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41.
C. M. Sykes I. W. A. Browne N. J. Jackson D. R. Marlow S. Nair P. N. Wilkinson R. D. Blandford J. Cohen C. D. Fassnacht D. Hogg T. J. Pearson A. C. S. Readhead D. S. Womble S. T. Myers A. G. de Bruyn M. Bremer G. K. Miley & R. T. Schilizzi 《Monthly notices of the Royal Astronomical Society》1998,301(2):310-314
We report the discovery of the most complex arcsec-scale radio gravitational lens system yet known. B1933+503 was found during the course of the CLASS survey and MERLIN and VLA radio maps reveal up to 10 components. Four of these are compact and have flat spectra; the rest are more extended and have steep spectra. The background lensed object appears to consist of a flat-spectrum core (quadruply imaged) and two compact 'lobes' symmetrically disposed relative to the core. One of the lobes is quadruply imaged while the other is doubly imaged. An HST observation of the system with the WFPC2 shows a galaxy with an axial ratio of 0.5, but none of the images of the background object is detected. A redshift of 0.755 has been measured for the lens galaxy. 相似文献
42.
Observational conditions for the formation and maintenance of filaments are reviewed since 1989 in the light of recent findings
on their structure, chirality, inferred magnetic topology, and mass flows. Recent observations confirm the necessary conditions
previously cited: (1) their location at a boundary between opposite-polarity magnetic fields (2) a system of overlying coronal
loops, (3) a magnetically-defined channel beneath, (4) the convergence of the opposite-polarity network magnetic fields towards
their common boundary within the channel and (5) cancellation of magnetic flux at the common polarity boundary. Evidence is
put forth for three additional conditions associated with fully developed filaments: (A) field-aligned mass flows parallel
with their fine structure (B) a multi-polar background source of small-scale magnetic fields necessary for the formation of
the filament barbs and (C) a handedness property known as chirality which requires them to be either of two types, dextral
or sinistral. One-to-one relationships have been established between the chirality of filaments and the chirality of their
filament channels and overlying coronal arcades. These findings reinforce earlier evidence that every filament magnetic field
is separate from the magnetic field of the overlying arcade but both are parts of a larger magnetic field system. The larger
system has at least quadrupolar footprints in the photosphere and includes the filament channel and subphotospheric magnetic
fields, This ‘systems’ view of filaments and their environment enables new perspectives on why arcades and channels are invariable
conditions for their existence.
Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1005026814076 相似文献
43.
A. R. Breen P. J. Moran C. A. Varley W. P. Wilkinson P. J. S. Williams W. A. Coles A. Lecinski J. Markkanen 《Annales Geophysicae》1998,16(10):1265-1282
Co-rotating interaction regions (CIRs) between fast and slow streams of plasma are a prominent feature of the solar wind. Measurements of interplanetary scintillation (IPS) using the three widely separated antennas of the EISCAT facility have been used to detect the compression regions at the leading edges of interaction regions and to determine the location and velocity of the structure. Observations show that interaction regions have developed as close to the Sun as 25–30 solar radii, a result supported by theoretical modelling which shows that the conditions needed for CIRs to develop exist inside 30 solar radii. 相似文献
44.
P. J. Moran A. R. Breen C. A. Varley P. J. S. Williams W. P. Wilkinson J. Markkanen 《Annales Geophysicae》1998,16(10):1259-1264
EISCAT observations of the interplanetary scintillation of a single source were made over an extended period of time, during which the orientation of the baselines between the two observing sites changed significantly. Assuming that maximum correlation between the scintillations observed at the two sites occurs when the projected baseline is parallel to the direction of plasma flow, this technique can be used to make a unique determination of the direction of the solar wind. In the past it has usually been assumed that the plasma flow is radial, but measurements of eleven sources using this technique have indicated conclusively that in at least six cases observed at mid or high heliocentric latitude there is a significant non-radial component directed in four cases towards the heliocentric equator and in two cases towards the pole. 相似文献
45.
