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971.
D. Burns J. E. Baldwin R. C. Boysen C. A. Haniff P. R. Lawson C. D. Mackay J. Rogers T. R. Scott D. St.-Jacques P. J. Warner D. M. A. Wilson & J. S. Young 《Monthly notices of the Royal Astronomical Society》1998,297(2):462-466
We report the first direct detection of long-term periodic diameter variations in a Mira variable. Angular diameter measurements of the 313-d period variable R Leonis at 833 nm and 940 nm obtained between 1996 February and 1997 June using the Cambridge Optical Aperture Synthesis Telescope (COAST) and the William Herschel Telescope (WHT) show a cyclic modulation of the apparent stellar diameter by approximately 35 per cent. The agreement between these new data and archival measurements from 1992 January suggests coherence in the modulation over a 5-yr period. Our data are consistent with recent models which suggest that, in photometric bands with only weak to moderate molecular contamination, periodic variations in stellar diameter of order 50 per cent can be maintained. The measurements indicate that the apparent stellar diameter was largest at visual phase 0.5 and that any phase shifts between the visual light curve and those at 833 and 940 nm were at most 0.05. The large offset (∼ 0.25) between the phase of the observed diameter maximum and that predicted for the photospheric continuum diameter variations suggests that our observations are more sensitive to the changing temperature structure of the outer atmosphere than to the deeper continuum-forming layers. 相似文献
972.
Y. C. Unruh A. Collier Cameron & E. Guenther 《Monthly notices of the Royal Astronomical Society》1998,295(4):781-798
We have mapped surface inhomogeneities on the classical T Tauri star DF Tau, using the Li i doublet at 670.8 nm, the Ca i lines at 612.2 nm and 643.9 nm and a calcium and iron blend at 646.3 nm. We find compelling evidence that there are hotspots with temperatures of more than 5000 K. Two of the hotspots produce line-profile deformations that can be traced as they move through the cross-correlated profiles. When one of the hotspots crosses the stellar disc, redshifted absorption components appear in the Na D lines. As these redshifted absorption features are usually tracers for mass-infall we interpret this hotspot as an accretion shock close to the stellar surface. Parts of the surface of DF Tau are covered with a hot chromosphere that is visible in the Ca ii infrared triplet lines and the narrow component of He i . We find no correlation between the veiling and the lines that originate from the hot chromosphere, suggesting that the veiling and the chromospheric emission are produced in physically distinct regions. 相似文献
973.
David Valls-Gabaud 《Monthly notices of the Royal Astronomical Society》1998,294(4):747-752
The detection of microlensing events from stars in the Large Magellanic Cloud and in the Galactic bulge raises important constraints on the distribution of dark matter and on galactic structure, although some events may be the result of a new type of intrinsic variability. When lenses are relatively close to the sources, we predict that chromatic and spectroscopic effects are likely to appear for a significant fraction of the microlensing events. These effects are due to the differential amplification of the limb and the centre of the stellar disc, and present a systematic dependence with wavelength and time that provides an unambiguous signature of a microlensing event (as opposed to a new type of intrinsic stellar variability). We present detailed predictions of the effects, using realistic model atmospheres. The observations of these effects provide a direct constraint on stellar atmospheres, allowing a three-dimensional reconstruction or imaging of its structure, a unique tool with which to test the current models of stellar atmospheres. 相似文献
974.
K. Golap N. Udaya Shankar S. Sachdev R. Dodson Ch. V. Sastry 《Journal of Astrophysics and Astronomy》1998,19(1-2):35-53
A new, meter-wave radio telescope has been built in the north-east of Mauritius, an island in the Indian Ocean, at a latitude
of -20.14‡. The Mauritius Radio Telescope (MRT) is a Fourier Synthesis T-shaped array, consisting of a 2048 m long East-West
arm and an 880 m long South arm. In the East-West arm 1024 fixed helices are arranged in 32 groups and in the South arm 16
trolleys, with four helices on each, which move on a rail are used. A 512-channel digital complex correlation receiver is
used to measure the visibility function. At least 60 days of observing are required for obtaining the visibilities up to 880
m spacing. The Fourier transform of the calibrated visibilities produces a map of the area of the sky under observation with
a synthesized beam width 4′ × 4.6′ sec(δ + 20.14‡) at 151.5 MHz.
The primary objective of the telescope is to produce a sky survey in the declination range –70‡ to –10‡ with a point source
sensitivity of about 200 mJy (3a level). This will be the southern sky equivalent of the Cambridge 6C survey. In this paper
we describe the telescope, discuss the array design and the calibration techniques used, and present a map made using the
telescope. 相似文献
975.
利用高分辨透射电子显微镜,结合能谱仪观察了20nm左右的胶态Au,在黄铁矿的[001]方向析出。固体原子象显示出Au的附近由于晶格畸变而空隙度较大。 相似文献
976.
