Serendipitous Asteroid Lightcurve Survey Using SuperWASP     

N. R. Parley  N. McBride  S. F. Green  C. A. Haswell  W. I. Clarkson  D. J. Christian  A. Collier-Cameron  N. A. Evans  A. Fitzsimmons  C. Hellier  S. T. Hodgkin  K. Horne  J. Irwin  S. R. Kane  F. P. Keenan  T. A. Lister  A. J. Norton  J. P. Osborne  D. Pollacco  R. Ryans  I. Skillen  R. A. Street  R. G. West  P. J. Wheatley 《Earth, Moon, and Planets》2005,97(3-4):261-268

The SuperWASP project is an ultra-wide angle search for extra solar planetary transits. However, it can also serendipitously detect solar system objects, such as asteroids and comets. Each SuperWASP instrument consists of up to eight cameras, combined with high-quality peltier-cooled CCDs, which photometrically survey large numbers of stars in the magnitude range 7–15. Each camera covers a 7.8 × 7.8 degree field of view. Located on La Palma, the SuperWASP-I instrument has been observing the Northern Hemisphere with five cameras since its inauguration in April 2004.The ultra-wide angle field of view gives SuperWASP the possibility of discovering new fast moving (near to Earth) asteroids that could have been missed by other instruments. However, it provides an excellent opportunity to produce a magnitude-limited lightcurve survey of known main belt asteroids. As slow moving asteroids stay within a single SuperWASP field for several weeks, and may be seen in many fields, a survey of all objects brighter than magnitude 15 is possible. This will provide a significant increase in the total number of lightcurves available for statistical studies without the inherent bias against longer periods present in the current data sets.We present the methodology used in the automated collection of asteroid data from SuperWASP and some of the first examples of lightcurves from numbered asteroids.  相似文献   

SuperWASP-North extrasolar planet candidates between 3^h < RA < 6^h     

W. I. Clarkson  B. Enoch  C. A. Haswell  A. J. Norton  D. J. Christian  A. Collier Cameron  S. R. Kane  K. D. Horne  T. A. Lister  R. A. Street  R. G. West  D. M. Wilson  N. Evans  A. Fitzsimmons  C. Hellier  S. T. Hodgkin  J. Irwin  F. P. Keenan  J. P. Osborne  N. R. Parley  D. L. Pollacco  R. Ryans  I. Skillen  P. J. Wheatley 《Monthly notices of the Royal Astronomical Society》2007,381(2):851-864

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The impact of correlated noise on SuperWASP detection rates for transiting extrasolar planets     

A. M. S. Smith  A. Collier Cameron  D. J. Christian  W. I. Clarkson  B. Enoch  A. Evans  C. A. Haswell  C. Hellier  K. Horne  J. Irwin  S. R. Kane  T. A. Lister  A. J. Norton  N. Parley  D. L. Pollacco  R. Ryans  I. Skillen  R. A. Street  A. H. M. J. Triaud  R. G. West  P. J. Wheatley  D. M. Wilson 《Monthly notices of the Royal Astronomical Society》2006,373(3):1151-1158

The evolution of the Alfvén turbulence due to three-wave interactions is discussed using kinetic theory for a collisionless, thermal plasma. There are three low-frequency modes, analogous to the three modes of compressible magnetohydrodynamics (MHD). When only Alfvén waves are considered, the known anisotropy of turbulence in incompressible MHD theory is reproduced. Inclusion of a fast mode wave leads to the separation of turbulence into two regimes: small wave numbers where three-wave processes involving a fast mode are dominant, and large wave numbers where the three Alfvén wave process is dominant. Possible application of the anisotropic Alfvén turbulence to the interstellar medium and dissipation of magnetic energy in magnetars are discussed.  相似文献   

Propagation of a hydraulic fracture parallel to a free surface     

X. Zhang  R. G. Jeffrey  E. Detournay 《国际地质力学数值与分析法杂志》2005,29(13):1317-1340

This paper analyses the plane strain problem of a fracture, driven by injection of an incompressible viscous Newtonian fluid, which propagates parallel to the free surface of an elastic half‐plane. The problem is governed by a hyper‐singular integral equation, which relates crack opening to net pressure according to elasticity, and by the lubrication equations which describe the laminar fluid flow inside the fracture. The challenge in solving this problem results from the changing nature of the elasticity operator with growth of the fracture, and from the existence of a lag zone of a priori unknown length between the crack tip and the fluid front. Scaling of the governing equations indicates that the evolution problem depends in general on two numbers, one which can be interpreted as a dimensionless toughness and the other as a dimensionless confining stress. The numerical method adopted to solve this non‐linear evolution problem combines the displacement discontinuity method and a finite difference scheme on a fixed grid, together with a technique to track both crack and fluid fronts. It is shown that the solution evolves in time between two asymptotic similarity solutions. The small time asymptotic solution corresponding to the solution of a hydraulic fracture in an infinite medium under zero confining stress, and the large time to a solution where the aperture of the fracture is similar to the transverse deflection of a beam clamped at both ends and subjected to a uniformly distributed load. It is shown that the size of the lag decreases (to eventually vanish) with increasing toughness and compressive confining stress. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Spatial distribution and seasonal variation in 18O/16O of modern precipitation and river water across the conterminous USA     

