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1.
A. Evans 《Astrophysics and Space Science》1997,251(1-2):293-302
The current status of our knowledge about the formation and evolution of dust and molecules in the environments of classical
novae is reviewed. We discuss the chemistry that leads to the formation of diatomic molecules and nucleation sites, dust formation
in nova winds, the properties and the processing of dust in nova environments, and the eventual fate of the dust. We also
discuss the environment of nova progenitors, and what this can tell us about the pre-nova evolution of close binary systems.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
2.
Travis S. Metcalfe 《Journal of Astrophysics and Astronomy》2005,26(2-3):273-281
The interpretation of pulsation data for sun-like stars is currently facing challenges quite similar to those faced by white
dwarf modelers ten years ago. The observational requirements for uninterrupted long-term monitoring are beginning to be satisfied
by successful multi-site campaigns and dedicated satellite missions. But exploration of the most important physical parameters
in theoretical models has been fairly limited, making it difficult to establish a detailed best-fit model for a particular
set of oscillation frequencies. I review the past development and the current state of white dwarf asteroseismology, with
an emphasis on what this can tell us about the road to success for asteroseismology of other types of stars. 相似文献
3.
Si-Qi Zheng Juan Li Jun-Zhi Wang Feng Gao Ya-Jun Wu Shu Liu Shang-Huo Li 《天文和天体物理学研究(英文版)》2022,(3):61-71
HOCN and HNCO abundance ratio in molecular gas can tell us the information of their formation mechanism.We performed high-sensitivity mapping observations of HO... 相似文献
4.
作者希望通过对国内外太阳物理学家多年来在太阳磁场精细结构方面的研究成果的回顾，探讨立足现有和将有的仪器设备，可能和应该从事的高分辨太阳磁场的研究工作。为突出重点，侧重评述１０００Ｇ以上的强磁场精细结构特征及与之相关的亮度特征的精细结构。 相似文献
5.
D. M. Worrall 《Astronomy and Astrophysics Review》2009,17(1):1-46
Jet physics is again flourishing as a result of Chandra’s ability to resolve high-energy emission from the radio-emitting structures of active galaxies and separate it from the X-ray-emitting thermal environments of the jets. These enhanced capabilities have coincided with an increasing interest in the link between the growth of super-massive black holes and galaxies, and an appreciation of the likely importance of jets in feedback processes. I review the progress that has been made using Chandra and XMM-Newton observations of jets and the medium in which they propagate, addressing several important questions, including: Are the radio structures in a state of minimum energy? Do powerful large-scale jets have fast spinal speeds? What keeps jets collimated? Where and how does particle acceleration occur? What is jet plasma made of? What does X-ray emission tell us about the dynamics and energetics of radio plasma/gas interactions? Is a jet’s fate determined by the central engine? 相似文献
6.
PETER JENNISKENS 《Earth, Moon, and Planets》2004,95(1-4):723-732
The successful application of modern observing techniques for Leonid storm observations show that meteor (shower) detections will have a bright future if the field will pursue difficult but important questions. How to forecast a satellite threatening meteor storm? What happens to the organic matter in meteors and can this be an important source of prebiotic molecules? What range of variations in composition and morphology exists among cometary grains and what does this tell us about the origin of the solar system? What long-period comets approach Earth orbit and can meteoroid streams provide early warning for giant impacts? What are the sources of interstellar and interplanetary grains? Just to mention a few. To answer these questions will need new technologies and facilities, some of which are being developed for other use. This may include NASA’s Stratospheric Observatory For Infrared and sub-millimeter Astronomy (SOFIA). In addition, big-science space missions can drive the field if meteor detections are an integral part. Special events, such as meteor outbursts and the “artificial meteor” from the reentry of sample return capsules from interplanetary space, can mobilize observing and theoretical efforts. These and other future opportunities are briefly discussed. 相似文献
7.
