Calculations of the effects of angular momentum on the early evolution of Jupiter     

Peter Bodenheimer 《Icarus》1977,31(3):356-368

The planet Jupiter is assumed to have formed as a subcondensation in the solar nebula. The initial phase of its evolution is one of hydrostatic contraction with radiative energy transport. Calculations of evolutionary sequences through this phase are presented, including the effects of angular momentum. The calculations are carried out in two space dimensions under the assumptions of axial symmetry, constancy of angular velocity on cylindrical surfaces about the rotation axis, a pressure-density relation given by the polytrope of index 3, conservation of angular momentum, and a homogeneous composition. The results show that under certain physically reasonable initial distributions of density and angular momentum the formation of a central planet and a rotating circumplanetary envelope is possible, while under assumptions a point of instability is reached that probably results in the breakup of the condensation by fission into two or more parts. The models are discussed with reference to the present angular momenta of Jupiter and its regular satellites.  相似文献   

The ion-composition of the plasma produced by impacts of fast dust particles     

B.-K. Dalmann  E. Grün  J. Kissel  H. Dietzel 《Planetary and Space Science》1977,25(2):135-147

The composition of the impact plasma produced by fast dust particles (v > 1 km/sec) hitting an Au or W target was measured both with a model of the HELIOS micrometeoroid experiment (low electric field at the target) and a high field detector. The plasma composition and the total plasma charge depend strongly on the impact velocity and the electric field strength at the target. Spectra of 9 different projectile-target combinations were analysed. Two types of spectra could be observed, depending on the projectile material. (1) Spectra of metals and hard dielectrics (Mohs' hardness ? 5). Particle constituents of low ionisation energy (e · u ? 7eV, e.g. Na, K, Al) dominate the spectra of these materials at impact velocities below 10 km/sec. At higher speed the relative intensities change and new ions with higher ionisation energies appear. (2) Spectra of soft dielectrics (Mohs' hardness < 3). Below 9 km/sec these materials produced less total charge than did the others. The highest masses were detected at 74 amu. The relative abundance of ions with low ionization energies such as Li, Na, K, etc. is comparatively small. Negative ions were also observed in the impact plasma. Their total number was found to be approximately 3–6% of that of the positive ions at 6 km/sec particle speed.  相似文献   

Turbulent viscosity and Jupiter's tidal Q     

Peter Goldreich  Philip D. Nicholson 《Icarus》1977,30(2):301-304

A recent estimate of tidal dissipation by turbulent viscosity in Jupiter's convective interior predicts that the current value of the planet's tidal Q ～ 5 × 10⁶. We point out a fundamental error in this calculation, and show that turbulent dissipation alone implies that at present Q ～ 5 × 10¹³. Our reduced estimat for the rate of tidal dissipation shows conclusively that tidal torques have produced only negligible modifications of the orbits of the Galilean satellites over the age of the solar system.  相似文献   

Bifurcation points in close binary evolution: Medium-mass binaries     

J. P. De Grève 《Astrophysics and Space Science》1982,84(2):447-456

The remaining core hydrogen burning lifetime after case B of mass transfer of the secondary (mass gaining) component in a medium mass close binary star is estimated, for mediummass binaries with primaries in the mass range 5M to 9M . From the comparison of this quantity with the helium burning time-scale of the remnant primary a critical mass ratioq _c is derived such that for larger values ofq, mass transfer from the secondary towards the primary starts before the latter has evolved into a white dwarf. Consequences for the advanced stages of medium mass binaries are discussed.  相似文献   

X-ray imaging of three flares during the impulsive phase     

André Duijveman  Peter Hoyng  Marcos E. Machado 《Solar physics》1982,81(1):137-157

The impulsive phases of three flares that occurred on April 10, May 21, and November 5, 1980 are discussed. Observations were obtained with the Hard X-ray Imaging Spectrometer (HXIS) and other instruments aboard SMM, and have been supplemented with Hα data and magnetograms. The flares show hard X-ray brightenings (16–30 keV) at widely separated locations that spatially coincide with bright Hα patches. The bulk of the soft X-ray emission (3.5–5.5 keV) originates from in between the hard X-ray brightenings. The latter are located at different sides of the neutral line and start to brighten simultaneously to within the time resolution of HXIS. Concluded is that:

1. The bright hard X-ray patches coincide with the footpoints of loops.
2. The hard X-ray emission from the footpoints is most likely thick target emission from fast electrons moving downward into the dense chromosphere.
3. The density of the loops along which the beam electrons propagate to the footpoints is restricted to a narrow range (10⁹ < n < 2 × 10¹⁰ cm^-3), determined by the instability threshold of the return current and the condition that the mean free path of the fast electrons should be larger than the length of the loop.
4. For the November 5 flare it seems likely that the acceleration source is located at the merging point of two loops near one of the footpoints.

