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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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129 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1995

Binary-binary interactions and the formation of the PSR B1620-26 triple system in M4

The hierarchical triple system containing the millisecond pulsar PSR B1620-26 in M4 is the first star system ever detected in a globular cluster. Such systems should form in globular clusters as a result of dynamical interactions between binaries. We propose that the triple system containing PSR B1620-26 formed through an exchange interaction between a wide primordial binary and a pre-existing binary millisecond pulsar. This scenario would have the advantage of reconciling the approximately 10(exp 9) yr timing age of the pulsar with the much shorter lifetime of the triple system in the core of M4.

Rasio, Frederic A.↗
NASA NTRS1994

Star cluster evolution with primordial binaries. 3: Effect of the Galactic tidal field

We present the results of N-body simulations of tidally limited star clusters with an initial population of 0%-20% binaries. We find that (1) if enough binaries are initially present, the binary fraction may fall to a minimum value, then increase at late times; (2) the cluster evaporation timescale is quite insensitive to the details of the initial binary distribution; (3) the cluster core radius stabilizes at a few percent of the half-mass radius when binaries are present, just as in the case of isolated clusters; and (4) there may be a marked difference between the spatial distribution of low-energy and high-energy binaries as the cluster evolves. Specifically, the spatial distribution of the lower energy systems is often substantially more extended than that of the more tightly bound pairs. At no time are our simulated clusters well described by simple dynamical models that neglect the close coupling between the binding energies and the center-of-mass energies of the binaries they contain.

Mcmillan, Steve↗
NASA NTRS1995

Building a better leapfrog

In stellar dynamical computer simulations, as well as other types of simulations using particles, time step size is often held constant in order to guarantee a high degree of energy conservation. In many applications, allowing the time step size to change in time can offer a great saving in computational cost, but variable-size time steps usually imply a substantial degradation in energy conservation. We present a meta-algorithm' for choosing time steps in such a way as to guarantee time symmetry in any integration scheme, thus allowing vastly improved energy conservation for orbital calculations with variable time steps. We apply the algorithm to the familiar leapfrog scheme, and generalize to higher order integration schemes, showing how the stability properties of the fixed-step leapfrog scheme can be extended to higher order, variable-step integrators such as the Hermite method. We illustrate the remarkable properties of these time-symmetric integrators for the case of a highly eccentric elliptical Kepler orbit and discuss applications to more complex problems.

Hut, Piet↗