Quenched Carbonaceous Composite: a laboratory analog for carbonaceous material in the interstellar medium.

We review the properties of Quenched Carbonaceous Composite (QCC), a residue produced from a hydrocarbon plasma, and the properties of its derivatives. A. Sakata and his colleagues have shown that QCC has a 220 nm absorption band, visible fluorescence matching the extended red emission seen in reflection nebulae, and infrared absorption bands that correspond to the infrared emission features in reflection nebulae, HII regions, and planetary nebulae. These properties make QCC a strong candidate material as a laboratory analog to the carbonaceous material in the interstellar medium. QCC is distinguished from the PAH hypothesis in that (1) it is a condensate composed of aromatic and aliphatic molecules, as well as radicals; (2) it exhibits a 220 nm absorption that is very similar in wavelength to the 217 nm absorption in the interstellar medium; (3) it exhibits visible fluorescence consistent with that seen in reflection nebulae; and (4) the bands at 7.7 and 8.6 microns are caused by ketone bands in oxidized QCC. The aromatic component in QCC is thought to be typically 1-4 rings, with the majority being about 1-2 rings.     

Structure and NIR feature of QCC: a laboratory analog of carbon dust.

We have produced thin films of quenched carbonaceous composite (QCC) by hydrocarbon plasma deposition. The effect of thermal annealing on QCC has been investigated to understand how QCC, as a laboratory analog of carbon dust, is transformed in the warm environment around evolved stars. Spectroscopic measurements have indicated that, by heating, the proportion of aromatic sp2 CH bonds increases relative to sp3 CH bonds. Carbon onion-like spherules of approximately 10 nm in diameter are found with electron microscopic images after "graphitization" of thermal annealing.     

Fullerenes in space.

The discovery and synthesis of fullerenes led to the hypothesis that they may be present and stable in interstellar space. Fullerenes have been reported in an impact crater on the LDEF spacecraft. Investigations of fullerenes in carbonaceous meteorites have yielded only small upper limits. Fullerene compounds and their ions could be interesting carrier molecules for some of the "diffuse interstellar bands" (DIBs), a long standing mystery in astronomy. We have detected two new diffuse bands that are consistent with laboratory measurements of the C60+, as first evidence for the largest molecule ever detected in space. Criteria for this identification are discussed. The inferred abundance (up to 0.9 % of cosmic carbon locked in C60+) suggests that fullerenes may play an important role in interstellar chemistry. We present new observations on DIB substructures consistent with fullerene compounds, and the search for neutral C60 in the diffuse medium.     

Spectroscopic properties of polycyclic aromatic hydrocarbons (PAHs) and astrophysical implications.

PAHs (polycyclic aromatic hydrocarbons) are probably present as a mixture of neutral and ionized species and are responsible for the set of infrared emission bands in the 2-15 microns regions, which are observed in many different objects like reflection and planetary nebulae and external galaxies. PAHs are suggested to be the most abundant free organic molecules and ubiquitous in space. PAHs might also exist in the solid phase, included in interstellar ices in dense clouds. A complex aromatic network is expected on interstellar grains in the diffuse interstellar medium. The existence of an aromatic kerogen-like structure in carbonaceous meteorites and its similarity with interstellar spectra suggests a link between interstellar matter and primitive Solar System bodies.     

Similarity of the infrared spectrum of an Orgueil organic polymer with interstellar organic compounds in the line of sight towards IRS 7.

We present a comparison between the IR spectrum of the galactic center source IRS 7 and the spectrum of a carbonaceous polymer from the Orgueil meteorite. We have obtained an almost perfect match between the two spectra in the region between 3020-2790 cm-1, which suggests that the chemical composition of the interstellar organic matter and that of the meteorite polymer are similar or that the meteoritic polymer could be a well preserved interstellar organic molecule. Assuming that the meteoritic polymer has the same C/H ratio as these interstellar molecules, we find that 45 % of the total abundance of carbon in the line of sight toward IRS 7 is trapped in such an interstellar organic grain material.     

