On the ionization of interstellar magnesium

It has been shown that two concentric ionization zones of interstellar magnesium must exist around each star: internal, with a radius coinciding with that of the zone of hydrogen ionizationS _H; and external, with a radius greater thanS _H, by one order. Unlike interstellar hydrogen, interstellar magnesium is ionized throughout the Galaxy. It also transpires that the ionizing radiation of ordinary hot stars cannot provide for the observed high degree of ionization of interstellar magnesium. The discrepance can be eliminated by assuming the existence of circumstellar clouds or additional ionization sources of interstellar magnesium (X-ray background radiation, high-energy particles, etc.). Stars of the B5 and B0 class play the main role in the formation of ionization zones of interstellar magnesium; the contribution of O class stars is negligible (<1%).     

Origin of the diffuse interstellar absorption bands

The influence of crystal structure and surface stresses on the spectrum of small interstellar particles has been investigated. Surface effects are predicted to result in the occurrence of pairs of features in the discrete absorption spectrum of interstellar dust. A simple relationship between the energy separation between lines of these pairs and their widths is derived which is tested against recent observational data on the diffuse interstellar band spectrum. Thirty of the diffuse bands can be accounted for on this basis by assuming that interstellar dust consists of a mixture of components of differing chemical composition.     

The Diffuse λ 2200 Å Interstellar Absorption Band and the Abundances of Neutral Interstellar Hydrogen and Sodium

The equivalent width of the diffuse interstellar absorption band W₂₂₀₀ and the abundances of neutral interstellar hydrogen and sodium derived from the interstellar absorption lines in the spectra of hot stars are well correlated each other.     

Influence of wall impacts on the Ulysses dust detector on understanding the interstellar dust flux

The Ulysses spacecraft orbits the Sun on a highly inclined orbit, and the impact ionization dust detector on board continuously measures interstellar dust grains with masses up to , penetrating deep into the Solar System. The flow direction is close to the mean apex of the Sun's motion through the local interstellar cloud (LIC), and the grains act as tracers of the physical conditions in the LIC. Previous analysis gave a velocity dispersion of up to 40^° for the interstellar grains. We partially re-analyzed the Ulysses interstellar dust data set, taking into account the detector's inner side walls. As the side walls have a sensitivity for dust impact detection almost identical to that of the instrument's target area, wall impactors must be taken into account for estimating the intrinsic velocity dispersion of the interstellar impactors and the interstellar dust flux value. Neglect of the sensor side walls overestimates the interstellar dust stream velocity dispersion by about 30% and the interstellar dust flux by about 20%.     

Interstellar molecules and the problem of laboratory data

The use of interstellar molecules as probes of physical conditions in interstellar clouds is hampered by the lack of basic laboratory data. The excitation of interstellar molecules is poorly understood because the nature of the interaction of molecules with radiation and with neutral particles is largely undknown. The mechanisms of formation and destruction of interstellar molecules are presently speculative, because little data exists in such areas as gas-phase ion-molecule reactions and exchange reactions, and reactions of various types on surfaces. Specific needs with regard to laboratory data are discussed in these and other areas. Operated by Associated Universities, Inc., under contract with the National Science Foundation.     

Interstellar Dust in the Solar System

We deduce the mass distribution and total mass density of interstellar dust streaming into the solar system and compare the results to the conditions of the very local interstellar medium (VLISM). The mass distribution derived from in situ measurements shows a gentler slope and includes larger grains, compared to a model distribution proposed for the wavelength dependence of the interstellar extinction. The mass density of grains in the solar system is consistent with that expected from measurements of the visible interstellar extinction and the abundance constraints of elements in the diffuse interstellar medium (ISM), instead of those in the VLISM. This may imply that interstellar dust grains are not associated with the VLISM and that the conditions of the grains are better represented by the ones expected in the diffuse ISM. If this is the case, then the flatter slope in the mass distribution and the detection of larger interstellar grains in the solar system may even indicate that coagulation growth of dust in the diffuse ISM is more effective than previously inferred. This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

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。     

Extraterrestrial microspherules and iron needles in the interstellar medium

Microspherules in Paleozoic-Mesozoic bedded chert, presumed to be of extraterrestrial origin and comprised of clusters of iron needles,may represent an early stage in the aggregation of the inner planets. A fraction of the constituent iron needles will be expected to be carried along with expanding gas to the periphery of the solar nebula where the outer planets and comets condensed. A substantial fraction of iron needles would escape into interstellar space and add to the population of interstellar grains. Iron needles could contribute substantially to interstellar polarization and to the infrared opacity of the interstellar medium.     

