A Detailed Study on the Equal Arrival Time Surface Effect in Gamma-Ray Burst Afterglows

Due to the relativistic motion of gamma-ray burst remnant and its deceleration in the circumburst medium, the equal arrival time surfaces at any moment are not spherical, rather, they are distorted ellipsoids. This will leave some imprints in the afterglows. We study the effect of equal arrival time surfaces numerically for various circumstances, i.e., isotropic fireballs, collimated jets, density jumps and energy injection events. For each case, a direct comparison is made between including and not including the effect. For isotropic fireballs and jets viewed on axis, the effect slightly hardens the spectra and postpones the peak time of the afterglows, but does not change the shapes of the spectra and light curves significantly. In the cases of a density jump or an energy injection, the effect smears out the variations in the afterglows markedly.     

太阳暗条活动的周期性研究

运用法国巴黎默东天文台记录的暗条目录资料构造了一个时间精度为每天的暗条数目序列,选用Scargle周期图和Morlet小波变换两种周期方法研究了这个序列的周期性,发现其存在4个显著的周期,它们分别是1557天、1141天、795天和367天,详细分析了这些周期的时变特征,并简单讨论了其中个别典型周期的相位、物理机制和相互关系．     

盘状星系的颜色星等关系

在Sloan数字巡天计划第二批释放的数据中选择了15257个面向的盘状星系,统计研究它们的颜色星等关系．结果表明3个颜色g-r、r-i、r-z均与r波段的绝对星等有紧密的相关关系,即:越亮的星系,颜色越红,而且色指数弥散越小．并且简单讨论了观测到的颜色星等关系对盘状星系的恒星形成历史的约束．     

The Multi-Wavelength Quasar Survey III. Quasars in Field 836

This is the third paper in a series connected with our Multiwavelength Quasar Survey. The survey is aimed to provide a quasar sample more complete than any previous survey by using a combined selection technique to reduce selection effects. We present the observational results for the X-ray candidates in field f836. We found 15 X-ray AGNs in this field of which eight are new discoveries. The X-ray data and optical spectra of these AGNs are given. We give the X-ray candidate selection criteria, which proved to be highly efficient in isolating X-ray AGNs.     

对孤立中子星1E1207.4-5209 X-射线回旋吸收线的理论分析

近来的观测表明,在射电宁静孤立中子星1E1207．4-5209的X-射线连续谱中存在几条等间隔的吸收线,能量分别为0．7、1．4和2．1keV．根据近年发展的四极近似下的量子回旋辐射理论,澄清了目前的一些疑问,肯定了它们是电子回旋吸收线,而不是质子回旋线．并从理论上确定了该中子星自转轴的空间取向．     

Short-Term Period Variation of Relative Sunspot Numbers

We use wavelet transform to analyze the daily relative sunspot number series over solar cycles 10-23. The characteristics of some of the periods shorter than ～ 600-day are discussed. The results exhibit not only the variation of some short periods in the 14 solar cy-cles but also the characteristics and differences around solar peaks and valley years. The short periodic components with larger amplitude such as ～27,～150 and ～360-day are obvious in some solar cycles,all of them are time-variable,also their lengths and amplitudes are vari-able and intermittent in time. The variable characteristics of the periods are rather different in different solar cycles.     

微波Ⅲ型爆发的观测特征

统计分析了国家天文台2．6-3．8 GHz高时间分辨率射电动态频谱仪在23周峰年期间(1998．4—2003．1)观测到的266个III型爆发．对这些事件的频率漂移、持续时间、偏振、带宽、开始和结束频率做了详细分析．开始和结束频率的统计分析表明,开始频率在一个非常大的范围,从小于2．6 GHz到大于3．8 GHz,而结束频率的截止区相对集中,从2．82-3．76 G．Hz．这些现象说明,电子加速的高度相当分散,在观测频率范围内具有正、负漂移率的III型爆发数基本相等,这可能意味着被加速的向上和向下传播的电子束在2．6—3．8 GHz范围有相同的比例．统计结果表明,微波III型爆发的辐射机制主要是等离子体辐射和电子回旋脉泽辐射过程．     

Velocity Space of Galactic O-B Stars

Based on the Hipparcos proper motions and available radial velocity data of O-B stars, we have re-examined the local kinematical structure of the young disk population of-1500 O-B stars not including the Gould-belt stars. A systematic warping motion of the stars about the direction to the Galactic center has been reconfirmed. A negative K-term implying a systematic contraction of stars in the solar vicinity has been detected. Two different distance scales are used in order to find out their impact on the kinematical parameters, and we conclude that the adopted distance scale plays an important role in characterizing the kinematical parameters at the present level of the measurement uncertainty.     

水产动物锌营养研究新进展

微量元素对水产动物的影响常常被忽略。早期对微量元素研究的重点限于渗透压调节及毒性[1]。微量元素可以说是目前鱼类营养研究需求当中最弱的一环,如Halver在1972年所编的《Fish Nutrition》一书就没有关于微量元素需求的章节[2]。日本学者在上世纪70年代才开始这方面的研究。1976年Nose首度系统地综述这方面的研究成果[3]。锌是目前微量元素在水产应用方面研究最多的一种。笔者就锌在水产动物养殖的应用研究进展进行综述,旨在为研制水产动物配合饲料和提高养殖效益提供参考资料。1锌的生物学作用锌是微量元素中生理功能最多的一种元素,…