Recent developments in space-borne zodiacal light photometry

The 1985 International Solar Polar Mission will provide the first opportunity to perform measurements from out of the ecliptic and from above the solar poles. Included in this mission is the Zodiacal Light/Background Starlight Experiment of the Ruhr-University Bochum, FRG (in collaboration with the State University of New York at Albany). The experiment is based on the use of a multicolor, sky-scanning photopolarimeter, which will be carried on the NASA S/C.The scientific objectives of the experiment are to investigate the intensity, polarization, and color of the diffuse sky brightness and determine the spatial distribution and physical properties of the interplanetary dust, including a possible interstellar component, as a function of S/C position in and out of the ecliptic.The instrument will allow simultaneous measurements in two separate wavelength bands. Measurements will be performed at 180, 220, 240, 280, 320, 350, 360, 440, 540, 640, 800 nm, including the state of polarization. Two different fields-of-view (1 sq deg and 5.6 sq deg) can be selected.The use of a microprocessor system in the instrument electronics will provide flexibility in measurement sequences and programs, on-board data processing and data quality control.     

Solar wind structure in the outer heliosphere

A solar wind parcel evolves as it moves outward, interacting with the solar wind plasma ahead of and behind it and with the interstellar neutrals. This structure varies over a solar cycle as the latitudinal speed profile and current sheet tilt change. We model the evolution of the solar wind with distance, using inner heliosphere data to predict plasma parameters at Voyager. The shocks which pass Voyager 2 often have different structure than expected; changes in the plasma and/or magnetic field do not always occur simultaneously. We use the recent latitudinal alignment of Ulysses and Voyager 2 to determine the solar wind slowdown due to interstellar neutrals at 80 AU and estimate the interstellar neutral density. We use Voyager data to predict the termination shock motion and location as a function of time.     

Coupling of the interstellar and interplanetary magnetic fields at the heliospheric interface: The effect of neutral hydrogen atoms

We present numerical results showing the effect of neutral hydrogen atoms on the solar wind (SW) interaction with the local interstellar medium (LISM), where the interstellar magnetic field (ISMF) is coupled to the interplanetary magnetic field (IMF) at the surface of the heliopause. The IMF on the inner boundary surrounding the Sun is specified in the form of a Parker spiral and self-consistently develops in accordance with the SW motion inside the heliopause. The model of the SW–LISM interaction involves both plasma and neutral components which are treated as fluids. The configuration is chosen where the ISMF is orthogonal to the LISM velocity and tilted 60° to the ecliptic plane. This orientation of the magnetic field is a possible explanation of the 2–3 kHz emission data which is believed to originate ahead of the heliopause. It is shown that the topology of the heliospheric current sheet is substantially affected by the ISMF. The interaction pattern dependence on the neutral hydrogen density is analyzed.     

纳米硅薄膜的氧化特性

将ｎｃ－Ｓｉ：Ｈ薄膜进行等离子和高温氧化处理，测量了样品的氢，氧含量，Ｒａｍａｎ谱，红外吸收谱，光致发光（ＰＬ），结果表明两种氧化方式都将氧掺入薄膜中，但不同处理方式氧在薄膜中的键合形式不同Ｒａｍａｎ谱表明氧化处理对薄膜中晶粒大小及晶态比没有影响，用晶粒－表面模型对氧化引起的光致发光（ＰＬ）蓝移进行了解释。     

Interstellar hydrogen bonding

This paper reports the first extensive study of the existence and effects of interstellar hydrogen bonding. The reactions that occur on the surface of the interstellar dust grains are the dominant processes by which interstellar molecules are formed. Water molecules constitute about 70% of the interstellar ice. These water molecules serve as the platform for hydrogen bonding. High level quantum chemical simulations for the hydrogen bond interaction between 20 interstellar molecules (known and possible) and water are carried out using different ab-intio methods. It is evident that if the formation of these species is mainly governed by the ice phase reactions, there is a direct correlation between the binding energies of these complexes and the gas phase abundances of these interstellar molecules. Interstellar hydrogen bonding may cause lower gas abundance of the complex organic molecules (COMs) at the low temperature. From these results, ketenes whose less stable isomers that are more strongly bonded to the surface of the interstellar dust grains have been observed are proposed as suitable candidates for astronomical observations.     

