Sputtering from grains with a size of tens of nanometers is important in a number of astrophysical scenarios [1]. Since excitations produced in a small, volatile grain by a cosmic ray ion can create `hot spots', thermal spike models have been applied to estimate the sputtering. However, these models work only over a very limited regime [2]. We use Molecular Dynamics (MD) calculations [3] to describe the energy transport and sputtering due to these `hot spots' in a grain with one quarter million particles, as a function of the energy deposited in the grain. We compare our results to the spike model as applied in [1] to the sputtering of small dust grains following the formation of a `hot spot', a model widely used in the astronomical community. We present a new model to estimate the final sputtering yield, and find that the sputtering of water could be several orders of magnitude larger than expected from previous models [1].
1-T. Hasegawa and E. Herbst, Mon. Not. R. Astron. Soc. \bf261 (1993) 83.
2-E. M. Bringa, R. E. Johnson and M. Jakas, Phys. Rev. B \bf60 (1999) 15107.
3-http://dirac.ms.virginia.edu/\~emb3t/grains/grains.html
[C3.002] Treating Numerical Instabilities in Irrotational Binary Neutron Star Coalescence Calculations
Joshua Faber, Frederic Rasio (M.I.T.)
The final burst of gravitational radiation emitted by
coalescing binary neutron stars carries direct information
about the neutron star fluid, and, in particular, about the
equation of state of nuclear matter at extreme densities.
Here, we present results from our latest post-Newtonian SPH
calculations of binary neutron star coalescence, using up to
10^6 SPH particles to compute with higher spatial
resolution than ever before the merger of an initially
irrotational system. We discuss the numerical difficulties
associated with instabilities which occur in such
calculations, and discuss their effect on predictions of
gravity wave signals and spectra.
[C3.003] Three-dimensional Modeling of Type Ia Supernova Explosions
Alexei Khokhlov (Naval Research Laboratory)
A deflagration explosion of a Type Ia Supernova (SNIa) is
studied using three-dimensional, high-resolution, adaptive
mesh refinement fluid dynamic calculations. Deflagration
speed in an exploding Chandrasekhar-mass carbon-oxygen white
dwarf (WD) grows exponentially, reaches approximately 30the speed of sound, and then declines due to a WD expansion.
Outermost layers of the WD remain unburned. The explosion
energy is comparable to that of a Type Ia supernova. The
freezing of turbulent motions by expansion appears to be a
crucial physical mechanism regulating the strength of a
supernova explosion. In contrast to one-dimensional models,
three-dimensional calculations predict the formation of
Si-group elements and pockets of unburned CO in the middle
and in central regions of a supernova ejecta. This, and the
presence of unburned outer layer of carbon-oxygen may pose
problems for SNIa spectra. Explosion sensitivity to initial
conditions and its relation to a diversity of SNIa is
discussed.
[C3.004] Mass Segregation and Evaporation in Globular Star Clusters
John Fregeau, Kriten Joshi, Simon Portegies Zwart, Frederic Rasio (MIT)
Using our recently developed dynamical Monte-Carlo code, we
study the segregation or evaporation of a tracer stellar
population with individual masses m_2 against a background
population with individual masses m_1. We consider both
light tracers (\mu \equiv m_2/m_1 < 1) and heavy tracers
(\mu > 1), and use King and Plummer model initial
conditions. In all our simulations we use 10^5 stars and
ignore the effects of binaries and stellar evolution. For
tidally truncated King models with very light tracers (\mu
\leq 10^-2) we find, by core collapse, a depletion of
tracers in the core and an enhancement in the halo. For some
initial conditions the final tracer number density in the
halo is greater than the initial tracer number density. We
discuss the implications of these results for the evolution
of planets and brown dwarfs in globular clusters. For heavy
tracers, we find that the characteristic time to sink into
the core goes like 1/\mu, as predicted by simple
theoretical arguments. This work was supported by NSF and
NASA.
[C3.005] Galaxy Collisions: Detailed Comparisons between Simulations and Observations
Nathan Hearn, Susan Lamb (Center for Theoretical Astrophysics, Department of Physics and Department of Astronomy, University of Illinois)
Simulations of galaxy collisions, when compared with
observations of collisional systems taken at multiple
wavelengths, allow one to uncover details in real galaxies,
such as significant perturbations from simple rotational
galactic disk motion, the history and development of
discrete, collision-induced star-forming regions in the
interstellar medium (ISM), and the amount of energy
deposited into the ISM by the collision. A new n-body/SPH
simulation code that incorporates a treatment of multiple
phases in the ISM is used to investigate the creation of hot
galactic halos and the formation of structure in galaxies
due to collisions. These results will aid in our
understanding of the history of star formation and the
formation of some structural features over time in
present-day galaxies.
[C3.006] An Information Link between the Large-Scale Structure of the Universe and Weak Gravitational Lensing Maps
Antonio C.C Guimarães (Brown University), Uro\vs Seljak (Princeton University), Robert H. Brandenberger (Brown University)
The determination of the Large-Scale Structure of the Universe (LSS) is one of the major goals of Cosmology. Images of distant galaxies are tangentially stretched in relation to mass concentrations present in their light path due to weak gravitational lensing. The statistical measurement of this effect defines maps (lensing maps) which contain information about the sources and lenses, and therefore about the LSS. We want to know which and how much information can be extracted from these maps.
We construct mock lensing maps from realizations of simulated LSS. N-body simulations provide snapshots of the mass distribution in the universe at several moments of its evolution. A multiple-plane lensing approximation is then used to calculate the convergence field (our weak gravitational lensing map). Because we know the statistical properties of both mock LSS's and their respective mock lensing maps, an "information link" can be established between them. The use of this information link on real lensing maps may constitute a powerful tool for the study of the LSS.