It is found that the total flare energy is always larger than the total energy residing in the beam electrons. However, it is also estimated that at the time of the peak of the impulsive hard X-ray emission a large fraction (at least 20%) of the dissipated flare power has to go into electron acceleration. The explanation of such a high acceleration efficiency remains a major theoretical problem.  相似文献   

Ce and Nd isotope geochemistry on island arc volcanic rocks with negative Ce anomaly: existence of sources with concave REE patterns in the mantle beneath the Solomon and Bonin island arcs   总被引：5，自引：0，他引：5  

Hiroshi Shimizu  Hideyuki Sawatari  Yousuke Kawata  Peter N. Dunkley  Akimasa Masuda 《Contributions to Mineralogy and Petrology》1992,110(2-3):242-252

¹³⁸Ce/¹⁴²Ce isotope ratios in Cenozoic island arc volcanic rocks are reported for the first time, together with isotope ratios of Nd and Sr and abundances of REE, Ba and Sr. The island arc volcanics studies here are boninites from Chichijima, the Bonin Islands, and basalts and andesites from the Solomon Islands. REE patterns of the island arc volcanic rocks from the Solmon Islands and the Bonin Islands are confirmed to have negative Ce anomalies. It is also disclosed that the majority of these island arc volcanic rocks show mainly positive values for both _Ce and _Nd. It is shown that these _Ce and _Ce values can hardly be interpreted by simple mixing between MORB and oceanic or continental crustal rocks; the former have positive _Nd and negative _Ce and the latter have negative _Ce and positive or negative _Nd. Existence of sources having positive _Ce and _Nd values is strongly suggested. If the sources are assumed to have been fractionated from CHUR (chondritic uniform reservoir) at the early or middle Precambrian era, the sources from which the volcanics were derived are concluded to have kept concave REE patterns with larger (La/Ce)_N and smaller (Nd/Sm)_N ratios than chondritic values over a substantial period of time, until the time of Cenozoic magmatism forming island arc volcanic rocks in question. During the periods of the Cenozoic magmatic activities and their related events, Ce anomalies are considered to have been created. From Ce and Nd isotope ratios, however, it is difficult to determine which of the following processes was responsible for the Ce anomaly; the incorporation process of subducted oceanic crust into magma at the mantle or the slab dehydration and metasomatism process. Nevertheless, so far as Ce and Nd isotopic ratios are concerned, incorporation of oceanic sediments did not take place to any clearly detectable degree.  相似文献   

Phase relationships in Buchan facies series pelitic assemblages: calculations with application to andalusite-staurolite parageneses in the Mount Lofty Ranges,South Australia     

Peter Dymoke  Michael Sandiford 《Contributions to Mineralogy and Petrology》1992,110(1):121-132

Low-pressure, medium- to high-temperature (Buchan-type) regional metamorphism of pelitic rocks in the Mount Lofty Ranges, South Australia, is defined by the development of biotite, staurolite-andalusite, fibrolite, prismatic sillimanite and migmatite zones. K-feldspar makes its first appearance in the prismatic sillimanite zone and here we restrict our discussion to lower grade assemblages containing prograde muscovite, concentrating particularly on well-developed andalusitestaurolite parageneses. In general, the spatial distribution and mineral chemical variation of these assemblages accord with the predictions of petrogenetic grids and P-T and T-X _Fe pseudo-sections constructed from the internally consistent data set of Holland and Powell (1990) in the system KFMASH, assuming a(H₂O) 1, although analysed white mica compositions are systematically more aluminous than predicted. Importantly, the stability ranges of most critical assemblages predicted by these grids and pseudo-sections coincide closely with P-T estimates calculated using the data set of Holland and Powell (1990) from the Mount Lofty Ranges assemblages. With the exception of Mn in garnet and Zn in one staurolite-cordierite-muscovite assemblage non-KFMASH components do not significantly appear to have affected the stability ranges of the observed assemblages. An apparent local reversal in isograd zonation in which andalusite first appears down-grade of staurolite suggests a metamorphic field gradient concave towards the temperature axis and, together with evidence for essentially isobaric heating of individual rocks, is consistent with the exposures representing an oblique profile through a terrain in which heat was dissipated from intrusive bodies at discrete structural levels.Mineral abbreviations used in figures als Al₂SiO₅ phase - bi biotite - chl chlorite - ky kyanite - ph phengite - sill sillimanite - and andalusite - cd cordieritc - gt garnet - mu muscovite - q quartz - st staurolite  相似文献   

