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准稳恒态宇宙学简介辛酉国际知名天文学家伯比奇（Ｇ．Ｂａｒｂｉｄｏｅ）、纳里卡（Ｊ．Ｖ．Ｎａ，ｌｉｋａ，）及霍伊尔（Ｆ．Ｈｏｙｌｅ）在１９９３年６月２０日出版的Ａ８ｔｒＯ刀刀刃ＭＪｏｎ，ｎｄ上发表了他们的准稳恒态宇宙学（ｔｗａｉ－ＳｔｅａｄｙＳｔａｔｅ...     

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许多读者盼望已久的8.5等星星图--《世纪天图》终于出版了。北京天文馆编印的这套星图原名为SKYATLAS(天图),系现代著名星图专家荷兰的W.Tirion的成名之作,他在吸收了《捷克星图》的诸多优     

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Evidence of rapid optical variability in selected narrow-line Seyfert 1 galaxies

We present the first results of a search for the presence of rapid optical variability in a sample of five Narrow-Line Seyfert 1 galaxies. We find clear evidence of rapid variability for IRAS 13224-3809 with variations occurring on time scales of an hour. However, the results are less conclusive for the other four sources in our sample, Markarian 766, PG 1244+026, PG 1404+226 and Arakelian 564. While there are several instances among these latter objects where there is a hint that variability may be present, IRAS 13224-3809 provides the only conclusive evidence of rapid optical variability detected to date.     

CHAMP加速仪资料的快速校标研究

对星载加速仪进行校标是有效利用星载加速仪测量数据的基础,目前校标方法都是建立在星载GPS资料处理的基础上,对处理软件和计算设备的要求都非常高.为了满足高层大气阻力研究的需要,提出了一种快速高效的校标方法,即利用GFZ公布的CHAMP卫星快速轨道作为观测资料,采用有尺度因子和线性偏差的加速仪测量值代替非引力模型摄动加速度...     

The Dushak-Erekdag survey of roAp stars

The search of roAp stars at Mt. Dushak-Erekdag Observatory was started in 1992 using the 0.8 m Odessa telescope equipped with a two-star high-speed photometer. We have observed more than a dozen stars so far and discovered HD 99563 as roAp star while BD+8087 is suspected to have rapid oscillations. Negative results of our observations for the search of rapid oscillations in four stars in NGC 752 are also discussed.     

A simple image forming technique suitable for multifrequency observations of solar radio bursts

A simple image forming system using a multielement interferometer for obtaining rapid pictures of solar radio bursts is described. A dispersive transmission line is used to feed the elements in series through directional couplers. Truly instantaneous pictures of solar activity can be obtained by placing a number of narrow frequency filters at the end of the I. F. amplifier in the main receiver, located at one end of the array.The two dimensional extension of this principle is examined in some detail. Multibeaming in the two arrays of a crossed grating interferometer can be combined with fast phase-scanning in one of the arrays to produce rapid pencil beam pictures. If log-periodic antennas are used, observations can even be made at widely different frequencies simultaneously. For illustration, some important parameters for simultaneous observations at 60, 90 and 120 MHz are estimated for an interferometer assumed to be located at a latitude of 30° N. The main advantage of the proposed system is that high-resolution rapid pictures of radio bursts can be obtained simultaneously at a number of frequencies with modest effort.     

Rapid tidewater glacier retreat: a comparison between Columbia Glacier, Alaska and Patagonian calving glaciers

Time-changes in the terminus positions of Patagonian grounded calving glaciers are studied. The framework for the study is a model of terminus retreat based on observations of Columbia Glacier, Alaska. The interpretation favored in this work is that rapid retreat is caused by the terminus thinning to near flotation and weakening of the ice by bottom crevasses. Both thinning and bottom crevasse formation are caused by the increase in near-terminus stretching during rapid retreat. The model is consistent with the behavior of calving Patagonian glaciers regardless of the salinity of the water body calved into. Continuity calculations on Glaciar San Rafael, Chile indicate internal voids, possibly in the form of bottom crevasses, as on Columbia Glacier.     