Heliospheric asymmetries due to the action of the interstellar magnetic field

We discuss the asymmetry of the heliospheric discontinuities obtained from the analysis of 3D modeling of the solar wind (SW) interaction with local interstellar medium (LISM). The flow of charged particles is governed by the ideal MHD equations and the flow of neutral particles is described by the Boltzmann equation. The emphasis is made on the asymmetries of the termination shock (TS) and the heliopause under the combined action of the interstellar and interplanetary magnetic fields (ISMF and IMF) in the presence of neutral hydrogen atoms whose transport through the heliosphere is modeled kinetically, using a Monte Carlo approach. We show that the deflection of neutral hydrogen flow from its original direction in the unperturbed LISM is highly anisotropic and evaluate a possible angle between the hydrogen deflection plane measured in the SOHO SWAN experiment and the plane containing the ISMF and LISM velocity vectors for different ISMF strengths. It is shown that the ISMF of a strength greater than 4 μG can account for the 10 AU difference in the TS heliocentric difference observed during its crossing by the Voyager 1 and Voyager 2 spacecraft, which however results in a larger discrepancy between the calculated and observed velocity distributions. The effect of a strong ISMF on the distribution of plasma quantities in the inner heliosheath and on 2–3 kHz radio emission is discussed.     

Production and evolution of carbonaceous material by ion irradiation in space.

We review recent experimental studies concerning the evolution, driven by ion irradiation, of carbonaceous material from frozen gas to a refractory molecular solid. Under further irradiation the latter changes to a polymer-like material and ultimately to amorphous carbon. Most of the results have been obtained by "in situ" and remote IR and Raman spectroscopy. The results have been applied to demonstrate that molecular solids may be easily formed by irradiation of frozen mantles in dense interstellar clouds. Polymer-like material and amorphous carbons may result by further irradiation of organic mantles on grains in the diffuse interstellar medium. Those grains, during the aggregation to form extended bodies like comets (T-Tau phase of the Sun), are further modified. These latter are also irradiated, after the comet formation, during their long stay in the Oort cloud. In particular it has been suggested that comet may develop an ion-produced cometary organic crust that laboratory evidences show to be stable against temperature increases experienced during passages near the Sun. The comparison between the Raman spectra of some IDP (Interplanetary Dust Particles) and the Raman spectra of some ion-produced amorphous carbons, is also discussed.     

Possible evidence of hydrocarbons released by the nucleus of Halley's comet.

After subtracting the intense dust-scattered continuum from the original spectra transmitted by the Vega 2 three-channel spectrometer, a broad-band emission emerges in the 342-375 nm spectral range when the cometocentric projected distance p is smaller than 5000 km. This newly detected emission varies as p-1, which implies that the involved molecule(s) has a parent-type behavior. The emission band presents four peaks at 347, 356, 364 and 373 nm. It is tentatively identified as being due to phenanthrene, a three-cycle aromatic condensed hydrocarbon. A determination of the gQ product, where g is the fluorescence quantum efficiency and Q the production rate gives gQ = 1.2 x 10(25). If g = 0.012, it comes Q = 1 x 10(27) s-1. The detection of phenanthrene in Halley's inner coma is an important argument in favor of a similarity of composition between cometary material and interstellar matter. It supports the hypothesis that comets have kept trace of the interstellar composition through the solar system formation epoch.     

Catalytic activity of interstellar grains: Formation of molecular hydrogen on amorphous silicates

Silicates constitute an important class of interstellar grain material and are the site of catalytic activities, most notably the formation of molecular hydrogen. Here we report an analysis of experiments conducted in the laboratory to measure the efficiency of formation of molecular hydrogen on amorphous silicates, a realistic analogue of interstellar dust grains. From the measurements, we also obtain the energetics of key processes in the reaction and information on the mechanism of reaction. Comparison with earlier measurements of molecular hydrogen formation on a sample of polycrystalline olivine shows that amorphous materials are more efficient catalysts.     

Ion relaxation processes in the heliospheric interface: how perturbed are ion distribution functions?

Charge-exchange processes between interstellar H-/O-atoms and protons of the bulk of the interstellar plasma flow downstream of the outer bowshock in the heliospheric interface induce secondary ions leading to non-relaxated velocity distribution functions. The relaxation of these freshly induced ions towards an equilibrium distribution occurs due to Coulomb interactions and wave–particle interactions with the background turbulence. Since Coulomb interactions are of low relevance, we study here in detail the effect of wave–particle interactions. To find the turbulence levels in the interface we consider the MHD-wave transformation at the outer shock surface between the interface and the local interstellar plasma. The turbulence in the outer interface region is shown to be dominated by incompressible Alfvén waves both for cases of quasiparallel and quasiperpendicular shocks. Also we show that waves propagating towards the shock are more intensive than those propagating away from it. The level of Alfvén turbulence in the interface is estimated using the recent data on local interstellar turbulence deduced from observations of interstellar scintillations of distant radiosources. Two proton relaxation processes are considered: quasilinear resonant interactions with Alfvén waves and non-linear self-induced wave–particle scattering. The corresponding diffusion coefficients are estimated, and typical time periods for protons and oxygen ions relaxation are shown to be of the same order of magnitude as H-/O-atoms passage time over the extent of the interface. This indicates that perturbed ion distribution functions must be expected there.     

