Interstellar polyynes and related species

The existence of the polyynes — molecules consisting essentially of long chains of carbon atoms — in the interstellar medium is a discovery that appears to be critical to our understanding of interstellar chemistry. The family relationships of these species to other interstellar species are explored as are their significance to theories of interstellar chemistry. Methods for deducing the numbers of related molecules are presented.     

Formation of complex chemical species in astrochemistry (a review)

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.     

Kinetic Monte Carlo method for simulating astrochemical kinetics: Hydrogen chemistry in diffuse clouds

We perform numerical simulations of the molecular hydrogen production on the surface of interstellar dust grains and its dissociation by the ultraviolet background in conditions typical for the interstellar medium. The kinetic version of the Monte Carlo method is used for the modeling of the catalytic chemical reactions on the surface of the dust fraction and in the surrounding medium. Our simulations show the importance of the interstellar dust particles for hydrogen chemistry in diffuse molecular clouds.     

Turbulent molecular clouds

Stars form within molecular clouds but our understanding of this fundamental process remains hampered by the complexity of the physics that drives their evolution. We review our observational and theoretical knowledge of molecular clouds trying to confront the two approaches wherever possible. After a broad presentation of the cold interstellar medium and molecular clouds, we emphasize the dynamical processes with special focus to turbulence and its impact on cloud evolution. We then review our knowledge of the velocity, density and magnetic fields. We end by openings towards new chemistry models and the links between molecular cloud structure and star-formation rates.     

The chemistry of interstellar nitrogen

A fairly complete but limited set of gas phase reactions involving nitrogen-bearing molecules is linked to a simple model of grain surface reactions. Calculations are performed attempting to simulate the nitrogen chemistry in interstellar clouds of low and high density. While it appears probable that grain surface reactions contribute to the chemistry in both régimes, conclusive evidence awaits observational and theoretical developments.     

Chemical Processes in Cometary Comae

Recent developments in the chemical modelling of cometary comae aredescribed. We discuss the cyanide chemistry and present new HCNobservations of the recent comet C/2002 C1 (Ikeya–Zhang). Theconnection between interstellar and cometary organic molecules isdiscussed from the perspective of recent theories of interstellargas-grain chemistry.     

The chemistry of transient microstructure in the diffuse interstellar medium

Transient microstructure in the diffuse interstellar medium (ISM) has been observed towards Galactic and extragalactic sources for decades, usually in lines of atoms and ions, and, more recently, in molecular lines. Evidently, there is a molecular component to the transient microstructure. In this paper, we explore the chemistry that may arise in such microstructure. We use a photodissociation region (PDR) code to model the conditions of relatively high density, low temperature, very low visual extinction and very short elapsed time that are appropriate for these objects. We find that there is a well-defined region of parameter space where detectable abundances of molecular species might be found. The best matching models are those where the interstellar microstructure is young (<100 yr), small (∼100 au) and dense  (>10⁴ cm⁻³)  .     

Probing the surfaces of interstellar dust grains: the adsorption of CO at bare grain surfaces

A solid-state feature was detected at around 2175 cm⁻¹ towards 30 embedded young stellar objects in spectra obtained using the Infrared Spectrometer and Array Camera at the European Southern Observatory Very Large Telescope. We present results from laboratory studies of CO adsorbed at the surface of zeolite wafers, where absorption bands were detected at 2177 and 2168 cm⁻¹ (corresponding to CO chemisorbed at the zeolite surface) and 2130 cm⁻¹ (corresponding to CO physisorbed at the zeolite surface), providing an excellent match to the observational data. We propose that the main carrier of the 2175-band is CO chemisorbed at bare surfaces of dust grains in the interstellar medium. This result provides the first direct evidence that gas–surface interactions do not have to result in the formation of ice mantles on interstellar dust. The strength of the 2175-band is estimated to be  ∼4 × 10⁻¹⁹ cm  molecule⁻¹. The abundance of CO adsorbed at bare grain surfaces ranges from 0.06 to 0.16 relative to H₂O ice, which is, at most, half of the abundance (relative to H₂O ice) of CO residing in H₂O-dominated ice environments. These findings imply that interstellar grains have a large (catalytically active) surface area, providing a refuge for interstellar species. Consequently, the potential exists for heterogeneous chemistry to occur involving CO molecules in unique surface chemistry pathways not currently considered in gas grain models of the interstellar medium.     

The physics of photodissociation regions

Photodissociation Regions (PDRs) are gas phases in which ultraviolet radiation plays a role in the heating or chemistry. The physics of PDRs determines the emitted radiation and physical conditions in both the diffuse atomic interstellar medium and the dense molecular phases. High energy laboratory experiments can provide constraints on the survival of small grains which dominate gas heating and in the interaction of X-rays with gas and grains.     

