X-shaped radio galaxies as observational evidence for the interaction of supermassive binary black holes and accretion disc at parsec scale     

F. K. Liu 《Monthly notices of the Royal Astronomical Society》2004,347(4):1357-1369

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Current plate motions   总被引：57，自引：0，他引：57  

C. DeMets  R. G. Gordon  D. F. Argus  S. Stein 《Geophysical Journal International》1990,101(2):425-478

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Circumstellar Silicate Mineralogy     

A.G.G.M. Tielens  L.B.F.M. Waters  F.J. Molster  K. Justtanont 《Astrophysics and Space Science》1997,255(1-2):415-426

This paper reviews spectra obtained with the SWS on board of ISO of dust shells around O-rich objects. These spectra reveal the presence of many new emission features between 10 and 45 μm. These bands are generally much narrower than the well-known 10 and 20 μm silicates features. The strength of these features relative to the underlying broad continuum varies from source to source (≅ 5-50%). The 10 μm region shows evidence for the presence of Al2O3 grains. At longer wavelength, the spectra are dominated by features due to crystalline olivine and pyroxene. The exact peak position of these features shows that the emitting grains consist of the Mg-rich end-members of these minerals with an Fe-content of < 10%. The underlying continuum is attributed to amorphous silicate grains. These observations of aluminum-rich and magnesium-rich compounds compare well with the thermodynamic condensation sequence of minerals expected for O-rich outflows. The observations also imply that freeze out (ie., kinetics) of this condensation sequence at different temperatures is an important characteristic of dust formation in these objects. It is suggested that the absence of Fe-rich silicates is a natural consequence of the low temperature at which gaseous Fe reacts with Mg-rich silicates in these outflows, resulting in amorphous grains with little characterizing spectral detail. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

ISO-SWS Spectra of Carbon Stars: Molecular Features and a Comparison with Models     

J. Hron  R. Loidl  F. Kerschbaum  U.G. Jørgensen 《Astrophysics and Space Science》1997,255(1-2):359-360

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Exposure history of the Torino meteorite     

R. Wieler  Th. Graf  P. Signer  S. Vogt  G. F. Herzog  C. Tuniz  D. Fink  L. K. Fifield  J. Klein  R. Middleton  A. J. T. Jull  P. Pellas  J. Masarik  G. Dreibus 《Meteoritics & planetary science》1996,31(2):265-272

Abstract— We determined He, Ne, Ar, ¹⁰Be, ²⁶Al, ³⁶Cl, and ¹⁴C concentrations, as well as cosmic-ray track densities and halogen concentrations in different specimens of the H6 chondrite Torino, in order to constrain its exposure history to cosmic radiation. The Torino meteoroid had a radius of ～20 cm and travelled in interplanetary space for 2.5–10 Ma. Earlier, Torino was part of a larger body. The smallest possible precursor had a radius of 55 cm and a journey through space longer than ～65 Ma. If the first-stage exposure took place in a body with a radius of >3 m or in the parent asteroid, then it lasted nearly 300 Ma. The example of Torino shows that it is easy to underestimate first-stage exposure ages when constructing two-stage histories.  相似文献   

Low-cost volcano surveillance from space: case studies from Etna, Krafla, Cerro Negro, Fogo, Lascar and Erebus     

Andrew J. L. Harris  Anna L. Butterworth  Richard W. Carlton  Ian Downey  Peter Miller  Pedro Navarro  David A. Rothery 《Bulletin of Volcanology》1997,59(1):49-64

 Satellite data offer a means of supplementing ground-based monitoring during volcanic eruptions, especially at times or locations where ground-based monitoring is difficult. Being directly and freely available several times a day, data from the advanced very high resolution radiometer (AVHRR) offers great potential for near real-time monitoring of all volcanoes across large (3000×3000 km) areas. Herein we describe techniques to detect and locate activity; estimate lava area, thermal flux, effusion rates and cumulative volume; and distinguish types of activity. Application is demonstrated using data for active lavas at Krafla, Etna, Fogo, Cerro Negro and Erebus; a pyroclastic flow at Lascar; and open vent systems at Etna and Stromboli. Automated near real-time analysis of AVHRR data could be achieved at existing, or cheap to install, receiving stations, offering a supplement to conventional monitoring methods. Received: 21 January 1997 / Accepted: 3 April 1997  相似文献   

Simulations of deep pencil-beam redshift surveys     

N. Yoshida  J. Colberg  S.D.M. White  A.E. Evrard  T.J. MacFarland †  H.M.P. Couchman  A. Jenkins  C.S. Frenk  F.R. Pearce  G. Efstathiou  J.A. Peacock  P.A. Thomas 《Monthly notices of the Royal Astronomical Society》2001,325(2):803-816

