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.     

Evidence for large organic molecules in the diffuse medium using optical high resolution spectroscopy.

The Diffuse Interstellar Bands (DIBs) are absorption lines observed in the line of sight toward reddened OB stars. Their ubiquitous detection in space indicates chemically stable and abundant carriers. High resolution spectroscopy led to the detection of substructures in the line profiles of a few DIBs, indicating a gas phase molecular origin of the carriers. Line profile studies are useful tools to derive information on the band carriers nature. In this paper we compared the velocity structure of the lambda 6613 angstroms DIB line profile to the NaD1 and CaII profiles toward 6 targets of the Perseus OB2 association.     

Propagation of cosmic ray nuclei above 50 GeV/amu

It is now well-known that the relative abundance of secondary cosmic ray nuclei which are produced by spallation in interstellar space depends on energies. The mechanism responsible for this energy dependence are not well understood because of the scarcity of data on the cosmic ray composition at energy above 50 GeV/amu. The University of Chicago experiment on the Spacelab-2 flown by the Space Shuttle in 1985 is aimed at the measurement of the elemental composition in this unexplored energy regime. Our latest results on the energy dependence of the secondary to primary abundance ratio using the pairs of elements B,C and N,O, are discussed.     

Organic chemistry by irradiation in space

The irradiation of grains and/or ices by particles from solar or stellar winds, as well as cosmic rays, induces the synthesis of molecular species. We have shown by in-situ infrared spectroscopy of irradiated samples that this chemistry may be responsible for the presence of organic compounds in a large variety of astrophysical sites such as: lunar and asteroidal regoliths, cometary nucleus, rings and satellites of outer planets, circumstellar shells, interstellar clouds. We present our experimental results concerning the nature and efficiency of C and N irradiation chemistries, and give plausible astrophysical implications.     

Measurement of cosmic ray H and He isotopes in a Balloon Borne Experiment with a Superconducting Solenoid Spectrometer

The Balloon Borne Experiment with a Superconducting Solenoid Spectrometer (BESS) was flown annually in 1993, 1994, and 1995. In this report we present the energy spectra and isotopic composition of cosmic ray H and He measured from the 1993 flight. The low energy fluxes of H and He agree with the IMP-8 satellite data for a 26 day period (7/14/93 – 8/9/93) that overlapped the BESS flight. Both ²H and ³He were well separated from ¹H and ⁴He. The measured spectra were corrected for the atmospheric overburden and compared with the interstellar/heliospheric propagation calculations.     

The solar wind shock termination

We analyse the possibility that the shock termination of the solar wind should occur at a heliocentric distance of 50 a.u. It is concluded that this is possible if the density of the interstellar medium near the Sun is of the order of 0.5 cm⁻³, or the pressure of low energy cosmic rays (less than about 300 MeV/nucleon) is of the order of 6×10⁻¹² dyn cm⁻², or the interstellar magnetic field strength is of the order of 8 microgauss, or some suitable combination of these. Such conditions would not normally be expected to prevail in the interstellar medium in the neighbourhood of the Sun. However, the possibility that a supernova explosion occurred nearby some 10⁵–10⁶ years ago must be taken seriously and in such circumstances the required conditions may be relatively easily achieved.     

Organic molecules in the gas phase of dense interstellar clouds.

Since a previous COSPAR review on this subject, the number of molecular species identified by astronomers in dense interstellar clouds or in the envelopes expelled by evolved stars has grown from about eighty to approximately one hundred. Recent detections in stellar envelopes include the radical CP, the second phosphorus-containing astronomical molecule; SiN, the first astronomical molecule with a Si-N bond; and the HCCN radical. In the dense interstellar clouds recent detections or verifications of previous possible identifications include the H3O+ ion, which is a critical intermediary in the production of H2O and O2; the CCO radical, which is isoelectronic with HCCN; the SO+ ion, which appears to be diagnostic of shock chemistry; two new isomers of cyanoacetylene, HCCNC and CCCNH; and the two cumulenes H2C3 and H2C4. Some recent work is also described on the mapping of interstellar clouds in multiple molecular transitions in order to separate variations in chemical abundance from gradients in physical parameters.     

Observational astrochemistry: recent results.