An elementary model for the dust cycle in galaxies

We give an elementary model for the evolution of dust in galaxies, based on abundance arguments. The model takes account of grain core production in both supernovae and giant stars, and includes mantle growth in the interstellar medium. Destruction of grain cores does not appear to be a dominant effect. We show that a self-consistent picture can be made in which the interstellar dust mass is an approximately constant fraction of the heavy element mass in the interstellar medium. This result is demonstrated to be essentially independent of outflow or inflow of interstellar material.     

A probability of encounter with interstellar comets and the likelihood of their existence

A theory of the probability of encounter of the Sun with an interstellar comet at a distance comparable to the Earth-Sun distance is formulated, and a general expression is derived establishing the relationship among the influx rate of interstellar comets, the perihelion distance, the space density of the comets, the Maxwellian distribution of comet velocities in the interstellar cloud, and the cloud's systematic velocity relative to the Sun. The fact that no comet with a strongly hyperbolic orbit has so far been observed is used to determine an upper limit of 6 × 10^?4 solar masses per cubic parsec (4 × 10^?26 gcm^?3) for the space density of interstellar comets. The theoretical distribution of semimajor axes of interstellar comets is derived to show that a strong hyperbolic excess must be present in the orbits of a majority of interstellar comets regardless of the dynamical characteristics of the comet cloud, except when the cloud is moving along with the Sun and the distribution of individual velocities has a very low dispersion. This case, however, implies a possibility of capture by the Sun and thus becomes a problem of an Oort-type cloud.     

On the optical properties of bacterial grains,I

We compute the detailed optical properties over the waveband 0.8 μm^?1?λ?10 μm^?1 for the bacterial grain model which we have discussed earlier. A model comprised of three biologically derived components, modified under interstellar conditions, is shown to be in close correspondence with the observed properties of interstellar dust. Data on interstellar extinction and polarization may be accounted for by this model.     

The structure of the IRAS05168+3634 star-forming region

Astrophysics and Space Science - Radioactive components of the interstellar medium provide an entirely-different and new aspect to the studies of the interstellar medium. Injected from sources of...     

A modified model for interstellar extinction

It is shown that available optical and ultraviolet data relating to the interstellar dust are elegantly explained on the basis of a modified microbal grain model. A model comprised of two biologically derived components, modified under interstellar conditions. Data on interstellar extinction, albedo and polarization may be accounted for by this model.     

Sample return of interstellar matter (SARIM)

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.     

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.     

Zum Dichteverhältnis zwischen interstellarem Staub und Gas

The density ratio between interstellar dust and gas is investigated using the colour excesses of the stars of Habing's list [17] and published 21 cm data. Generally there does not exist a correlation between the amount of neutral hydrogen in the line of sight and the interstellar extinction. In the contrary the scattering of the data is considerable. The influences falsifying the density ratio are discussed whereby the cooling of the interstellar clouds reaching large distances from the galactic plane was considered schematically. From the discussion of the results it follows that at present a reliable determination of the interstellar density ratio between dust and gas is impossible. The necessity of direct observations of the interstellar H₂ but also the determination of the kinetic temperature of the HI in separate regions are pointed out.     

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.     

Theoretische Untersuchungen über den interstellaren Staub. IV. Silikatteilchen und diffuse interstellare Banden

Transition metal ions in the crystal lattices of the interstellar silicate grains are suggested to produce the diffuse interstellar absorption features.     

Formation of E-cyanomethamine in a nitrile rich environment

Recently a new molecule, cyanomethamine, has been detected towards Sagittarius B2(N)(Sgr B2(N)). Studying the formation mechanisms of complex interstellar molecules is difficult. Hence,a theoretical quantum chemical approach for analyzing the reaction mechanism describing the formation of interstellar cyanomethamine through detected interstellar molecules and radicals(NCCN+H) is discussed in the present work. Calculations are performed by using quantum chemical techniques, such as Density Functional Theory(DFT) and M?ller-Plesset perturbation(MP2) theory with a 6-311G(d,p)basis set, both in the gas phase and in icy grains. The proposed reaction path(NCCN+H+H) has exothermicity with no barrier which indicates the possibility of cyanomethamine formation in the interstellar medium.