1,196 research outputs found
Numerical two-dimensional calculations of the formation of the solar nebula
Numerical two dimensional calculations of the formation of the solar nebula are presented. The following subject areas are covered: (1) observational constraints of the properties of the initial solar nebula; (2) the physical problem; (3) review if two dimensional calculations of the formation phase; (4) recent models with hydrodynamics and radiative transport; and (5) further evolution of the system
Architecture and data processing alternatives for the tse computer. Volume 4: Image rotation using tse operations
The tse computer's capability of achieving image congruence between temporal and multiple images with misregistration due to rotational differences is reported. The coordinate transformations are obtained and a general algorithms is devised to perform image rotation using tse operations very efficiently. The details of this algorithm as well as its theoretical implications are presented. Step by step procedures of image registration are described in detail. Numerous examples are also employed to demonstrate the correctness and the effectiveness of the algorithms and conclusions and recommendations are made
In Situ Formation and Dynamical Evolution of Hot Jupiter Systems
Hot Jupiters, giant extrasolar planets with orbital periods shorter than ~10
days, have long been thought to form at large radial distances, only to
subsequently experience long-range inward migration. Here, we propose that in
contrast with this picture, a substantial fraction of the hot Jupiter
population formed in situ via the core accretion process. We show that under
conditions appropriate to the inner regions of protoplanetary disks, rapid gas
accretion can be initiated by Super-Earth type planets, comprising 10-20 Earth
masses of refractory composition material. An in situ formation scenario leads
to testable consequences, including the expectation that hot Jupiters should
frequently be accompanied by additional low-mass planets with periods shorter
than ~100 days. Our calculations further demonstrate that dynamical
interactions during the early stages of planetary systems' lifetimes should
increase the inclinations of such companions, rendering transits rare.
High-precision radial velocity monitoring provides the best prospect for their
detection.Comment: 19 pages, 10 figures, accepted to Ap
Evolution of Ohmically Heated Hot Jupiters
We present calculations of thermal evolution of Hot Jupiters with various
masses and effective temperatures under Ohmic dissipation. The resulting
evolutionary sequences show a clear tendency towards inflated radii for
effective temperatures that give rise to significant ionization of alkali
metals in the atmosphere, compatible with the trend of the data. The degree of
inflation shows that Ohmic dissipation, along with the likely variability in
heavy element content can account for all of the currently detected radius
anomalies. Furthermore, we find that in absence of a massive core, low-mass hot
Jupiters can over-flow their Roche-lobes and evaporate on Gyr time-scales,
possibly leaving behind small rocky cores.Comment: Accepted to The Astrophysical Journal (2011) 735-2, 9 pages, 8
figures, updated figures 2-
Numerical studies of collapsing interstellar clouds
Numerical simulation of the structure and evolution of interstellar clouds was initiated. Steps were taken toward an integrated treatment of the dynamical, thermal, and chemical processes entering model calculations. A detailed study was made of radiative transfer in molecular lines to allow model predictions to be tested against empirical data. The calculations have successfully reproduced and explained several observed cloud properties, including abundances of complex molecular species and the apparent depletion of CO in dense cores
Protoplanetary Formation and the FU Orionis Outburst
The following three publications which reference the above grant from the NASA Origins of Solar Systems program are attached and form the final technical report for this project. The research involved comparisons of the spectral energy distributions of FU Orionis objects with theoretical models and associated studies of the structure of the outbursting accretion disks, as well as related studies on the effects of magnetic fields in disks, which will lead in the future to models of FU Orionis outbursts which include the effects of magnetic fields. The project was renewed under a new grant NAGW-4456, entitled 'Effects of FU Orionis Outbursts on Protoplanetary Disks'. Work now being prepared for publication deals more specifically with the issue of the effects of the outbursts on protoplanetary formation. Models of the spectral energy distribution of FU Orionis stars. A simple model of a buoyant magnetic dynamo in accretion disks and a numerical study of magnetic buoyancy in an accretion disk have been submitted
Formation of Giant Planets by Concurrent Accretion of Solids and Gas inside an Anti-Cyclonic Vortex
We study the formation of a giant gas planet by the core--accretion
gas--capture process, with numerical simulations, under the assumption that the
planetary core forms in the center of an anti-cyclonic vortex. The presence of
the vortex concentrates particles of centimeter to meter size from the
surrounding disk, and speeds up the core formation process. Assuming that a
planet of Jupiter mass is forming at 5 AU from the star, the vortex enhancement
results in considerably shorter formation times than are found in standard
core--accretion gas--capture simulations. Also, formation of a gas giant is
possible in a disk with mass comparable to that of the minimum mass solar
nebula.Comment: 27 pages, 4 figures, ApJ in pres
Protostellar collapse: rotation and disk formation
We present some important conclusions from recent calculations pertaining to
the collapse of rotating molecular cloud cores with axial symmetry,
corresponding to evolution of young stellar objects through classes 0 and begin
of class I. Three main issues have been addressed: (1) The typical timescale
for building up a preplanetary disk - once more it turned out that it is of the
order of one free-fall time which is decisively shorter than the widely assumed
timescale related to the so-called 'inside-out collapse'; (2) Redistribution of
angular momentum and the accompanying dissipation of kinetic (rotational)
energy - together these processes govern the mechanical and thermal evolution
of the protostellar core to a large extent; (3) The origin of
calcium-aluminium-rich inclusions (CAIs) - due to the specific pattern of the
accretion flow, material that has undergone substantial chemical and
mineralogical modifications in the hot (exceeding 900 K) interior of the
protostellar core may have a good chance to be advectively transported outward
into the cooler remote parts (beyond 4 AU, say) of the growing disk and to
survive there until it is incorporated into a meteoritic body.Comment: 4 pages, 4 figure
Coupled evolutions of the stellar obliquity, orbital distance, and planet's radius due to the Ohmic dissipation induced in a diamagnetic hot Jupiter around a magnetic T Tauri star
We revisit the calculation of the Ohmic dissipation in a hot Jupiter
presented in Laine et al. (2008) by considering more realistic interior
structures, stellar obliquity, and the resulting orbital evolution. In this
simplified approach, the young hot Jupiter of one Jupiter mass is modelled as a
diamagnetic sphere with a finite resistivity, orbiting across tilted stellar
magnetic dipole fields in vacuum. Since the induced Ohmic dissipation occurs
mostly near the planet's surface, we find that the dissipation is unable to
significantly expand the young hot Jupiter. Nevertheless, the planet inside a
small co-rotation orbital radius can undergo orbital decay by the dissipation
torque and finally overfill its Roche lobe during the T Tauri star phase. The
stellar obliquity can evolve significantly if the magnetic dipole is
parallel/anti-parallel to the stellar spin. Our results are validated by the
general torque-dissipation relation in the presence of the stellar obliquity.
We also run the fiducial model in Laine et al. (2008) and find that the
planet's radius is sustained at a nearly constant value by the Ohmic heating,
rather than being thermally expanded to the Roche radius as suggested by the
authors.Comment: about 40 pages, 10 figures, Accepted for publication in The
Astrophysical Journa
- …