Ⅱ型超新星爆发的一个计算模型——坍缩阶段

本文提出了一个质量为15M_⊙的Ⅱ型超新星爆发坍缩阶段的计算方案,并讨论了我们采用这一方案进行计算所得到的部分结果。在电子俘获率的计算中,我们考虑了逆反应和中子、质子质量差的影响,降低了坍缩过程中电子数密度的减少,使得在我们的结果中最大下落速度U_(max)和达到最大下落速度那一点的质量M_(max)都较大(分别为3.06×10~9厘米/秒和0.76M_⊙)。这两个量较大是有利于反弹后激波传出铁镍核引起Ⅱ型超新星爆发的。在我们的中微子传输模型中,在光学厚和光学薄阶段分别采用中微子渗漏模型和中微子平衡扩散模型,并采用灰大气模型讨论了中微子沉淀对坍缩的影响。计算结果表明,中微子沉淀对坍缩的影响很小,能量沉淀与中微子能损的比值不超过10~(-5),动量沉淀与引力加速度的比值不超过10~(-6)。     

中子星质量分布与诞生方式的研究

统计研究了63对双星系统中的72颗中子星(NS)的测量质量,其中包括18对X射线双星(XB)、9对双中子星(DNS)、4对中子星主序星系统(NSMS)、32对中子星白矮星系统(NSWD).运用Monte-Carlo随机抽样的方法,模拟出NS的质量分布,然后基于模拟结果进行统计分析.通过质量的统计研究,发现其质量呈双峰分布,分别集中在(1.328±0.220)M_⊙和(1.773±0.416)M_⊙.值得注意的是,在不考虑DNS的情况下,发现其质量分布仍然是双峰分布,质量集中在(1.360±0.337)M_⊙和(1.854±0.322)M_⊙.18颗DNS质量为单峰分布,平均质量为(1.330±0.0089)M_⊙.NS质量的双峰结构显示出,其可能有两种诞生方式.认为可能是铁核塌缩超新星爆发和电子俘获超新星爆发.DNS质量的单峰结构意味着DNS诞生演化机制可能与其他双星系统不同.为了进一步研究中子星质量分布的特性,将53颗测量到自旋周期的NS在20 ms处分为两组,分别为毫秒中子星(MSP,Ps≤20 ms)和正常中子星(PSR,Ps20 ms),发现这两类NS质量也都呈现出双峰分布,而且MSP的平均质量要比PSR的平均质量大～0.22 M_⊙.这表明NS在诞生后吸积约0.22 M_⊙的物质时,将可能成为MSP.根据NS质量与周期在M-Ps图上的分布,拟合出质量与周期之间的关系为:M=1.4+(Ps/ms)~(-3/2)M_⊙.     

新前身星模型对超新星爆发的影响

采用2002年Woosley给出的前身星模型,使用"WZYWS9"程序数值模拟了质量为11-40M⊙的Ⅱ型超新星的爆发过程.计算结果显示新模型对Ⅱ型超新星塌缩、激波传播及爆发都有不同程度的影响.此外,还讨论了激波初始能量的定义.     

高能中微子天文学简介─—兼谈中微子应用

高能中微子天文学简介─—兼谈中微子应用许梅随着人们对中微子的许多性质与运动、变化规律日益加深的了解，以及更多中微子探测装置的建立，可以预见中微子天文学在２１世纪初将会有较大的发展。恒星（包括太阳）内部、超新星爆发过程、星系（包括银河系）核心、类星体以...     

Ⅱ型超新星爆发物理机制的研究概况

本文是一篇关于Ⅱ型超新星爆发物理机制研究情况的综述文章,现阶段Ⅱ型超新星爆发物理机制的研究是在计算机模拟计算的基础上进行的,在Ⅱ型超新星爆发的模拟计算中,要涉及到很多物理问题,对于不同的计算模型中对这些问题的不同的处理方法,本文都尽可能地予以介绍,另外,对于这一领域中现在还存在着的问题和可能的解决问题的途径,本文也做了一些讨论。     

双中子星质量分布的统计研究

通过对12对双中子星(DNS)系统进行质量分布统计,得到其质量加权平均值为(1.339±0.042)M_⊙,其中主星和伴星的质量加权平均值分别为(1.439±0.036)M_⊙和(1.239±0.020)M_⊙.主星平均质量比伴星平均质量高,表明主星可能通过吸积获得质量,或者主星的前身星的质量更大.据此可以分析大质量恒星通过超新星爆发形成中子星的物理过程.此外还发现,DNS的总质量集中在一个比较狭小的范围(2.5–2.8 M_⊙),这说明DNS的质量形成受到伴星的影响.经过进一步的分析注意到DNS的质量比接近于1(略大于1),这可能暗示DNS系统的前身星质量比较相近.通过分析12对DNS在中子星的磁场强度-自旋周期关系图(B-P_s图)中的分布,发现DNS主星磁场强度约10~(10)Gs,自转周期约50 ms;PSR J1906+0746和PSR J0737-3039B处在正常脉冲星序列,磁场强度约10~(12)Gs,这说明两者没有吸积加速过程.     

