RApid Temporal Survey (RATS) – II. Followup observations of four newly discovered short-period variables     

Gavin Ramsay  Ralf Napiwotzki  Pasi Hakala  Harry Lehto 《Monthly notices of the Royal Astronomical Society》2006,371(2):957-962

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A new saturated/unsaturated model for stormwater infiltration systems     

Dale Browne  Ana Deletic  Gavin M. Mudd  Tim D. Fletcher 《水文研究》2008,22(25):4838-4849

Infiltration systems are widely used as an effective urban stormwater control measure. Most design methods and models roughly approximate the complex physical flow processes in these systems using empirical equations and fixed infiltration rates to calculate emptying times from full. Sophisticated variably saturated flow models are available, but rarely applied owing to their complexity. This paper describes the development and testing of an integrated one‐dimensional model of flow through the porous storage of a typical infiltration system and surrounding soils. The model accounts for the depth in the storage, surrounding soil moisture conditions and the interaction between the storage and surrounding soil. It is a front‐tracking model that innovatively combines a soil‐moisture‐based solution of Richard's equation for unsaturated flow with piston flow through a saturated zone as well as a reservoir equation for flow through a porous storage. This allows the use of a simple non‐iterative numerical solution that can handle ponded infiltration into dry soils. The model is more rigorous than approximate stormwater infiltration system models and could therefore be valuable in everyday practice. A range of test cases commonly used to test soil water flow models for infiltration in unsaturated conditions, drainage from saturation and infiltration under ponded conditions were used to test the model along with an experiment with variable depth in a porous storage over saturated conditions. Results show that the model produces a good fit to the observed data, analytical solutions and Hydrus. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

XMM–Newton observations of the eclipsing polar V2301 Oph     

Gavin Ramsay †  Mark Cropper 《Monthly notices of the Royal Astronomical Society》2007,379(3):1209-1216

We present XMM–Newton observations of the eclipsing polar V2301 Oph which cover nearly 2.5 binary orbital cycles and two eclipses. This polar is believed to have the lowest magnetic field strength (7 MG) of any known polar. We find evidence for structure in the X-ray eclipse profile which shows a 'standstill' feature lasting  26 ± 4  s. This allows us to place an upper limit on the mass of the white dwarf of  ∼1.2 M_⊙  . We find no evidence for quasi-periodic oscillations (QPOs) in the frequency range 0.02–10 Hz. This coupled with the absence of QPOs in RXTE data suggests that, if present, any oscillations in the shock front have a minimal effect on the resultant X-ray flux. We find no evidence for a distinct soft X-ray component in its spectrum – it therefore joins another seven systems which do not show this component. We suggest that those systems which are asynchronous, have low mass-transfer rates or have accretion occurring over a relatively large fraction of the white dwarf are more likely to show this effect. We find that the specific mass-transfer rate has to be close to 0.1 g cm⁻² s⁻¹ to predict masses which are consistent with that derived from our eclipse analysis. This may be due to the fact that the low magnetic field strength allows accretion to take place along a wide range of azimuth.  相似文献   

Imaging and integral-field spectroscopy of shocked H₂ around G25.65+1.05     

Stephen P. Todd  Suzanne K. Ramsay Howat 《Monthly notices of the Royal Astronomical Society》2006,367(1):238-246

The results of B -band CCD imaging linear polarimetry obtained for stars from the Hipparcos catalogue are used to re-examine the distribution of the local interstellar medium towards the IRAS 100-μm emission void in the Lupus dark clouds. The analysis of the obtained parallax–polarization diagram assigns to the dark cloud Lupus 1 a distance between 130 and 150 pc and assures the existence of a low column density region coincident with the observed infrared void. Moreover, there are clear indications of the existence of absorbing material at distances closer than 60–100 pc, which may be associated with the interface boundary between the Local Bubble and its neighbourhood Loop I superbubble.  相似文献   

Radio observations of X-ray pulsators     

M. J. Coe  G. J. Gavin 《Astrophysics and Space Science》1983,89(1):169-172

A detailed search has been performed at 10.7 GHz for any pulsed radio emission from four X-ray pulsators (A0535+26, X Persei, AE Aquarii and H2252-035). The results obtained indicate no radio emission-pulsed or otherwise is present at a level of ≥ 50 mJy (two standard deviations upper limit). This value is considerably more sensitive than the previous studies carried out on these sources and presents problems in the understanding of compact, magnetised stellar objects.  相似文献   

