双星演化与大样本恒星演化

主要介绍大样本恒星演化所面临的困难、为解决困难所做的努力及对未来的展望．

Orbit Determination Using Satellite-to-Satellite Tracking Data

Satellite-to-Satellite tricking (SST) data can be used to determine the orbits of spacecraft in two ways. One is combined orbit determination, which combines SST data with ground-based tracking data and exploits the enhanced tracking geometry. The other is the autonomous orbit determination, which uses only SST. The latter only fits some particular circumstances since it suffers the rank defect problem in other circumstances. The proof of this statement is presented. The nature of the problem is also investigated in order to find an effective solution. Several. methods of solution are discussed. The feasibility of the methods is demonstrated by their application to a simulation.

The Effect of Solar Activity on the Annual Precipitation in the Beijing Area

Using continuous wavelet transform, we examine the relationship between solar activity and the annual precipitation in the Beijing area. The results indicate that the annual precipitation is closely related to the variation of sunspot numbers, and that solar activity probably plays an important role in influencing the precipitation on land.

Gamma-Ray Bursts: Afterglows and Central Engines

Gamma-ray bursts (GRBs) are the most intense transient gamma-ray events in the sky; this, together with the strong evidence (the isotropic and inhomogeneous distribution of GRBs detected by BASTE) that they are located at cosmological distances, makes them the most energetic events ever known. For example, the observed radiation energies of some GRBs are equivalent to the total convertion into radiation of the mass energy of more than one solar mass. This is thousand times stronger than the energy of a supernova explosion. Some unconventional energy mechanism and extremely high conversion efficiency for these mysterious events are required. The discovery of host galaxies and association with supernovae at cosmological distances by the recently launched satellite of BeppoSAX and ground based radio and optical telescopes in GRB afterglow provides further support to the cosmological origin of GRBs and put strong constraints on their central engine. It is the aim of this article to review the possible central engines, energy mechanisms, dynamical and spectral evolution of GRBs, especially focusing on the afterglows in multi-wavebands.

Active Optics in LAMOST

Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) is one of the major national projects under construction in China. Active optics is one of the most important technologies for new large telescopes. It is used for correcting telescope errors generated by gravitational and thermal changes. Here, however, we use this technology to realize the configuration of LAMOST, -a task that cannot be done in the traditional way. A comprehensive and intensive research on the active optics used in LAMOST is also reported, including an open-loop control method and an auxiliary closed-loop control method. Another important development is in our pre-calibration method of open-loop control, which is with some new features: simultaneous calculation of the forces and displacements of force actuators and displacement actuators; the profile of mirror can be arbitrary; the mirror surface shape is not expressed by a fitting polynomial, but is derived from the mirror surface shape formula which is highly accurate; a proof is given that the solution of the pre-calibration method is the same as the least squares solution.

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.

Afterglow Light Curves of Jetted Gamma-ray Burst Ejecta in Stellar Winds

Optical and radio afterglows arising from shocks by relativistic conical ejecta running into pre-burst massive stellar winds are revisited. Under the homogeneous thin-shell approximation and a realistic treatment for the lateral expansion of jets, our results show that a notable break exists in the optical light curve in most cases we calculated in which the physical parameters are varied within reasonable ranges. For a relatively tenuous wind which cannot decelerate the relativistic jet to cause a light curve break within days, the wind termination shock due to the ram pressure of the surrounding medium occurs at a small radius, namely, a few times 1017 cm. In such a structured wind environment, the jet will pass through the wind within several hours and run into the outer uniform dense medium. The resulting optical light curve flattens with a shallower drop after the jet encounters the uniform medium, and then declines deeply, triggered by runaway lateral expansion.

Spectral Analysis of the Flare of 1998 November 11 based on the Multi-cloud Model

We have obtained 2D spectra of Ha and CaII λ8542A for the flare of 1998 November 11, and derived its 2D velocity field and integrated intensity field. The velocity distribution shows that the red-shift and blue-shift velocities lie respectively in the northern and southern parts of the flare and that the maximum velocity seems to be located in two footpoints of the flare loop system. The integrated intensity distribution shows that the CaIIλ8542A line is formed at a lower height than the Ha line, we used ’multi-cloud model’ (MCM) to obtain four parameters for the two lines (Doppler width, △λD, Doppler shift, △λ0, line source function, S, and optical depth at the line center, TO). We also estimated the column number densities of hydrogen at the second level, N2, and of the ionized calcium at the third level, N3, as well as the kinetic temperature, Tc. The wide Hα profile at the loop top may be explained by an overlapping of two or more elementary profiles. It is shown that the uncertainty in calibration does not affect the derived Doppler shift and line broadening, only the source function and optical depth.

