Neoproterozoic high-pressure/low-temperature metamorphic rocks in the Avalon terrane, southern New Brunswick, Canada     

C. E. White  S. M. Barr  R. A. Jamieson  P. H. Reynolds 《Journal of Metamorphic Geology》2001,19(5):519-530

High‐P/low‐T metamorphic rocks of the Hammondvale metamorphic suite (HMS) are exposed in an area of 10 km² on the NW margin of the Caledonian (Avalon) terrane in southern New Brunswick, Canada. The HMS is in faulted contact on the SE with c. 560–550 Ma volcanic and sedimentary rocks and co‐magmatic plutonic units of the Caledonian terrane. The HMS consists of albite‐ and garnet‐porphyroblastic mica schist, with minor marble, calc‐silicate rocks and quartzite. Pressure and temperature estimates from metamorphic assemblages in the mica schist and calc‐silicate rocks using TWQ indicate that peak pressure conditions were 12.4 kbar at 430 °C. Peak temperature conditions were 580 °C at 9.0 kbar. ⁴⁰Ar/³⁹Ar muscovite ages from three samples range up to 618–615 Ma, a minimum age for high‐P/low‐T metamorphism in this unit. These ages indicate that the HMS is related to the c. 625–600 Ma subduction‐generated volcanic and plutonic units exposed to the SE in the Caledonian terrane. The ages are also similar to those obtained from detrital muscovite in a Neoproterozoic‐Cambrian sedimentary sequence in the Caledonian terrane, suggesting that the HMS was exposed by latest Neoproterozoic time and supplied detritus to the sedimentary units. The HMS is interpreted to represent a fragment of an accretionary complex, similar to the Sanbagawa Belt in Japan. It confirms the presence of a major cryptic suture between the Avalon terrane sensu stricto and the now‐adjacent Brookville terrane.  相似文献   

High-resolution Doppler images of the spotted contact binary AE Phe     

J. R. Barnes  T. A. Lister  R. W. Hilditch  A. Collier Cameron 《Monthly notices of the Royal Astronomical Society》2004,348(4):1321-1331

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Mapping potential fields on the surfaces of rapidly rotating stars     

G. A. J. Hussain  M. Jardine  A. Collier Cameron 《Monthly notices of the Royal Astronomical Society》2001,322(3):681-688

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Further images of α Persei G dwarfs     

J.R. Barnes  A. Collier Cameron  D.J. James  D. Steeghs 《Monthly notices of the Royal Astronomical Society》2001,326(3):1057-1066

We present two images of intermediate and low axial inclination G dwarfs (AP 149 and AP 193) in the young open cluster α Persei, and compare these with previous images of intermediate and high axial inclination objects in this cluster. All stars show starspots at high latitudes, with one star exhibiting a strong polar spot. Although low-latitude features are found on all stars to some degree, the detection of spots on AP 193 is marginal. The apparent difference in starspot morphology from one object to the next is probably the result of a stellar magnetic cycle, although the exact effect on the starspot distribution throughout a cycle is unknown.
Polar spots are found in many Doppler images of rapidly rotating cool stars. In the past, their existence has been called into question, and it has been suggested that they could be the manifestations of NLTE (e.g. chromospheric filling in of line profiles) effects rather than real photospheric features. We assume the polar spots to be real photospheric features, and conclude that the flat-bottomed nature of the profile shape can be attributed to photospheric polar spots. The degree of truncation of the profile depends not only on spot size and strength, but also on the effective foreshortening of the polar region, a function of axial inclination.
H α is in emission on AP 149 which shows a double peak at most phases. The time-series of the profile shows an s-wave pattern as the position of these peaks changes throughout the rotation cycle. We attribute this to coronal clouds located above the stellar surface in synchronous orbit. A maximum-entropy tomogram is derived revealing four distinct emission regions located near and above the corotation radius.  相似文献   

Saturation properties of the Archontis dynamo     

Robert Cameron  David Galloway 《Monthly notices of the Royal Astronomical Society》2006,365(3):735-746

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The coronal structure of Speedy Mic – I. A densely packed prominence system beyond corotation     

