短周期彗星表面水冰升华分布研究

彗星是太阳系遗留的原始星子,研究彗星彗核的演化对理解太阳系其他天体的形成和演化历史具有重要意义.在太阳的辐射作用下,彗星携带的挥发性成分会发生升华,并带动尘埃运动,造成彗核物质的损失.因此,彗核的升华活动对其表面形貌甚至整体形状演化都会产生影响.从IAU (International Astronomical Union) MPC (Minor Planet Center)获取轨道数据,并考虑了彗核的自转以及进动,利用MONET (Mass lossdriven shape evolution model)形状演化模型对短周期彗星做数值模拟,计算得到了短周期彗星1P/Halley、9P/Tempel 1、 19P/Borrelly、 67P/C-G (Churyumov-Gerasimenko)、 81P/Wild 2和103P/Hartley 2在一个轨道周期内的太阳辐射能量以及表面侵蚀深度的分布,结合其动力学参数讨论了自转、进动和公转等特性对其表面水冰升华分布的影响以及造成南北侵蚀差异的可能性.     

彗木相撞的可压缩分层流体模型

提出一个彗木相撞的修正了的线性模型．在这个模型中,将木星大气视为一个转动的、分层的、可压缩和无粘滞的流体层．结果表明,虽然大部分撞击能量仍然转换成内波能量,但不能忽视可压缩效应．     

彗星动力学研究综述

彗星是太阳系中天文学的重要研究对象．它涉及到天体物理、化学、天体力学等多种领域。近年的研究表明,彗星可能是揭开太阳系起源和演化之谜的突破口,还可能与生命的起源有关．本文旨在对彗星动力学的发展情况作一简单的回顾和评述．     

用心看星，感受“鹿林彗星”——记星云天文社观星活动

2008年2月28日,昆明三中、昆明滇池中学星云天文社的40来名天文爱好者,坐车前往东川红土地,观察鹿林彗星。     

彗星等离子体某些特征的讨论

本文讨论了彗星中尘埃粒子的充电机制 ,带电特性和平衡电势的变化规律 ,分析了彗星尘埃的破碎特性和临界半径 ,得出了很有意义的结果     

类水星系外行星偏振特性研究

通过对不可分辨水星偏振相位曲线的研究了解类水星不可分辨系外行星的偏振特性,为用偏振探测手段寻找类水星系外行星提供有力的依据.通过贝叶斯非线性拟合得到水星测光相位曲线和偏振相位曲线,进而得到不可分辨水星的偏振相位曲线.从该曲线中得出以下结果: (1)水星在不可分辨情况下在可见光波段其偏振度的量级为10-12;(2)垂直于散射平面和平行于散射平面的最大偏振度相当,且它们所对应的相位角相对于可分辨情况下发生了明显的改变;(3)在相位角大于158°时不可分辨水星的偏振度几乎为零.     

彗星动态榜

最新发现 2007年11月里发现并命名了5颗新彗星,其中有一颗是重新发现的周期彗星。     

离子彗星的稳定性

介绍了彗星等离子体的结构和稳定性的研究情况，着重于离子彗尾，更着重于介绍在这方面国内的工作。     

我与鹿林的擦肩之旅

在2009年的春季来一次星空之旅的想法是去年冬季成立昆明三中、滇池中学天文社时最初的心愿。等到来年2月份开学时,天之旅的天文大佬苏老师终于传来消息,将联合我校天文社,组织一次东川红土地观测彗星之旅。     

Hale-Bopp彗星自转轴指向的确定

根据上海天文台1．56米望远镜提供的Hale-Bopp彗星近核观测资料,利用两种不同的方法对该彗星的自转轴指向进行了测定．两种方法求出的自转轴指向结果非常接近,Hale-Bopp彗星自转轴指向点的赤经为0h14m32s,赤纬为-49°09′35″(2000年历元)．     

A Disconnection Event of Comet Lulin†

The cometary disconnection event (DE) is the separation of the entire cometary tail or a part of it from the cometary head. It is one of the most spectacular phenomena of comets. The driving mechanism remains unclear, and at present there are many competitive theories to explain the onset of DE. However, the variable solar wind is suspected to play a major role. Comet Lulin exhibited a DE on 4th Feb. 2009. The data around this date are analyzed, and it is found that the comet Lulin had already endured a DE on 3rd Feb. 2009. By comparing the morphologies of the plasma tails in these two DEs, it is concluded that the DE which occurred on 3rd Feb. 2009 is another DE, which is distinct from that of 4th Feb. 2009. In this paper, we describe the results of analysis on the DE dated 3rd Feb. 2009. The measured velocity of disconnection motion is about 68 km/s, and the calculated onset time of this DE is 3.635 ± 0.215 Feb. 2009 in UT decimal date. Combining the orbital characteristics of Comet Lulin before and after the DE occurrence and the solar-wind data measured by the STEREO-A spacecraft, it is concluded that the DE which occurred on 3rd Feb. 2009 was probably caused by the magnetic reconnection due to the interaction between the comet and a coronal mass ejection (CME).     

On the origin of HNC in Comet Lee

We have modelled the chemistry occurring in the coma of Comet Lee and have critically evaluated the possible routes leading to HNC. We show that the observed levels of HNC cannot be produced by ion–molecule chemistry, or by reactions of energetic H atoms with HCN. Rather, it appears that HNC is injected into the coma following the photodestruction of an unknown precursor. We discuss the possible nature of the parent of HNC and conclude that photofragmentation of large HCN polymers, such as polyaminocyanomethylene (PACM), is responsible. The degradation of hydrogen cyanide polymers may constitute a common source of HNC in comets, accounting for HNC/HCN ratios in the range measured in Lee and Hyakutake (≈ 0.06–0.12). The high HNC/HCN ratio measured in Hale–Bopp (≈0.2) and its heliocentric variation may, however, require an additional source.     

