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James, John D.

doi:10.1023/a:1005933001413

Cited by 11 publications

(21 citation statements)

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“…A cartesian grid is therefore selected. We use here in fact Fourier transform N ‐body code with the James (1977) method to avoid the influence of Fourier images. The useful grid is 256 2 × 128, corresponding to (60 kpc) 2 × 30 kpc, implying a cell size of 234 pc.…”

Section: N‐body Simulationsmentioning

confidence: 99%

Global lopsided instability in a purely stellar galactic disc

Saha

Combes

Jog

2007

Monthly Notices of the Royal Astronomical Society

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It is shown that pure exponential discs in spiral galaxies are capable of supporting slowly varying discrete global lopsided modes, which can explain the observed features of lopsidedness in the stellar discs. Using linearized fluid dynamical equations with the softened self-gravity and pressure of the perturbation as the collective effect, we derive self-consistently a quadratic eigenvalue equation for the lopsided perturbation in the galactic disc. On solving this, we find that the ground-state mode shows the observed characteristics of the lopsidedness in a galactic disc, namely the fractional Fourier amplitude A$_1$ increases smoothly with the radius. These lopsided patterns precess in the disc with a very slow pattern speed with no preferred sense of precession. We show that the lopsided modes in the stellar disc are long-lived because of a substantial reduction ($\sim$ a factor of 10 compared to the local free precession rate) in the differential precession. The numerical solution of the equations shows that the ground-state lopsided modes are either very slowly precessing stationary normal mode oscillations of the disc or growing modes with a slow growth rate depending on the relative importance of the collective effect of the self-gravity. N-body simulations are performed to test the spontaneous growth of lopsidedness in a pure stellar disc. Both approaches are then compared and interpreted in terms of long-lived global $m=1$ instabilities, with almost zero pattern speed.Comment: 15 pages, 23 figures, accepted in MNRA

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Section: N‐body Simulationsmentioning

confidence: 99%

Global lopsided instability in a purely stellar galactic disc

Saha

Combes

Jog

2007

Monthly Notices of the Royal Astronomical Society

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“… Loop over all N particles using cloud‐in‐cell interpolation to build up the discretized density distribution ρ ijk =ρ( x ijk ). Calculate the potential Φ ijk corresponding to this ρ ijk using James' (1977) method (see ). Looping again over all N particles, use a finite‐difference approximation to estimate accelerations −∂Φ/∂ x at the mesh points surrounding each particle, then interpolate the value of the acceleration at the particle's location using the same cloud‐in‐cell scheme employed in step (i). …”

Section: Potential Solvermentioning

confidence: 99%

“…I thank James Binney, Walter Dehnen and Ben Moore for helpful discussions, and the Royal Society for financial support. James (1977) describes an economical method for calculating the solution to Poisson's equation,…”

Section: Ac K N Ow L E D G M E N T Smentioning

confidence: 99%

“…I have focused here on describing James' method using the firstorder approximation of the Laplacian (A20). James (1977) shows how it is possible to apply the same ideas to higher order approximations, albeit at the expense of much more involved bookkeeping. I find that the resulting minor changes in the Green's function G i jk have no detectable effect for the realistic large-N situations described in Section 4.…”

Section: A6 Performancementioning

confidence: 99%

“…sums up. For completeness, I include in an appendix an explanation of James' (1977) method, which is used in .…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

GROMMET: an N-body code for high-resolution simulations of individual galaxies

Magorrian

2007

Monthly Notices of the Royal Astronomical Society

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This paper presents a fast, economical particle‐multiple‐mesh N‐body code optimized for large‐N modelling of collisionless dynamical processes, such as black hole wandering or bar–halo interactions, occurring within isolated galaxies. The code has been specially designed to conserve linear momentum. Despite this, it also has variable softening and an efficient block‐time‐step scheme: the force between any pair of particles is calculated using the finest mesh that encloses them both (respecting Newton's third law) and is updated only on the longest time‐step of the two (which conserves momentum). For realistic galaxy models with N≳ 106, it is faster than the fastest comparable tree code by factors ranging from ∼2 (using single time‐steps) to ∼10 (multiple time‐steps in a concentrated galaxy).

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Tidal Tails Around Galactic Globular Clusters

Meylan¹,

Léon

Combes³

From Extrasolar Planets to Cosmology: The VLT Opening Symposium

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Cited by 11 publications

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Global lopsided instability in a purely stellar galactic disc

Global lopsided instability in a purely stellar galactic disc

GROMMET: an N-body code for high-resolution simulations of individual galaxies

Tidal Tails Around Galactic Globular Clusters

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