Nd-, Sr-, O-isotopic and chemical evidence for a two-stage contamination history of mantle magma in the Central-Alpine Bergell intrusion     

Friedhelm von Blanckenburg  Gretchen Früh-Green  Karlheinz Diethelm  Peter Stille 《Contributions to Mineralogy and Petrology》1992,110(1):33-45

Two different contamination processes have been identified as having been operative in the genesis of a plutonic suite: initial contamination of a mantle source, and subsequent crustal contamination of uprising partial melts from the mantle. These processes are indicated by a detailed analyses of Nd, Sr, and oxygen isotopes together with major-and trace-elements of the 32–30 Ma calc-alkaline Bergell intrusion. This intrusion is located at the suture of the Alpine continental collision zone and contains rock types capable of discriminating between mantle and intracrustal processes. A range from basaltic-andesitic dykes in the surrounding country rocks, cumulitic hornblendites, gabbros, tonalite, granodiorite and lamprophyres, to pegmatites and aplites, is exposed in this single intrusion. The results of REE modelling and isotopic compositions of the basic members suggest that the cumulates were fractionated from a picrobasaltic liquid originating by partial melting of enriched subcontinental mantle (_Nd=+4). Increases in ⁸⁷Sr/⁸⁶Sr (0.7055) and ¹⁸O(+6.7) in these samples relative to the mantle array and compositions of other Periadriatic intrusions are most likely the result of an initial contamination of the mantle source by dehydration or partial melting of altered subducted oceanic crust. Slight differentiation of such a picrobasaltic liquid produced the basaltic-andesitic dykes. Simultaneous fractional crystallization and contamination of the uprising magma by continental crust produced crustal isotopic signatures which increase with acidity to values of (_Nd=-7.6), ⁸⁷Sr/⁸⁶Sr=0.716 and ¹⁸O=+10. The crustal imprint and LREE enrichment in the dominating tonalite increase with decreasing crystallization depth which indicates that the tonalites were emplaced in several distinct batches with different degrees of contamination. Shoshonitic lamprophyres, which intruded into the partly solidified granodiorite, were generated in a deep, strongly contaminated mantle source. The posttectonic 26 Ma Novate leucogranite is not cogenetic with the main Bergell body, but rather formed from a predominantly crustal source. If the described features are indeed due to mantle source contamination processes, which are well known for volcanic arcs, it must be concluded that these may also play a significant role in the genesis of calcalkaline plutonic suites.  相似文献   

Synchronous aperture synthesis observations of pulsars     

R. G. Strom  H. W. Van Someren Gréve 《Astrophysics and Space Science》1990,171(1-2):351-355

By modifying the online software of the Westerbork Synthesis Radio Telescope it is possible to sample the radio emission from a field containing a pulsar synchronously with the pulsed signal. Recording the emission from eight separate temporal windows, we can simultaneously observe both the on-pulse and off-pulse signals. We are using this technique for three different kinds of pulsar investigation: (a) to check and improve the positions of some pulsars; (b) to look for unpulsed components; and (c) to search for weak extended emission around pulsars. Observations have been carried out at 6, 21, 49, and 92 cm. Examples of results from all three types of investigation are given.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.  相似文献   

Investigation of the electrostatic charging of dust particles in a Paul-trap     

S. Pintér  J. Švestka  E. Grün 《Astrophysics and Space Science》1990,171(1-2):217-218

Dust particles (glass, tungsten, and nickel) with sizes ranging from 0.25 to 3m were levitated in a Paul-trap and charged by ions or electrons. For ions the particle potential is limited at field strength of about 1×10⁹ V m^–1 by a temperature-dependent discharge mechanism. The particles interaction with 2 to 20 keV electrons always leads to positive surface potentials which can be explained in terms of a decreased absorption of electrons by small particles. Micrometer sized agglomerates were used for the investigation of the electrostatic fragmentation. Fragmentation takes place in a twofold manner: small surface flufl can be removed or the parent particle can be disrupted into smaller agglomerates.Paper presented at the 11th European Regional Astronomical Meetings of the IAU on New Windows to the Universe, held 3–8 July, 1989, Tenerife, Canary Islands, Spain.  相似文献