排序方式: 共有66条查询结果,搜索用时 46 毫秒
31.
徐兰平 《中国天文和天体物理学报》1987,(1)
利用暗星云L134的光学观测及分子谱线观测的结果,估算了它的某些基本物理参数,讨论了该星云的稳定性及能量问题。 发现在L134的演化过程中,热压力及转动在制约其自引力坍缩中起一定作用,但不是重要因素,而磁场的支撑作用可能是比较重要的,L134不是在自由下落时间尺度t_(ff)上引力坍缩,而可能是在一个比较长的双极扩散时间尺度t_D上收缩。 本文还计算了L134的冷却率及加热率,表明引力克服热压力作功不是暗星云L134的有效加热源;宇宙线是L134的一个加热源,它能提供所需能量的~20%;磁场通过双极扩散释放能量可能为L134提供了一个重要的加热源。 相似文献
32.
N. G. Kantharia W. M. Goss D. Anish Roshi Niruj R. Mohan Francois Viallefond 《Journal of Astrophysics and Astronomy》2007,28(1):41-53
We report multi-frequency radio continuum and hydrogen radio recombination line observations of HII regions near l = 24.8°, b = 0.1° using the Giant Metrewave Radio Telescope (GMRT) at 1.28 GHz (n = 172), 0.61 GHz (n = 220) and the Very Large Array (VLA) at 1.42 GHz (n = 166). The region consists of a large number of resolved HII regions and a few compact HII regions as seen in our continuum
maps, many of which have associated infrared (IR) point sources. The largest HII region at l = 24.83° and b = 0.1° is a few arcmins in size and has a shell-type morphology. It is a massive HII region enclosing ∼550 M⊙ with a linear size of 7 pc and an rms electron density of ∼110 cm−3 at a kinematic distance of 6 kpc. The required ionization can be provided by a single star of spectral type O5.5.
We also report detection of hydrogen recombination lines from the HII region at l = 24.83° and b = 0.1° at all observed frequencies near V
lsr
= 100 km s−1. We model the observed integrated line flux density as arising in the diffuse HII region and find that the best fitting model
has an electron density comparable to that derived from the continuum. We also report detection of hydrogen recombination
lines from two other HII regions in the field. 相似文献
33.
Ed Churchwell 《Astronomy and Astrophysics Review》1990,2(2):79-123
Summary Ultracompact (UC)HII regions are manifestations of newly formed massive stars that are still embedded in their natal molecular cloud. They are among the brightest and most luminous single objects in the Galaxy at far infrared and radio wavelengths. Recent high spatial resolution studies, particularly at radio wavelengths, have greatly contributed to our understanding of these dynamic objects and the impact they have on their environment. A summary is given of our current understanding of the physical properties, morphologies, dynamics, number and distribution in the Galaxy, and molecular environments of UCHII regions. Recent models of the circumnebular dust imply that the graphite/silicate abundance ratio is about half that of dust in the diffuse interstellar medium. The dust cocoons are large, cool, and optically thick shortward of a few microns. There are apparently between 1700 and 3000 UCHII regions in the Galaxy. This represents 10–20% of the total O star population. There are too many UCHII regions (just counting those studied with the VLA) to be consistent with the short dynamical lifetimes of this very compact stage of evolution. Both the morphologies and the large number can be understood if UC HII regions are bow shocks. Models of stellar wind supported bow shocks are discussed and consequences for the dynamics and morphologies of the ionized and molecular gas are explored. 相似文献
34.
We report the first detection of molecular hydrogen emission in the vicinity of a Wolf-Rayet star and nebula. The spatial distribution of the excited molecular gas is filamentary and is not correlated with the distribution of the ionised gas as traced by optical emission lines. The typical H2 surface brightness in the filaments is 5× 10–5 ergs s–1 cm–2 str–1. We demonstrate that the excitation mechanism can be shocks or fluorescence from the strong ultraviolet flux of the WR star. 相似文献
35.
