行星状星云NGC 2242的红外辐射

被Zwicky等人列为星系的NGC 2242,后来刘继英等人发现它具有发射特征并认为可能是行星状星云。前原英夫等人用有缝光谱肯定了它是一个行星状星云。我们证认它是IRAS06304+4448。根据IRAS Point Source Catalog所提供的25μm和60μm的辐射流量,我们得到了这一行星状星云的尘埃温度T_d=130K,光学厚度τ_(25μm)=1.98×10~(-7)和尘埃的总质量M_d=1.0×10~(-7)到1.8×10~(-6)M_⊙之间。     

狐狸座哑铃星云——M27

狐狸座哑铃星云—Ｍ２７在全天的行星状星云中,狐狸座哑铃星云无疑是最美丽的一个,它列于梅西耶星团星云星表的第２７位,故又称为Ｍ２７星云。在行星状星云中它并不是最大的,也不是最亮的。由于较大的行星状星云均比较暗,而最明亮的行星状星云又很小,因此狐狸座的哑...     

星云中的行星？——行星状星云研究新进展

最近,罗切斯特大学的天文学家宣布了他们关于行星状星云的研究新进展,结果显示,围绕星云中心恒星公转的伴星甚至是大质量行星,可能对那些星云奇特外貌及物质组分的成因至关重要。     

行星状星云测距的研究现状

行星状星云是研究恒星演化、星际介质与星系化学形成历史与演化等问题的重要探针。距离是行星状星云的基本物理参数,对研究其大小、光度、电离质量、形成率、空间密度和在银河系内的分布等性质至关重要。河内行星状星云距离的研究已有几十年历史,但其测距结果的准确性普遍偏低,仅有31颗距离的不确定度在20%内。概述了行星状星云测距的9种主要方法,即:三角视差法、星团成员法、膨胀视差法、分光视差法、红化方法、Na D线吸收法、中心重力法、统计方法、运动学方法。着重介绍运动学测距法,用于测量受银道面上消光严重或没有可观测中心星但射电较明亮的行星状星云距离,为将来进一步的测距工作提供参考。     

恒星死亡之前的精采亮相——行星状星云的风采

“哈勃”给我们带来的惊喜行星状星云是银河系中一种数量较多、外形美丽的气体星云。１８世纪末期,英国著名的天文学家威廉·赫歇尔首先发现了这类天体,并把它们命名为行星状星云。后来,随着大望远镜的相继问世,人们陆陆续续又发现了许多行星状星云,并且通过观测和研...     

正在蒸发的原行星盘

在茧状星云深处,年轻恒星坍缩并有行星形成。天文学家在托洛洛山4米望远镜拍摄的高分辨率的船底星云图像中现已发现12个这样的茧状星云,天文学上称它们为原行星盘。船底星云是第二个发现含有原行星盘的星云。另一个是由夏威夷的凯克望远镜和哈勃空间望远镜拍摄的猎户星云。     

揭开行星状星云形状之谜

在宇宙深处,有一类天体最鲜艳夺目、最能惹人遐思,那就是分布在深邃星空里绚丽多姿的星云。它们色彩艳丽、变幻莫测,或如舒卷的彩云,或如铺开的壮锦,强烈冲击着我们的视觉,尽显神奇大自然的魅力。行星状星云是星云大家族最负盛名的成员,它们都有完整和谐的外形,却又有着超乎想象的千姿百态,似乎隐藏着某种秘不可知的奥秘,无愧为大自然最令人惊叹的神来之笔。自1779年英国天文学家威廉·赫歇尔发现第一个行星状星云(M57)以来,它们就一直吸引着天文学家好奇的眼睛。     

行星状星云的形状与环绕的伴星有关

有迹象表明,实际上所有的中、高金属度恒星都环绕着某种东西。天文学家是通过观察恒星膨胀的气体遗迹得出这一推论的。以色列海法大学索科尔认为一颗濒死恒星在经历红巨星阶段后抛射的行星状星云的形状揭示了它的轨道伴星的大小和本原。 行星状星云是宇宙中最漂亮的     

双极行星状星云形成的Monte—Carlo分析

在行星状星云形成过程中双星起着非常重要的作用,本文采用Ｍｏｎｔｅ－Ｃａｒｌｏ方法,研究了双星演化过程在行星状星云形成中的作用,研究了不同的双星质量比分布、恒星初始－终止质量关系,星族参数、公共包层的理论模型等对结果的影响。     

行星形成方式的探讨

行星形成的方式,目前主要有两种见解:一种认为,行星是星子集聚而成,另一种认为,行星是由星云物质经过势井聚集为原行星而形成。笔者认为,角动量守恒定律,是认识太阳系起源和行星、卫星形成方式的重要钥匙。某一行星区的星云物质绕太阳转动的角动量总和(A_c)减去该区今日行星轨道角动量(A_p)应当等于该区行星自转角动量(A_r),即A_c-A_p=△A=A_r。但计算结果,A_c-A_p=△A>A_r。这就证明,行星是经过星云环形成的。文中计算了星云环内外边界的位置,即星云环的宽度,并提出一些新的看法,可能为行星形成方式的研究提供一些有益的线索。     

Nonsteady objects associated with star-forming regions. Relationship to stellar associations, infrared sources, and water masers

The relationship of stellar associations, IRAS point sources, and water masers with two types of objects, which were discovered primarily at Byurakan, is investigated. They are cometary nebulae and Herbig-Haro (H-H) objects. It is shown that almost all of these objects are affiliated with OB or T associations. Two groupings of nonsteady objects have been found. They may belong to unknown T associations. About half of the cometary nebulae and H-H objects were found to be affiliated with IRAS point sources; 22% of the H-H objects and 8% of the cometary nebulae are associated with water masers. Translated from Astrofizika, Vol. 41. No. 4, pp. 585–598, October–December, 1998.     