A New 2MASS／2df Selected Sample of Pairs of Galaxies and Calibration of Merging Rate in the Local Universe

We present a new sample of 37 close major-merger galaxy pairs, selected from the 2-degree field redshift survey of the two-micron all-sky survey (2MASS) galaxies. The selection criteria for our near-infrared pairs are more closely related to galaxy mass (a very important parameter in galaxy evolution models) than those for optical selected samples. Our sample benefits enormously from the high homogeneity and accuracy of the 2MASS database, and false matchings are minimized by the essentially three-dimensional selection procedure. Taking into account the biases, we find that 1.96 (±0.4)% of galaxies are in close major-merger pairs. This indicates a local merging rate of 1.0%, in good agreement with the results in recent studies of optical selected pairs in the local universe. The results derived with our sample have high confidence.

Determination of the Thickness of Non-Edge-on Disk Galaxies

We propose a method to determine the thickness of non-edge-on disk galaxies from their observed structure of spiral arms, based on the solution of the truly three-dimensional Poisson's equation for a logarithmic disturbance of density and under the condition where the self-consistency of the density wave theory is no longer valid. From their measured number of arms, pitch angle and location of the innermost point of the spiral arms, we derive and present the thicknesses of 34 spiral galaxies.

R－Process Nucleosynthesis and Galactic Chemical Evolution of the Ba Peak Elements

Nucleosynthesis yield is a very important parameter of the Galactic chemical evolution model. We adopt the same method as Tsufimoto to derive the r-process yields of various mass SNe Ⅱ at low metallicities from the new observed [Ba/Fe]-[Fe/H] trend. Fhrthermore, we present a new formula of r-process nucleosynthesis yields. We also consider the various neutron sources and set up four cases, namely A, B, C and D to calculate the abundance evolution of Ba peak elements in the solar neighbourhood. Our results show that the r-process could be associated with a secondary event in massive stars (i.e., 18 M⊙ < M < 50 M⊙). Therefore, the r-process could be associated with a secondary event in massive stars. Both the neutron source and the seed nuclei must be freshly manufactured by the stars instead of depending upon the initial metallicity abundance.

Ellerman Bombs, Type Ⅱ White-light Flares and Magnetic Reconnection in the Solar Lower Atmosphere

Ellerman bombs and Type Ⅱ white-light flares share many common features despite the large energy gap between them. Both are considered to result from local heating in the solar lower atmosphere. This paper presents numerical simulations of magnetic reconnection occurring in such a deep atmosphere, with the aim to account for the common features of the two phenomena. Our numerical results manifest the following two typical characteristics of the assumed reconnection process: (1) magnetic reconnection saturates in -600-900 s, which is just the lifetime of the two phenomena; (2) ionization in the upper chromosphere consumes quite a large part of the energy released through reconnection, making the heating effect most significant in the lower chromosphere. The application of the reconnection model to the two phenomena is discussed in detail.

Spin Evolution of Neutron Stars in OB/X-ray Binaries

We have investigated the relation between the orbital period Porb and the spin period Ps of neutron stars in OB/X-ray binaries.By simulating the timedevelopment of the mass loss rate and radius expansion of a 20M(◎)donor star,we have calculated the detailed spin evolution of the neutron star before steady wind accretion occurs(that is,when the break spin period is reached),or when the OB star begins evolving off the main sequence or has filled its Roche lobe.Our results are compatible with the observations of OB/X-ray binaries.We find that in relatively narrow systems with orbital periods less than tens of days,neutron stars with initial magnetic field B0 stronger than about 3 × 1012 G can reach the break spin period to allow steady wind accretion in the main sequence time,whereas neutron stars with B0 ＜ 3 × 1012 G and/or in wide systems would still be in one of the pulsar,rapid rotator or propeller phases when the companion evolves off the main sequence or fills its Roche lobe.Our results may help understand the various characteristics of the observed OB/neutron star binaries along with their distributions in the Ps -Porb diagram.

Chromospheric Internetwork Oscillations at Various Locations of the Quiet Sun

We analyze oscillation behaviours in chromospheric internetwork regions using spectral observations of the CⅡ1334A line obtained with the Solar Ultraviolet Measurements of Emitted Radiation spectrograph (SUMER) aboard Solar and Heliospheric Obse rvatory (SOHO). Three areas, 26 × 120arcsec2 each,at the various latitudes from the disk center to the north polar coronal hole, were rastered with a cadence of about 40-60 s in the solar minimum year. We obtained the time evolution of two-dimensional (2D) line intensity, continuum and line core shift. The continuum and the line shift show ～3 min chromospheric oscillations in the internetwork regions underlying the coronal hole as well as at the disk center. We find that the CⅡ1334A line shift oscillates with an average speed of ～1.7 km s-1, independent of the latitude, while its coherent scale decreases with latitude. On the other hand, the oscillation amplitude of the continuum around the 1334A and the phase delay between the Doppler shift and continuum slightly increase with latitude.

