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961.
HE Jurui WANG Aiguo RUI Xingjian LI Chunhai Nanjing Institute of Geology Mineral Resources Nanjing Jiangsu 《《地质学报》英文版》2004,78(2):375-379
In the Precambrian System of the Yangtze and Cathaysian plates six ore-bearing formations can be identified: the Cu-Pb-Zn-bearing formations in volcanic rocks of marine facies of the Neoarchean-Paleoproterozoic, Cu-Au-bearing formations and Pb-Zn-bearing formations in volcanic rocks of marine facies of the Mesoproterozoic, Pb-Zn-bearing formations in volcaniclastic rock and carbonate rock of the Neoproterozoic, Fe-Mn-bearing formations in the volcaniclastic rock of the Neoproterozoic, and Ni-Cr-serpentine-bearing formations in ophiolite and ultrabasic rock of the Meso- and Neoproterozoic. They were mostly formed in the marginal rift valleys of the Yangtze and Cathaysian plates, where occur stratabound and stratiform ore deposits, thermal deposits and porphyry polymetallic deposits. The six regions with ore-bearing formations have good prospects for ore deposits. 相似文献
962.
M. Güdel 《Astronomische Nachrichten》2008,329(2):218-221
The XMM‐Newton Extended Survey of the Taurus Molecular Cloud (XEST) is a survey of the nearest large star‐forming region, the Taurus Molecular Cloud (TMC), making use of all instruments on board the XMM‐Newton X‐ray observatory. The survey, presently still growing, has provided unprecedented spectroscopic results from nearly every observed T Tauri star, and from ≈50% of the studied brown dwarfs and protostars. The survey includes the first coherent statistical sample of high‐resolution spectra of T Tauri stars, and is accompanied by an U ‐band/ultraviolet imaging photometric survey of the TMC. XEST led to the discovery of new, systematic X‐ray features not possible before with smaller samples, in particular the X‐ray soft excess in classical T Tauri stars and the Two‐Absorber X‐ray (TAX) spectra of jet‐driving T Tauri stars. This paper summarizes highlights from XEST and reviews the key role of this large project. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
963.
Nagayoshi Ohashi 《Astrophysics and Space Science》2008,313(1-3):101-107
Protoplanetary disks are the most probable sites where planet formation takes place. According to theory, planet formation
in protoplanetary disks should show remarkable signatures, such as a gap/hole or a spiral structure. In fact, recent high-angular
and high-sensitivity observations in millimeter and submillimeter wavelengths, as well as optical/near-IR wavelengths, have
shown such structures in protoplanetary disks. Two particular examples of such disks around AB Aurigae and HD 142527 are discussed
here, with an emphasis on results obtained using the Submillimeter Array. These disks—and their probable planet formation—will
be very important future targets for ALMA to study the physical process of planet formation in detail. 相似文献
964.
R. Cesaroni 《Astrophysics and Space Science》2008,313(1-3):23-28
The advent of ALMA is bound to improve our knowledge of OB star formation dramatically. Here, we present an overview of this
topic outlining how high angular resolution and sensitivity may contribute to shed light on the structure of high-mass star
forming regions and hence on the process itself of massive star formation. The impact of this new generation instrument will
range from establishing the mass function of pre-stellar cores inside IR-dark clouds, to investigating the kinematics of the
gas from which OB stars are built up, to assessing or ruling out the existence of circumstellar accretion disks in these objects. 相似文献
965.
Valentín Bujarrabal 《Astrophysics and Space Science》2008,313(1-3):209-214
Planetary nebulae (PNe) are formed in a very fast process. In just about 1000 years, the nebula evolves from a spherical and
slowly expanding AGB envelope to a PN, with usually axial symmetry and high axial velocities. Molecular lines are known to
probe most of the nebular material in young PNe and protoplanetary nebulae (PPNe), and are therefore very useful to study
such an impressive evolution. Many quantitative results on these objects have been so obtained, including general structure,
total mass and density distribution, kinetic temperatures, velocity fields, etc. Existing observations probe both the gas
accelerated by post-AGB shocks and the quiescent components. But the study of crucial regions to understand PN formation (recently
shocked shells, regions heated by the stellar UV and inner rotating disks) requires observations at higher frequency and with
better spatial resolution.
