2,424 research outputs found
Gas Giant Protoplanets Formed by Disk Instability in Binary Star Systems
We present a suite of three dimensional radiative gravitational hydrodynamics
models suggesting that binary stars may be quite capable of forming planetary
systems similar to our own. The new models with binary companions do not employ
any explicit artificial viscosity, and also include the third (vertical)
dimension in the hydrodynamic calculations, allowing for transient phases of
convective cooling. The calculations of the evolution of initially marginally
gravitationally stable disks show that the presence of a binary star companion
may actually help to trigger the formation of dense clumps that could become
giant planets. We also show that in models without binary companions, which
begin their evolution as gravitationally stable disks, the disks evolve to form
dense rings, which then break-up into self-gravitating clumps. These latter
models suggest that the evolution of any self-gravitating disk with sufficient
mass to form gas giant planets is likely to lead to a period of disk
instability, even in the absence of a trigger such as a binary star companion.Comment: 52 pages, 28 figure
Extrasolar planet taxonomy: a new statistical approach
In this paper we present the guidelines for an extrasolar planet taxonomy.
The discovery of an increasing number of extrasolar planets showing a vast
variety of planetary parameters, like Keplerian orbital elements and
environmental parameters, like stellar masses, spectral types, metallicity
etc., prompts the development of a planetary taxonomy. In this work via
principal component analysis followed by hierarchical clustering analysis, we
report the definition of five robust groups of planets. We also discuss the
physical relevance of such analysis, which may provide a valid basis for
disentangling the role of the several physical parameters involved in the
processes of planet formation and subsequent evolution. For instance, we were
able to divide the hot Jupiters into two main groups on the basis of their
stellar masses and metallicities. Moreover, for some groups, we find strong
correlations between metallicity, semi-major axis and eccentricity. The
implications of these findings are discussed.Comment: accepted for publication on Ap
Flux-Limited Diffusion Approximation Models of Giant Planet Formation by Disk Instability
Both core accretion and disk instability appear to be required as formation
mechanisms in order to explain the entire range of giant planets found in
extrasolar planetary systems. Disk instability is based on the formation of
clumps in a marginally-gravitationally unstable protoplanetary disk. These
clumps can only be expected to contract and survive to become protoplanets if
they are able to lose thermal energy through a combination of convection and
radiative cooling. Here we present several new three dimensional, radiative
hydrodynamics models of self-gravitating protoplanetary disks, where radiative
transfer is handled in the flux-limited diffusion approximation. We show that
while the flux-limited models lead to higher midplane temperatures than in a
diffusion approximation model without the flux-limiter, the difference in
temperatures does not appear to be sufficiently high to have any significant
effect on the formation of self-gravitating clumps. Self-gravitating clumps
form rapidly in the models both with and without the flux-limiter. These models
suggest that the reason for the different outcomes of numerical models of disk
instability by different groups cannot be attributed solely to the handling of
radiative transfer, but rather appears to be caused by a range of numerical
effects and assumptions. Given the observational imperative to have disk
instability form at least some extrasolar planets, these models imply that disk
instability remains as a viable giant planet formation mechanism.Comment: 30 pages, 15 figures. Astrophysical Journal, in press (May 10 issue
Dynamical constraints on the origin of the moon
Six different categories of models for the formation of the moon within the context of the general theory of terrestial planet formation by the accumulation of protoplanets are discussed. These catagories are: (1) rotational fission; (2) precipitation fission; (3) intact capture; (4) disintegrative capture; (5) binary accretion; and (6) giant impact accretion. It appears that the only plausable mechanism proposed thus far involves the formation of the Moon following a giant impact that ejects portions of the differentiated Earth's mantle and parts of the impacting body into circumterrestrial orbit
Phase noise measurements of the 400-kW, 2.115-GHz (S-band) transmitter
The measurement theory is described and a test method to perform phase noise verification using off-the-shelf components and instruments is presented. The measurement technique described consists of a double-balanced mixer used as phase detector, followed by a low noise amplifier. An FFT spectrum analyzer is then used to view the modulation components. A simple calibration procedure is outlined that ensures accurate measurements. A block diagram of the configuration is presented as well as actual phase noise data from the 400 kW, 2.115 GHz (S-band) klystron transmitter
Tidal disruption of inviscid protoplanets
Roche showed that equilibrium is impossible for a small fluid body synchronously orbiting a primary within a critical radius now termed the Roche limit. Tidal disruption of orbitally unbound bodies is a potentially important process for planetary formation through collisional accumulation, because the area of the Roche limit is considerably larger then the physical cross section of a protoplanet. Several previous studies were made of dynamical tidal disruption and different models of disruption were proposed. Because of the limitation of these analytical models, we have used a smoothed particle hydrodynamics (SPH) code to model the tidal disruption process. The code is basically the same as the one used to model giant impacts; we simply choose impact parameters large enough to avoid collisions. The primary and secondary both have iron cores and silicate mantles, and are initially isothermal at a molten temperature. The conclusions based on the analytical and numerical models are summarized
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