光深对大质量恒星形成团块化学性质研究的影响

本文使用文献中的N₂H⁺(1-0)、H¹³CO⁺(1-0)、HCN(1-0)和HN¹³C(1-0)谱线数据研究大质量恒星形成团块的化学性质和演化,发现H¹³CO⁺和HN¹³C的丰度受H₂柱密度的影响. 由于从A阶段到B阶段这两个丰度的中值增加了近10倍,H¹³CO⁺和HN¹³C适合追踪大质量恒星形成团块的演化. 从A到B阶段四种分子丰度增长速度从高到低依次为H¹³CO⁺、HCN、HN¹³C、N₂H⁺. 结果表明进行光学薄分子谱线的高分辨率观测对于研究大质量恒星形成团块的化学演化是必要的.     

氢化富勒烯能否解释天文光谱中的21 μm辐射特征?

目前在天文环境中探测到了C₆₀、C₇₀、C₆₀⁺,极大地刺激了对星周包层中富勒烯衍生物的研究. 原行星状星云是富勒烯在天文环境下的可能形成源,其红外光谱中具有丰富的、还未能认证的特征谱带,其中在21 μm处的一条谱带尤为神秘. 当富勒烯被氢化,分子的对称性被破坏,能够激活新的红外振动谱,这有可能部分解释天文光谱中的红外谱带. 本文对氢化富勒烯的理论振动谱进行研究,考查了氢化富勒烯能否作为21 μm辐射的载体,详细讨论了各种支持和反对的证据,并且推测了可能贡献21 μm特征的氢化富勒烯的氢化程度.     

苯和苯胺在深紫外光照射下的电离和解离

本文利用自主研制的反射式飞行时间质谱仪结合177.3 nm深紫外激光研究了苯和苯胺分子的光电离与光解离过程. 质谱实验发现苯在177.3 nm皮秒激光作用下发生高效电离并观测到不对称C-C键解离形成的以C₄H₃⁺为主的较小碎片峰. 相比之下,苯胺的深紫外光电离中主要产生一个C₅H₆^+·离子自由基和一个较小丰度的C₆H₆^+·碎片,分别对应于CNH分子和NH自由基的去除. 结合第一性原理计算,诠释了苯和苯胺这两个仅有一个氨基差异的分子光解离路径,揭示苯和苯胺分子中氢原子转移对于C-C或C-N键断裂的关键重要作用.     

InGaAsP SBH激光器光束质量的非傍轴分析

计算了InGaAsPSBH激光器的TE₀₀模,并利用非傍轴矢量矩理论,分析了平行于p-n结方向上的光学质量因子M_y²在以往有关M²的计算中,往往忽略了包层中光场的贡献,因此得出M²小于1的结论当半导体激光器的激活层的尺寸远小于发射波长时,大部分光场将渗透到包层中,因此,包层的光场是不能忽略的考虑到激活层和包层中的光场对M²的影响,给出了非傍轴半导体激光M²的精确表达式结果表明,M_y大于1.     

甲基环己烷在9∽15.5 eV能量区的真空紫外光电离研究

利用具有同步辐射源的反射式飞行时间质谱仪,研究甲基环己烷的真空紫外光电离和光解离. 观测到母体离子C₇H₁₄⁺和碎片离子C₇H₁₃⁺,C₆H₁₁⁺,C₆H₁₀⁺,C₅H₁₀⁺,C₅H₉⁺,C₄H₈⁺,C₄H₇⁺和C₃H₅⁺的光电离效率曲线. 测定甲基环己烷的电离能为9.80±0.03 eV,通过光电离效率曲线确定其碎片离子的出现势. 在B3LYP/6-31G(d)水平上对过渡态、中间体和产物离子的优化结构进行表征,并使用G3B3方法计算其能量. 提出主要碎片离子的形成通道. 分子内氢迁移和碳开环是甲基环己烷裂解途径中最重要的过程.     

F−(H2O)+CH3I配体交换反应动力学

本文介绍F^?(H₂O)+CH₃I→[FCH₃I]^?+H₂O在交叉分子束碰撞能量0.3∽2.6 eV的配体交换动力学成像结果. 产物的动能受到弱键结合配合物的稳定性的影响,大量水分子的内部激发不利于中间物有效的能量重新分配,随着碰撞增加,低动能受到抑制. 在0.3 eV时,内部亲核取代非常重要,为形成I^?和I^?(H₂O)的竞争性亲核取代途径提供了依据.     

