Numerical simulations of high-speed solar wind streams within 1 AU and their signatures at 1 AU     

Z. Smith  M. Dryer 《Solar physics》1991,131(2):363-383

A parametric study of the evolution within, and signatures at, 1 AU of high-speed streams is performed with the use of a MHD, 21/2-D, time-dependent model. This study is an extension of an earlier one by Smith and Dryer (1990) who examined the ecliptic plane consequences of relatively short-duration, energetic solar disturbances. The present study examines both the erupting and corotating parts of long-duration, high-speed streams characteristic of coronal hole flows. By examining the variation of the simulated plasma velocity, density, temperature, and magnetic field at 1 AU, as well as the location of the solar coronal hole sources relative to the observer at 1 AU, we are able to provide some insight into the identification of the solar sources of interplanetary disturbances. We present and discuss two definitions for angle locating the solar source of interplanetary disturbances at 1 AU.We apply our results to the suggestion by Hewish (1988) that low-latitude coronal holes are suitably positioned to be the sources of major geomagnetic storms when the holes are in the eastern half of the solar hemisphere at the time of the commencement of the storm. Our results indicate that, for these cases, the streams emanating from within the hole must be very fast, greater than 1000 km s^–1, or very wide, greater than 60°, at the inner boundary of 18 solar radii in our simulation.  相似文献   

Melting in the martian mantle: Shergottite formation and implications for present‐day mantle convection on Mars     

Walter S. KIEFER 《Meteoritics & planetary science》2003,38(12):1815-1832

Abstract— Radiometric age dating of the shergottite meteorites and cratering studies of lava flows in Tharsis and Elysium both demonstrate that volcanic activity has occurred on Mars in the geologically recent past. This implies that adiabatic decompression melting and upwelling convective flow in the mantle remains important on Mars at present. I present a series of numerical simulations of mantle convection and magma generation on Mars. These models test the effects of the total radioactive heating budget and of the partitioning of radioactivity between crust and mantle on the production of magma. In these models, melting is restricted to the heads of hot mantle plumes that rise from the core‐mantle boundary, consistent with the spatially localized distribution of recent volcanism on Mars. For magma production to occur on present‐day Mars, the minimum average radioactive heating rate in the martian mantle is 1.6 times 10^?12 W/kg, which corresponds to 39% of the Wanke and Dreibus (1994) radioactivity abundance. If the mantle heating rate is lower than this, the mean mantle temperature is low, and the mantle plumes experience large amounts of cooling as they rise from the base of the mantle to the surface and are, thus, unable to melt. Models with mantle radioactive heating rates of 1.8 to 2.1 times 10 ^?12 W/kg can satisfy both the present‐day volcanic resurfacing rate on Mars and the typical melt fraction observed in the shergottites. This corresponds to 43–50% of the Wanke and Dreibus radioactivity remaining in the mantle, which is geochemically reasonable for a 50 km thick crust formed by about 10% partial melting. Plausible changes to either the assumed solidus temperature or to the assumed core‐mantle boundary temperature would require a larger amount of mantle radioactivity to permit present‐day magmatism. These heating rates are slightly higher than inferred for the nakhlite source region and significantly higher than inferred from depleted shergottites such as QUE 94201. The geophysical estimate of mantle radioactivity inferred here is a global average value, while values inferred from the martian meteorites are for particular points in the martian mantle. Evidently, the martian mantle has several isotopically distinct compositions, possibly including a radioactively enriched source that has not yet been sampled by the martian meteorites. The minimum mantle heating rate corresponds to a minimum thermal Rayleigh number of 2 times 10⁶, implying that mantle convection remains moderately vigorous on present‐day Mars. The basic convective pattern on Mars appears to have been stable for most of martian history, which has prevented the mantle flow from destroying the isotopic heterogeneity.  相似文献   

Extreme galactic wind and Wolf–Rayet features in infrared mergers and infrared quasi-stellar objects     

S. Lípari  †  R. Terlevich  ‡  R. J. Díaz  †  Y. Taniguchi  W. Zheng  †  Z. Tsvetanov  G. Carranza  H. Dottori 《Monthly notices of the Royal Astronomical Society》2003,340(1):289-303

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Star-Driven Wind and Jet Models     

C. Sauty  K. Tsinganos  E. Trussoni  Z. Meliani 《Astrophysics and Space Science》2003,287(1-4):25-30

We outline some main results from recent analytical modelling of axisymmetric jets from the coronae of young stars and compare them to disk-wind and X-wind models. We emphazise the roles of the magnetic rotator and the disk in the formation and the evolution of the jet. We conjecture that with time both the efficiency of the magnetic rotator and the role of the disk as a primary source for the wind decline.  相似文献   

High-speed outflows driven by the 30 Doradus starburst     

M. P. Redman  Z. A. Al-Mostafa  J. Meaburn  M. Bryce 《Monthly notices of the Royal Astronomical Society》2003,344(3):741-747

