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The photometer (ISOPHOT) on the Infrared Space Observatory (ISO) has proved to be invaluable for investigating the dust around main sequence stars (both prototypes and candidate Vega-like stars). The long wavelength camera (at 60 and 90 μm) has been used to map the area around the stars to establish whether the dust disk is extended. Low-resolution spectra between 5.8 and 11.6 μm show whether the...
We performed laboratory as well as microgravity experiments in which we studied the impact of small fractal aggregates consisting of micrometer-sized dust particles onto solid targets at various velocities. Slow bombardment of the target in the laboratory results in the formation of a fluffy dust layer in which gravity-induced compaction is observed. In order to reduce the gravitational aggregate...
We describe a new direct numerical method for simulating planetesimal dynamics in which N~10 6 or more bodies can be evolved simultaneously in three spatial dimensions over hundreds of dynamical times. This represents several orders of magnitude improvement in resolution over previous studies. The advance is made possible through modification of a stable and tested cosmological code optimized...
We present numerical simulations of the formation of the planetary companions to 47 UMa, ρ CrB, and 51 Peg. They are assumed to have formed in situ according to the basic model that a core formed first by accretion of solid particles, then later it captured substantial amounts of gas from the protoplanetary disk. In most of the calculations we prescribe a constant accretion rate for the solid core...
Planetary accretion from planetesimals to protoplanets is investigated using three-dimensional N-body simulations. The effect of gas drag due to solar nebula is included and realistic-sized planetesimals with a standard material density are used, with which the growth time scale of planetesimals is realistic. In agreement with the earlier works (E. Kokubo and S. Ida 1996, Icarus123, 180-191; 1998,...
At some stage during the chondrule (and refractory inclusion) formation process, many of these objects accreted fine-grained mantles of dust. Observations suggest that the mantle thickness is directly proportional to the chondrule-core radius. Following the proposal of H. C. Connolly, Jr., and S. G. Love (1998, Science280, 62-67), we demonstrate numerically how this effect can be produced by the hypersonic...
The coagulation equation, which is widely used for modeling growth in planet formation and other astrophysical problems, is the mean-rate equation that describes the evolution of the mass spectrum of a collection of particles due to successive mergers. A numerical code that can yield accurate solutions to the coagulation equation with a reasonable number of mass bins is developed, and it is used to...
Herbig Ae/Be (HAeBe) stars are pre-main sequence objects of moderate mass representing the early evolutionary stages of β Pic-type stars. The objects of both kinds are surrounded by dust disks/shells, and the dust is believed to be continually replenished by comet-like bodies orbiting close to the stars. As the dust particles in the β Pictoris disk are likely to be as fluffy as cometary dust is, it...
We investigate the orbital evolution of 10 13 - to 10 25 -g planetesimals near 1 AU and in the asteroid belt (near 2.6 AU) prior to the stage of evolution when the mutual perturbations between the planetesimals become important. We include nebular gas drag and the effects of Jupiter and Saturn at their present masses and in their present orbits. Gas drag introduces a size-dependent...
The process that melted and formed the chondrules, millimeter-sized glassy beads within meteorites, has not been conclusively identified. Origin by lightning in the solar nebula is consistent with many features of chondrules, but no viable model of lightning has yet been advanced. We present a model demonstrating how lightning could be generated in the solar nebula which differs from previous models...
Transient redshifted events monitored in the spectrum of β Pictoris have been interpreted for many years as resulting from the evaporation of numerous comet-like bodies in the vicinity of this stars. This motivated the investigation of dynamical mechanisms responsible for the origin of these star-grazing comets. Among various ideas, a model involving mean-motion resonances with a jovian-like planet...
We compare the HIFOGS 10-μm spectra of Comet C/1995 (O1) (Hale-Bopp) to the mid-IR spectra of interplanetary dust particles (IDPs). The four epochs of Hale-Bopp silicate features, at 2.8 AU (pre-perihelion), 1.2 AU (pre-perihelion), 0.93 AU (10 days after perihelion), and 1.7 AU (post-perihelion) have different spectral shapes. At smaller heliocentric distances, r h =<1.7 AU, there appears...
Analytical formulas are derived for the rates of evolution of the mean square orbital eccentricities and inclinations of a general population of planetesimals. For planetesimals on crossing orbits, the derivations based upon the local-velocity formalism of P. Hornung et al. (1985, Icarus64, 295-307) and upon the Hill-variable formalism of S. Ida et al. (1993, Mon. Not. R. Astron. Soc.) and H. Tanaka...
We have used the James Clerk Maxwell Telescope in Hawaii to search at submillimeter wavelengths for continuum emission from dust, and spectral line emission from carbon monoxide (CO) gas, in the neighborhood of HR 4796A. This young star has a dusty disk with a central cavity, where planets may have formed. We detect the dust component at a wavelength of 850 μm, and the inferred mass of solid material...
Adaptive optics (0.15'' resolution) infrared images of the rings and satellites of Saturn were obtained in August 1995 as the Earth was crossing the ring plane. Twelve clumps were detected in the F ring, including HST S5 and S7 objects. For the first time H magnitudes were obtained for Prometheus, Pandora, Telesto, and Calypso, and J magnitudes for Epimetheus, Janus, Mimas, Telesto, and Helene.
We have reevaluated the impact rates for the planets from ecliptic comets using the integrations in H. Levison and M. Duncan (1997, Icarus 127, 13-32; LD97). We find that the current impact rates on the giant planets are actually about four times smaller than LD97's values due to differences in methods of calculating the relevant timescales. The newly calculated impact rates are listed in Table I...
The atmospheric structure of Triton in the altitude range 25-150 km shows an unexpectedly steep thermal gradient of 0.26 K km -1 above 50 km altitude, with a nearly isothermal profile below. The upper part of the profile can be explained by downward conduction of heat deposited by magnetospheric electrons and solar UV. However, the atmospheric temperature below 50 km is too cold for identified...
We explore the effects of collisional evolution on putative Vulcanoid ensembles in the region between 0.06 and 0.21 AU from the Sun in order to constrain the probable population density and population structure of this region today. Dynamical studies have shown that the Vulcanoid Zone (VZ) could be populated. However, we find that the frequency and energetics of collisional evolution this close to...
We present 2.2 μm (K) imaging infrared (IR) polarimetry of Comet Hale-Bopp at three different epochs: 1996 April and August and 1997 April. We also present 1.5- and 1.7-μm imaging polarimetry and photometry from 1.7 to 3.8 μm in 1997 April. In 1996 April and August the comet was =< 0.5% polarized in the K band. By 1997 April the comet was strongly polarized from 1.5 to 2.2 μm-more polarized than...
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