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1.
本文分析类星体０９１７＋６２在波长６ｃｍ和１１ｃｍ上快速变化（时标１天）的结构函数．讨论在什么条件下，这种快速变化可用星际折射闪烁来解释．结果表明，折射闪烁解释对星际介质和射电源结构提出了相当明确的限制：散射介质应为连续介质，其有效距离应０．４ｋｐｃ；射电源应包含０．０５—０．１ｍａｓ的致密结构．对快变射电源方向上脉冲星的测量以确定星际介质特性和用ＶＬＢＩ测量快变射电源中的小角径成分，将是检验星际折射闪烁解释的必要途径． 相似文献
2.
钱善 《中国天文和天体物理学报》1995,(3)
本文探讨脉冲星ＰＳＲ２２１７＋４７分米波段流量变化的星际折射闪烁解释。利用衍射闪烁测量所获得的星际介质参数和连续介质的折射闪烁理论，计算了多频率（０．３１，０．４２，０．６１和０．７５ＧＨｚ）上的折射闪烁结构函数，并与观测结构函数加以比较。结果表明，如果星际介质电子密度不均匀性具有幂律谱，那么幂律指数β＝４要比β＝１１／３（即Ｋｏｌｍｏｇｏｒｏｖ谱）能更好地符合观测。 相似文献
3.
本探讨脉冲星ＰＳ４２２１７＋４７分米波段流量变化的星际折射闪烁解释。利用衍射闪烁测量所获得的星际介质参数和连续介质的折射闪烁理论，计算了多频率（０．３１，０．４２，０．６１和０．７５ＧＨｚ）上的折射闪烁结构函数，并与观测结构函数加以比较，结果表明，如果星际介质电子密度不均匀性具有幂律谱，那么幂律指数β＝１１／３（即Ｋｏｌｍｏｇｏｒｏｖ谱）能更好地符合观测。 相似文献
4.
利用星际介质的折射闪烁解释在ＢＬ Ｌａｃ天体０７１６＋７１中观测到的射电快速变化的结构函数，确定了对射电源的结构和散射介质特性所提出的条件，为了解释这个源内观测到的射电变化的“快模式”和“慢模式”的转换，必须考虑射电源内致密结构的角径或运动状态的快速变化，射电变化和光学变化的相 性仍然是折射闪烁解释的难于克服的困难。 相似文献
5.
本文报道南天区5GHzVLBI普查式观测结果．首次观测是在1992年11月期间进行的，共观测了23个河外射电源，获得了20个河外射电源的VLBI高分辨率的射电图象．有15个射电源呈现核喷流结构，1个有双向喷流，3个未分解，末发现有致密观源．在16个核喷流（包括一个双向喷流源）源中有11个呈现弯曲喷流现象．此外还首次发现有3个源中可能有超光速运动现象． 相似文献
6.
南天区20个河外射电源的VLBI研究 总被引：6，自引：5，他引：1
本报道南天区５ＧＨｚ普查式观测结果，首次观测是在１９９２年１１月期间进行的，共观测２３个河外射电源，获得了２０个河外射电源的ＶＬＢＩ高分辨率的射电图象，有１５个射电源呈现核喷流结构，１个有双向喷流，３个未分解，未发现有致密双源，在１６个核喷流（包括一个双向喷流源）源中有１１个呈现弯曲喷流现象。此外还首次发现了３个源中可能有超光速运动现象。 相似文献
7.
蒋栋荣 《中国天文和天体物理学报》1995,(1)
本文对ＶＬＢＩ观测得到的河外射电源致密核ｃｏｒｅ的视角大小进行了统计研究，发现对单个源平均上视角大小近似反比于观测频率，与目前的模型相一致。在５ＧＨｚ上，在红移范围０．０４＜ｚ＜２．５内，平均的ｃｏｒｅ视角大小近似为常数，在非均匀喷流模型框架下，一种可能的解释是在河外射电源致密结构中磁场存在着演化。 相似文献
8.
韩金林 《中国天文和天体物理学报》1995,(2)
研究表明，高频射电源与低频射电源相比，前者中的类星体比例更大。３ＣＲ低频射电源（Ｓ１７８ＭＨｚ＞９Ｊｙ）中有１７．８％是类星体，而在２．７ＧＨｚ亮射电源样本中（Ｓ２．７ＧＨｚ≥２．０Ｊｙ），有３５．６％是类星体。更有趣的是，５１８个５ＧＨｚ亮射电源中（Ｓ５ＧＨｚ≥１．０Ｊｙ），至少有２９１个（≥５６％）是类星体。因此，我们认为高频亮射电源的证认是发现类星体的有效手段。 相似文献
9.