We create mock pencil-beam redshift surveys from very large cosmological N -body simulations of two cold dark matter (CDM) cosmogonies, an Einstein–de Sitter model ( τ CDM) and a flat model with Ω₀=0.3 and a cosmological constant (ΛCDM). We use these to assess the significance of the apparent periodicity discovered by Broadhurst et al. Simulation particles are tagged as 'galaxies' so as to reproduce observed present-day correlations. They are then identified along the past light-cones of hypothetical observers to create mock catalogues with the geometry and the distance distribution of the Broadhurst et al. data. We produce 1936 (2625) quasi-independent catalogues from our τ CDM (ΛCDM) simulation. A couple of large clumps in a catalogue can produce a high peak at low wavenumbers in the corresponding one-dimensional power spectrum, without any apparent large-scale periodicity in the original redshift histogram. Although the simulated redshift histograms frequently display regularly spaced clumps, the spacing of these clumps varies between catalogues and there is no 'preferred' period over our many realizations. We find only a 0.72 (0.49) per cent chance that the highest peak in the power spectrum of a τ CDM (ΛCDM) catalogue has a peak-to-noise ratio higher than that in the Broadhurst et al. data. None of the simulated catalogues with such high peaks shows coherently spaced clumps with a significance as high as that of the real data. We conclude that in CDM universes, the regularity on a scale of ∼130  h ⁻¹ Mpc observed by Broadhurst et al. has a priori probability well below 10⁻³.  相似文献   

Large-scale structure in the ELAIS S1 Survey     

E. A. Gonzalez-Solares  S. Oliver  C. Gruppioni  F. Pozzi  C. Lari  M. Rowan-Robinson  S. Serjeant  F. La Franca  M. Vaccari 《Monthly notices of the Royal Astronomical Society》2004,352(1):44-48

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Geochemistry and shock petrography of the Crow Creek Member,South Dakota,USA: Ejecta from the 74‐Ma Manson impact structure     

Crispin KATONGO  Christian KOEBERL  Brian J. WITZKE  Richard H. HAMMOND  Raymond R. ANDERSON 《Meteoritics & planetary science》2004,39(1):31-51

Abstract— The Crow Creek Member is one of several marl units recognized within the Upper Cretaceous Pierre Shale Formation of eastern South Dakota and northeastern Nebraska, but it is the only unit that contains shock‐metamorphosed minerals. The shocked minerals represent impact ejecta from the 74‐Ma Manson impact structure (MIS). This study was aimed at determining the bulk chemical compositions and analysis of planar deformation features (PDFs) of shocked quartz; for the basal and marly units of the Crow Creek Member. We studied samples from the Gregory 84‐21 core, Iroquois core and Wakonda lime quarry. Contents of siderophile elements are generally high, but due to uncertainties in the determination of Ir and uncertainties in compositional sources for Cr, Co, and Ni, we could not confirm an extraterrestrial component in the Crow Creek Member. We recovered several shocked quartz grains from basal‐unit samples, mainly from the Gregory 84‐21 core, and results of PDF measurements indicate shock pressures of at least 15 GPa. All the samples are composed chiefly of SiO₂ (29–58 wt%), Al₂O₃ (6–14 wt%), and CaO (7–30 wt%). When compared to the composition of North American Shale Composite, the samples are significantly enriched in CaO, P₂O₅, Mn, Sr, Y, U, Cr, and Ni. The contents of rare earth elements (REE), high field strength elements (HFSE), Cr, Co, Sc, and their ratios and chemical weathering trends, reflect both felsic and basic sources for the Crow Creek Member, an inference, which is consistent with the lithological compositions in the environs of the MIS. The high chemical indices of alteration and weathering (CIA' and CIW': 75–99), coupled with the Al₂O₃‐(CaO*+Na₂O)‐K₂O (A‐CN'‐K) ratios, indicate that the Crow Creek Member and source rocks had undergone high degrees of chemical weathering. The expected ejecta thicknesses at the sampled locations (409 to 219 km from Manson) were calculated to range from about 1.9 to 12.2 cm (for the present‐day crater radius of Manson), or 0.4 to 2.4 cm (for the estimated transient cavity radius). The trend agrees with the observed thicknesses of the basal unit of the Crow Creek Member, but the actually observed thicknesses are larger than the calculated ones, indicating that not all of the basal unit comprises impact ejecta.  相似文献   

Dynamical and compositional assessment of near‐Earth object mission targets     

Richard P. BINZEL  Ettore PEROZZI  Andrew S. RIVKIN  Alessandro ROSSI  Alan W. HARRIS  Schelte J. BUS  Giovanni B. VALSECCHI  Stephen M. SLIVAN 《Meteoritics & planetary science》2004,39(3):351-366

Abstract— Using an H‐plot analysis, we identify 234 currently known near‐Earth objects that are accessible for rendezvous with a “best case” delta‐V of less than 7 km/s. We provide a preliminary compositional interpretation and assessment of these potential targets by summarizing the taxonomic properties for 44 objects. Results for one‐half (22) of this sample are based on new spectroscopic measurements presented here. Our approach provides an easy‐to‐update method for giving guidelines to both observers and mission analysts for focusing on objects for which actual mission opportunities are most likely to be found. Observing prospects are presented for categorizing the taxonomic properties of the most accessible targets that are not yet measured.  相似文献