脉冲星星际闪烁的研究进展

综述了脉冲星星际闪烁观测研究的进展，对脉冲星星际闪烁现象，星际介质中电子密度涨落谱，散射等离子体在银河系中的分面等方面的最新研究结果作了介绍。星际闪烁现象和昨际介质的深入理解，使脉冲星星际闪烁已成为研究诸如脉冲星辐射区结构和脉冲星速度等脉冲星本身性质的重要工具。     

Processing of cometary grains at the nucleus surface

Cometary material inevitably undergoes chemical changes before and on leaving the nucleus. In seeking to explain comets as the origin of many IDPs (interplanetary dust particles), an understanding of potential surface chemistry is vital. Grains are formed and transformed at the nucleus surface; much of the cometary volatiles may arise from the organic material. In cometary near-surface permafrost, one expects cryogenic chemistry with crystal growth and isotope. This could be the hydrous environment where IDPs form. Seasonal and geographic variations imply a range of environmental conditions and surface evolution. Interplanetary dust impacts and electrostatic forces also have roles in generating cometary dust. The absence of predicted cometary dust ‘envelopes’ is compatible with the wide range of particle structures and compositions. Study of IDPs would distinguish between this model and alternatives that see comets as aggregates of core-mantle grains built in interstellar clouds.     

Interstellar scintillation of compact extragalactic radio sources

The recent discovery of radio variability of a quasar on short time-scales (hours) prompts us to examine what is expected in respect of the interstellar scintillation of very compact, extragalactic radio sources. We find that large-amplitude, rapid, variability is predicted at commonly observed radio frequencies (1–20 GHz) over the vast majority of the extragalactic sky. As a guide to assist observers in understanding their data, we demonstrate simple techniques for predicting the effects of interstellar scintillation on any extragalactic source.     

The inventory of interstellar materials available for the formation of the solar system

Tremendous progress has been made in the field of interstellar dust in recent years through the use of telescopic observations, theoretical studies, laboratory studies of analogs, and the study of actual interstellar samples found in meteorites. It is increasingly clear that the interstellar medium (ISM) contains an enormous diversity of materials created by a wide range of chemical and physical processes. This understanding is a far cry from the picture of interstellar materials held as recently as two decades ago, a picture which incorporated only a few generic types of grains and few molecules. In this paper, I attempt to review some of our current knowledge of the more abundant materials thought to exist in the ISM. The review concentrates on matter in interstellar dense molecular clouds since it is the materials in these environments from which new stars and planetary systems are formed. However, some discussion is reserved for materials in circumstellar environments and in the diffuse ISM. The paper also focuses largely on solid materials as opposed to gases since solids contain a major fraction of the heavier elements in clouds and because solids are most likely to survive incorporation into new planetary systems in identifiable form. The paper concludes with a discussion of some of the implications resulting from the recent growth of our knowledge about interstellar materials and also considers a number of areas in which future work might be expected to yield important results.     

Carbon — From Space to Laboratory

In this review, the nature of carbon-containing molecules and carbonaceous solids present in meteorites, comets, and the interstellar medium is discussed. Carbon plays an active role in the lifecycle of stars and the interstellar medium. It is the basis of a rich interstellar chemistry and the main component of pre-biotic organic material in space. The aim of the review is to build a bridge between astronomical spectroscopy and laboratory studies relevant to the investigation of cosmic carbon. Special emphasis is given to the structural variety of carbon-containing species and their characterization by experimental techniques. This revised version was published online in July 2006 with corrections to the Cover Date.     

The formation of heavy hydrocarbons in molecular clouds

Laboratory data on the conversion of solid methane into large hydrocarbons by particle radiation are used to estimate the fraction of interstellar carbon converted by this process into refractory form. We find that the maximum fraction of carbon that can be converted into refractory form during the life of a dense core within an interstellar cloud is in the range of 1–5 per cent. The implication of this result is that the conversion of enough carbon into refractory form to contribute significantly to interstellar extinction requires the frequent passage of material into and out of dense cores. If so, then interstellar clouds must exist for at least 10 Myr. However, these conclusions should be regarded as preliminary until confirmed by further laboratory studies of the particle irradiation of complex ice mixtures.     