Andrea Dutton  Bruce H. Wilkinson  Jeffrey M. Welker  Gabriel J. Bowen  Kyger C. Lohmann 《水文研究》2005,19(20):4121-4146

We report a quantitative analysis of regional differences in the the oxygen isotope composition of river water and precipitation across the USA because data are now available to undertake a more geographically and temporally extensive analysis than was formerly possible. Maps of modern, mean annual δ¹⁸O values for both precipitation (δ¹⁸O_PPT) and river water (δ¹⁸O_RIV) across the 48 contiguous states of the USA have been generated using latitude and elevation as the primary predictors of stable isotope composition while also incorporating regional and local deviations based on available isotopic data. The difference between these two maps was calculated to determine regions where δ¹⁸O_RIV is significantly offset from local δ¹⁸O_PPT. Additional maps depicting seasonal and extreme values for δ¹⁸O_RIV and δ¹⁸O_PPT were also constructed. This exercise confirms the presence of regions characterized by differences in δ¹⁸O_RIV and δ¹⁸O_PPT and specifically identifies the magnitude and regional extent of these offsets. In particular, the Great Plains has δ¹⁸O_RIV values that are more positive than precipitation, while much of the western USA is characterized by significantly lower δ¹⁸O_RIV values in comparison with local δ¹⁸O_PPT. The most salient feature that emerged from this comparison is the ‘catchment effect’ for the rivers. Because river water is largely derived from precipitation that fell upstream of the sample locality (i.e. at higher elevations) δ¹⁸O_RIV values are often lower than local δ¹⁸O_PPT values, particularly in catchments with high‐elevation gradients. Seasonal patterns in the isotopic data substantiate the generally accepted notion that amplitudes of δ¹⁸O variation are greatly dampened in river water relative to those of local precipitation. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Morphology and origin of palimpsests on Ganymede based on Galileo observations     

Kevin B. Jones  James W. Head III  Jeffrey M. Moore 《Icarus》2003,164(1):197-212

Palimpsests are large, circular, low-relief impact scars on Ganymede and Callisto. These structures were poorly understood based on Voyager-era analysis, but high-resolution Galileo images allow more detailed inspection. We analyze images of four Ganymedean palimpsests targeted by Galileo: Memphis and Buto Faculae, Epigeus, and Zakar. Ganymedean craters and Europan ring structures are used as tools to help better understand palimpsests, based on morphologic similarities. From analysis of Galileo images, palimpsests consist of four surface units: central plains, an unoriented massif facies, a concentric massif facies, and outer deposits. Using as a tie point the location in these structures where secondary craters begin to appear, outer deposits of palimpsests are analogous to the outer ejecta facies of craters; the concentric massif facies of palimpsests are analogous to the pedestal facies of craters; and the unoriented massif facies and central plains are analogous to crater interiors. These analogies are supported by the presence of buried preexisting structure beneath the outer two and absence of buried structure beneath the inner two units. Our observations indicate that palimpsest deposits represent fluidized impact ejecta, rather than cryovolcanic deposits or ancient crater interiors.  相似文献   

Blowing in the wind: I. Velocities of chondrule-sized particles in a turbulent protoplanetary nebula     

Jeffrey N Cuzzi  Robert C Hogan 《Icarus》2003,164(1):127-138

Small but macroscopic particles—chondrules, higher temperature mineral inclusions, metal grains, and their like—dominate the fabric of primitive meteorites. The properties of these constituents, and their relationship to the fine dust grains which surround them, suggest that they led an extended existence in a gaseous protoplanetary nebula prior to their incorporation into their parent primitive bodies. In this paper we explore in some detail the velocities acquired by such particles in a turbulent nebula. We treat velocities in inertial space (relevant to diffusion), velocities relative to the gas and entrained microscopic dust (relevant to accretion of dust rims), and velocities relative to each other (relevant to collisions). We extend previous work by presenting explicit, closed-form solutions for the magnitude and size dependence of these velocities in this important particle size regime, and we compare these expressions with new numerical calculations. The magnitude and size dependence of these velocities have immediate applications to chondrule and CAI rimming by fine dust and to their diffusion in the nebula, which we explore separately.  相似文献   

ISO Observations of Classical Novae     

A. Salama  P. Barr  J. Clavel  R. N. Jenkins  K. Leech  M.F. Kessler  T. Lim  L. Metcalfe  B. Schulz  A. Evans  S. P. S. Eyres 《Astrophysics and Space Science》1997,255(1-2):227-235

We describe the ISO programme to observe classical novae. The programme includes observations of novae during and shortly after eruption, and old novae. ISO observations of far infrared fine structure lines are providing us with information about physical conditions in nova ejecta which complement and extend knowledge obtained from ground-based observations. Surprisingly, we are getting little information about dust in nova systems, despite the fact that many novae are prolific dust-producers. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

A seismic refraction study of the western Tuz Gölü basin, central Turkey     

C. Gürbüz  J. R. Evans 《Geophysical Journal International》1991,106(1):239-251

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Searching for stars in high-velocity clouds     

J. Davies  S. Sabatini  L. Davies  S. Linder  S. Roberts  R. Smith  Rh. Evans 《Monthly notices of the Royal Astronomical Society》2002,336(1):155-158

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