One of the most remarkable properties of radio pulsars is their rotational stability which allows many uses as clocks, For
instance they enable us to determine the shapes and sizes of binary orbits, to study general relativistic effects in strong
gravitational fields, to demonstrate the existance of gravitational radiation from binary systems, to permit the detection
of extra solar planets, and also to put limits on the long period gravitational wave background. However, some display timing
imperfections which tell us about the insides of neutron stars. This review describes the basic physics of slowdown and how
period instabilities seem to be related to the rate of slowdown and the presence of internal superfluid liquid. Careful studies
of glitches and the subsequent rotational behaviour of the pulsars can provide valuable information on the internal structure
of neutron stars. 相似文献
8.
Our Sun and planetary system were born about 4.5 billion years ago. How did this happen, and what is the nature of our heritage from these early times? This review tries to address these questions from an astrochemical point of view. On the one hand, we have some crucial information from meteorites, comets and other small bodies of the Solar System. On the other hand, we have the results of studies on the formation process of Sun-like stars in our Galaxy. These results tell us that Sun-like stars form in dense regions of molecular clouds and that three major steps are involved before the planet-formation period. They are represented by the prestellar core, protostellar envelope and protoplanetary disk phases. Simultaneously with the evolution from one phase to the other, the chemical composition gains increasing complexity. In this review, we first present the information on the chemical composition of meteorites, comets and other small bodies of the Solar System, which is potentially linked to the first phases of the Solar System??s formation. Then we describe the observed chemical composition in the prestellar core, protostellar envelope and protoplanetary-disk phases, including the processes that lead to them. Finally, we draw together pieces from the different objects and phases to understand whether and how much we inherited chemically from the time of the Sun??s birth. 相似文献
9.
Summary. Metallicity is a key parameter that controls many aspects in the formation and evolution of stars and galaxies. In this review
we focus on the metal deficient galaxies, in particular the most metal-poor ones, because they play a crucial r?le in the
cosmic scenery. We first set the stage by discussing the difficult problem of defining a global metallicity and how this quantity
can be measured for a given galaxy. The mechanisms that control the metallicity in a galaxy are reviewed in detail and involve
many aspects of modern astrophysics: galaxy formation and evolution, massive star formation, stellar winds, chemical yields,
outflows and inflows etc. Because metallicity roughly scales as the galactic mass, it is among the dwarfs that the most metal-poor
galaxies are found. The core of our paper reviews the considerable progress made in our understanding of the properties and
the physical processes that are at work in these objects. The question on how they are related and may evolve from one class
of objects to another is discussed. While discussing metal-poor galaxies in general, we present a more detailed discussion
of a few very metal-poor blue compact dwarf galaxies like IZw18. Although most of what is known relates to our local universe,
we show that it pertains to our quest for primeval galaxies and is connected to the question of the origin of structure in
the universe. We discuss what do QSO absorption lines and known distant galaxies tell us already? We illustrate the importance
of star-forming metal-poor galaxies for the determination of the primordial helium abundance, their use as distance indicator
and discuss the possibility to detect nearly metal-free galaxies at high redshift from Ly emission.
Received 19 August 1999 / Published online: 15 February 2000 相似文献
10.
Milan M. Ćirković 《Astrophysics and Space Science》1998,262(4):497-508
If a significant fraction of QSO absorption line systems arises in halos of normal galaxies, absorber statistical data will
tell us a lot about the structure of the gaseous envelopes of galaxies. Comparison of a class of density profile models for
the metal-absorbing halos of luminous galaxies with the recent Lyα empirical data is presented. Cosmological mass fraction
contained in such gas is also briefly discussed. It is shown that important constraints on the model parameters can be inferred
in this way.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
11.
Although we can observe current activity on Saturn's satellite Enceladus with Cassini, insight into past activity is best achieved (for now) through studying the impact crater distributions. Furthermore, approximation of terrain ages can only be attained through calculations using crater densities and estimations of impact rates in the saturnian system. Here we focus on what the impact crater distribution in Enceladus' heavily cratered plains can tell us about Enceladus' geologic history. We use Cassini ISS images to count craters in the heavily cratered plains on Enceladus, along with Rhea, Dione, Tethys and Mimas as references, to develop and compare their size-frequency distributions. Comparisons of our counts show that Enceladus' cratered plains distribution is unique in that it appears to have a relative deficiency of craters for diameters ?2 km and ?6 km compared to the other satellites' heavily cratered plains. Our data also indicates that the impact crater density within the cratered plains changes with latitude. Specifically, both the north and south mid-latitude regions have approximately three times higher density than the equatorial region. We hypothesize that the “missing” small and large craters in Enceladus' cratered plains is due to a combination of viscous relaxation of the larger craters, and burial of the relaxed large craters and small craters by south polar plume and possibly E-ring material. We also conclude that the spatial density distribution is not consistent with recent polar wander. 相似文献
12.
