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1.
T.D. Thoroughgood V.S. Dhillon S.P. Littlefair T.R. Marsh D.A. Smith 《Monthly notices of the Royal Astronomical Society》2001,327(4):1323-1333
We present spectroscopy of the eclipsing recurrent nova U Sco. The radial velocity semi-amplitude of the primary star was found to be from the motion of the wings of the He ii λ 4686-Å emission line. By detecting weak absorption features from the secondary star, we find its radial velocity semi-amplitude to be . From these parameters, we obtain a mass of for the white dwarf primary star and a mass of for the secondary star. The radius of the secondary is calculated to be , confirming that it is evolved. The inclination of the system is calculated to be , consistent with the deep eclipse seen in the light-curves. The helium emission lines are double-peaked, with the blueshifted regions of the disc being eclipsed prior to the redshifted regions, clearly indicating the presence of an accretion disc. The high mass of the white dwarf is consistent with the thermonuclear runaway model of recurrent nova outbursts, and confirms that U Sco is the best Type Ia supernova progenitor currently known. We predict that U Sco is likely to explode within ∼700 000 yr. 相似文献
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Palaeoproterozoic A-type felsic magmatism in the Khetri Copper Belt, Rajasthan, northwestern India: petrologic and tectonic implications 总被引:1,自引:0,他引:1
Summary A number of small Palaeoproterozoic granitoid plutons were emplaced in the Khetri Copper Belt, which is an important Proterozoic
metallogenic terrane in the northeastern part of Aravalli mountain range. Contiguous Biharipur and Dabla plutons are located
about 15 km southeast of Khetri, close to a 170 km long intracontinental rift zone. The plutons are composed of amphibole-bearing
alkali-feldspar granites, comprising microcline-albite granite, albite granite and late-stage microgranite. The albite granite
in Biharipur is confined to the margins of the pluton, and shows extensive commingling with the synchronous mafic plutonics.
Geochemically, the albite granites are characterised by low K2O (∼0.5 wt.%) and elevated Na2O (∼7.0 wt.%) abundances. By contrast, the microcline-albite granite does not show any significant mafic-granite interactions
and shows normal concentrations of alkali elements. The granitoids display high concentrations of the rare earth (except Eu)
and high field strength elements, high values of Ga/Al (>2.5), agpaitic index and Fe*-number. These features together with their alkaline metaluminous and ferroan nature classify the rocks as typical A-type
within-plate granites. All the granitoid facies display similar REE and incompatible element profiles indicating their cogenetic
nature. These granitoids were emplaced in a shallow crustal chamber under relatively low pressures, high temperature (≥850 °C)
and relatively oxidising conditions. The oxidised nature, HFSE concentrations and Nd isotope data (ɛNd = −1.3 to −2.9) favour
derivation of these granitoid rocks from crustal protoliths. The generation of albite granite is attributed to the replacement
of alkali feldspar and plagioclase of the original granite by pure albite as a consequence of pervasive infiltration of a
high Na/(Na + K) fluid at the late-magmatic stage. This model may have wider significance for the generation of albite granites/low-K
granites or albitites in other areas. The A-type plutonism under consideration seems to be an outcome of ensialic rifting
of the Bhilwara aulacogen. 相似文献
3.
Characterisation of the Dabla Granitoids, North Khetri Copper Belt, Rajasthan, India: Evidence of Bimodal Anorogenic Felsic Magmatism 总被引:1,自引:0,他引:1
Naveen Chaudhri Parampreet Kaur Martin Okrusch Annette Schimrosczyk 《Gondwana Research》2003,6(4):879-895
The Palaeoproterozoic Dabla granitoid pluton of the North Khetri Copper Belt is located to the east of a NNE-SSW trending lineament with numerous albite-rich intrusives, the intraplate ‘albitite line’. The Dabla pluton is essentially made up of calcic amphibole-bearing granitoids, displaying a concentric bimodal distribution of alkali-feldspar granites, comprising a microcline-albite granite and an albite-granite. The dominant rock type is pink-coloured granite, which is characterised by quartz, microcline, albite and hastingsitic hornblende, and occurs in the marginal parts of the pluton. The volumetrically subordinate albite-granite in the central part of the pluton is invariably white in colour, non-foliated and is mainly composed of quartz, albite and amphibole of actinolite to ferro-actinolite composition. The albite-granite is characterised by low K2O (0.06-0.09%), Rb (<5 ppm) and Ba (<20 ppm), high Na2O (7.19-7.36%) and high Na/K ratios (122.4-185.2) as compared to the granite. These rocks are not subjected to any metamorphic overprint, especially the albite-granite, which shows pristine abundances of major and trace elements. The rocks are highly evolved as reflected in their high SiO2 (72 to 78%) contents and high DI (89.5-97) values. The Dabla granitoids are characterised by similar REE and spider patterns, displaying LREE enriched slopes, flat HREE profiles and strong negative Sr, P, Ti and Eu anomalies suggesting their comagmatic nature. Nevertheless, the granite is relatively more fractionated [(La/Yb)N = 3.89-8.19] and show higher REE abundances (466-673 ppm) as compared to the albite-granite [(La/Yb)N = 1.97-2.96; REE = 220-277 ppm]. Distinctive features of these rocks are their low Ca (0.21-1.53%), Mg (<0.02-0.19%), Al (11.84-12.96%) and Sr (12-46 ppm) abundances, high Zr (155-631 ppm), Y (67-156 ppm), Nb (14-91 ppm), and Ga (20-31 ppm) concentrations and high Fe*-number, high Ga/Al ratio and high agpaitic index (AI) values. These features, coupled with their ferroan, alkaline and metaluminous nature, are typical of within-plate aluminous A-type granites. The geochemical data further indicate that the Dabla magma was generated at fairly high temperature, apparently in an upper mantle region, under relatively low H2O activities and reduced conditions and emplaced at a shallow depth in an extensional tectonic environment. 相似文献
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Rayleigh’s method of approximation is employed to find out the reflection and transmission coefficients due to an incident
plane SH wave at a corrugated interface between a laterally and vertically inhomogeneous anisotropic elastic solid half-space
and a laterally and vertically inhomogeneous isotropic visco-elastic solid half-space. The lateral and vertical inhomogeneities
are described by the exponential variations of elastic parameters. The formulae of reflection and transmission coefficients
are derived in closed form for the first-order approximation of the corrugation. The effects of the corrugation of the interface,
the inhomogeneity, the anisotropy, the visco-elasticity and the frequency of the incident wave on these coefficients are studied
analytically and numerically for a specific model containing a periodic interface. The results of earlier workers have been
reduced as particular cases from the present formulation. 相似文献
7.
A numerical technique for delineation of soil mapping units using multi-spectral remote sensing data
Ravinder Kaur S K Bhadra M Bhavanarayana B C Panda 《Journal of the Indian Society of Remote Sensing》1998,26(4):149-160
A numerical technique for transformation of ground based sail spectral information into soil mapping — unit information, in terms of the total information content index has been proposed. The study carried out on 14 surface soil samples. widely differing in their physical appearance of colour and collected from different parts of India, revealed that total information content index could distinctly discriminate between the contrasting soil physiographic units with black cotton, red and sandy soil types. A comparison of the proposed index with the conventionally used two or three waveband specific indices (e.g. NIR/Red and NIR-Red/Red-Green) showed that the proposed index was more characteristic of the various soil types studied. Further, unlike the conventional 2-D indices, the proposed, numerical technique lead to the complete compression of the information contained in the entire reflectance spectrum (irrespective of the number of wavebands) to a single characteristic value in 1-D Space and a simplified 1-D clustering analysis. 相似文献
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