二硫化碳分子在204 nm附近的光解离动力学研究：S(3PJ)+CS(X1Σ+)产物通道

本文用时间切片离子速度影像技术研究CS₂分子在204 nm附近的光解离动力学. 在201.36、203.10、204.85和206.61 nm这四个解离波长下,实验清楚地观测到S(³P_J)+CS(X¹Σ⁺)产物通道. 在实验获得的S(³P_J=2,1,0)影像中,对应的CS(X¹Σ⁺)产物的振动态结构得到了部分的分辨. 通过对影像的分析,还获得了解离的总平动能谱以及产物的各项异性参数. 实验观察到的相对小的各项异性参数表明产物更倾向于经历了间接的光解离过程. 这一通道的自旋－轨道禁阻特征也说明了非绝热效应在二硫化碳紫外光解离生成S(³P_J=2,1,0)+CS(X¹Σ⁺)的过程中发挥了重要作用.     

环戊酮光电离解离的实验和理论研究

本文介绍了真空紫外光电离质谱结合理论计算研究环戊酮单分子的光电离解离过程. 在9.0∽15.5 eV能量范围内,测量了环戊酮离子及其碎片离子的光电离效率曲线. 通过光电离效率曲线,将环戊酮分子的电离能确定为9.23±0.03 eV,并确认碎片离子为：C₅H₇O⁺,C₄H₅O⁺,C₄H₈⁺,C₃H₃O⁺,C₄H₆⁺,C₂H₄O⁺,C₃H₆⁺,C₃H₅⁺,C₃H₄⁺,C₃H₃⁺,C₂H₅⁺, C₂H₄⁺. 利用量子化学计算方法,在ωB97X-D/6-31+G(d,p)理论水平基础上,提出了C₅H₈O⁺的解离机制. 通过对环戊酮解离路径的分析,发现开环和氢迁移过程为环戊酮离子解离的主要路径.     

OCS分子在里德堡F态的真空紫外光解动力学：S(3PJ=2,1,0)产物通道

本文利用可调谐真空紫外光源和时间切片离子速度成像技术研究了OCS分子的真空紫外光解动力学. 在对应OCS里德堡F态的五个光解波长下(133.26 nm∽139.96 nm)实验采集了S(³P_J=2,1,0)产物的离子影像,从中发现了两个解离通道：S(³P_J=2,1,0)+CO(X¹Σ⁺)和S(³P_J=2,1,0)+CO(A³π),其中前者为主要通道. 离子影像中CO产物的振动结构可部分分辨. 从离子影像中提取出了S(³P_J=2,1,0)+CO(X¹Σ⁺)通道的产物总平动能分布、各向异性参数和CO振动态分支比等信息. 发现了对应OCS在F态的几个低振动态下光解的产物各向异性参数取负值,而对应F态的几个高振动态下光解产物的各向异性参数为正值. 另外,同一光解波长下三种S产物S(³P₂)、S(³P₁)和S(³P₀)的各向异性参数也不相同. 经分析,这些现象可能来源于激发区域的其它不同对称性的电子态的贡献,从而导致解离过程中同时存在平行解离和垂直解离. 本工作有利于进一步理解OCS真空紫外光解中的非绝热耦合作用.     

中子星内部非奇异-奇异夸克物质的相变

研究了中子星内部从两味夸克物质到三味夸克物质的相变过程。发现这个过程的时标短至10^-7s,并且在相变中奇异夸克所参加的半轻子过程是中微子能量损失的主要过程。这样,1.4M_⊙质量的中子星内部的非奇异-奇异夸克物质相变会有几个10⁵¹erg的能量以中微子形式发射出去,这将表现为一种中微子爆现象。     

Maximum stellar iron core mass

An analytical method of estimating the mass of a stellar iron core, just prior to core collapse, is described in this paper. The method employed depends, in part, upon an estimate of the true relativistic mass increase experienced by electrons within a highly compressed iron core, just prior to core collapse, and is significantly different from a more typical Chandrasekhar mass limit approach. This technique produced a maximum stellar iron core mass value of 269 × 10³⁰ kg (1.35 solar masses). This mass value is very near to the typical mass values found for neutron stars in a recent survey of actual neutron star masses. Although slightly lower and higher neutron star masses may also be found, lower mass neutron stars are believed to be formed as a result of enhanced iron core compression due to the weight of non-ferrous matter overlying the iron cores within large stars. And, higher mass neutron stars are likely to be formed as a result of fallback or accretion of additional matter after an initial collapse event involving an iron core having a mass no greater than 2.69 × 10³⁰ kg     