The retention of spallation products in interstellar grains

Stimulated by recent studies indicating the possible survival of presolar grains in certain meteorites, the importance of recoil loss for the retention of spallation products in submicrometer-sized interstellar dust during irradiation by high-energy cosmic ray protons has been calculated. The model presented incorporates range straggling effects, a realistic distribution of interstellar grain sizes, and utilizes an accurate theoretical formalism for the fragmentation recoil momenta. Apart from an only vague understanding of possible grain composition, the greatest uncertainty concerns the intrinsic material density of interstellar dust which determines the recoil range for any given momentum. It is found that even allowing for a fivefold variation of density values, the retention against recoil is substantial: for example, some 20 to 50% of all ³⁸Ar nuclei resulting from high-energy interaction remain trapped, depending on the target element considered. Retentivities for the various spallation reactions contributing to ³⁸Ar have been calculated and are used to deduce an interstellar spallogenic production rate. The results are then considered in the light of recent discoveries of ⁴⁰Ar³⁹Ar apparent ages in excess of 4.53×10⁹ years for some inclusions from the meteorite Allende. Limitations of both the theoretical and experimental efforts presently preclude conclusive statements regarding the question of interstellar grain survival. However, a procedure is outlined whereby this issue might be clarified in future investigations.     

The detection of acetaldehyde in cold dust clouds

Observations of the 1(01) --> 0(00) rotational transitions of A and E state acetaldehyde are reported. The transitions were detected, for the first time in interstellar space, in the cold dust clouds TMC-1 and L134N, and in Sgr B2. This is also the first time acetaldehyde has been found in a dust cloud and is the most complex oxygen-bearing molecule yet known in this environment. We find a column density of 6 x 10(12) cm-2 in TMC-1, comparable to many other species detected there, and an approximately equal column density in L134N. In the direction of Sgr B2, the CH3CHO profile appears to consist of broad emission features from the hot molecular cloud core, together with absorption features resulting from intervening colder material. We also report the possible detection of HC9N toward IRC +10 degrees 216 through its J = 33 --> 32 transition. Implications for cold dust cloud chemistry and excitation are discussed.     

Polyatomic molecules,molecular ions,and radicals of astrophysical interest,i

This paper has been devoted to basic molecular studies of polyatomics. A critical analysis of the 356 available references in literature has been made to select 98 polyatomic molecules, molecular ions, and radicals containing three, four, and five atoms of astrophysical significance. The results have been arranged in a text-cum-tabular form. The compilation contains various information for each molecule, such as the spectral region, transition levels, astrophysical objects, where the respective molecules have been detected (say, comet, meteorite, Sun, planet, star, interstellar matter, interstellar cloud, molecular cloud, interstellar space, Galaxy, etc.).A few important areas of active research in laboratory astrophysics have also been identified in this article: laboratory astrophysics, molecular cloud chemistry, isotopic abundance, planetary and cometary atmospheres through satellites. Seventy-five new polyatomic molecules (containing three, four, and five atoms) of astrophysical significance have also been listed.Astrophysics and Space Science Review Paper I     

The Interstellar Heliopause Probe: Heliospheric Boundary Explorer Mission to the Interstellar Medium

The Sun, driving a supersonic solar wind, cuts out of the local interstellar medium a giant plasma bubble, the heliosphere. ESA, jointly with NASA, has had an important role in the development of our current understanding of the Suns’ immediate neighborhood. Ulysses is the only spacecraft exploring the third, out-of-ecliptic dimension, while SOHO has allowed us to better understand the influence of the Sun and to image the glow of interstellar matter in the heliosphere. Voyager 1 has recently encountered the innermost boundary of this plasma bubble, the termination shock, and is returning exciting yet puzzling data of this remote region. The next logical step is to leave the heliosphere and to thereby map out in unprecedented detail the structure of the outer heliosphere and its boundaries, the termination shock, the heliosheath, the heliopause, and, after leaving the heliosphere, to discover the true nature of the hydrogen wall, the bow shock, and the local interstellar medium beyond. This will greatly advance our understanding of the heliosphere that is the best-known example for astrospheres as found around other stars. Thus, IHP/HEX will allow us to discover, explore, and understand fundamental astrophysical processes in the largest accessible plasma laboratory, the heliosphere.     

The interstellar magnetic field near the Galactic center

We review the current observational knowledge of the interstellar magnetic field within ∼150 pc ofthe Galactic center. We also discuss the various theoretical scenarios that have been put forward to explain the existing observations. Our critical overview leads to two important conclusions: (1) The interstellar magnetic field near the GC is approximately poloidal on average in the diffuse intercloud medium and approximately horizontal in dense interstellar clouds. (2) In the general intercloud medium, the field is relatively weak and probably close to equipartition with cosmic rays (B ∼ (6–20) μ G), but there exist a number of localized filaments where the field is much stronger (some filaments could possibly have B ≳ 1 mG). In dense interstellar clouds, the field is probably rather strong, with typical values ranging between a few 0.1 mG and a few mG (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)