2,293 research outputs found
Formation of the resonant system HD 60532
Among multi-planet planetary systems there are a large fraction of resonant
systems. Studying the dynamics and formation of these systems can provide
valuable informations on processes taking place in protoplanetary disks where
the planets are thought have been formed. The recently discovered resonant
system HD 60532 is the only confirmed case, in which the central star hosts a
pair of giant planets in 3:1 mean motion resonance. We intend to provide a
physical scenario for the formation of HD 60532, which is consistent with the
orbital solutions derived from the radial velocity measurements. Observations
indicate that the system is in an antisymmetric configuration, while previous
theoretical investigations indicate an asymmetric equilibrium state. The paper
aims at answering this discrepancy as well. We performed two-dimensional
hydrodynamical simulations of thin disks with an embedded pair of massive
planets. Additionally, migration and resonant capture are studied by
gravitational N-body simulations that apply properly parametrized
non-conservative forces. Our simulations suggest that the capture into the 3:1
mean motion resonance takes place only for higher planetary masses, thus
favouring orbital solutions having relatively smaller inclination i=20 degrees.
The system formed by numerical simulations qualitatively show the same
behaviour as HD 60532. We also find that the presence of an inner disk (between
the inner planet and the star) plays a very important role in determining the
final configurations of resonant planetary systems. Its damping effect on the
inner planet's eccentricity is responsible for the observed antisymmetric state
of HD 60532.Comment: 7 pages, 7 figures, Accepted for publication in Astronomy &
Astrophysic
Stability and Formation of the Resonant System HD 73526
Based on radial velocity measurements it has been found recently that the two
giant planets detected around the star HD 73526 are in 2:1 resonance. However,
as our numerical integration shows, the derived orbital data for this system
result in chaotic behavior of the giant planets, which is uncommon among the
resonant extrasolar planetary systems.
We intend to present regular (non-chaotic) orbital solutions for the giant
planets in the system HD 73526 and offer formation scenarios based on combining
planetary migration and sudden perturbative effects such as planet-planet
scattering or rapid dispersal of the protoplanetary disk. A comparison with the
already studied resonant system HD 128311, exhibiting similar behavior, is also
done.
The new sets of orbital solutions have been derived by the Systemic Console
(www.oklo.org). The stability of these solutions has been investigated by the
Relative Lyapunov indicator, while the migration and scattering effects are
studied by gravitational N-body simulations applying non-conservative forces as
well. Additionally, hydrodynamic simulations of embedded planets in
protoplanetary disks are performed to follow the capture into resonance.
For the system HD 73526 we demonstrate that the observational radial velocity
data are consistent with a coplanar planetary system engaged in a stable 2:1
resonance exhibiting apsidal corotation. We have shown that, similarly to the
system HD 128311, the present dynamical state of HD 73526 could be the result
of a mixed evolutionary process melting together planetary migration and a
perturbative event.Comment: 12 pages, 14 figures, accepted in A&A, v2: technical change
Detailed survey of the phase space around Nix and Hydra
We present a detailed survey of the dynamical structure of the phase space
around the new moons of the Pluto - Charon system. The spatial elliptic
restricted three-body problem was used as model and stability maps were created
by chaos indicators. The orbital elements of the moons are in the stable domain
both on the semimajor axis - eccentricity and - inclination spaces. The
structures related to the 4:1 and 6:1 mean motion resonances are clearly
visible on the maps. They do not contain the positions of the moons, confirming
previous studies. We showed the possibility that Nix might be in the 4:1
resonance if its argument of pericenter or longitude of node falls in a certain
range. The results strongly suggest that Hydra is not in the 6:1 resonance for
arbitrary values of the argument of pericenter or longitude of node.Comment: Published in MNRAS. 10 pages, 7 figures, 4 table
Collectivity evolution in the neutron-rich Pd isotopes towards the N=82 shell closure
The neutron-rich, even-even 122,124,126Pd isotopes has been studied via
in-beam gamma-ray spectroscopy at the RIKEN Radioactive Isotope Beam Factory.