J. O. Stenflo 《Astronomy and Astrophysics Review》1989,1(1):3-48
Summary The Sun provides us with a unique astrophysics laboratory for exploring the fundamental processes of interaction between a turbulent, gravitationally stratified plasma and magnetic fields. Although the magnetic structures and their evolution can be observed in considerable detail through the use of the Zeeman effect in photospheric spectral lines, a major obstacle has been that all magnetic structures on the Sun, excluding sunspots, are smaller than what can be resolved by present-day instruments. This has led to the development of indirect, spectral techniques (combinations of two or more polarized spectral lines), which overcome the resolution obstacle and have revealed unexpected properties of the small-scale magnetic structures. Indirect empirical and theoretical estimates of the sizes of the flux elements indicate that they may be within reach of planned new telescopes, and that we are on the verge of a unified understanding of the diverse phenomena of solar and stellar activity.In the present review we describe the observational properties of the smallscale field structures (while indicating the diagnostic methods used), and relate these properties to the theoretical concepts of formation, equilibrium structure, and origin of the surface magnetic flux.On leave from Institute of Astronomy, ETH-Zentrum, CH-8092 Zürich, SwitzerlandThe National Center for Atmospheric Research is sponsored by the National Science Foundation 相似文献
13.
B. E. Turner 《Astrophysics and Space Science》1995,224(1-2):297-303
The list of detected refractory-element (RE) species in IRC10216 is now large enough to try to assess their chemistry, and the fraction of each that escapes in gas phase to the ISM. The former may tell us how grains are formed, the latter whether mass-loss from evolved stars is important in determining interstellar elemental depletions as distinct from accretion processes in the ISM. We expect that much of the Si chemistry is now understood and about 25% of Si escapes as a gas. Other REs are less well understood but most should be more volatile than Si. For many of the REs, O-rich CSEs should behave similarly to C-rich ones.Operated by Associated Universities, Inc., under cooperative agreement with the National Science Foundation 相似文献
14.
R.J.R. Williams D. Ward-Thompson A.P. Whitworth 《Monthly notices of the Royal Astronomical Society》2001,327(3):788-798
We present hydrodynamical simulations of the formation, structure and evolution of photoionized columns, with parameters based on those observed in the Eagle Nebula. On the basis of these simulations we argue that there is no unequivocal evidence that the dense neutral clumps at heads of the columns were cores in the pre-existing molecular cloud. In our simulations, a variety of initial conditions leads to the formation and maintenance of near-equilibrium columns. Therefore, it is likely that narrow columns will often occur in regions with large-scale inhomogeneities, but that observations of such columns can tell us little about the processes by which they formed. The manner in which the columns in our simulations develop suggests that their evolution may result in extended sequences of radiation-induced star formation. 相似文献
15.
Sarah K. Noble Lindsay P. Keller Carl M. Pieters 《Meteoritics & planetary science》2005,40(3):397-408
Abstract— We have analyzed a suite of lunar regolith breccias in order to assess how well space weathering products can be preserved through the lithification process and therefore whether or not it is appropriate to search for space weathering products in asteroidal regolith breccia meteorites. It was found that space weathering products, vapor/sputter deposited nanophase‐iron‐bearing rims in particular, are easily identified in even heavily shocked/compacted lunar regolith breccias. Such rims, if created on asteroids, should thus be preserved in asteroidal regolith breccia meteorites. Two additional rim types, glass rims and vesicular rims, identified in regolith breccias, are also described. These rims are common in lunar regolith breccias but rare to absent in lunar soils, which suggests that they are created in the breccia‐forming process itself. While not “space weathering products” in the strictest sense, these additional rims give us insight into the regolith breccia formation process. The presence or absence of glass and/or vesicular rims in asteroidal regolith breccias will likewise tell us about environmental conditions on the surface of the asteroid body on which the breccia was created. 相似文献
16.