N. J. Dunstone  J. R. Barnes  A. Collier Cameron  M. Jardine 《Monthly notices of the Royal Astronomical Society》2006,365(2):530-538

We present new observations of the prominence system on the K3 dwarf Speedy Mic (BO Mic, HD 197890). Using an improved technique to track the absorption features in Hα we find a very active prominence system with approximately 10 prominences on the observable hemisphere per rotation. From a total of 25 prominences, we find an average axial distance of  (2.85 ± 0.54) R _*  which is twice the corotation radius above the stellar surface. We discuss the consequences of these observations on the nature of the supporting magnetic structures. Two consecutive nights, with complete phase coverage, combined with a further night after a three-night gap allow us to study the evolution of the prominence system on two different time-scales. Several of the prominences have counterparts at similar phases on consecutive nights. During this interval, many prominences show evidence for evolution in their heights and phases of observation. Five nights (13 rotation cycles) later, we recover many prominences at approximately the same phases. Whilst individual prominences change axial distances or appear/reappear from night-to-night, the underlying prominence supporting structures appear to be stable over as many as 13 stellar rotations.  相似文献   

Results from the Wide-Angle Search for Planets prototype (WASP0) – I. Analysis of the Pegasus field     

Stephen R. Kane  rew Collier Cameron  Keith Horne  David James  Tim A. Lister  Don L. Pollacco  Rachel A. Street  Yiannis Tsapras 《Monthly notices of the Royal Astronomical Society》2004,353(2):689-696

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An application of fuzzy logic to the assessment of aquifers' pollution potential     

E. Cameron  G. Peloso 《Environmental Geology》2001,40(11-12):1305-1315

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Electron capture in carbon dwarf supernovae     

T. J. Mazurek  J. W. Truran  A. G. W. Cameron 《Astrophysics and Space Science》1974,27(2):261-291

The rates of electron capture on heavier elements under the extreme conditions predicted for dwarf star supernovae have been computed, incorporating modifications that seem to be indicated by present experimental results. An estimate of the maximum possible value of such rates is also given. The distribution of nuclei in nuclear statistical equilibrium has been calculated for the range of expected supernovae conditions, including the effects of the temperature dependence of nuclear partition functions. These nuclide abundance distributions are then used to compute nuclear equilibrium thermodynamic properties. The effects of the electron capture on such equilibrium matter are discussed. The results of supernova numerical hydrodynamics incorporating the computed equilibrium properties and the influence of electron capture are presented. In the context of the ‘carbon detonation’ supernova model, the dwarf central density required to assure core collapse to a neutron star configuration is found to be slightly higher than that obtained by Bruenn (1972) with the electron capture rates of Hansen (1966).  相似文献   

Surface composition of magnetic neutron stars     

Leonard C. Rosen  A. G. W. Cameron 《Astrophysics and Space Science》1972,15(1):137-152

The relative abundances of seven constitutent nuclei, He⁴, C¹², O¹⁶, Ne²⁰, Mg²⁴, Si²⁸ and Fe⁵⁶, are calculated as a function of time for neutron star atmospheres within which exist magnetic fields of the order of 10¹³G. The opacity, equation of state of the electrons, and cooling rate of the magnetic star are discussed, and it is shown to be a reasonable approximation to assume an atmosphere to be isothermal. The effects of particle diffusion are included in the nuclear reaction network. Computations are performed both for a constant mass atmosphere and for an atmosphere in which mass is being ejected. It is found that the final abundances are model independent as long as the initial model contains predominantly He⁴. The relative abundances are compared to the cosmic ray spectrum. For both the constant mass and mass loss atmospheres, nucleosynthesis proceeds virtually completely to Fe⁵⁶. However the outermost layers of the envelope, in which no mass is being ejected, are composed almost entirely of He⁴ with trace amounts of Fe⁵⁶. After the loss of about 10²¹ g, only Fe⁵⁶ is ejected from atmospheres expelling mass.A portion of the research on which this paper was based was performed while L. C. Rosen was present at the Lawrence Radiation Laboratory, Livermore, California.  相似文献