Organic synthesis in the coma of Comet Hale–Bopp?

Several organic molecules have now been detected in the coma of Hale–Bopp. These species may either emanate from the nucleus, or, as has been suggested by Bockelée–Morvan et al., could be synthesized in the coma. We have modelled the gas phase chemistry which occurred in the coma of Hale–Bopp, concentrating on the observed organic molecules HCOOH, HCOOCH₃, HC₃N and CH₃CN. We find that gas phase chemical reactions are unable to synthesize the observed abundances of these molecules, so all these species are most probably present in the nuclear ice. We briefly discuss the implications of this result for the connection between cometary and interstellar ices.     

Orbit of Comet C/1857 D1 (d'Arrest)

Comet C/ 1857 D1 (d'Arrest) is one of a large number of comets with parabolic orbits. Given that there are sufficient observations of the comet, 299 in right ascension and 279 in declination, it proves possible to calculate a better orbit. The calculations are based on a 12th order predictor‐corrector method. The comet's orbit is highly elliptical, e = 0.99982 and, from calculated mean errors, statistically different from a parabola. The comet will not return for at least 44000 years and thus represents no immediate NEO threat (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The 'silent world' of Comet 15P/Finlay

Comet 15P/Finlay is unusual in that, contrary to ab initio expectations, it demonstrates no apparent linkage to any known meteor shower. Using data contained within the Electronic Atlas of Dynamical Evolutions of Short-Period Comets, we evaluate theoretical shower radiants for Comet 15P/Finlay, but find no evidence to link it to any meteoric anomalies in recorded antiquity. This result, however, must be tempered by the fact that any Comet 15P/Finlay-derived meteoroids will have a low, 16 km s⁻¹, encounter velocity with Earth's atmosphere. Typically, therefore, one would expect mostly faint meteors to be produced during an encounter with a Comet 15P/Finlay-derived meteoroid stream. We have conducted a D -criterion survey of meteoroid orbits derived from three southern hemisphere meteor radar surveys conducted during the 1960s, and again we find no evidence for any Comet 15P/Finlay-related activity. Numerical calculations following the orbital evolution of hypothetical meteoroids ejected from the comet, at each perihelion epoch since 1886, indicate that Jovian perturbations effectively 'drive' the meteoroids to orbits with nodal points beyond the Earth's orbit. The numerical calculations indicate that, even if Comet 15P/Finlay had been a copious emitter of meteoroids during the past 100 years, virtually none of them would have evolved into orbits capable of being sampled by the Earth. There are good observational data, however, to suggest that Comet 15P/Finlay is becoming a transitional comet–asteroid object, and that it has probably not been an efficient producer of meteoroids during the past several hundreds of years.     

Evolution of Comet Nucleus Rotation

The secular evolution of comet nucleus rotation states subject to outgassing torques is studied. The dynamical model assumes that the nucleus inertia ellipsoid is axially symmetric. The outgassing torques acting on the surface are modeled using standard cometary activity formulae. The general rotational equations of motion are derived and separately averaged over the fast rotational dynamics terms and the comet orbit. Special cases where the averaging assumptions cannot be applied are evaluated separately. The modification of the comet orbit due to comet outgassing is neglected. Resulting from this analysis is a system of secular differential equations that describes the dynamics of the comet nucleus angular momentum and rotation state. We find that the qualitative secular evolution of the rotation state is controlled by a single parameter that combines parameters related to the comet orbit and parameters related to the nucleus surface geometry and activity. From this solution, we find qualitatively different evolutionary paths for comet nuclei whose entire surface is active, as compared to nuclei with only a single active region. For surface activity models between these extremes, we show that certain evolutionary paths are more likely than others. Additionally, our solution indicates that a comet nucleus' rotational angular momentum will tend to increase over time, potentially contributing to the observed phenomenon of comet nucleus splitting.     

Follow‐up observations of Comet 17P/Holmes after its extreme outburst in brightness end of October 2007

We present follow‐up observations of comet 17/P Holmes after its extreme outburst in brightness, which occurred end of October 2007. We obtained 58 V‐band images of the comet between October 2007 and February 2008, using the Cassegrain‐Teleskop‐Kamera (CTK) at the University Observatory Jena. We present precise astrometry of the comet, which yields its most recent Keplerian orbital elements. Furthermore, we show that the comet's coma expands quite linearly with a velocity of about 1650 km/s between October and December 2007. The photometric monitoring of comet 17/P Holmes shows that its photometric activity level decreased by about 5.9 mag within 105 days after its outburst (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

New measures of the orientation of the linear structure in the sunward hemisphere of the coma of Comet 19P/Borrelly: apparitions of 1994, 2001, and 2008

The sky‐projected orientation (position angle) of the axis (line of maximum density or maximum brightness) of the long time‐known, linear structure (LS) in the sunward hemisphere of the coma of Comet 19P/Borrelly is measured on 45 photographs taken by different observers under different projection conditions and covering three consecutive apparitions (1994, 2001, and 2008) for a total time interval of 5174 days. The analysis of the results by a tomographic approach yields an LS axis constantly oriented towards a fixed point in the space, at Right Ascension 214°.4 ± 0°.5 and Declination –7°.0 ± 0°.5 (J2000), corresponding to an obliquity of 103°.5 ± 1° and an orbital longitude of 147°.2 ± 1°, throughout the relevant interval. Such coordinates are close to the ones found by other authors for the spatial orientation of the nucleus spin axis during the apparitions of 1994 and 2001. In the hypothesis of an LS orientation aligned with the nucleus spin axis, the new results confirm the previous ones and show that this orientation remained unchanged during the subsequent 2008 apparition (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)