首届东亚VLBI国际研讨会(2008年3月20-22日,上海)

2008年3月20-22日,东亚VLBI研讨会(East Asia VLBI Workshop)在中国科学院上海天文台召开.共76位代表注册参加了会议,他们分别来自澳大利亚(1人)、韩国(10人)、日本(19人)和中国(46人).     

海量星表融合系统（XMaS_VO）的设计与开发

将不同波段的星表、特别是巡天项目产生的大型星表进行交叉证认,一直是进行多波段天文学研究,尤其是数据挖掘、统计分析研究的瓶颈.本文开发和实现了一个不依赖于特定数据库的海量星表融合系统(简称为XMaS_VO),用户能够方便地使用此系统的服务进行星表的上传及自动入库、交叉证认等工作.此外,XMaS_VO具备可移植性,如果用户需要进行很大数量的或者大型星表的交叉证认服务,可以自己建立数据库,方便地将此工具移植到自己的服务器上,自己使用或者开放服务给他人.随着该系统的进一步发展和应用.天文学家将可以轻松自如地获得他们需要的多波段融合数据,自由地选取参数和匹配的结果.从而可以更加有效地从事海量数据处理和分析工作.     

压强梯度与前身星模型Ws15M⊙超新星爆发

针对前身星模型Ws15M⊙,采用程序WLYW89数值模拟了超新星瞬时爆发过程;数值结果表明,在不增大压强的前提下,适当调节坍缩和反弹阶段的压强梯度,超新星瞬时爆发是可以获得成功的.在有限的引力释放能量的情况下,压强梯度的调整增加了对流传能机制,可以缩短瞬时爆发所用的时间,提高爆发能量,使得瞬时强爆炸能够成功.     

一种扩大FAST视场的方法

所有的大口径射电望远镜都存在这样一个问题：在其分辨率和灵敏度提高的同时，视场变小．而且口径越大，视场越小．这成为大口径望远镜不可回避的矛盾．要解决这个矛盾，可以在望远镜的焦平面上放置Ⅳ个分立馈源．让它们同时工作，这样可以看作把视场扩大了Ⅳ倍．望远镜的工作效率提高Ⅳ倍．但是这样做的缺点是——视场不连续．且馈源数目Ⅳ受到望远镜焦比(F／D)的限制．采用致密焦面阵(dense focal plane array)就可以很好地解决这个问题．致密焦面阵的单元不是喇叭口天线，而是无方向性的Vivaldi天线(Vivaldi antenna)．要把Vivaldi阵列应用到望远镜上，需要对单个Vivaldi天线和Vivaldi阵列的电性能有清楚的认识，并能根据需要来设计照明方向图．还要知道大望远镜的焦面上电磁场的分布情况，借此判断能否应用Vivaldi阵列，以及给出Vivaldi单元的分路赋权网络．主要给出了FAST的焦面场的分布情况．并说明应用Vivaldi阵列的可能性．     

作者须知

1摘要中文摘要每篇论文前应附有对文章内容准确概括而不加注释或评论的简要陈述,其内容应包括:研究目的、方法、结果和结论.摘要一般应写成报道性文摘,也可写成报道/指示性文摘.一般不用图、表、化学结构式和非公用的符号或述语,也不宜引用正文中的图、表、公式.摘要采用第三人称的写法,不使用"本文"、"作者"等作为主语.中文摘要的篇幅一般以200字左右为宜.     

热亚矮星的研究进展

热亚矮星以其独特的性质受到人们日益关注.它们是年老椭圆星系中良好的紫外源,系统地研究热亚矮星的观测特征和形成机制可以帮助我们理解恒星演化、椭圆星系中"紫外超"现象的起源和球状星团的动力学演化.热亚矮星的形成模型主要包括单星模型和双星模型.双星模型包含三种渠道:公共包层抛射渠道、稳定的洛希瓣物质交流渠道和双氦白矮星并合渠道.该文系统地总结了热亚矮星的观测特征,并简要介绍了它们的形成机制.     

云南天文台1m红外望远镜的主镜热力学分析

云南天文台1m红外太阳望远镜是多功能、多波段的太阳望远镜,望远镜使用过程中主镜的热变形直接关系这系统的光学精度,建立光学系统的光机热结合的分析方法,可以直观的得到热辐射对光学系统的影响结果,使得望远镜的设计阶段就能评估热变形对系统的精度影响,确定光学元件是否满足要求.     