本对ＶＬＢＩ观测得到的河外射电源致密核ｃｏｒｅ的视角大小进行了统计研究，发现对单个源平均上视角大小近似反比于观测频率，与目前的模型相一致。在５ＧＨｚ上，在红移范围０．０４＜ｚ＜２．５内，平均的ｃｏｒｅ视角大小近似为常数，在非均匀喷流模型框架下，一种可能的解释是在河外射电源致密结构中磁场存在着演化。 相似文献
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《中国天文和天体物理学报》2014,(9)
正Research in Astronomy and Astrophysics publishes original research papers and reviews 011 all liranchcs of astronoiriy and astrophysics.Reviews arc by invitation only.Important new results that require rapid publication can be submitted as a Letter(Letters must be restricted in length 相似文献
12.
Laura Schaefer 《Icarus》2004,169(1):216-241
We modified the MAGMA chemical equilibrium code developed by Fegley and Cameron (1987, Earth Planet. Sci. Lett. 82, 207-222) and used it to model vaporization of high temperature silicate lavas on Io. The MAGMA code computes chemical equilibria in a melt, between melt and its equilibrium vapor, and in the gas phase. The good agreement of MAGMA code results with experimental data and with other computer codes is demonstrated. The temperature-dependent pressure and composition of vapor in equilibrium with lava is calculated from 1700 to 2400 K for 109 different silicate lavas in the ONaKFeSiMgCaAlTi system. Results for five lavas (tholeiitic basalt, alkali basalt, Barberton komatiite, dunite, and a molten type B1 Ca, Al-rich inclusion) are discussed in detail. The effects of continuous fractional vaporization on chemistry of these lavas and their equilibrium vapor are presented. The predicted abundances (relative to Na) of K, Fe, Si, Al, Ca, and Ti in the vapor equilibrated with lavas at 1900 K are lower than published upper limits for Io's atmosphere (which do not include Mg). We predict evaporative loss of alkalis, Fe, and Si during volcanic eruptions. Sodium is more volatile than K, and the Na/K ratio in the gas is decreased by fractional vaporization. This process can match Io's atmospheric Na/K ratio of 10±3 reported by Brown (2001, Icarus 151, 190-195). Silicon monoxide is an abundant species in the vapor above lavas. Spectroscopic searches are recommended for SiO at IR and mm wavelengths. Reactions of metallic vapors with S- and Cl-bearing volcanic gases may form other unusual gases including MgCl2, MgS, MgCl, FeCl2, FeS, FeCl, and SiS. 相似文献
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《中国天文和天体物理学报》2014,(10)
正Research in Astronomy and Astrophysics publishes original research papers and reviews on all branches of astronomy and astrophysics.Reviews are by invitation only.Important new results that require rapid publication can be submitted as a Letter(Letters must be restricted in length to 6 printed pages).Authors who submit a paper are expected to be able to certify that the paper is original work, 相似文献
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Laura Schaefer 《Icarus》2005,173(2):454-468
We use chemical equilibrium calculations to model the speciation of alkalis and halogens in volcanic gases emitted on Io. The calculations cover wide temperature (500-2000 K) and pressure (10−6 to 10+1 bars) ranges, which overlap the nominal conditions at Pele (T=1760 K, P=0.01 bars). About 230 compounds of 11 elements (O, S, Li, Na, K, Rb, Cs, F, Cl, Br, I) are considered. The elemental abundances for O, S, Na, K, and Cl are based upon observations. CI chondritic elemental abundances relative to sulfur are used for the other alkalis and halogens (as yet unobserved on Io). We predict the major alkali species in Pele-like volcanic gases and the percentage distribution of each alkali are LiCl (73%), LiF (27%); NaCl (81%), Na (16%), NaF (3%); KCl (91%), K (5%), KF (4%); RbCl (93%), Rb (4%), RbF (3%); CsCl (92%), CsF (6%), Cs (2%). Likewise the major halogen species and the percentage distribution of each halogen are NaF (88%), KF (10%), LiF (2%); NaCl (89%), KCl (11%); NaBr (89%), KBr (10%), Br (1%); NaI (61%), I (30%), KI (9%). We predict the major halogen condensates and their condensation temperatures at P=0.01 bar are NaF (1115 K), LiF (970 K); NaCl (1050 K), KCl (950 K); KBr (750 K), RbBr (730 K), CsBr (645 K); and solid I2 (200 K). We also model disequilibrium chemistry of the alkalis and halogens in the volcanic plume. Based on this work and our prior modeling for Na, K, and Cl in a volcanic plume, we predict the major loss processes for the alkali halide gases are photolysis and/or condensation onto grains. Their estimated photochemical lifetimes range from a few minutes for alkali iodides to a few hours for alkali fluorides. Condensation is apparently the only loss process for elemental iodine. On the basis of elemental abundances and photochemical lifetimes, we recommend searching for gaseous KCl, NaF, LiF, LiCl, RbF, RbCl, CsF, and CsCl around volcanic vents during eruptions. Based on abundance considerations and observations of brown dwarfs we also recommend a search of Io's extended atmosphere and the Io plasma torus for neutral and ionized Li, Cs, Rb, and F. 相似文献
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Li Xin-nan Zhang Hai-ying Cui Xiang-qun Jiang Zi-bo Zheng Yi Liu Xing-tao Ni Hou-kun 《Chinese Astronomy and Astrophysics》2012
A special stressed annular polishing technique is proposed to mill the off-axis aspheric sub-mirrors of a large segmented mirror with an annular polishing machine. Based on the basic principle of stressed annular polishing technique, a set of special stressing mechanisms are designed to convert milling the aspheric surfaces of sub-mirrors with different off-axis distances into milling the spherical surfaces with identical radii of curvature, so that they can be pol- ished simultaneously on a continuous polishing machine. It took about contin- uous 40 hours to polish a scaled-down mirror of the planning Chinese Future Giant Telescope (CFGT) using this technique. This mirror has the 330 mm di- ameter, 3.6 m off-axis distance, and the 21.6 m radius of curvature, and its max- imum asphericity is 16 micron. The experiment shows that this method has a high effciency, suits batch manufacturing, especially the batch manufacturing of aspheric sub-mirrors of the segmented primary mirror of an extremely large aperture telescope. 相似文献
19.
