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1.
Abstract– We studied three large (2–4 mm diameter) igneous‐textured inclusions in the Buzzard Coulee (H4) chondrite using microanalytical techniques (OLM, SEM, EMPA, SIMS) to better elucidate the origins of igneous inclusions in ordinary chondrites. The inclusions are clasts that come in two varieties (1) white inclusions Bz‐1 and Bz‐2 represent a nearly holocrystalline assemblage of low‐Ca and high‐Ca pyroxene (63–66 area%) and cristobalite (33–36%) and (2) tan inclusion Bz‐3 is glass‐rich (approximately 60%) with low‐Ca and high‐Ca pyroxene phenocrysts. The bulk compositions of the inclusions determined by modal reconstruction are all SiO2‐rich (approximately 67 wt% for Bz‐1 and Bz‐2, approximately 62% for Bz‐3), but Bz‐3 is enriched in incompatible elements (e.g., REE approximately 4–5 × CI abundances), whereas Bz‐2 and Bz‐1 are depleted in those elements that are most incompatible in pyroxene (e.g., La‐Ho approximately 0.15–0.4 × CI abundances). These bulk compositions do not resemble what one would expect for partial or complete shock melting of a chondritic precursor, and show no evidence for overall volatility control. We infer that the inclusions originated through igneous differentiation and FeO reduction, with Bz‐3 forming as an “andesitic” partial melt (approximately 30–40% partial melting of an H chondrite precursor), and Bz‐1 and Bz‐2 forming as pyroxene‐cristobalite cumulates from an Si‐rich melt. We suggest that both types of melts experienced a period of transit through a cold, low‐pressure space environment in which cooling, FeO reduction, and interaction with a vapor occurred. Melts may have been lofted into space by excavation or splashing during collisions, or by pyroclastic volcanism. Our results indicate intriguing similarities between the inclusions in Buzzard Coulee and the silicates in some iron (IIE‐type) and stony iron (IVA‐type) meteorites, suggesting a genetic relationship.  相似文献   

2.
Turbulent plane‐shear flow is found to show same basic effects of mean‐fieldMHD as rotating turbulence. In particular, the mean electromotive force (EMF) includes highly anisotropic turbulent diffusion and alpha‐effect. Only magnetic diffusion remains for spatially‐uniform turbulence. The question is addressed whether in this case a self‐excitation of a magnetic field by so‐called sher‐current dynamo is possible and the quasilinear theory provides a negative answer. The streamaligned component of the EMF has the sign opposite to that required for dynamo. If, however, the turbulence is not uniform across the flow direction then a dynamo‐active α ‐effect emerges. The critical magnetic Reynolds number for the alpha‐shear dynamo is estimated to be slightly above ten. Possibilities for cross‐checking theoretical predictions with MHD experiments are discussed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

3.
A plane‐shear flow in a fluid with forced turbulence is considered. If the fluid is electrically‐conducting then a mean electromotive force (EMF) results even without basic rotation and the magnetic diffusivity becomes a highly anisotropic tensor. It is checked whether in this case self‐excitation of a large‐scale magnetic field is possible (so‐called W̄ × J̄ ‐dynamo) and the answer is NO. The calculations reveal the cross‐stream components of the EMF perpendicular to the mean current having the wrong signs, at least for small magnetic Prandtl numbers. After our results numerical simulations with magnetic Prandtl number of about unity have only a restricted meaning as the Prandtl number dependence of the diffusivity tensor is rather strong. If, on the other hand, the turbulence field is strati.ed in the vertical direction then a dynamo‐active α ‐effect is produced. The critical magnetic Reynolds number for such a self‐excitation in a simple shear flow is slightly above 10 like for the other – but much more complicated – flow patterns used in existing dynamo experiments with liquid sodium or gallium. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

4.
Nova V5116 Sgr 2005 No. 2, discovered on 2005 July 4, was observed with XMM‐Newton in March 2007, 20 months after the optical outburst. The X‐ray spectrum showed that the nova had evolved to a pure supersoft X‐ray source, indicative of residual H‐burning on top of the white dwarf. The X‐ray light‐curve shows abrupt decreases and increases of the flux by a factor 8 with a periodicity of 2.97 h, consistent with the possible orbital period of the system. The EPIC spectra are well fit with an ONe white dwarf atmosphere model, with the same temperature both in the low and the high flux periods. This rules out an intrinsic variation of the X‐ray source as the origin of the flux changes, and points to a possible partial eclipse as the origin of the variable light curve. The RGS high resolution spectra support this scenario showing a number of emission features in the low flux state, which either disappear or change into absorption features in the high flux state. A new XMM‐Newton observation in March 2009 shows the SSS had turned off and V51 16 Sgr had evolved into a weaker and harder X‐ray source (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