A Large Glitch in the Crab Pulsar

Using a new pulsar timing system at the 25-m radio telescope of Urumqi Astronomical Observatory, we have detected a large glitch in the Crab pulsar which occurred in 2000 July. The size of the gfitch is Av/v ～ 2.4 × 10-8, with a rela tive increment in frequency derivative Av/v ～ 5 × 10-3. The observing system is introduced and the observed properties of the glitch are discussed.

Two Sympathetic Homologous CMEs on 2002 May 22

Sympathetic coronal mass ejections (CMEs) usually occur in different active regions connected by interconnecting magnetic loops, while homologous CMEs occur within the same active region with an almost the same background magnetic field, and so are similar in shapes. Two sympathetic CMEs erupted within 3 hours on 2002 May 22, originating from the same active region, AR 9948. Their multi-wavelength data were collected and analyzed. It is suggested that emerging flux triggered the occurrence of the first CME and the corresponding flare, the reconnection inflow of which in turn triggered the eruption of the second CME.Based on the fact that the two sympathetic CMEs have many similarities, in their shapes, their low-lying dimming areas, etc., we tentatively propose, for the first time, the phenomenon of sympathetic homologous CMEs.

Magnetic Field Strengths and Structures from Radio Observations of Solar Active Regions

Radio observations of some active regions (ARs) obtained with theNobeyama radioheliograph at λ=1.76 cm are used for estimating the magnetic fieldstrength in the upper chromosphere, based on thermal bremsstrahlung. The resultsare compared with the magnetic field strength in the photosphere from observa-tions with the Solar Magnetic Field Telescope (SMFT) at Huairou Solar ObservingStation of Beijing Astronomical Observatory. The difference in the magnetic fieldstrength between the two layers seems reasonable. The solar radio maps of active re-gions obtained with the Nobeyama radioheliograph, both in total intensity (I-map)and in circular polarizations (V-map), are compared with the optical magnetogramsobtained with the SMFT. The comparison between the radio map in circular polar-ization and the longitudinal photospheric magnetogram of a plage region suggeststhat the radio map in circular polarization is a kind of magnetogram of the upperchromosphere. The comparison of the radio map in total intensity with the photo-spheric vector magnetogram of an AR shows that the radio map in total intensitygives indications of magnetic loops in the corona, thus we have a method of definingthe coronal magnetic structure from the radio I-maps at λ=1.76 cm. Analysingthe I-maps, we identified three components: (a) a compact bright source; (b) a nar-row elongated structure connecting two main magnetic islands of opposite polarities(observed in both the optical and radio magnetograms); (c) a wide, diffuse, weakcomponent that corresponds to a wide structure in the solar active region whichshows in most cases an S or a reversed S contour, which is probably due to thedifferential rotation of the Sun. The last two components suggest coronal loopson different spatial scales above the neutral line of the longitudinal photosphericmagnetic field.

The Influence of Ion-Acoustic Turbulence on the Electron Acceleration in the Reconnecting Current Sheet

Through solving the single electron equation of motion and the FokkerPlanck equation including the terms of electric field strength and ion-acoustic turbulence, we study the influence of the ion-acoustic wave on the electron acceleration in turbulent reconnecting current sheets. It is shown that the ion-acoustic turbulence which causes plasma heating rather than particle acceleration should be considered. With typical parameter values, the acceleration time scale is around the order of 10-6 s, the accelerated electrons may have approximately a power-law distribution in the energy range 20 ～ 100 keV and the spectral index is about 3～10, which is basically consistent with the observed hard X-ray spectra in solar flares.

南天自行计划的进展和精度

TheYale／SanJuan南天自行计划（SouthernProperMotionProgram）简称SPM。SPM是美国里克（Lick）天文台北天自行计划（NPM）在南天的延伸。根据SPM计划，最终在南天相对暗的星系测定出大约一百万颗天体的绝对自行、位置、星等和颜色。SPM最初目的是研究银河系结构。现在SPM计划的目的已扩大了许多，其中包括建立一个暗的二级恒星参考系（secondaryreferencesystemofstars）；实现和Hipparcos自行系统以及河外参考架的连接。本文根据SPM扩展了的研究目的，着重介绍SPM计划研究的领域、进展和精度。

An Analysis of Average Pulsar Profiles and A Study of the ρ-P relation of Pulsars

Using the method of Gaussian Fit Separation of Average Profile (GFSAP), we re-examine the average profiles of nine pulsars at several frequencies,ranging from 408-1642 MHz. This method enables us to obtain the number of components for each pulsar, and the parameters for each component, the width, position and amplitude. The ρ-P relation for the inner cone and outer cone are studied separately, and the results are, respectively, ρ = p-0.51±0.05 and ρ = p-0.42±0.06. The results can be interpreted as a confirmation of the double-cone structure of pulsar emission beams. The altitudes of emission region, and the radius-to-frequency-map(RFM) are also examined; for the outer cone, we obtained r(y) ∝ v-0.19±0.09.