the Lower Old Red Sandstone,north of Milford Haven,southwest Dyfed,Wales: 20–23 May 1977     

J.R.L. Allen  R.G. Thomas  B.P.J. Williams 《Proceedings of the Geologists' Association. Geologists' Association》1981,92(4):251-267

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Computational models for dune time-lag: Population structures and the effects of discharge pattern and coefficient of change     

J.R.L. Allen 《Sedimentary Geology》1976,16(2):99-130

An earlier model for dune time-lag in periodically varying unidirectional flows (J.R.L. Allen, 1976) is modified so as to treat more realistically the stochastic behaviour of dunes and the ability of the individual to change in height during its life-span.The improved model shows that hydrograph shape could substantially influence dune behaviour in unsteady flows. For the same flow period and extreme discharge values, a reduction in the relative duration of the high-water stages causes an increase in the phase differences between dune dimensions and flow, and an increase in the dimensions averaged over the flow cycle as compared with the similarly averaged dimensions given no lag. The relative range of dimensions over the flow cycle is little affected.The time-dependent structure of the dune populations is explored using histograms of the instantaneous values of dune wavelength, height and age. At small values of the time ratio (ratio of characteristic dune life-span to flow period), the dunes invariably are unimodally distributed in wavelength, height and age, and the relative dispersion of these properties is small. At intermediate ratios, dune properties are bimodally distributed and moderately to highly dispersed over much of each flow cycle, usually the later part and sometimes the whole of the low-water phase. Dune properties are at all times highly dispersed and, broadly, unimodally distributed when the time ratio is large. There is a close correlation between the patterns in time of dune creation rate, population structure, the average values and relative dispersions of dune dimensions, and the phase difference evaluated for each instant.An increase of the coefficient of change of dune height decreases the equivalent phase difference for height, diminishes the calculated wavelength and height averaged over the flow cycle, but increases the ranges of height and wavelength. Increasing the coefficient has no apparent effect on the equivalent phase difference for wavelength.  相似文献   

Reply by P. Allen     

P. Allen 《Proceedings of the Geologists' Association. Geologists' Association》1976,87(4):433-442

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