977.
浅海回填区域的地震映象效果分析 总被引:3,自引:0,他引:3
地震映象法是近期工程物探在工程地质与环境地质勘察中新出现的1种浅层地震探测方法。本文主要介绍该方法的实用方法技术与主要特点及其实际应用效果。并通过奥运工程勘察实例详细分析了该方法在复杂的浅海人工回填区域中不同的填入物与地质体在时间剖面上所展现的各种不同波形特征。 相似文献
978.
979.
In this study, an empirical model for predicting urban evapotranspiration (ET) is examined for the Phoenix metropolitan area that is in a subtropical desert climate using in situ ET measurements from a local flux tower and remotely sensed moderate-resolution imaging spectroradiometer land products. Annual ET maps of Phoenix are then created for the period from 2001 to 2015 using the empirical model developed. A time-series trend analysis is finally performed using predicted ET maps to discover the spatio-temporal patterns of ET changes during the study period. Results suggest that blue-sky albedo and land surface temperature are two statistically significant variables explanatory to model urban ET for Phoenix. Areas that have experienced significant increases of ET are highly spatially clustered, and are mainly found on the outskirts of the city, while areas of decreasing ET are generally associated with highly developed areas, such as downtown Phoenix. 相似文献
980.
THE CRUSTAL SHALLOW STRUCTURES AND FAULT ACTIVITY DETECTION IN XINYI SECTION OF TAN-LU FAULT ZONE 下载免费PDF全文
GU Qin-ping XU Han-gang YAN Yun-xiang ZHAO Qi-guang LI Li-mei MENG Ke YANG Hao WANG Jin-yan JIANG Xin MA Dong-wei 《地震地质》1979,42(4):825-843
The Tan-Lu fault zone is the largest active tectonic zone in eastern China, with a complex history of formation and evolution, and it has a very important control effect on the regional structure, magmatic activity, the formation and distribution of mineral resources and modern seismic activity in eastern China. Xinyi City has a very important position as a segmental node in the Shandong and Suwan sections of the Tan-Lu fault zone. Predecessors have conducted research on the spatial distribution, occurrence and activity characteristics of the shallow crustal faults in the Suqian section of the Tan-Lu belt, and have obtained some new scientific understandings and results. However, due to different research objectives or limitations of research methods, previous researches have either focused on the deep crustal structure, or targeted on the Suqian section or other regions. However, the structural style and deep-shallow structural association characteristics of Xinyi section of Tan-Lu belt have not been well illustrated, nor its activity and spatial distribution have been systematically studied. In order to investigate the shallow crustal structure features, the fault activities, the spatial distribution and the relationship between deep and shallow structures of the Xinyi section of the Tan-Lu Fault, we used a method combining mid-deep/shallow seismic reflection exploration and first-break wave imaging. Firstly, a mid-deep seismic reflection profile with a length of 33km and a coverage number greater than 30 was completed in the south of Xinyi City. At the same time, using the first arrival wave on the common shot record, the tomographic study of the shallow crust structure was carried out. Secondly, three shallow seismic reflection profiles and one refraction tomography profile with high resolution across faults were presented. The results show that the Xinyi section of Tan-Lu fault zone is a fault zone composed of five concealed main faults, with a structural pattern of “two grabens sandwiched by a barrier”. The five main faults reveal more clearly the structural style of “one base between two cuts” of the Tan-Lu fault zone. From west to east, the distribution is as follows: on the west side, there are two high-angle faults, F4 and F3, with a slot-shaped fault block falling in the middle, forming the western graben. In the middle, F3 and F2, two normal faults with opposite dip directions, are bounded and the middle discontinuity disk rises relatively to form a barrier. On the east side, F2 and F1, two conjugate high-angle faults, constitute the eastern graben. The mid-deep and shallow seismic reflection profiles indicate that the main faults of the Xinyi section of Tan-Lu fault zone have a consistent upper-lower relationship and obvious Quaternary activities, which play a significant role in controlling the characteristics of graben-barrier structure and thickness of Cenozoic strata. The shape of the reflective interface of the stratum and the characteristics of the shallow part of the fault revealed by shallow seismic reflection profiles are clear. The Mohe-Lingcheng Fault, Xinyi-Xindian Fault, Malingshan-Chonggangshan Fault and Shanzuokou-Sihong Fault not only broke the top surface of the bedrock, but also are hidden active faults since Quaternary, especially the Malingshan-Chonggangshan Fault which shows strong activity characteristics of Holocene. The results of this paper provide a seismological basis for an in-depth understanding of the deep dynamics process of Xinyi City and its surrounding areas, and for studying the deep-shallow tectonic association and its activity in the the Xinyi section of the Tan-Lu Fault. 相似文献