5.
The semi‐regular variable star RU Vulpeculae (RU Vul) is being observed visually since 1935. Its pulsation period and amplitude are declining since ∼1954. A leading hypothesis to explain the period decrease in asymptotic giant branch (AGB) stars such as RU Vul is an ongoing flash of the He‐burning shell, also called a thermal pulse (TP), inside the star. In this paper, we present a CCD photometric light curve of RU Vul, derive its fundamental parameters, and test if the TP hypothesis can describe the observed period decline. We use CCD photometry to determine the present‐day pulsation period and amplitude in three photometric bands, and high‐resolution optical spectroscopy to derive the fundamental parameters. The period evolution of RU Vul is compared to predictions by evolutionary models of the AGB phase. We find that RU Vul is a metal‐poor star with a metallicity [M/H] = –1.59 ± 0.05 and an effective surface temperature of Teff = 3634 ± 20 K. The low metallicity of RU Vul and its kinematics indicate that it is an old, low‐mass member of the thick disc or the halo population. The present day pulsation period determined from our photometry is ∼108 d, the semiamplitude in the V ‐band is 0.39 ± 0.03 mag. The observed period decline is found to be well matched by an evolutionary AGB model with stellar parameters comparable to those of RU Vul. We conclude that the TP hypothesis is in good agreement with the observed period evolution of RU Vul. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

6.
Almost 900 reports were presented at the planetary congress EPSC 2010 in Rome. The congress took place in the building of the Pontifical University of Saint Thomas Aquinas. The report by A. Morbidelli et al. “The Origin of the Small Mass of Mars” was among the reports that drew the greatest attention of the participants.  相似文献   

7.
Zircon in five samples of variably comminuted, melted, and hydrothermally altered orthogneiss from the Maniitsoq structure of southern West Greenland yield a weighted mean 207Pb/206Pb age of 3000.9 ± 1.9 Ma (ion probe data, n = 37). The age data constitute a rare example of pervasive and nearly complete isotopic resetting of zircon during a regional hydrothermal event. Many zircon grains are homogeneous or display weak flame‐like patterns in backscattered electron images. Other grains show complex internal textures, where homogeneous, high‐U fronts commonly cut across relict igneous‐type oscillatory zonation. Inclusions of quartz, plagioclase, mica, and other Al ± Na ± Ca ± Fe‐bearing silicates are very common. In two samples, selective replacement of zircon with baddeleyite occurs along concentric zones with relict igneous zonation, and as specks a few microns large within recrystallized, high‐U areas. We interpret the 3000.9 ± 1.9 Ma date as the minimum age of the recently proposed impact structure at Maniitsoq. The great geographical extent and intensity of the hydrothermal event suggest massive invasion of water into the currently exposed crust, implying that the age of the hydrothermal alteration would closely approximate the age of the proposed impact at Maniitsoq. At the western margin of the Taserssuaq tonalite complex, which postdates the Maniitsoq event, a 207Pb/206Pb mean age of 2994.6 ± 3.4 Ma obtained from zircon has mostly retained igneous‐type oscillatory zonation. A subsequent thermal event at approximately 2975 Ma is recorded in several samples by zircon with baddeleyite replacement textures.  相似文献   

8.
With the increasingly precise measurement of the cosmic microwave background (CMB), cosmology has entered an era where a model's predictions become testable to percent‐level accuracy. In particular, the CMB spectrum has so far provided impressive support for the scenario of inflation, first invented to solve outstanding problems of standard cosmology. While current data (COBE, WMAP etc.) have already constrained cosmological parameters like Ω0 to high precision, next generation instruments such as the PLANCK satellite should give access to specific characteristics of the inflationary mechanism itself. Another tantalizing idea has been discussed in this context: Given the enormous expansion of the Universe during the phase of inflation, could it be that even Planck scale physics has been stretched to observable distances and is therefore within grasp in the CMB observations? In this contribution, I discuss the possibility of carrying through the calculation of the perturbation spectrum from an ansatz for short distance physics right to its imprint in the CMB. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

