Numerical simulations of aligned neutron star magnetospheres     

I. A. Smith  F. C. Michel  P. D. Thacker 《Monthly notices of the Royal Astronomical Society》2001,322(2):209-217

We present detailed numerical simulations of the magnetosphere of an isolated neutron star in which the spin and magnetic dipole axes of the star are aligned. We demonstrate that stable charge distributions are always found, rather than particle outflows. A stable magnetosphere consists of a dome above the polar cap containing plasma of one charge and an equatorial belt containing plasma of the other sign: E · B =0 inside both of these. These are separated by a vacuum gap in which E · B ≠0 ( ρ =0 instead). We show that the charge distribution used in the 'standard' Goldreich–Julian pulsar model is inherently unstable: it collapses to a stable configuration that is very similar to the others illustrated here. An instructive video of this collapse is available at http://spacsun.rice.edu/~ian/. For typical pulsars, the stable solution has no particles near to the light cylinder, and if there were any there then their loss from the system would not lead to a replacement from the star (in contradiction to the explicit assumption used in the Goldreich–Julian model). We discuss the generic effects of pair creation, in particular as an additional source of ionization in the vacuum gap. The overall effect is simply to reduce the value of E · B in the vacuum gap so that the pair-production rate drops towards zero. A dome, disc and gap geometry is still the resulting solution. In conclusion, we confirm previous studies that the aligned rotator cannot make an active pulsar.  相似文献   

Intermediate-metallicity, high-velocity stars and Galactic chemical evolution   总被引：2，自引：0，他引：2  

S. G. Ryan  I. M. Smith 《Monthly notices of the Royal Astronomical Society》2003,341(1):199-212

High signal-to-noise ratio spectra were obtained of 10 high-proper-motion stars having  −1 ≲[Fe/H] < 0  , and a comparable number of disc stars. All but two of the high-proper-motion stars were confirmed to have  [Fe/H] > −1.0  , some approaching solar metallicity, but, even so, earlier measurements overestimated the metallicities and velocities of some of these stars. Models of stellar populations were used to assign membership probabilities to the Galactic components to which the high-velocity stars might belong. Many were found to be more probably thick-disc than halo objects, despite their large space motions, and two might be associated with the inner Galaxy. It may be necessary to reassess contamination of previous halo samples, such as those used to define the metallicity distribution, to account for contamination by high-velocity thick-disc stars, and to consider possible subcomponents of the halo.
The change in [α/Fe] ratios at  [Fe/H]≃−1.0  is often used to constrain the degree and timing of Type Ia supernova nucleosynthesis in Galactic chemical-evolution models. [Ti/Fe] values were measured for eight of the high-velocity stars. Both high- and low-[Ti/Fe] halo stars exist; likewise high- and low-[Ti/Fe] thick-disc stars exist. We conclude that the [Ti/Fe]'break' is not well defined for a given population; nor is there a simple, continuous evolutionary sequence through the break. Implications for the interpretation of the [α/Fe] break in terms of SN Ia time-scales and progenitors are discussed. The range of [Ti/Fe] found for high -velocity (low rotation) thick-disc stars contrasts with that for the low -velocity (high rotation) thick-disc sample studied by Prochaska et al.  相似文献   

Continuum and spectral line observations of the OH Megamaser galaxy Arp 220     

E. Rovilos  P. J. Diamond  C. J. Lonsdale  C. J. Lonsdale  H. E. Smith 《Monthly notices of the Royal Astronomical Society》2003,342(2):373-382

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Far-infrared photometry of deeply embedded outflow sources     

D. Froebrich  M. D. Smith  K.-W. Hodapp  J. Eislöffel 《Monthly notices of the Royal Astronomical Society》2003,346(1):163-176

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Radiative transfer in disc galaxies – III. The observed kinematics of dusty disc galaxies     

Maarten Baes †  Jonathan I. Davies  Herwig Dejonghe  Sabina Sabatini  Sarah Roberts  Rhodri Evans  Suzanne M. Linder  Rodney M. Smith  W. J. G. de Blok 《Monthly notices of the Royal Astronomical Society》2003,343(4):1081-1094

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Emission linewidths and QSO black hole mass estimates from the 2dF QSO Redshift Survey     

E. A. Corbett  S. M. Croom  B. J. Boyle  H. Netzer  L. Miller  P. J. Outram  T. Shanks  R. J. Smith  K. Rhook 《Monthly notices of the Royal Astronomical Society》2003,343(3):705-718

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A photometric–spectroscopic analysis and the evolutionary status of the Algol-type binary U Coronae Borealis     

S. K. Yerli  M. J. Sarna  S. Zo&#;a  Robert Connon Smith  G. Tovmassian 《Monthly notices of the Royal Astronomical Society》2003,342(4):1349-1360

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Enhancement of the inertial navigation system for the Morpheusautonomous underwater vehicles     

Grenon  G. An  P.E. Smith  S.M. Healey  A.J. 《Oceanic Engineering, IEEE Journal of》2001,26(4):548-560

This paper presents the design and development of an enhanced inertial navigation system that is to be integrated into the Morpheus autonomous underwater vehicle at Florida Atlantic University. The inertial measurement unit is based on the off-the-shelf Honeywell HG1700-AG25 3-axis ring-laser gyros and three-axis accelerometers and is aided with ground speed measurements obtained using an RDI Doppler-velocity-log sonar. An extended Kalman filter has been developed, which fuses together asynchronously the inertial and Doppler data, as well as the differential Global Positioning System positional fixes whenever they are available. A complementary filter was implemented to provide a much smoother and stable attitude estimate. Thus far, preliminary study has been made on characterizing the inertial navigation system-based navigation system performance, and the corresponding results and analyzes are provided  相似文献   

Evidence for cospatial optical and radio polarized emission in active galactic nuclei     

Denise C. Gabuzda  Elizaveta A. Rastorgueva  Paul S. Smith  Shane P. O'Sullivan 《Monthly notices of the Royal Astronomical Society》2006,369(4):1596-1602

We investigate the relationship between the optical and radio emission of active galactic nuclei (AGN) by analysing optical and 15+22+43 GHz Very Long Baseline Array (VLBA) polarization observations simultaneous to within a day for 11 BL Lacertae (BL Lac) objects and the blazar 3C279. We have determined and corrected for the Faraday rotation measures in the very long baseline interferometry (VLBI) cores, enabling us to compare the intrinsic (zero-wavelength) VLBI-core polarization angles and the optical polarization angles χ_opt. A clear alignment between these two angles emerges in the transition toward higher radio frequencies, and a prominent peak at 0° is visible in the distribution of |χ_opt−χ_43 GHz|. This correlation implies that the magnetic-field orientations in the regions giving rise to the optical and radio polarization are the same, and can be easily understood if the radio and optical polarization are roughly cospatial. It is difficult to rule out the possibility that they arise in different regions in a straight jet with a uniform magnetic-field structure, but this seems less likely, since the VLBI jets of AGN are often bent on parsec-scales. This may suggest that much or all of the strong optical polarization in these sources arises in the inner radio jets, possibly associated with the formation and emergence of compact new VLBI components.  相似文献   

Velocity study of axisymmetric protostellar jets with molecular cooling     

Anthony Moraghan  Michael D. Smith  Alexander Rosen 《Monthly notices of the Royal Astronomical Society》2006,371(3):1448-1458

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