Ionospheric plasma bubble zonal drift: a methodology using OI 630 nm all-sky imaging systems

With the recent advances in all-sky imaging technology for nightglow emission studies, the F-region OI 630 nm emission has become an important tool for ionospheric/thermospheric coupling studies. At equatorial and low latitude regions, the all-sky imaging observations of the OI 630 nm emission show quasi north-south aligned intensity depletion bands, which are the optical signatures of large scale F-region plasma irregularities. By observing the motion of the intensity depleted bands it is possible to infer the ionospheric plasma zonal velocity of the depletion. The north-south aligned structures seen in the field of view of the all-sky imaging system corotate with the ionospheric plasma, so that by calculating the spatial displacements occurring during successive OI 630 nm emission images we can infer the ionospheric plasma drift velocity. However, the plasma bubbles have their own internal space-time dynamics leading to changes in their shape and dimensions and this may induce some errors in the calculated drift velocities. In this paper we take into account the space-time changes in the plasma bubbles in order to calculate the ionospheric plasma zonal drift velocities using the OI 630 nm nightglow emission.     

Polycyclic aromatic hydrocarbon ions and the diffuse interstellar bands.

Neutral naphthalene (C10H8), phenanthrene (C14H10), and pyrene (C16H10) absorb strongly in the ultraviolet and may contribute to the extinction curve. High abundances are required to produce detectable structures. The cations of these PAHs absorb in the visible. C10H8+ has 12 discrete absorption bands which fall between 6800 and 5000 angstroms. The strongest band at 6741 angstroms falls close to the weak 6742 angstroms diffuse interstellar band (DIB). Five other weaker bands also match DIBs. The possibility that C10H8+ is responsible for some of the DIBs can be tested by searching for new DIBs at 6520, 6151, and 5965 angstroms, other moderately strong naphthalene cation band positions. If C10H8+ is indeed responsible for the 6742 angstroms feature, it accounts for 0.3% of the cosmic carbon. The spectrum of C16H10+ is dominated by a strong band at 4435 angstroms in an Ar matrix and 4395 angstroms in a Ne matrix, a position which falls very close to the strongest DIB, that at 4430 angstroms. If C16H10+, or a closely related pyrene-like ion is indeed responsible for the 4430 angstroms feature, it accounts for 0.2% of the cosmic carbon. We also report an intense, very broad UV-to-visible continuum which is associated with both ions and could explain how PAHs convert interstellar UV and visible radiation into IR.     

XMM-Newton observation of Vela shrapnel D

The ROSAT all-sky survey discovered several ‘shrapnels’, showing boomerang structures outside the Vela SNR. We observed the shrapnel D in the eastern limb of the Vela SNR with the XMM-Newton satellite. There is an X-ray bright ridge structure in our FOV running from north to south. There is also an optical bright ridge structure running parallel to that in X-ray about 3′ in the east. These suggest that the shrapnel D is now interacting with an interstellar cloud. Applying the VNEI model to X-ray spectra of various regions, we find that the plasma state of the eastern region of the X-ray ridge is significantly different from that of the western region. The X-ray spectra in the western region can be well fitted with a single temperature component. Abundances of heavy elements are almost uniform, whereas they are heavily overabundant (except Fe): the relative abundances to the solar values are O ∼5, Ne ∼8, Mg ∼8, Fe ∼1. It must have originated from the ejecta of the SN. We find that the plasma in the eastern part of the ridge consists of two temperature components: one component (hot plasma) representing the ejecta while the other (cold plasma) represents the interstellar cloud or swept-up ISM. These two components must have contacted to each other, indicating to form a contact discontinuity. Around northern part of the contact discontinuity, we found wavelike structures of which the typical scales are comparable with that of the Rayleigh–Taylor instability.