9.
Abstract— Queen Alexandra Range (QUE) 93148 is a small (1.1 g) olivine‐rich achondrite (mg 86) that contains variable amounts of orthopyroxene (mg 87) and kamacite (6.7 wt% Ni), with minor augite. Olivine in QUE 93148 contains an unusual suite of inclusions: (1) 5 × 100 μm sized lamellae with a CaO‐ and Cr2O3‐rich (～10 and 22 wt%, respectively) composition that may represent a submicrometer‐scale intergrowth of chromite and pyroxene(s); (2) 75 × 500 μm sized lamellar symplectites composed of chromite and two pyroxenes, with minor metal; (3) 15–20 μm sized, irregularly‐shaped symplectites composed of chromite and pyroxene(s); (4) 100–150 μm sized, elliptical inclusions composed of chromite, two pyroxenes, metal, troilite, and rare whitlockite. Type 1, 2, and 3 inclusions probably formed by exsolution from the host olivine during slow cooling, whereas type 4 more likely resulted from early entrapment of silicate and metallic melts followed by closed‐system oxidation. Queen Alexandra Range 93148 can be distinguished from most other olivine‐rich achondrites (ureilites, winonaites, lodranites, acapulcoites, brachinites, Eagle‐Station‐type pallasites, and pyroxene pallasites), as well as from mesosiderites, by some or all of the following properties: O‐isotopic composition, Fe‐Mn‐Mg relations of olivine, CaO and Cr2O3 contents of olivine, orthopyroxene compositions, molar Cr/(Cr + Al) ratios of chromite, metal composition, texture, and the presence of the inclusions. In terms of many of these properties, it shows an affinity to main‐group pallasites. Nevertheless, it cannot be identified as belonging to this group. Meteorite QUE 93148 appears to be a unique achondrite. Possibly it should be considered to be a pyroxene pallasite that is genetically related to main‐group pallasites. Alternatively, it may be derived from the mantle of the pallasite (howardite‐eucrite‐diogenite?) parent body.  相似文献   

10.
Abstract— We report data for 14 mainly labile trace elements (Ag, Au, Bi, Cd, Cs, Ga, In, Rb, Sb, Se, Te, Tl, U, and Zn) in eight whole‐rock lunar meteorites (Asuka [A‐] 881757, Dar al Gani [DaG] 262, Elephant Moraine [EET] 87521, Queen Alexandra Range [QUE] 93069, QUE 94269, QUE 94281, Yamato [Y‐] 793169, and Y‐981031), and Martian meteorite (DaG 476) and incorporate these into a comparative study of basaltic meteorites from the Moon, Mars, and V‐type asteroids. Multivariate cluster analysis of data for these elements in 14 lunar, 13 Martian, and 34 howardite, eucrite, and diogenite (HED) meteorites demonstrate that materials from these three parents are distinguishable using these markers of late, low‐temperature episodes. This distinguishability is essentially as complete as that based on markers of high‐temperature igneous processes. Concentrations of these elements in 14 lunar meteorites are essentially lognormally distributed and generally more homogeneous than in Martian and HED meteorites. Mean siderophile and labile element concentrations in the 14 lunar meteorites indicate the presence of a CI‐equivalent micrometeorite admixture of 2.6% When only feldspathic samples are considered, our data show a slightly higher value of 3.4% consistent with an increasing micrometeorite content in regolith samples of higher maturity. Concentrations of labile elements in the 8 feldspathic samples hint at the presence of a fractionated highly labile element component, possibly volcanic in origin, at a level comparable to the micrometeorite component. Apparently, the process(es) that contributed to establishing lunar meteorite siderophile and labile trace element contents occurred in a system open to highly labile element transport.  相似文献   

11.
Abstract— Alteration of surficial suevites at Ries crater, Germany was studied by means of X‐ray diffraction and scanning electron microscopy. Here, we discuss the origin of hydrous silicate (clay) phases in these suevites that have been previously interpreted as resulting from post‐impact hydrothermal processes. The results of this study indicate that the dominant alteration phases are dioctahedral Al‐Fe montmorillonite and halloysite, which are typical low temperature clay minerals. We suggest that the surficial suevites are not altered by hydrothermal processes and that alteration occurred by low temperature subsurface weathering processes. If the surficial suevites were indeed hydrothermally modified during the early stages of post‐impact cooling, then the alteration was of limited character and is completely masked by later weathering.  相似文献   