太阳系的元素丰度分布与AGB星慢中子俘获元素

通过对AGB星演化模型的理论计算结果和51颗AGB星的观测丰度进行重新分析,发现任何AGB星与慢中子俘获过程(s过程)主要分量对应的重元素(简称SMH元素)丰度分布都与对应的太阳系s过程主要分量的元素丰度分布相似,这表明,任意AGB星SMH元素丰度分布的迭加结果与对应的太阳系s过程主要分量的元素丰度分布相似,由此得出结论:太阳系s过程主要分量的重元素丰度分布模式是一个典型的模式,可以作为标准用于单星重元素丰度的研究.     

OH/IR stars: Very long period variables with extreme mass loss rates on their nature and their distribution in the galaxy

Seldom are simple models sufficiently accurate to describe nature. The long period OH/IR stars with a well ordered, spherically symmetric, strong outflow of matter are such an exception. The variability of the central stars and the large dimension of the circumstellar dust shell enable a direct, geometrical determination of the distance to individual objects. Then most basic stellar quantities, such as mass, luminosity, mass loss rate, etc., may be derived. The values found indicate that OH/IR stars represent the last stage in the evolution of intermediate mass stars. In a relatively short ‘superwind’ phase a large fraction of the stellar mass is ejected and the objects are on the verge of becoming a planetary nebula or a white dwarf.The strength of the OH maser emission, and the accurate distance and velocity information, make the OH/IR stars particularly suited for the study of galactic structure. They are one of the few stellar populations that are detectable at large distances, even in the very centre of our Galaxy. The fact that they are found in the bulge of our Galaxy, seems to indicate that at least until recently (? 10⁹ years ago) star formation has been going on there.     

The origin of the strongest magnetic fields in dwarfs

White dwarfs have frozen in magnetic fields ranging from below the measurable limit of about 3×10³ to 10⁹ G. White dwarfs with surface magnetic fields in excess of 1 MG are found as isolated single stars and relatively more often in magnetic cataclysmic variables. Some 1253 white dwarfs with a detached low-mass main-sequence companion have been identified in the Sloan Digital Sky Survey (SDSS) but none of these shows sufficient evidence for Zeeman splitting of hydrogen lines for a magnetic field in excess of 1 MG. If such high magnetic fields in white dwarfs result from the isolated evolution of a single star then there should be the same fraction of high field white dwarfs among this SDSS binary sample as among single stars. Thus, we deduce that the origin of such high magnetic fields must be intimately tied to the formation of cataclysmic variables (CVs). The formation of a CV must involve orbital shrinkage from giant star to main-sequence star dimensions. It is believed that this shrinkage occurs as the low-mass companion and the white dwarf spiral together inside a common envelope. CVs emerge as very close but detached binary stars that are then brought together by magnetic braking or gravitational radiation. We propose that the smaller the orbital separation at the end of the common envelope phase, the stronger the magnetic field. The magnetic cataclysmic variables (MCVs) originate from those common envelope systems that almost merge. Those common envelope systems that do merge are the progenitors of the single high field white dwarfs. Thus all highly magnetic white dwarfs, be they single stars or the components of MCVs, have a binary origin. This accounts for the relative dearth of single white dwarfs with fields of 10⁴–10⁶ G. Such intermediate-field white dwarfs are found preferentially in cataclysmic variables. The bias towards higher masses for highly magnetic white dwarfs is expected if a fraction of these form when two degenerate cores merge in a common envelope. From the space density of single highly magnetic white dwarfs we estimate that about three times as many common envelope events lead to a merged core as to a cataclysmic variable.     

Future solar systems

Widely regarded as pathological variable stars – with erratic photometric and spectroscopic behavior of unknown physical origin – 20 years ago, T Tauri stars (TTSs) turned out in the last decade to be promising laboratories for observing the formation of solar systems such as ours. This is because circumstellar, presumably protoplanetary disks were found to surround a large fraction of them. While evidence for disks was primarily indirect until 1995, recent high resolution imaging confirmed earlier claims that the infrared (IR) and ultraviolet (UV) excesses seen in the spectral energy distribution (SED) of these stars were due to disk emission. The activity displayed by young stellar objects at all wavelengths is due to the interaction between the circumstellar disk and the magnetized star and to non-stationary accretion/ejection phenomena. In this review, we briefly summarize properties of these young solar-type stars and describe their circumstellar disks in some detail, focusing on current optical, infrared and millimeter high angular resolution observations that now allow us to resolve the disks.     