More than 80 molecular species have now been observed by astronomers in the dense interstellar clouds where stars and planets form or in the envelopes expelled by evolved stars. Elemental constituents of these compounds include all of the "biogenic" elements, hydrogen, carbon, nitrogen, oxygen, sulfur, and (most recently) phosphorus. In addition, silicon is found in several molecules, and a series of metal halides have recently been detected in the outflowing envelope of a nearby carbon star. Additions to the list of known interstellar molecules since the last COSPAR meeting are discussed individually. Recent measurements of the hydrogen isotopic fractionation for the cyclic molecule C3H2 are described; values up to 10,000 times the cosmic deuterium-to-hydrogen ratio are found. Knowledge of the chemical reservoirs for the major volatile elements and a comparison between observed molecular abundances and theoretical models are both discussed.     

Comets and life.

Some of the chemical species which have been detected in comets include H2O, HCN, CH3CN, CO, CO2, NH3, CS, C2 and C3. All of these have also been detected in the interstellar medium, indicating a probable relationship between interstellar dust and gas clouds and comets. Laboratory experiments carried out with different mixtures of these molecules give rise to the formation of the biochemical compounds which are necessary for life, such as amino acids, purines, pyrimidines, monosaccharides, etc. However, in spite of suggestions to the contrary, the presence of life in comets is unlikely. On the other hand, the capture of cometary matter by the primitive Earth is considered essential for the development of life on this planet. The amount of cometary carbon-containing matter captured by the Earth, as calculated by different authors, is several times larger than the total amount of organic matter present in the biosphere (10(18)g). The major classes of reactions which were probably involved in the formation of key biochemical compounds are discussed. Our tentative conclusions are that: 1) comets played a predominant role in the emergence of life on our planet, and 2) they are the cosmic connection with extraterrestrial life.     

Hot atoms in cosmic chemistry

High energy chemical reactions and atom molecule interactions might be important for cosmic chemistry with respect to the accelerated species in solar wind, cosmic rays, colliding gas and dust clouds and secondary knock-on particles in solids. “Hot” atoms with energies ranging from a few eV to some MeV can be generated via nuclear reactions and consequent recoil processes. The chemical fate of the radioactive atoms can be followed by radiochemical methods (radio GC or HPLC). Hot atom chemistry may serve for laboratory simulation of the reactions of energetic species with gaseous or solid interstellar matter. Due to the effective measurement of 10⁸–10¹⁰ atoms only it covers a low to medium dose regime and may add to the studies of ion implantation which due to the optical methods applied are necessarily in the high dose regime.

Experimental results are given for the systems: C/H₂O (gas), C/H₂O (solid, 77 K), N/CH₄ (solid, 77K) and C/NH₃ (solid, 77 K). Nuclear reactions used for the generation of 2 to 3 MeV atoms are: ¹⁴N(p, ) ¹¹C, ¹⁶O(p, pn) ¹¹C and ¹²C(d,n) ¹³N with 8 to 45 MeV protons or deuterons from a cyclotron. Typical reactions products are: CO, CO₂, CH₄, CH₂O, CH₃OH, HCOOH, NH₃, CH₃NH₂, cyanamide, formamidine, guanidine etc. Products of hot reactions in solids are more complex than in corresponding gaseous systems, which underlines the importance of solid state reactions for the build-up of precursors for biomolecules in space. As one of the major mechanisms for product formation, the simultaneous or fast consecutive reactions of a hot carbon with two target molecules (reaction complex) is discussed.     

Low and medium energy gamma-ray astronomy — present status and future aspects

During the last few years quite some progress has been achieved in the field of low and medium energy gamma-ray astronomy below about 30 MeV. Gamma rays from the galactic center and anti-center region have been detected, which require a high interstellar electron flux in the 100 MeV range, if they are predominantly diffuse in nature. Though the Crab pulsar and its nebula are still the only galactic gamma-ray sources which definitely have been detected, some recently determined upper limits to the gamma-ray fluxes of other radio pulsars are close to the theoretically expected values. Active galaxies seem to have a maximum of luminosity in the range between several 100 keV and a few MeV and, therefore, are of special interest. First observational results have been reported on the Seyfert galaxies NGC 4151 and MCG 8-11-11, and the radio galaxy CenA. The nature of the diffuse cosmic gamma-ray component at low gamma-ray energies is not yet solved. Unresolved active galaxies are good candidates for its origin.Considering the present status of gamma ray astronomy the study of galactic sources like radio pulsars and the unidentified high energy gamma-ray sources, the Milky Way as a whole, active galaxies and the diffuse cosmic sky seem to be the prime targets for broad band observations below 30 MeV in the GRO area. An unexplored field like that of low energy gamma-ray astronomy, however, is always open for surprises.     