Excited states at 499(9), 590(11), and 686(17) keV were found in the three
isotopes, which we assign to the respective 2+ -> 0+ decays. In addition, a
candidate for the 4+ state at 1164(20) keV was observed in 122Pd. The resulting
Ex(2+) systematics are essentially similar to those of the Xe (Z=54) isotopic
chain and theoretical prediction by IBM-2, suggesting no serious shell
quenching in the Pd isotopes in the vicinity of N=82
Alpha-induced cross sections of 106Cd for the astrophysical p-process
The 106Cd(alpha,gamma)110Sn reaction cross section has been measured in the
energy range of the Gamow window for the astrophysical p-process scenario. The
cross sections for 106Cd(alpha,n)109Sn and for 106Cd(alpha,p)109In below the
(alpha,n) threshold have also been determined. The results are compared with
predictions of the statistical model code NON-SMOKER using different input
parameters. The comparison shows that a discrepancy for 106Cd(alpha,gamma)110Sn
when using the standard optical potentials can be removed with a different
alpha+106Cd potential. Some astrophysical implications are discussed.Comment: 10 pages, 9 figures, accepted for publication in Phys. Rev
Plaquette operators used in the rigorous study of ground-states of the Periodic Anderson Model in dimensions
The derivation procedure of exact ground-states for the periodic Anderson
model (PAM) in restricted regions of the parameter space and D=2 dimensions
using plaquette operators is presented in detail. Using this procedure, we are
reporting for the first time exact ground-states for PAM in 2D and finite value
of the interaction, whose presence do not require the next to nearest neighbor
extension terms in the Hamiltonian. In order to do this, a completely new type
of plaquette operator is introduced for PAM, based on which a new localized
phase is deduced whose physical properties are analyzed in detail. The obtained
results provide exact theoretical data which can be used for the understanding
of system properties leading to metal-insulator transitions, strongly debated
in recent publications in the frame of PAM. In the described case, the lost of
the localization character is connected to the break-down of the long-range
density-density correlations rather than Kondo physics.Comment: 34 pages, 5 figure
Spectral signatures of disk eccentricity in young binary systems: I. Circumprimary case
Star formation occurs via fragmentation of molecular clouds, which means that
the majority of stars born are a members of binaries. There is growing evidence
that planets might form in circumprimary disks of medium-separation binaries.
The tidal forces caused by the secondary generally act to distort the
originally circular disk to an eccentric one. To infer the disk eccentricity
from high-res NIR spectroscopy, we calculate the fundamental band emission
lines of the CO molecule emerging from the atmosphere of the disk. We model
circumprimary disk evolution under the gravitational perturbation of the
orbiting secondary using a 2D grid-based hydrodynamical code, assuming
alpha-type viscosity. The hydrodynamical results are combined with our spectral
code based on the double-layer disk model to calculate the CO molecular line
profiles. We find that the orbital velocity distribution of the gas parcels
differs significantly from the circular Keplerian fashion, thus the line
profiles are asymmetric in shape. The magnitude of asymmetry is insensitive to
the binary mass ratio, the magnitude of viscosity, and the disk mass. In
contrast, the disk eccentricity, thus the level of the line profile asymmetry,
is influenced significantly by the binary eccentricity and the disk geometrical
thickness. We demonstrate that the disk eccentricity profile in the
planet-forming region can be determined by fitting the high-resolution CO line
profile asymmetry using a simple 2D spectral model that accounts for the
velocity distortions caused by the disk eccentricity. Thus, with our novel
approach the disk eccentricity can be inferred with high-resolution near-IR
spectroscopy prior to the era of high angular resolution optical or radio
direct-imaging. By determining the disk eccentricity in medium-separation young
binaries, we might be able to constrain the planet formation theories.Comment: 15 pages, 10 figures. Accepted by A&
The Blazhko behaviour of RR Geminorum I - CCD photometric results in 2004
Extended CCD monitoring of RR Gem revealed that it is a Blazhko type RRab
star with the shortest Blazhko period (7.23d) and smallest modulation amplitude
(Delta Mmax<0.1 mag) currently known. The short period of the modulation cycle
enabled us to obtain complete phase coverage of the pulsation at each phase of
the modulation. This is the first multicolour observation of a Blazhko star
which is extended enough to define accurate mean magnitudes and colours of the
variable at different Blazhko phases. Small, but real, changes in the intensity
mean colours at different Blazhko phases have been detected. The Fourier
analysis of the light curves shows that, in spite of the mmag and smaller order
of the amplitudes, the triplet structure is noticeable up to about the 14th
harmonic. The modulation is concentrated to a very narrow, 0.2 phase range of
the pulsation, centred on the supposed onset of the H emission during rising
light. These observational results raise further complications for theoretical
explanation of the long known but poorly understood Blazhko phenomenon.Comment: 10 pages, 12 figures, 3 tables. Accepted for publication in Astronomy
and Astrophysic
MOOC for AR VR training: obstacles, challenges and Usability
This paper provides a case study of massive open online course (MOOC) for augmented reality (AR) and virtual reality (VR). The research studies the obstacles, challenges and usability issues entailed in the management of a novel MOOC for AR and VR training. The electronic learning form of MOOC has been adapted and made available for a number of universities and organizations. It brings learning opportunities for university students and industrial professionals to go through online-based courses on their own pace, and some MOOCs provide certifications for specialized subjects. However, the nature of working on AR and VR requires specialized equipment such as mobile tablets with high computing capability, workstation with fast graphic processing units (GPU) and head-mount-devices (HMD). This case study investigation outlines an overview of the potential obstacles and issues with the intention of how MOOC addresses best practices and the fundamental requirements of AR and VR training
A new procedure for computing the factor of safety using the Morgenstern-Price method
By employing the same assumption regarding interslice forces as that used in the Morgenstern-Price method, two concise recurrence relations between interslice forces and interslice moments are derived which satisfy both force and moment equilibrium conditions. The Newton-Raphson method is used for determining the factor of safety and the associated scaling parameter of the interslice force function. Algebraic derivatives required in the solution process are evolved in a recursive manner which can be easily implemented in a computer program. The choices of initial values of safety factor and scaling parameter are suggested. The procedure proposed in this paper proves to be efficient and solutions converge rapidly.published_or_final_versio
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