Virginia Trimble 《Astronomy and Astrophysics Review》1991,3(1):1-46
Summary The basic scheme of nucleosynthesis (building of heavy elements from light ones) has held up very well since it was first proposed more than 30 years ago by E.M. Burbidge, G.R. Burbidge, A.G.W. Cameron, W.A. Fowler, and F. Hoyle. Significant advances in the intervening years include (a) observations of elemental and a few isotopic ratios in many more extrasolar-system sites, including metal-poor dwarf irregular galaxies, where very little has happened, and supernovae and their remnants, where a great deal has happened, (b) recognition of the early universe as good for making all the elements up to helium, (c) resolution of heavy element burning in stars into separate carbon, neon, oxygen, and silicon burning, with fine tuning of the resulting abundances by explosive nucleosynthesis in outgoing supernova shock waves, (d) clarification of the role of Type I supernovae, (e) concordance between elements produced in short-lived and long-lived stars with those that increased quickly and slowly over the history of the galaxy, and (f) calibration of calculations of the evolution and explosion of massive stars against the detailed observations of SN 1987A. The discussion presupposes a reader (a) with some prior knowledge of astronomy at the level of recognizing what is meant by an A star and an AGB star and (b) with at least a mild interest in how we got to where we currently are. 相似文献
36.
《New Astronomy》2022
Recently, a nitrogen iceberg was proposed as a possible origin for the first interstellar object, 1I/2017 U1, also known as ‘Oumuamua. Here, we show that the mass budget in exo-Pluto planets necessary to explain the detection of ‘Oumuamua as a nitrogen iceberg chipped off from a planetary surface requires a mass of heavy elements exceeding the total quantity locked in stars with 95% confidence, making the scenario untenable because only a small fraction of the mass in stars ends in exo-Plutos. 相似文献
37.
本文作者通过对猎户座KL区的观测、分析与计算,阐明CH3CN分子转动谱线系作为分子云核与恒星形成区探针的可能性和优越性.并对观测该线系所需要的仪器条件进行了讨论. 相似文献
38.
本文在“OH/IR脉泽源的空间分布和光度函数”一文的基础上,对其所用的127个已有光学或红外证认的OH脉泽源的空间运动特性进行了分析,找到各类OH/IR脉泽源的视向速度与银河系较差自转运动的偏离以及各种速度分离下源的运动特点,同时利用文[1]所得的已证认OH/IR源的空间真实密度分布,导出了它们的速度分布模型N(l,v)。对与新证认的非IRC红外源(通常是在更长波长上观测到的)成协的OH/IR源发现有一以银心为心的约为50km/s的径向膨胀运动。文章最后对已证认和未证认的OH/IR脉泽源的差别和联系进行了讨论。 相似文献
39.
Roger Ferlet 《Astronomy and Astrophysics Review》1999,9(3-4):153-169
Summary. Substantial progress in the field of the Local Interstellar Medium has been largely due to recent launches of space missions,
mostly in the UV and X–ray domains, but also to ground-based observations, mainly in high resolution spectroscopy. However,
a clear gap seems to remain between the wealth of new data and the theoretical understanding. This paper gives an overview
of some observational aspects, with no attempt of completeness or doing justice to all the people involved in the field. As
progress rarely evolves in straight paths, we can expect that our present picture of the solar system surroundings is not
definitive.
Received 30 October 1998 相似文献
40.
Ralf Srama Thomas Stephan Eberhard Grün Norbert Pailer Anton Kearsley Amara Graps Rene Laufer Pascale Ehrenfreund Nicolas Altobelli Kathrin Altwegg Siegfried Auer Jack Baggaley Mark J. Burchell James Carpenter Luigi Colangeli Francesca Esposito Simon F. Green Hartmut Henkel Mihaly Horanyi Annette Jäckel Sascha Kempf Neil McBride Georg Moragas-Klostermeyer Harald Krüger Pasquale Palumbo Andre Srowig Mario Trieloff Peter Tsou Zoltan Sternovsky Oliver Zeile Hans-Peter Röser 《Experimental Astronomy》2009,23(1):303-328
The scientific community has expressed strong interest to re-fly Stardust-like missions with improved instrumentation. We
propose a new mission concept, SARIM, that collects interstellar and interplanetary dust particles and returns them to Earth.
SARIM is optimised for the collection and discrimination of interstellar dust grains. Improved active dust collectors on-board
allow us to perform in-situ determination of individual dust impacts and their impact location. This will provide important
constraints for subsequent laboratory analysis.
The SARIM spacecraft will be placed at the L2 libration point of the Sun–Earth system, outside the Earth’s debris belts and
inside the solar-wind charging environment. SARIM is three-axes stabilised and collects interstellar grains between July and
October when the relative encounter speeds with interstellar dust grains are lowest (4 to 20 km/s). During a 3-year dust collection
period several hundred interstellar and several thousand interplanetary grains will be collected by a total sensitive area
of 1 m2. At the end of the collection phase seven collector modules are stored and sealed in a MIRKA-type sample return capsule.
SARIM will return the capsule containing the stardust to Earth to allow for an extraction and investigation of interstellar
samples by latest laboratory technologies. 相似文献