Planetary Nebulae

This review summarizes spectroscopic and imaging results obtained on board the Infrared Space Observatory (ISO) on well-known planetary nebulae: the young nebula NGC 7027, and two fully evolved nearby nebulae, the Dumbbell and the Helix. This revised version was published online in August 2006 with corrections to the Cover Date.     

Far infrared emission from three new planetary nebulae

As dust emission in the far infrared (FIR) is a characteristic property of planetary nebulae we searched the Infrared Astronomical Satellite (IRAS) point-source catalogue for confirmatory evidence on the two new possible planetary nebulae S 68 and 248 - 5 identified by Fesen, Gull & Heckathorn (1983) and the high-excitation planetary nebula 76 + 36 detected by Sanduleak (1983). We identify the nebulae 248 - 5 and 76 + 36 with IRAS sources 07404 - 3240 and 17125 + 4919, respectively and have determined their dust temperature, total FIR emission and optical depth. We also set a lower limit ranging in value from 1.2 × 10^-6 to 3.7 × 10^-5 forM _dust /M _bd of the nebula 248 - 5 depending on whether its grain material is silicate or graphite. S 68 could not be identified with an IRAS source.     

The compact nebulae cn1 and cn2, coupled to infrared stellar clusters

This is a study of the compact nebulae cn1 and cn2 situated in the extended, bright nebula S235. ¹²CO observations reveal the presence of blue and red outflows (i.e., a bipolar outflow) from the molecular cloud in which these nebulae are embedded. cn1 and cn2 are shown to be coupled to IR clusters of young stars, some of which have dust disks or envelopes (these are so-called young stellar objects, YSOs), with the YSOs grouped around the center of the clusters. cn1 is coupled to the infrared point source IRAS05377 + 3548, whose IR colors are close to those of T Tau stars. A chain of objects emerging from S235 (which clearly implies they are coupled in terms of evolution) is studied. These are the compact nebulae S235 A, B, and C, and the Herbig-Haro objects GGD5 and GGD6. A group of IR stars associated with GGD6 is also studied.     

The Magnetic Field Effect on Planetary Nebulae

In our previous work on the 3-dimensional dynamical structure of planetary nebulae the effect of magnetic field was not considered. Recently Jordan et al. have directly detected magnetic fields in the central stars of some planetary nebulae. This discovery supports the hypothesis that the non-spherical shape of most planetary nebulae is caused by magnetic fields in AGB stars. In this study we focus on the role of initially weak toroidal magnetic fields embedded in a stellar wind in altering the shape of the PN. We found that magnetic pressure is probably influential on the observed shape of most PNe.     

The Relative Sizes of Planetary Nebulae

The sizes of planetary nebulae are poorly known, principally because the distances to these sources are not very well established. We point out in the following, however, that if one is careful in selecting nebulae having particular ranges of galactic latitude, and narrow ranges of surface brightness, then it should be possible to establish mean trends in nebular diameter. We have, in this way, been able to determine that where brightness temperatures are the same, then circular and elliptical sources, and the nuclei of bipolar nebulae (BPNe) all have closely similar mean dimensions. It is also likely that circular and elliptical sources have closely similar masses (the case of the BPNe is less clear). Finally, we note that halos are typically ∼3 times larger than circular and elliptical PNe, and the lobes of BPNe are ∼5 times as large, making the latter envelopes the largest of all nebular structures. This revised version was published online in July 2006 with corrections to the Cover Date.     

Far-infrared emission from ring nebulae

Ring nebulae are known to form around stars like the Wolf-Rayet and the Of stars. The dust in these nebulae is heated by the central star and, therefore, provides a positive clue to the origin of the nebulae, complementing the optical techniques. A systematic search has been carried out to study the infra-red emission from these nebulae based on the IRAS data. The influence of the local interstellar material properties on the formation of nebular dust is studied.     

Statistical and Physical Study of One-Sided Planetary Nebulae

We have investigated the spatial orientation of one-sided Planetary Nebulae. Most of them if not all are interacting with the interstellar medium. Seventy percent of the nebulae in our sample have inclination angles larger than 45^° to the galactic plane and 30% of the inclination angles are less than 45^°. Most of the selected objects are old, evolved planetary nebulae with large dimensions, and not far away from the galactic plane. Seventy-five percent of the objects are within 160 pc from the galactic plane. The enhanced concavity arc can be explained physically as a result of the `planetary nebulae – interstellar matter' interaction. We have discussed the possible effect of the interstellar magnetic field in the concavity regions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Chemical Evolution of the System of Galactic Planetary Nebulae

The problem of the chemical evolution of the system of Galactic planetary nebulae, starting with the early stage of development of the Galaxy, is investigated. The radial and vertical gradients of C, N, O, Ne, Ar, Cl, and S abundances are determined for different ages of the precursor stars of the nebulae. A statistically significant age dependence of the gradients is derived.     

Pulsar Wind Nebulae in Egret Error Boxes

A remarkable number of pulsar wind nebulae (PWN) are coincident with EGRET γ-ray sources. X-ray and radio imaging studies of unidentified EGRET sources have resulted in the discovery of at least six new pulsar wind nebulae (PWN). Stationary PWN (SPWN) appear to be associated with steady EGRET sources with hard spectra, typical for γ-ray pulsars. Their toroidal morphologies can help determine the geometry of the pulsar which is useful for constraining models of pulsed γ-ray emission. Rapidly moving PWN (RPWN) with more cometary morphologies seem to be associated with variable EGRET sources in regions where the ambient medium is dense compared to what is typical for the ISM.