超新星坍缩与中微子泄漏

本文用简化的中微子泄漏模式代替输运方程，计算超新星坍缩过程中的中微子变化，通过调节模式中的参数可改变中微子的俘陷密度，使之达到较为合适的值，还讨论了在中微子俘陷密度到达之前，特定密度区段（10~(-10)－5×10~(11)g／cm~3）内使电子俘获率有显著变化的一种参数方法及研究结果。     

超新星坍缩与中微子泄漏

本用简化的中微子泄漏模式代替输运方程，计算超新星坍缩过程中的中微子变化。通过调节模式中的能数可改变中微子的俘陷密度使之达到较为合适的值，还讨论了在中微子俘陷密度到达之前，特定密度区段（１０＾１０－５×１０＾１１ｇ／ｃｍ＾３）内使电子俘获率有显变化的一种参数方法及研究结果。     

“冰立方”发现宇宙线各向异性分布

虽然仍然在建造中,但位于南极的冰立方中微子天文台已经开始产出科学结果,其中就包括了它本未设计来研究的新现象。“冰立方”是用来探测难以捉摸但却极具科学价值的中微子的。它所专注的是穿过地球的高能中微子,这些中微子携带了在北半球天空中可见的超新星爆发或者和黑洞等高能事件有关的信息。     

激变食变星Ⅲ.AC Cancri

AC Cnc是周期为7~h13~m的类新星食变星。由于AC Cnc是双谱食双星,而且具有较对称的食,所以在对激变食变星的系统研究中,我们选择了该双星来进行观测。本文利用拟合光变曲线的方法对AC Cnc进行了测光解分析、并得到轨道倾角i=74.5°±0.8°,白矮星质量M_1=0.74±0.07M_⊙,晚型星质量M_2=0.97±0.08M_⊙。AC Cnc中吸积盘的径向温度分布可以近似地表示为T(r)∝r~(-0.5),吸积盘边缘温度为7600K。晚型星向白矮星的质量转移率大约为7×10~(-9)M_⊙yr~(-1)。AC Cnc的距离近似地等于500±100pc。     

A thermodynamic model of high temperature lava vaporization on Io

We modified the MAGMA chemical equilibrium code developed by Fegley and Cameron (1987, Earth Planet. Sci. Lett. 82, 207-222) and used it to model vaporization of high temperature silicate lavas on Io. The MAGMA code computes chemical equilibria in a melt, between melt and its equilibrium vapor, and in the gas phase. The good agreement of MAGMA code results with experimental data and with other computer codes is demonstrated. The temperature-dependent pressure and composition of vapor in equilibrium with lava is calculated from 1700 to 2400 K for 109 different silicate lavas in the ONaKFeSiMgCaAlTi system. Results for five lavas (tholeiitic basalt, alkali basalt, Barberton komatiite, dunite, and a molten type B1 Ca, Al-rich inclusion) are discussed in detail. The effects of continuous fractional vaporization on chemistry of these lavas and their equilibrium vapor are presented. The predicted abundances (relative to Na) of K, Fe, Si, Al, Ca, and Ti in the vapor equilibrated with lavas at 1900 K are lower than published upper limits for Io's atmosphere (which do not include Mg). We predict evaporative loss of alkalis, Fe, and Si during volcanic eruptions. Sodium is more volatile than K, and the Na/K ratio in the gas is decreased by fractional vaporization. This process can match Io's atmospheric Na/K ratio of 10±3 reported by Brown (2001, Icarus 151, 190-195). Silicon monoxide is an abundant species in the vapor above lavas. Spectroscopic searches are recommended for SiO at IR and mm wavelengths. Reactions of metallic vapors with S- and Cl-bearing volcanic gases may form other unusual gases including MgCl₂, MgS, MgCl, FeCl₂, FeS, FeCl, and SiS.     