The $\text{D}\text{H}$ ratio in the atmosphere of Uranus: Detection of the R₅(1) line of HD     

L. Trafton  D.A. Ramsay 《Icarus》1980,41(3):423-429

Observations of Uranus during the 1975, 1976, and 1978 apparitions reveal a weak absorption at the wavelength of the R₅(1) line of HD with equivalent width $\text{1.0 ± 0.4}\text{m}\text{A}\text{?}$. The $\text{D}\text{H}$ ratio in Uranus' atmosphere implied by this line and other published spectra is (4.8 ± 1.5) × 10^?5, and may not be significantly different from that in the atmospheres of Jupiter and Saturn. In addition, the spectra exhibit two weak absorption at $\text{6044.76 ± 0.02}\text{and}\text{6045.54 ± 0.02}\text{A}\text{?}$ which we were unable to identify. No trace of absorption is visible near these wavelengths or near the HD wavelength in a laboratory spectrum of 4.92 km-am CH₄ which we obtained in an attempt to identify these absorption features and to verify that the HD feature does not arise from CH₄.  相似文献   

RApid Temporal Survey (RATS) – I. Overview and first results     

Gavin Ramsay  Pasi Hakala 《Monthly notices of the Royal Astronomical Society》2005,360(1):314-321

We present the aim and first results of the RApid Temporal Survey (RATS) made using the Wide Field Camera on the Isaac Newton Telescope. Our initial survey covers 3 square degrees, reaches a depth of   V ∼ 22.5  and is sensitive to variations on time-scales as short as 2 min: this is a new parameter space. Each field was observed for over 2 h in white light, with 12 fields being observed in total. Our initial analysis finds 45 targets which show significant variations. Around half of these systems show quasi-sinusoidal variations: we believe they are contact or short period binaries. We find four systems which show variations on a time-scale less than 1 h. The shortest period system has a period of 374 s. We find two systems which show a total eclipse. Further photometric and spectroscopic observations are required to fully identify the nature of these systems. We outline our future plans and objectives.  相似文献   

Origin of Mercury’s double magnetopause: 3D hybrid simulation study with A.I.K.E.F.     

Joachim Müller  Sven Simon  Yung-Ching Wang  Uwe Motschmann  Daniel Heyner  Josef Schüle  Wing-Huen Ip  Gero Kleindienst  Gavin J. Pringle 《Icarus》2012,218(1):666-687

During the first and second Mercury flyby the MESSENGER spacecraft detected a dawn side double-current sheet inside the Hermean magnetosphere that was labeled the “double magnetopause” (Slavin, J.A. et al. [2008]. Science 321, 85). This double current sheet confines a region of decreased magnetic field that is referred to as Mercury’s “dayside boundary layer” (Anderson, M., Slavin, J., Horth, H. [2011]. Planet. Space Sci.). Up to the present day the double current sheet, the boundary layer and the key processes leading to their formation are not well understood. In order to advance the understanding of this region we have carried out self-consistent plasma simulations of the Hermean magnetosphere by means of the hybrid simulation code A.I.K.E.F. (Müller, J., Simon, S., Motschmann, U., Schüle, J., Glassmeier, K., Pringle, G.J. [2011]. Comput. Phys. Commun. 182, 946–966). Magnetic field and plasma results are in excellent agreement with the MESSENGER observations. In contrast to former speculations our results prove this double current sheet may exist in a pure solar wind hydrogen plasma, i.e. in the absence of any exospheric ions like sodium. Both currents are similar in orientation but the outer is stronger in intensity. While the outer current sheet can be considered the “classical” magnetopause, the inner current sheet between the magnetopause and Mercury’s surface reveals to be sustained by a diamagnetic current that originates from proton pressure gradients at Mercury’s inner magnetosphere. The pressure gradients in turn exist due to protons that are trapped on closed magnetic field lines and mirrored between north and south pole. Both, the dayside and nightside diamagnetic decreases that have been observed during the MESSENGER mission show to be direct consequences of this diamagnetic current that we label Mercury’s “boundary-layer-current“.  相似文献   