大质量恒星的形成:理论与观测

文章简要叙述了有关大质量恒星形成的理论以及相关观测证据。目前大质量恒星形成的理论主要有两种，即吸积说和并合说．吸积说认为，大质量星可能与小质量星形成于相似的过程；并合说主张大质量星可能是由小质量年轻星碰撞合并而成．解决这两种理论争论的关键在于在大质量星附近能否观测到吸积盘的存在，最新的观测表明大质量星更有可能是通过吸积增加自身的质量，但最终解决这一问题可能还需要更多的观测证据。文章还提出了一些本领域尚未解决的问题，为感兴趣的研究者提供参考。     

Les premières étoiles

The oldest stars of the Galaxy are quite different from common stars, like our Sun. Understanding why it is so, requires to open the question in a cosmological perspective. After the Big Bang, and for at least 300 000 years, the Universe was nearly uniform, and had a very simple chemical composition formed during the hot phase of the Big Bang: only hydrogen, helium and traces of other light elements, deuterium, ³ He, and ⁷ Li. This composition is known as “primordial”. At a later time, about one or two billion years after the Big Bang, condensations developped at all scales, the smallest ones being stars. The most massive stars, reaching very high temperatures at their center, transformed their initial composition by thermonuclear reactions, producing all common elements observed in the solar system, carbon, nitrogen, oxygen, etc. These elements were dispersed into the interstellar medium by mass-ejection at the final stage of evolution of these massive stars, and recycled by subsequent generations of stars. The first stars must have been formed with the primordial composition, whereas later generations had an increasing proportion of elements produced by stellar nucleosynthesis. Intensive searches of stars with no, or very little elements produced by stellar nucleosynthesis have been performed during the last 20 years. Actually more than 100 stars were discovered with a very low proportion of such elements, one thousandth of the proportion in the Sun (in which they amount to about 1.7% by mass), or less. But no star was found with less that 1/10,000 of the solar proportion. So no “primordial” star has been observed yet. The reason why is still an open question.     

Effect of binarity on the local stellar mass density

Summary Considering the existence of many unresolved binary systems among the stars used to derive the stellar luminosity function, we have estimated the increase in the total mass density in the solar neighbourhood. Such an increase depends on the fraction of stars which are unresolved binaries, but conservative estimates give a value larger than 0.004M _⊙ pc⁻³. Paper presented at the Congress ?Galactic and Extragalactic Dark Matter?, Roma, 28 to 30 June 1983.     

Phase transition to color-flavor-locked matter and condensation of Goldstone bosons in neutron star matter

Deconfinement phase transition and condensation of Goldstone bosons in neutron star matter are investigated in a chiral hadronic model (also referred as to the FST model) for the hadronic phase (HP) and in the color-flavor-locked (CFL) quark model for the deconfined quark phase. It is shown that the hadronic-CFL mixed phase (MP) exists in the center of neutron stars with a small bag constant, while the CFL quark matter cannot appear in neutron stars when a large bag constant is taken. Color superconductivity softens the equation of state (EOS) and decreases the maximum mass of neutron stars compared with the unpaired quark matter. The K⁰ condensation in the CFL phase has no remarkable contribution to the EOS and properties of neutron star matter. The EOS and the properties of neutron star matter are sensitive to the bag constant B, the strange quark mass m_s and the color superconducting gap Δ. Increasing B and m_s or decreasing Δ can stiffen the EOS which results in the larger maximum masses of neutron stars.     

Numerical solution of the radiative transfer equation in spherically symmetric dust shells

An efficient numerical method is presented for solving problems of radiative transfer in dust shells with spherical symmetry. The method can be applied to a wide variety of radiative transfer problems in planetary atmospheres, circumstellar dust envelopes and extended stellar atmospheres. The computational procedure and practical considerations for implementing the method are described in detail. As an illustration, the method is used to determine the grain temperature distribution and far i.r. emission from interstellar dust clouds associated with compact HII regions. Generalizations to problems involving cylindrical geometry and multi-temperature dust shells are discussed in the appendices.