制冷HEMT低噪声放大器偏置电源的研制

高电子迁移率晶体管(HEMT)目前被广泛应用于高灵敏度(低噪声)射电天文接收机中. 在低温制冷环境下,其低噪声性能更佳,但对偏置供电系统要求很高,只有在特定的偏置条件下才能得到最佳的低噪声、高增益、高稳定性.本文提供了一套可调试、高稳定、高可靠性、带远程监控功能的可供多级低温制冷HEMT管的偏置电源的设计思路、方法和制作,使在低温制冷状态下的HEMT管能够稳定、安全、可靠地工作在最佳状态.     

Interacting system NGC 7805/6 (Arp 112) and its tidal dwarf galaxy candidate

We present results from our Giant Metrewave Radio Telescope(GMRT)HⅠ,Himalayan Chandra Telescope(HCT)Hα,1 m Sampurnanand Telescope(ST)and 1.3 m Devasthal Fast Optical Telescope(DFOT)deep optical observations of the NGC 7805/6(Arp 112)system to test KUG 2359+311’s tidal dwarf galaxy(TDG)candidacy and explore the properties of the interacting system.Our GMRT HⅠmap shows no HⅠdetection associated with KUG 2359+311,nor any HⅠtail or bridge-like structure connecting KUG 2359+311 to the NGC 7805/6 system.Our HCT Hαimage,on the other hand,displays strong detections in KUG 2359+311,with net SFR0.035±0.009 M_⊙yr^-1.The Hαdata constrain the redshift of KUG 2359+311 to 0.00≤z≤0.043,compared to the redshift of NGC 7806 of0.015.TDGs detected to date have all been HⅠrich,and displayed HⅠ,ionised gas and stellar tidal debris trails(bridges or tails)linking them to their parent systems.However,neither our HⅠdata nor our optical imaging,while three magnitudes deeper than SDSS,reveals a tidal trail connecting KUG 2359+311 to NGC 7805/6.Lack of HⅠ,presence of an old stellar population,ongoing star formation and reasonably high SFR compared to normal dwarf galaxies suggest that KUG 2359+311 may not be an Arp 112 TDG.It is most likely a case of a regular gas-rich dwarf galaxy undergoing a morphological transformation after having lost its entire gas content to an interaction with the Arp 112 system.Redshift and metallicity from future spectroscopic observations of KUG 2359+311 would help clarify the nature of this enigmatic structure.     

历法发展的一种模式

历法从起源到发展成熟完善的过程,首先是建立纪日制度,进而确立规范的纪月法,最后完成的才是纪年法.从3个少数民族历法发展的形态看,这种历法发展进程的模式,虽不能断言都必然如此,但至少这是一种发展模式.     

Radar signal delay in the Dvali-Gabadadze-Porrati gravity in the vicinity of the Sun

In this paper we examine the recently introduced Dvali-Gabadadze-Porrati (DGP) gravity model. We use a space-time metric in which the local gravitation source dominates the metric over the contributions from the cosmological flow. Anticipating ideal possible solar system effects, we derive expressions for the signal time delays in the vicinity of the Sun. and for various ranges of the angle θ of the signal approach, The time contribution due to DGP correction to the metric is found to be proportional to b ^3/2/c ² r ₀. For r ₀ equal to 5 Mpc and θ in the range [−π/3,π/3], Δt is equal to 0.0001233 ps. This delay is extremely small to be measured by today’s technology but it could be probably measurable by future experiments.     

On the generation of low-frequency waves in the solar wind in the front of the bow shock

The generation of low-frequency waves in the solar wind by the flux of protons accelerated in the magnetosheath is considered. It is shown that pulsations are produced in two partly overlapping frequency ranges. The growth rate of waves is maximal when the angle θ between the direction of the interplanetary magnetic field and the front of the bow shock is not equal $\text{π}\text{2}$. The dependence of the increment of perturbation on the solar wind velocity is analysed. A satisfactory agreement between theory and experimental results on the connection of Pc3–4 properties and parameters of the solar wind is obtained.     