A model of rapid burster MXB 1730-335

A model of rapid burster MXB 1730-335, the source of type II X-ray burst is proposed, based on the Rayleigh-Taylor instability due to interaction of relativistic electrons produced by the rapid rotation of a highly magnetized neutron star, and the infalling accreted matter through the magnetic funnel at the poles. Conclusions are made that type II X-ray burster may be a constant source of cosmic rays and such a mechanism may be the progenitor of some forms of nebulae.Permanent address: Imphal College, Imphal, Manipur.     

Timescale Analysis of Spectral Lags

A technique for timescale analysis of spectral lags performed directly in the time domain is developed. Simulation studies are made to compare the time domain technique with the Fourier frequency analysis for spectral time lags. The time domain technique is applied to studying rapid variabilities of X-ray binaries and γ-ray bursts. The results indicate that in comparison with the Fourier analysis the timescale analysis technique is more powerful for the study of spectral lags in rapid variabilities on short time scales and short duration flaring phenomena.     

Rapid optical variability in radio-quiet QSOs

We report results of the observations at the Vainu Bappu Observatory and the Uttar Pradesh State Observatory of eight radio-quiet quasi-stellar objects (RQQSOs) during 1996–99. This is a part of our ongoing programme to search for intranight optical variability in RQQSOs. Additional evidence for very rapid variability in three of the five optically bright and very luminous RQQSOs we had observed earlier, 1049−006, 1444+408 and 1630+377, was found. Of the three newly observed RQQSOs, the data for 0043+039 are too noisy to allow conclusions about variability to be drawn, but 0748+294 and 0824+098 show strong hints of microvariability. We also present a summary of the results from our entire programme to date, which includes observations of 16 radio-quiet QSOs and one radio-weak QSO, and compare the general properties of rapid variability in radio-quiet versus radio-loud AGN as determined from our work and that of several other groups. Observations of this kind are likely to play a key role in understanding the relative contributions of accretion discs and relativistic plasma jets to rapid optical fluctuations of AGN.     

Vesicle dynamics during the atmospheric entry heating of cosmic spherules

Cosmic spherules are unique igneous objects that form by melting due to gas drag heating during atmospheric entry heating. Vesicles are an important component of many cosmic spherules since they suggest their precursors had finite volatile contents. Vesicle abundances in spherules decrease through the series porphyritic, glassy, barred, to cryptocrystalline spherules. Anomalous hollow spherules, with large off‐center vesicles occur in both porphyritic and glassy spheres. Numerical simulation of the dynamic behavior of vesicles during atmospheric flight is presented that indicates vesicles rapidly migrate due to deceleration and separate from nonporphyritic particles. Modest rotation rates of tens of radians s^?1 are, however, sufficient to impede loss of vesicles and may explain the presence of small solitary vesicles in barred, cryptocrystalline and glassy spherules. Rapid rotation at spin rates of several thousand radians s^?1 are required to concentrate vesicles at the rotational axis and leads to rapid growth by coalescence and either separation or retention depending on the orientation of the rotational axis. Complex rapid rotations that concentrate vesicles in the core of particles are proposed as a mechanism for the formation of hollow spherules. High vesicle contents in porphyritic spherules suggest volatile‐rich precursors; however, calculation of volatile retention indicates these have lost >99.9% of volatiles to degassing prior to melting. The formation of hollow spherules, by rapid spin, necessarily implies preatmospheric rotations of several thousand radians s^?1. These particles are suggested to represent immature dust, recently released from parent bodies, in which rotations have not been slowed by magnetic damping.     

The resonant excitation of transverse oscillations in coronal loops

We suggest a way of self-consistently solving the problem of the excitation and rapid damping of coronal loop oscillations observed from the TRACE (Transition Region and Coronal Explorer) satellite. Oscillations are excited on the dispersion branch of fast magnetoacoustic waves, which propagate mainly across the magnetic field. The rapid damping of the observed oscillations is governed by the dispersion spreading of the pulse of these waves that was produced, for example, by a solar flare. The fundamental oscillation period is close to the period of the fundamental mode. Dissipative processes attributable to the nonideality of the plasma and the coronal-loop footpoints play no fundamental role.