12.
Numerical models dealing with the planetary scale differentiation of Mercury are presented with the short‐lived nuclide, 26Al, as the major heat source along with the impact‐induced heating during the accretion of planets. These two heat sources are considered to have caused differentiation of Mars, a planet with size comparable to Mercury. The chronological records and the thermal modeling of Mars indicate an early differentiation during the initial ~1 million years (Ma) of the formation of the solar system. We theorize that in case Mercury also accreted over an identical time scale, the two heat sources could have differentiated the planets. Although unlike Mars there is no chronological record of Mercury's differentiation, the proposed mechanism is worth investigation. We demonstrate distinct viable scenarios for a wide range of planetary compositions that could have produced the internal structure of Mercury as deduced by the MESSENGER mission, with a metallic iron (Fe‐Ni‐FeS) core of radius ~2000 km and a silicate mantle thickness of ~400 km. The initial compositions were derived from the enstatite and CB (Bencubbin) chondrites that were formed in the reducing environments of the early solar system. We have also considered distinct planetary accretion scenarios to understand their influence on thermal processing. The majority of our models would require impact‐induced mantle stripping of Mercury by hit and run mechanism with a protoplanet subsequent to its differentiation in order to produce the right size of mantle. However, this can be avoided if we increase the Fe‐Ni‐FeS contents to ~71% by weight. Finally, the models presented here can be used to understand the differentiation of Mercury‐like exoplanets and the planetary embryos of Venus and Earth.  相似文献   

13.
1E 1207.4–5209 is an X‐ray source located at the centre of the supernova remnant (SNR) PKS 1209–52 (G296.5+10.0) and is thought to be an isolated neutron star (INS) associated with the SNR. Its optical spectrum shows several absorption lines and the X‐ray spectrum exhibits three variable absorption features at what appears to be harmonically related wavelengths, the latter being interpreted as due to cyclotron resonance. However, there are several serious problems, uncertainties and difficulties in the above association (SNR/INS) and in the interpretation of the spectra. In view of these, we suggest an alternative explanation of the observed spectra in terms of blueshifts. This implies that the optical and X‐ray absorption spectra are due to the central object of the SNR in association with two separate absorption clouds ejected at successively increasing speeds. The clouds have their origins in jets resulting from the merger of two very massive compact stars. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

14.
In this study, we present CCD UBV photometry of poorly studied open star clusters, Dolidze 36, NGC 6728, NGC 6800, NGC 7209, and Platais 1, located in the first and second Galactic quadrants. Observations were obtained with T100, the 1-m telescope of the TÜB?TAK National Observatory. Using photometric data, we determined several astrophysical parameters such as reddening, distance, metallicity and ages and from them, initial mass functions, integrated magnitudes and colours. We took into account the proper motions of the observed stars to calculate the membership probabilities. The colour excesses and metallicities were determined independently using two-colour diagrams. After obtaining the colour excesses of the clusters Dolidze 36, NGC 6728, NGC 6800, NGC 7209, and Platais 1 as \(0.19\pm0.06\), \(0.15\pm0.05\), \(0.32\pm0.05\), \(0.12\pm 0.04\), and \(0.43\pm0.06\) mag, respectively, the metallicities are found to be \(0.00\pm0.09\), \(0.02\pm0.11\), \(0.03\pm0.07\), \(0.01\pm0.08\), and \(0.01\pm0.08\) dex, respectively. Furthermore, using these parameters, distance moduli and age of the clusters were also calculated from colour-magnitude diagrams simultaneously using PARSEC theoretical models. The distances to the clusters Dolidze 36, NGC 6728, NGC 6800, NGC 7209, and Platais 1 are \(1050\pm90\), \(1610\pm190\), \(1210\pm150\), \(1060\pm90\), and \(1710\pm250\) pc, respectively, while corresponding ages are \(400\pm100\), \(750\pm150\), \(400\pm100\), \(600\pm100\), and \(175\pm50\) Myr, respectively. Our results are compatible with those found in previous studies. The mass function of each cluster is derived. The slopes of the mass functions of the open clusters range from 1.31 to 1.58, which are in agreement with Salpeter’s initial mass function. We also found integrated absolute magnitudes varying from ?4.08 to ?3.40 for the clusters.  相似文献   

15.
A correlation analysis is made of the spatial distribution of galaxies in the Coma, Bridge, and A1367 clusters, which form the Coma supercluster. The scale of the clustering of galaxies and the variation in their density distribution with the main parameters of the galaxies– luminosity, morphological type, and observed H I deficiency in the 21 cm line– are evaluated. The mass-to-luminosity ratios are computed for the spiral galaxies in the Coma, Bridge, and A1367 clusters. It is suggested that a larger fraction of hypothetical dark matter may be concentrated in the spiral galaxies which predominantly populate the subclusters previously identified by us within these clusters than in the spiral galaxies observed in the peripheral regions of the clusters.  相似文献   