Photographs of the Sun in the XUV-region

X-ray photographs obtained with a zone plate camera on October 3, 1967 in the wavelength band 49.5–52.5 Å have been investigated photometrically.The most intense X-ray emission corresponds with active regions in H and Ca ii. About one quarter of the total solar flux is emitted by the three brightest X-ray sources (A, E and J). X-ray emission from quiet regions is also observed. Limb brightening is found, also at the poles, which indicates a higher electron density at the poles than during solar minimum.The brightest X-ray regions have a very small core of the order of 20. No relation to magnetic field strengths of sunspots has been found. However, a correlation with active prominences cannot be ruled out. X-ray source A is related either to prominence activity or to flare activity. One X-ray region (J) is probably related to flare activity.Assuming an electron temperature of 3 × 10⁶K to 5 × 10⁶K for coronal active regions an emission measure of a few times 10⁴⁹ cm^–3 is derived, which yields an electron density of a few times 10¹⁰ cm^–3.     

On the abundance of chlorine in the Sun

A low-noise photoelectric scan which includes the predicted position of the Cli transition 4s ⁴ P _5/2-4 _p ⁴ D ⁰ _7/2 provides inconclusive evidence for the presence of the line in the solar photospheric spectrum. An upper limit logN(Cl) 5.5 is derived. It is pointed out that the fundamental vibration rotation band of HC1 at 3.3 should be detectable in the sunspot spectrum unless logN(Cl) < 4.6. Sunspot spectra may also provide the isotopic abundance ratio N(Cl³⁵)/N(Cl³⁷).A new derivation of the chlorine abundance for the Orion nebula is presented: logN(Cl) 5.8. It is suggested that a cosmic abundance logN(Cl) = 5.5 to 5.8 be adopted.Operated by the Association of Universities for Research in Astronomy Inc., under contract with the National Science Foundation.     

Enrichment in volatiles in the giant planets of the Solar System

We propose an interpretation of the enrichments in volatiles observed in the four giant planets with respect to the solar abundance. It is based on the assumption that volatiles were trapped in the form of solid clathrate hydrates and incorporated in planetesimals embedded in the feeding zones of each of the four giant planets. The mass of trapped volatiles is then held constant with time. The mass of hydrogen and of not trapped gaseous species continuously decreased with time until the formation of the planet was completed, resulting in an increase in the ratio of the mass of trapped volatiles to the mass of hydrogen (Gautier et al., Astrophys. J. 550 (2001) L227). The efficiency of the clathration depends upon the amount of ice available in the early feeding zone. The quasi-uniform enrichment in Ar, Kr, Xe, C, N, and S observed in Jupiter is reproduced because all volatiles were trapped. The non-uniform enrichment observed in C, N and S in Saturn is due to the fact that CH₄, NH₃, and H₂S were trapped but not CO and N₂. The non-uniform enrichment in C, N and S in Uranus and Neptune results from the trapping of CH₄, CO, NH₃ and H₂S, while N₂ was not trapped. Our scenario permits us to interpret the strongly oversolar sulfur abundance inferred by various modelers to be present in Saturn, Uranus and Neptune for reproducing the microwave spectra of the three planets. Abundances of Ar, Kr and Xe in these three are also predicted. Only Xe is expected to be substantially oversolar. The large enrichment in oxygen in Neptune with respect to the solar abundance, calculated by Lodders and Fegley (Icarus 112 (1994) 368) from the detection of CO in the upper troposphere of the planet, is consistent with the trapping of volatiles by clathration. The upper limit of CO in Uranus does not exclude that this process also occurred in Uranus.     

On the Abundance of Holmium in the sun

The abundance of holmium (Z=67) in the Sun remains uncertain. The photospheric abundance, based on lines of Hoii, has been reported as + 0.26±0.16 (on the usual scale where log(H) = 12.00), while the meteoritic value is + 0.51±0.02. Cowan-code calculations have been undertaken to improve the partition function for this ion by including important contributions from unobserved levels arising from the (4f ¹¹6p+4f ¹⁰(5d+6s)²) group. Based on 6994 computed energy levels, the partition function for Hoii is 67.41 for a temperature of 6000 K. This is 1.5 times larger than the value derived from the 49 published levels. The new partition function alone leads to an increase in the solar abundance of Ho to log (Ho) =+ 0.43. This is within 0.08 dex of the meteoritic abundance. Support for this result has been obtained through LTE spectrum synthesis calculations of a previously unidentified weak line at 3416.38. Attributing the feature to Hoii, the observations may be fitted with log (Ho) =+ 0.53. This calculation assumes log (gf)=0.25 and is uncertain by at least 0.1 dex.     