Yehouda Enzel Rivka Amit Uri Dayan Onn Crouvi Ron Kahana Baruch Ziv David Sharon 《Global and Planetary Change》2008,60(3-4):165-192
Modern-day synoptic-scale eastern Mediterranean climatology provides a useful context to synthesize the diverse late Pleistocene (60–12 ka) paleohydrologic and paleoenvironmental indicators of past climatic conditions in the Levant and the deserts to its south and east. We first critically evaluate, extract, and summarize paleoenvironmental and paleohydrologic records. Then, we propose a framework of eastern Mediterranean atmospheric circulation features interacting with the morphology and location of the southeast Mediterranean coast. Together they strongly control the spatial distribution of rainfall and wind pattern. This cyclone–physiography interaction enforces the observed rainfall patterns by hampering rainfall generation south and southeast of the latitude of the north Sinai coast, currently at 31°15′.The proposed framework explains the much-increased rains in Lebanon and northern Israel and Jordan as deduced from pollen, rise and maintenance of Lake Lisan, and speleothem formation in areas currently arid and semiarid. The proposed framework also accounts for the southward and eastward transition into semiarid, arid, and hyperarid deserts as expressed in thick loess accumulation at the deserts' margins, dune migration from west to east in the Sinai and the western Negev, and the formation of hyperarid (< 80 mm yr− 1) gypsic–salic soils in the southern Negev and Sinai. Our climatic synthesis explains the hyperarid condition in the southern Negev, located only 200–250 km south of the much-increased rains in the north, probably reflecting a steeper rainfall gradient than the present-day gradient from the wetter Levant into its bordering southern and eastern deserts.At present, the rainiest winter seasons in Lebanon and northern and central Israel are associated with more frequent (+ 20%), deeper Cyprus Lows traversing the eastern Mediterranean at approximately the latitude of southern Turkey. Even these wettest years in northern Israel do not yield above average annual rainfall amounts in the hyperarid southern Negev. This region is mainly influenced by the Active Red Sea Troughs that produce only localized rains. The eastern Mediterranean Cyprus Lows also produce more dust storms and transport higher amounts of suspended dust to the loess area than any other atmospheric pattern. Concurrent rainfall and dust are essential to the late Pleistocene formation of the elongated thick loess zone along the desert northern margin. Even with existing dust storms, the lack of rain and very sparse vegetation account for the absence of late Pleistocene loess sequences from the southern Negev and the formation of hyperarid soils.When the north Sinai coast shifted 30–70 km northwest due to last glacial global sea level lowering, the newly exposed coastal areas supplied the sand and dust to these active eastern Mediterranean cyclones. This enforced the latitude of the northern boundary of the loess zone to be directly due east of the LGM shoreline. This shift of coast to the northwest inhibited rainfall in the southern Levant deserts and maintained their hyperaridity. Concurrently, frequent deep eastern Mediterranean Cyprus Lows were funneled along the northern Mediterranean increasing (probably doubling) the rains in central and northern Israel, Lebanon, southwestern Syria and northern Jordan. These storms and rains formed lakes, forests, and speleothems only a short distance north of the deserts in the southern Levant. 相似文献
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Philippe Stee 《Astrophysics and Space Science》2003,286(1-2):225-236
Interferometry in the visible provides milliarcsecond spatial resolution and thus has been used for studying the circumstellar
environment of active hot stars. In this paper I will illustrate how the visibility modulus and phase can be used to better
constrain the physics of Be disks through results from the VLA, the MkII and the GI2T interferometers. I will insist on the
importance and the potential of coupling high angular resolution with high spectral resolution to the study of Be shells.
Finally I will present a possible study of the circumstellar disk of Be stars using the VLTI.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献