相似文献
966.
The thermal regime of the baryons behind shock waves arising in the process of virialization of dark matter halos is governed at certain conditions by radiation of HD lines. A small fraction of the shocked gas can cool down to the temperature of the cosmic microwave background (CMB). We estimate an upper limit for this fraction: at z = 10 it increases sharply from about qT ∼ 10–3 for dark halos of M = 5 × 107 M⊙ to ∼ 0.1 for halos with M = 108 M⊙. Further increase of the halo mass does not lead however to a significant growth of qT – the asymptotic value for M ≫ 108 M⊙ is 0.3. We estimate the star formation rate associated with such shock waves, and show that they can provide a small but not negligible fraction of the star formation. We argue that extremely metal‐poor low‐mass stars in the Milky Way may have been formed from primordial gas behind such shocks. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
967.
Jonathan Horner Olivier Mousis Jonathan I. Lunine 《Planetary and Space Science》2008,56(12):1585-1595
We consider the role of deuterium as a potential marker of location and ambient conditions during the formation of small bodies in our Solar system. We concentrate in particular on the formation of the regular icy satellites of Jupiter and the other giant planets, but include a discussion of the implications for the Trojan asteroids and the irregular satellites. We examine in detail the formation of regular planetary satellites within the paradigm of a circum-Jovian subnebula. Particular attention is paid to the two extreme potential subnebulae—“hot” and “cold”. In particular, we show that, for the case of the “hot” subnebula model, the D:H ratio in water ice measured from the regular satellites would be expected to be near-Solar. In contrast, satellites which formed in a “cold” subnebula would be expected to display a D:H ratio that is distinctly over-Solar. We then compare the results obtained with the enrichment regimes which could be expected for other families of icy small bodies in the outer Solar system—the Trojan asteroids and the irregular satellites. In doing so, we demonstrate how measurements by Laplace, the James Webb Space Telescope, HERSCHEL and ALMA will play an important role in determining the true formation locations and mechanisms of these objects. 相似文献
968.
969.
Sean N. Raymond †‡ Rory Barnes Avi M. Mandell †‡ 《Monthly notices of the Royal Astronomical Society》2008,384(2):663-674
To date, two planetary systems have been discovered with close-in, terrestrial-mass planets . Many more such discoveries are anticipated in the coming years with radial velocity and transit searches. Here we investigate the different mechanisms that could form 'hot Earths' and their observable predictions. Models include: (1) in situ accretion; (2) formation at larger orbital distance followed by inward 'type 1' migration; (3) formation from material being 'shepherded' inward by a migrating gas giant planet; (4) formation from material being shepherded by moving secular resonances during dispersal of the protoplanetary disc; (5) tidal circularization of eccentric terrestrial planets with close-in perihelion distances and (6) photoevaporative mass-loss of a close-in giant planet. Models 1–4 have been validated in previous work. We show that tidal circularization can form hot Earths, but only for relatively massive planets with very close-in perihelion distances (≲0.025 au), and even then the net inward movement in orbital distance is at most only 0.1–0.15 au. For planets of less than , photoevaporation can remove the planet's envelope and leave behind the solid core on a Gyr time-scale, but only for planets inside 0.025–0.05 au. Using two quantities that are observable by current and upcoming missions, we show that these models each produce unique signatures, and can be observationally distinguished. These observables are the planetary system architecture (detectable with radial velocities, transits and transit timing) and the bulk composition of transiting close-in terrestrial planets (measured by transits via the planet's radius). 相似文献
970.