The Ushnus in the astronomy of the Inca culture

Inferences are made about the relationship that existed between the Ushnus, pyramid-shaped, terraced structures used by the Incas in the most important ceremonies of the Tawantinsuyo, and Inka Astronomy. We draw attention to Ayni, Kawsaypacha, Duality, and Tinkuy principles, multidimensional codes of conduct and wisdom that are at the root of the Andean cosmovision and on their perception of the world and the Cosmos. These principles, examined as postulates, allow to elaborate axiomatic propositions to identify the Ushnus with ancient Astronomy practices. In a complementary statement, starting from a bi-conditional proposition, we may infer through reciprocal corollaries that the Inka earliest roots to a holistic learning and educational ambient in the Tawantinsuyo was not elitist, instead it was based on a epistemological construct that differs from the corresponding Western educational ambients. An epistemological and cognitive approach allows to identify an ancient elaborate process of knowledge construction, based on the four fundamental principles, corresponding to different levels of assimilation and comprehension. As a complementary aspect, we identify some of the most preserved Ushnus of the Inka “Empire.” Then we complement this contribution with a broader interpretation for the Ushnus.     

Some regularities in the variation of the Balmer line profiles in the P Cyg spectrum

In the Coudé focus of the 2 m RCC telescope at the National Astronomical Observatory of the Bulgarian Academy of Science 47 spectrograms covering the range from 3500 to 4900 Å (about 1400 Å) with a reciprocal dispersion of 9 Å mm^–1 and a spectral resolution of 0.18 Å were obtained. The photometric and position behaviour of Balmer lines were investigated over a long time-scale, i.e. March 1981 to August 1982.The hydrogen line profiles were rectified in the way discribed by de Groot (1969). It is found that the absorption consists of three and sometimes four components. Their position behaviour may be expalined by the existence of two kinds of shells: pulsating and steadily expanding, and it is quite possible that shells of the first type may become shells of the second type in the outer parts of the P Cyg envelope.The total emission and absorption equivalent widths of the H11, H9, and H lines change with conspicuous minima and maxima. The amplitude of these variations increases with decrease in the upper quantum number. For example,W _tot ^abs change by about 38% for H and 22% for H9.Our data suggest a periodic change in the radial velocities, intensity of each separate absorption component, total equivalent widths and profiles.     

Role of anisotropy of the initial particle distribution in the acceleration in collapsing solar-flare traps

We consider the behavior of charged particles with an anisotropic initial velocity distribution in a magnetic trap with approaching mirrors in connection with the problem of particle acceleration in solar flares. We show that, irrespective of the charge sign, the efficiency of confinement and acceleration increases with increasing anisotropy factor of the initial distribution α = (T_⊥/T_∥)^1/2. For a positive electric potential of the trap plasma relative to the mirrors, the emerging additional effect of ion expulsion form the trap increases with α_i. The derived estimate of the electric potential suggests an amplification of the initial perturbation and the development of instability.     

On the origin of the solar system and the exceptional position of the Sun in the Galaxy

The solar system's position in the Galaxy is an exclusive one, since the Sun is close to the corotation circle, which is the place where the angular velocity of the galactic differential rotation is equal to that of density waves displaying as spiral arms. Each galaxy contains only one corotation circle; therefore, it is an exceptional place. In the Galaxy, the deviation of the Sun from the corotation is very small — it is equal to ΔR/R _⊙≈0.03, where ΔR=R _c ?R _⊙,R _c is the corotation distance from the galactic center andR _⊙ is the Sun's distance from the galactic center. The special conditions of the Sun's position in the Galaxy explain the origin of the fundamental cosmogony timescalesT ₁≈4.6×10⁹ yr,T ₂?10⁸ yr,T ₃?10⁶ yr detected by the radioactive decay of various nuclides. The timescaleT ₁ (the solar system's ‘lifetime’) is the protosolar cloud lifetime in a space between the galactic spiral arms. The timescaleT ₂ is the presolar cloud lifetime in a spiral arm.T ₃ is a timescale of hydrodynamical processes of a cloud-wave interaction. The possibility of the natural explanation of the cosmogony timescales by the unified process (on condition that the Sun is near the state of corotation) can become an argument in favour of the fact that the nearness to the corotation is necessary for the formation of systems similar to the Solar system. If the special position of the Sun is not incidental, then the corotation circles of our Galaxy, as well as those of other galaxies, are just regions where situations similar to ours are likely to be found.