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Infrared Study of T Tauri Stars Based on IRAS and 2MASS Observations     

P. Zhang  Y. Q. Ni  Z. Q. Fu  J. H. He 《Astrophysics and Space Science》2006,306(1-2):77-92

The IRAS and 2MASS associations for 193 T Tauri stars are identified in this paper. From the color–color diagrams and spectral index, it is found that the IR excesses for most samples are due to thermal emission from the circumstellar material, as suggested previously. It is also found that the IR excesses at IRAS region for few T Tauri stars and the near-IR excesses for some T Tauri stars are likely attributed to free-free emission or free-bound emission from the circumstellar ionized gas. Moreover, It is found in deredened J–H versus H–K color–color diagram that there is a slight separation in different spectral groups. The T Tauri stars locus equation in J–H versus H–K color–color diagram for our sample is also presented.  相似文献   

Interpretation of transient electromagnetic soundings over three-dimensional structures for the central-loop configuration   总被引：2，自引：0，他引：2  

Gregory A. Newman  Walter L. Anderson  Gerald W. Hohmann 《Geophysical Journal International》1987,89(3):889-914

Summary. An assessment is made of the bias of fitting constrained layered-earth models to transient electromagnetic data obtained over 3-D structures. In this assessment we use the central-loop configuration and show that accurate estimates of the depth of burial of 3-D structures can be obtained with layered-earth model fitting. However, layered-earth interpretations are not reliable for estimating depth extents and resistivities of 3-D structures. When layered earths are used for interpretation, it is advantageous in some cases to use data based on the magnetic field instead of the voltage. A magnetic-field definition of apparent resistivity, in contrast to a definition based on the voltage, eliminates apparent-resistivity overshoots and undershoots in the data. A resistivity undershoot in the data can produce an extraneous and misleading layer in an interpretation of a 3-D resistive structure. Due to 3-D effects, apparent-resistivity soundings (magnetic field and voltage) may rise so steeply at late times that it may not be possible to fit a sounding to a reasonable layered-earth model. Truncating such a sounding, over a buried conductor, allows for a reasonable layered-earth fit and an accurate estimate of the depth to the conductor. However, the resistivity of the conductor is overestimated.
Measurements of the horizontal field in the central-loop configuration can map 3-D structures, provided the sensor is located accurately at the centre of the transmitting loop. Horizontal-field calculations show that the transients peak on the flanks of a 3-D structure, but are depressed over the structure's centre. Weak transient responses flanked by two large transient responses, which are opposite in sign, locate the structure. The sign reversal is caused by a corresponding reversal in the currents that are channelled through or deflected away from conductive or resistive structures, respectively.  相似文献   

Coincident seismic reflection/refraction studies of the continental lithosphere: a global review   总被引：5，自引：0，他引：5  

Walter D. Mooney  Thomas M. Brocher 《Geophysical Journal International》1987,89(1):1-6

Summary. Vertical-incidence reflection profiling has identified several characteristic features of the continental Iithosphere including a generally transparent upper crust, a reflective lower crust, reflections from the crust-mantle boundary, and a commonly transparent upper mantle. The underlying physical causes of these characteristic features remain poorly understood. This review summarizes additional information brought to bear on the physical properties of these characteristic crustal structures through the use of coincident wide-angle refraction profiling.  相似文献   

The origin of subdwarf B stars – II     

Z. Han  Ph. Podsiadlowski  P. F. L. Maxted  T. R. Marsh 《Monthly notices of the Royal Astronomical Society》2003,341(2):669-691

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A search for the optical and near-infrared counterpart of the accreting millisecond X-ray pulsar XTE J1751−305     

P. G. Jonker  G. Nelemans  Z. Wang  A. K. H. Kong  D. Chakrabarty  M. Garcia  P. J. Groot  M. van der Klis  T. Kerr  B. Mobasher  M. Sullivan  T. Augusteijn  B. W. Stappers  P. Challis  R. P. Kirshner  J. Hjorth  A. Delsanti 《Monthly notices of the Royal Astronomical Society》2003,344(1):201-206

We have obtained optical and near-infrared images of the field of the accreting millisecond X-ray pulsar XTE J1751−305. There are no stars in the 0.7-arcsec error circle (0.7 arcsec is the overall uncertainty arising from tying the optical and X-ray images and from the intrinsic uncertainty in the Chandra X-ray astrometric solution). We derive limiting magnitudes for the counterpart of   R > 23.1, I > 21.6, Z > 20.6, J > 19.6  and   K > 19.2  . We compare these upper limits with the magnitudes one would expect for simple models for the possible donor stars and the accretion disc subject to the reddening observed in X-rays for XTE J1751−305 and when put at the distance of the Galactic Centre (8.5 kpc). We conclude that our non-detection does not constrain any of the models for the accretion disc or possible donor stars. Deep, near-infrared images obtained during quiescence will, however, constrain possible models for the donor stars in this ultracompact system.  相似文献