The defining characteristics of intermediate polars – the case of three-candidate systems     

Gavin Ramsay  Peter J. Wheatley  A. J. Norton  Pasi Hakala  Darren Baskill 《Monthly notices of the Royal Astronomical Society》2008,387(3):1157-1162

Intermediate polars (IPs) are a group of cataclysmic variables (CVs) which are thought to contain white dwarfs which have a magnetic field strength in the range ∼0.1–10 MG. A significant fraction of the X-ray sources detected in recent deep surveys has been postulated to consist of IPs. Until now two of the defining characteristics of IPs have been the presence of high (and complex) absorption in their X-ray spectra and the presence of a stable modulation in the X-ray light curve which is a signature of the spin period, or the beat period, of the accreting white dwarf. Three CVs, V426 Oph, EI UMa and LS Peg, have characteristics which are similar to IPs. However, there has been only tentative evidence for a coherent period in their X-ray light curve. We present the results of a search for coherent periods in XMM–Newton data of these sources using an autoregressive analysis which models the effects of red noise. We confirm the detection of a ∼760 s period in the soft X-ray light curve of EI UMa reported by Reimer et al. and agree that this represents the spin period. We also find evidence for peaks in the power spectrum of each source in the range 100–200 s which are just above the 3σ confidence level. We do not believe that they represent genuine coherent modulations. However, their X-ray spectra are very similar to those of known IPs. We believe that all three CVs are bona fide IPs. We speculate that V426 Oph and LS Peg do not show evidence for a spin period since they have closely aligned magnetic and spin axes. We discuss the implications that this has for the defining characteristics of IPs.  相似文献   

The Yungul carbonatite dykes associated with the epithermal fluorite deposit at Speewah, Kimberley, Australia: carbon and oxygen isotope constraints on their origin     

L. G. Gwalani  K. A. Rogers  A. Demény  D. I. Groves  R. Ramsay  A. Beard  P. J. Downes  A. Eves 《Mineralogy and Petrology》2010,98(1-4):123-141

The Yungul carbonatite dykes at Speewah in the Kimberley region of Western Australia were emplaced along a north-trending splay from the northeast-trending Greenvale Fault located at the western boundary of the Halls Creek Orogen. The Yungul carbonatite dykes intrude a thick composite sill of the Palaeoproterozoic Hart Dolerite (~1,790 Ma), consisting of tholeiitic dolerite and gabbro with its felsic differentiates that form the Yilingbun granophyres and associated granites. The carbonatite dykes consist of massive, calcite carbonatite that host very coarse, pegmatitic veins and pods of calcite, and have largely replaced (carbonatitized) and fenitized the country rock Hart Dolerite suite in a zone up to 150 m wide. Dykes of red-brown siliceous fluidized-breccia and epithermal-textured veins consisting of bladed quartz, adularia and fluorite are closely associated with the carbonatite dykes. The Yungul carbonatites are closely associated with fluorite occurrences with resources currently reported as 6.7 Mt at 24.6% CaF₂. The precise age of the Yungul carbonatite is not known, although it is believed to be post early Cambrian. The total REE content of the Yungul carbonatite is low (174.0–492.8 ppm; La/Yb 2.28–10.74) and thus atypical for calciocarbonatite. Chondrite-normalized REE patterns for the carbonatite are relatively flat compared to average calciocarbonatite, and show small negative Eu anomalies. These unusual geochemical features may have been acquired from the Hart Dolerite suite during emplacement of the carbonatite, a process that involved extensive replacement and fenitization of country rocks. Carbon and oxygen isotope compositions of massive calcite carbonatite and the coarse calcite veins and pods from the carbonatite suggest a deep-seated origin. The C and O isotope compositions show an overall positive correlation that can be attributed to both magmatic and magmatic-hydrothermal processes in their evolution. The magmatic δ¹³C-δ¹⁸O trend is also indicative of crustal contamination and/or low-temperature water/rock exchange. The carbon isotopic compositions have δ¹³C values that range from about ?5.2‰ to ?6.3‰ that support a mantle-derived origin for the Yungul carbonatites and are consistent with earlier conclusions based on whole-rock geochemistry and radiogenic isotopes studies.  相似文献