4,999 research outputs found
N-body Simulations of Satellite Formation around Giant Planets: Origin of Orbital Configuration of the Galilean Moons
As the number of discovered extrasolar planets has been increasing, diversity
of planetary systems requires studies of new formation scenarios. It is
important to study satellite formation in circumplanetary disks, which is often
viewed as analogous to formation of rocky planets in protoplanetary disks. We
investigated satellite formation from satellitesimals around giant planets
through N-body simulations that include gravitational interactions with a
circumplanetary gas disk. Our main aim is to reproduce the observable
properties of the Galilean satellites around Jupiter through numerical
simulations, as previous N-body simulations have not explained the origin of
the resonant configuration. We performed accretion simulations based on the
work of Sasaki et al. (2010), in which an inner cavity is added to the model of
Canup & Ward (2002, 2006). We found that several satellites are formed and
captured in mutual mean motion resonances outside the disk inner edge and are
stable after rapid disk gas dissipation, which explains the characteristics of
the Galilean satellites. In addition, owing to the existence of the disk edge,
a radial compositional gradient of the Galilean satellites can also be
reproduced. An additional objective of this study is to discuss orbital
properties of formed satellites for a wide range of conditions by considering
large uncertainties in model parameters. Through numerical experiments and
semianalytical arguments, we determined that if the inner edge of a disk is
introduced, a Galilean-like configuration in which several satellites are
captured into a 2:1 resonance outside the disk inner cavity is almost
universal. In fact, such a configuration is produced even for a massive disk
and rapid type I migration. This result implies the inevitability of a Galilean
satellite formation in addition to providing theoretical predictions for
extrasolar satellites.Comment: 20 pages, 9 figures, accepted for publication in Ap
Suppression of type I migration by disk winds
Planets less massive than Saturn tend to rapidly migrate inward in
protoplanetary disks. This is the so-called type I migration. Simulations
attempting to reproduce the observed properties of exoplanets show that type I
migration needs to be significantly reduced over a wide region of the disk for
a long time. However, the mechanism capable of suppressing type I migration
over a wide region has remained elusive. The recently found turbulence-driven
disk winds offer new possibilities. We investigate the effects of disk winds on
the disk profile and type I migration for a range of parameters that describe
the strength of disk winds. We also examine the in situ formation of close-in
super-Earths in disks that evolve through disk winds. The disk profile, which
is regulated by viscous diffusion and disk winds, was derived by solving the
diffusion equation. We carried out a number of simulations and plot here
migration maps that indicate the type I migration rate. We also performed
N-body simulations of the formation of close-in super-Earths from a population
of planetesimals and planetary embryos. We define a key parameter, Kw, which
determines the ratio of strengths between the viscous diffusion and disk winds.
For a wide range of Kw, the type I migration rate is presented in migration
maps. These maps show that type I migration is suppressed over the whole
close-in region when the effects of disk winds are relatively strong (Kw <
100). From the results of N-body simulations, we see that type I migration is
significantly slowed down assuming Kw = 40. We also show that the results of
N-body simulations match statistical orbital distributions of close-in
super-Earths.Comment: 5 pages, 4 figures, accepted for publication in A&A Letter
Fission fragment mass reconstruction from Si surface barrier detector measurement
A method for plasma delay and pulse-height defect corrections for Si surface
barrier detectors (SBD) is presented. Based on known empirical formulae, simple
approximations involving the measured time-of-flight (TOF) and energy of the
ions were found and a mass reconstruction procedure was developed. The
procedure was applied for obtaining the fission fragment mass and angular
distributions from the Ni+Au reaction at 418 MeV and 383 MeV
incident energy using an array of eight SBDs.Comment: 3 pages, 1 table, 3 figures, submitted to NIM A ; 4 pages, 1 table, 5
figures, added discussion and figure
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