P. Poulain 《Solar physics》1981,70(2):229-235
More and more observations tend to prove that the lower corona is very heterogeneous and that the active regions are quite exclusively arch-structured. So, we have attempted to see what would be the result of simulations of a corona structured only with arches. In a previous work we had made the computations for both the K-corona and the 5303 emission line corona, for which we have much observational data. The complexity of computations has led us to make the comparisons with observations for the vertical intensity gradients only. A priori, it seemed impossible to obtain a simulation close to reality with a corona structured only with arches, at least as we have defined them in this paper, the important fact being a conspicuous lack of matter beyond a certain height. We have made new simulations with a different electron density distribution and for a different region. These latter calculations show us that the material can be confined in the feet of very high arches or in open structures as has already been suggested. 相似文献
17.
Norman H. Sleep 《Earth, Moon, and Planets》2006,99(1-4):343-358
Antineutrino data constrain the concentrations of the heat producing elements U and Th as well as potentially the concentration
of K. Interpretation is similar to but not homologous with gravity. Current geoneutrino physics efficiently asks simple questions
taking advantage of what is already known about the Earth. A few measurements with some sites in the ocean basins will constrain
the concentration of U and Th in the crust and mantle and whether the mantle is laterally heterogeneous. These results will
allow Earth science arguments about the formation, chemistry, and dynamics of the Earth to be turned around and appraised.
In particular, they will tell whether the Earth accreted its expected share of these elements from the solar nebula and how
long radioactive heat will sustain active geological processes on the Earth. Both aspects are essential to evaluating the
Earth as a common or rare habitable planet. 相似文献
18.
Sarbani Basu 《Astrophysics and Space Science》2010,328(1-2):43-50
Helioseismology has given us a unique window into the solar interior. Helioseismic data have enabled us to study the internal structure and dynamics with unprecedented detail. This has also allowed us to use the Sun as a laboratory to study the basic properties of stellar matter. We describe how helioseismology is used to determine solar structure and what we have learned about the Sun so far. We also describe how knowledge of the solar structure can be used to constrain the physics inputs. 相似文献
19.
V. I. Shematovich 《Solar System Research》2012,46(6):391-407
In recent years, a rapid growth in a new area of space studies??astrochemistry??has been observed. Its subject is the chemical evolution and chemical diversity of interstellar matter. Molecules yield unique information concerning physical conditions in the interstellar medium and, in particular, in the star-formation regions, through spectral observations of the matter in the gas-phase and dust fractions via rotational and vibrational transitions of interstellar molecules. Moreover, an understanding of the chemistry of molecules can tell us about the lifetime and history of the observed objects. Such an understanding, however, requires detailed chemical knowledge of the gas-phase reactions and grain-surface chemical processes that very often take place under rather exotic conditions strongly differing from those for chemical reactions in the laboratory. Note that the interests of chemists and astronomers in this new area are different: chemists are more likely to be interested in chemical diversity throughout the Universe, whereas astronomers are more likely to use molecules as probes of physical processes. 相似文献
20.
Regina E. Schulte-Ladbeck 《Astrophysics and Space Science》1994,221(1-2):347-356
I review polarimetric observations of presumably single, hot, luminous stars. The stellar types discussed are OB stars, B[e] supergiants, Luminous Blue Variables (LBV), Wolf-Rayet (W-R) stars, and type II supernovae (SN). It is shown that variable, intrinsic polarization is a common phenomenon in that part of the Hertzsprung-Russell (HR) diagram which these stars occupy. However, much observational work remains to be done before we can answer the most basic, statistical questions about the polarimetric properties of different groups of hot, luminous stars. Insight into the diagnostic power of polarization observations has been gained, but cannot be exploited without detailed models. Thus, while polarimetric observations do tell us that the mass-loss processes of all types of massive stars are time-dependent and anisotropic, the significance that this might have for the accuracy of their stellar parameters and evolutionary paths remains elusive. 相似文献