Instructions for authors

正Research in Astronomy and Astrophysics publishes original research papers and reviews 011 all liranchcs of astronoiriy and astrophysics.Reviews arc by invitation only.Important new results that require rapid publication can be submitted as a Letter(Letters must be restricted in length     

Instructions for authors

正Research in Astronomy and Astrophysics publishes original research papers and reviews on all branches of astronomy and astrophysics.Reviews are by invitation only.Important new results that require rapid publication can be submitted as a Letter(Letters must be restricted in length to 6 printed pages).Authors who submit a paper are expected to be able to certify that the paper is original work,     

Research in Astronomy and Astrophysics CONTENTS

正~~     

Alkali and halogen chemistry in volcanic gases on Io

We use chemical equilibrium calculations to model the speciation of alkalis and halogens in volcanic gases emitted on Io. The calculations cover wide temperature (500-2000 K) and pressure (10⁻⁶ to 10⁺¹ bars) ranges, which overlap the nominal conditions at Pele (T=1760 K, P=0.01 bars). About 230 compounds of 11 elements (O, S, Li, Na, K, Rb, Cs, F, Cl, Br, I) are considered. The elemental abundances for O, S, Na, K, and Cl are based upon observations. CI chondritic elemental abundances relative to sulfur are used for the other alkalis and halogens (as yet unobserved on Io). We predict the major alkali species in Pele-like volcanic gases and the percentage distribution of each alkali are LiCl (73%), LiF (27%); NaCl (81%), Na (16%), NaF (3%); KCl (91%), K (5%), KF (4%); RbCl (93%), Rb (4%), RbF (3%); CsCl (92%), CsF (6%), Cs (2%). Likewise the major halogen species and the percentage distribution of each halogen are NaF (88%), KF (10%), LiF (2%); NaCl (89%), KCl (11%); NaBr (89%), KBr (10%), Br (1%); NaI (61%), I (30%), KI (9%). We predict the major halogen condensates and their condensation temperatures at P=0.01 bar are NaF (1115 K), LiF (970 K); NaCl (1050 K), KCl (950 K); KBr (750 K), RbBr (730 K), CsBr (645 K); and solid I₂ (200 K). We also model disequilibrium chemistry of the alkalis and halogens in the volcanic plume. Based on this work and our prior modeling for Na, K, and Cl in a volcanic plume, we predict the major loss processes for the alkali halide gases are photolysis and/or condensation onto grains. Their estimated photochemical lifetimes range from a few minutes for alkali iodides to a few hours for alkali fluorides. Condensation is apparently the only loss process for elemental iodine. On the basis of elemental abundances and photochemical lifetimes, we recommend searching for gaseous KCl, NaF, LiF, LiCl, RbF, RbCl, CsF, and CsCl around volcanic vents during eruptions. Based on abundance considerations and observations of brown dwarfs we also recommend a search of Io's extended atmosphere and the Io plasma torus for neutral and ionized Li, Cs, Rb, and F.     

Study on the Stressed Mirror Polishing with a Continuous Polishing Machine for Large Aperture Off-axis Aspheric Mirrors

A special stressed annular polishing technique is proposed to mill the off-axis aspheric sub-mirrors of a large segmented mirror with an annular polishing machine. Based on the basic principle of stressed annular polishing technique, a set of special stressing mechanisms are designed to convert milling the aspheric surfaces of sub-mirrors with different off-axis distances into milling the spherical surfaces with identical radii of curvature, so that they can be pol- ished simultaneously on a continuous polishing machine. It took about contin- uous 40 hours to polish a scaled-down mirror of the planning Chinese Future Giant Telescope (CFGT) using this technique. This mirror has the 330 mm di- ameter, 3.6 m off-axis distance, and the 21.6 m radius of curvature, and its max- imum asphericity is 16 micron. The experiment shows that this method has a high effciency, suits batch manufacturing, especially the batch manufacturing of aspheric sub-mirrors of the segmented primary mirror of an extremely large aperture telescope.     

Born–Infeld type phantom model in the ω–ω′ plane

In this paper, we investigate the dynamics of Born–Infeld (B–I) phantom model in the ω–ω′ plane, which is defined by the equation of state parameter for the dark energy and its derivative with respect to N (the logarithm of the scale factor a). We find the scalar field equation of motion in ω–ω′ plane, and show mathematically the property of attractor solutions which correspond to ω _φ ∼−1, Ω _φ =1, which avoid the “Big rip” problem and meets the current observations well.      

A Comparison of Several Image Locating Algorithms in Astronomical Instruments

In astronomical observations at optical wavelengths, a fast image tracking system can be adopted to reduce the effects of the atmospheric seeing and telescopic tracking error, and therefore improve the observing efficiency. Aiming at the need of astronomical observations, totally 5 kinds of algorithms in two categories were selected to make a comparative study on their accuracies and stabilities under different noise conditions by both numerical experiment and laboratory test. The results indicate that the normalized cross-correlation method and barycenter method have not only a higher accuracy but also a better reliability against interferences, they will be applied to the high-resolution spectrograph of the Xinglong 2.16 m telescope and the scienti?c instruments of the SONG (Stellar Observations Network Group) project, respectively.