John E. Cooper Roger A. Rulifson J. Jeffrey Isely Sara E. Winslow 《Estuaries and Coasts》1998,21(2):307-317
Juvenile striped bass,Morone saxatilis, collected in Albemarle Sound, North Carolina, during 1988–1992 were examined for food habits and growth. Ages estimated from otoliths collected in 1990–1992 were used to determine individual spawning dates and growth in total length and weight. The majority of striped bass examined had been spawned in mid-May 1990, mid-May to early June 1991, and June to early July 1992. Mysid shrimp was the dominant prey taxon and was consumed in all size classes examined. Mysid shrimp were consumed at twice the rate of copepods and 10 times more frequently than cladocerans. Fishes were a minor prey taxon. The number of mysid shrimp consumed increased with increasing length of striped bass. A higher percentage of mysid shrimp were consumed in the more saline waters of the central sound than in the less saline western sound. The opposite trend was found for consumed fishes. Increases in total length were linear from July to October, but increases in weight were not. Weight increased less rapidly in younger striped bass and more rapidly in older striped bass than either length or age. Quadratic and logarithmic equations accurately predicted weight from measures of total length but weight could not be predicted from age nor could age be predicted from total length. Estimating growth from total length at time of capture may be comparing fish of different ages. Age estimation from otoliths allowed us to determine that growth rates were similar among years and that differences in observed total length over time were due to different spawning times and not growth rates. 相似文献
46.
Pedro Augusto Peter N. Wilkinson Ian W.A. Browne 《Astrophysics and Space Science》1998,261(1-4):261-264
In this paper we present a subsample of 55 flat-spectrum radio sources dominated by (∼ 100 mas) kpc-scale structure, selected
from a parent sample of 1665 VLA sources. Most are core-jets and 23 are CSO/MSO candidates. Properties of the subsample are
discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
47.
Browne Patnaik Wilkinson & Wrobel 《Monthly notices of the Royal Astronomical Society》1998,293(3):257-287
We present a catalogue of 781 compact radio sources in the declination range 0° ≤ δB1950 ≤ +20° whose positions have been measured to an rms accuracy of about 14 mas with the Very Large Array (VLA). These sources are primarily intended for use as phase calibration sources for the Jodrell Bank MERLIN. However, they will also be suitable as phase calibrators for the VLA and can be considered as candidate phase calibrators for very long-baseline interferometry (VLBI) networks. 相似文献
48.
L.J. King N. Jackson R.D. Blandford M.N. Bremer I.W.A. Browne A.G. de Bruyn C. Fassnacht L. Koopmans D. Marlow P.N. Wilkinson 《Monthly notices of the Royal Astronomical Society》1998,295(2):L41-L44
We report the discovery, using NICMOS on the Hubble Space Telescope , of an arcsec-diameter Einstein ring in the gravitational lens system B1938+666. The lensing galaxy is also detected, and is most likely an early-type galaxy. Modelling of the ring is presented and compared with the radio structure from MERLIN maps. We show that the Einstein ring is consistent with the gravitational lensing of an extended infrared component, centred between the two radio components. 相似文献
49.
N. Jackson S. Nair I. W. A. Browne P. N. Wilkinson T. W. B. Muxlow A. G. de Bruyn L. Koopmans M. Bremer I. Snellen G. K. Miley R. T. Schilizzi S. Myers C. D. Fassnacht D. S. Womble A. C. S. Readhead R. D. Blandford & T. J. Pearson 《Monthly notices of the Royal Astronomical Society》1998,296(3):483-490
A new four-image gravitational lens system, B0712+472, has been discovered during the Cosmic Lens All-Sky Survey. This system consists of four flat-spectrum radio images that are also seen on a Hubble Space Telescope ( HST ) image, together with the lensing galaxy. We present MERLIN, VLA and VLBA maps and WHT spectra of the system as well as the HST images. The light distribution of the lensing galaxy is highly elongated and so too is the mass distribution deduced from modelling. We suggest a redshift of ∼1.33 for the lensed object; the lens redshift will require further investigation. The discovery of this new system further increases the ratio of four-image to two-image lens systems currently known, exacerbating problems of required ellipticity of matter distributions in lensing galaxies. 相似文献
50.