16.
We give the results of parameter fitting of the magnetic clouds (MCs) observed by the Wind spacecraft for the three-year period 2013 to the end of 2015 (called the “Present” period) using the MC model of Lepping, Jones, and Burlaga (J. Geophys. Res.95, 11957, 1990). The Present period is almost coincident with the solar maximum of the sunspot number, which has a broad peak starting in about 2012 and extending to almost 2015. There were 49 MCs identified in the Present period. The modeling gives MC quantities such as size, axial attitude, field handedness, axial magnetic-field strength, center time, and closest-approach vector. Derived quantities are also estimated, such as axial magnetic flux, axial current density, and total axial current. Quality estimates are assigned representing excellent, fair/good, and poor. We provide error estimates on the specific fit parameters for the individual MCs, where the poor cases are excluded. Model-fitting results that are based on the Present period are compared to the results of the full Wind mission from 1995 to the end of 2015 (Long-term period), and compared to the results of two other recent studies that encompassed the periods 2007?–?2009 and 2010?–?2012, inclusive. We see that during the Present period, the MCs are, on average, slightly slower, slightly weaker in axial magnetic field (by 8.7%), and larger in diameter (by 6.5%) than those in the Long-term period. However, in most respects, the MCs in the Present period are significantly closer in characteristics to those of the Long-term period than to those of the two recent three-year periods. However, the rate of occurrence of MCs for the Long-term period is \(10.3~\mbox{year}^{-1}\), whereas this rate for the Present period is \(16.3~\mbox{year}^{-1}\), similar to that of the period 2010?–?2012. Hence, the MC occurrence rate has increased appreciably in the last six years. MC Type (N–S, S–N, All N, All S, etc.) is assigned to each MC; there is an inordinately large percentage of All S, by about a factor of two compared to that of the Long-term period, indicating many strongly tipped MCs. In 2005, there was a distinct change in variability and average value (viewed at \(1/2\) year averages) of the duration, MC speed, axial magnetic field strength, axial magnetic flux, and total current to lower values. In the Present period, upstream shocks occur for 43% of the 49 cases; for comparison, the Long-term rate is 56%.  相似文献   

17.
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18.
A spectral variability study of the two Narrow Line Seyfert 1 galaxies NGC 4051 and IRAS13224–3809 is presented. Both sources show a high degree of flux and spectral variability. The nuclear emission, lightly absorbed by warm material, has been decomposed into a direct power law emission and an ionized disc reflection plus constant emission from distant material. The ionized disc reflection component does not follow the variations of the primary component. Its flux is linearly correlated with the one of the power law component only at low fluxes, while it is almost constant at medium high‐flux. This behavior is expected when the light bending effect is important. If so, most of the primary emission comes from only a few gravitational radii from the black hole. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)  相似文献   

19.
The Gao‐Guenie H5 chondrite that fell on Burkina Faso (March 1960) has portions that were impact‐melted on an H chondrite asteroid at ~300 Ma and, through later impact events in space, sent into an Earth‐crossing orbit. This article presents a petrographic and electron microprobe analysis of a representative sample of the Gao‐Guenie impact melt breccia consisting of a chondritic clast domain, quenched melt in contact with chondritic clasts, and an igneous‐textured impact melt domain. Olivine is predominantly Fo80–82. The clast domain contains low‐Ca pyroxene. Impact melt‐grown pyroxene is commonly zoned from low‐Ca pyroxene in cores to pigeonite and augite in rims. Metal–troilite orbs in the impact melt domain measure up to ~2 mm across. The cores of metal orbs in the impact melt domain contain ~7.9 wt% of Ni and are typically surrounded by taenite and Ni‐rich troilite. The metallography of metal–troilite droplets suggest a stage I cooling rate of order 10 °C s?1 for the superheated impact melt. The subsolidus stage II cooling rate for the impact melt breccia could not be determined directly, but was presumably fast. An analogy between the Ni rim gradients in metal of the Gao‐Guenie impact melt breccia and the impact‐melted H6 chondrite Orvinio suggests similar cooling rates, probably on the order of ~5000–40,000 °C yr?1. A simple model of conductive heat transfer shows that the Gao‐Guenie impact melt breccia may have formed in a melt injection dike ~0.5–5 m in width, generated during a sizeable impact event on the H chondrite parent asteroid.  相似文献   

20.
In this work, we explore many cosmological implications of a four-dimensional cosmology dominated by quintessence with a static traversable wormhole, spatio-temporal varying G and by taking into account a decaying cosmological constant and a decaying graviton mass by means of an additional bimetric tensor in Einstein’s field equations proposed by Visser in 1998.  相似文献   

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