磁暴期间电离层电磁离子回旋波的地方时分布差异

利用Swarm卫星的高精度(50 Hz)磁场观测数据,对2015年3月16-25日磁暴期间中纬度电离层电磁离子回旋(EMIC)波时空分布特征进行了研究.结果表明:晨侧EMIC波事件数与昏侧大致相当,午前时段明显多于子夜前时段.昏侧EMIC波高发生率与等离子体羽状结构有关,晨侧EMIC波高发生率与太阳风动压增强及稠密冷等...     

The ‘soot line’: Destruction of presolar polycyclic aromatic hydrocarbons in the terrestrial planet-forming region of disks

Interstellar material is highly processed when subjected to the physical conditions that prevail in the inner regions of protoplanetary disks, the potential birthplace of habitable planets. Polycyclic aromatic hydrocarbons (PAHs) are abundant in the interstellar medium, and they have also been observed in the disks around young stars, with evidence for some modification in the latter. Using a chemical model developed for sooting flames, we have investigated the chemical evolution of PAHs in warm (1000–2000 K) and oxygen-rich (C/O < 1) conditions appropriate for the region where habitable planets may eventually form. Our study focuses on (1) delineating the conditions under which PAHs will react and (2) identifying the key reaction pathways and reaction products characterizing this chemical evolution. We find that reactions with H, OH and O are the main pathways for destroying PAHs over disk timescale at temperatures greater than about 1000 K. In the process, high abundances of C₂H₂ persist over long timescales due to the kinetic inhibition of reactions that eventually drive the carbon into CO, CO₂ and CH₄. The thermal destruction of PAHs may thus be the cause of the abundant C₂H₂ that has been observed in disks. We propose that protoplanetary disks have a ‘soot line’, within which PAHs are irreversibly destroyed via thermally-driven reactions. The soot line will play an important role, analogous to that of the ‘snow line’, in the bulk carbon content of meteorites and habitable planets.     

Impacts of the PAH size and the radiation intensity on the IR features of illuminated dust within the reflection nebulae

Interstellar dust grains are illuminated in the reflection nebulae. Under conditions of the PAH size and the intensity of the interstellar radiation field, we follow their impact on the PAH aromatic infrared bands using the numerical DustEM code. For a dust model consisting of PAH, amorphous C and amorphous silicate, the PAH size varies in a range from 0.31 to 4.9 nm while the radiation intensity varies by a scale factor from 0.1 to 10⁴. Various trends of the results show the effect of varying both the PAH size and the radiation intensity on the strength of the aromatic mid-IR bands. Through small PAH sizes less than 0.7 nm, the grain temperature distribution of PAHs shows a small variation within 2–3 K at low radiation intensity while it increases to 15 and 8 K for PAH⁰ and PAH⁺, respectively, at higher radiation intensity. In final the variability in these results reveals the evolution of the dust grains under the physical space conditions of the reflection nebulae. In the mid-IR region, the contributions of PAH⁰ and PAH⁺ in the total SED intensity agree with the proportions of these PAHs observed in some reflection nebulae having higher radiation intensities.     

Chemical evolution in space--a source of prebiotic molecules.

In Laboratory Astrophysics at Leiden University a laboratory analog for following the chemical evolution of interstellar dust in space shows that the dust contains the bulk of organic material in the universe. We follow the photoprocessing of low temperature (10 K) mixtures of ices subjected to vacuum ultraviolet radiation in simulation of interstellar conditions. The most important, but necessary, difference is in the time scales for photo-processing. One hour in the laboratory is equivalent to one thousand years in low density regions of space and as much as, or greater than, ten thousand to one million years in the depths of dense molecular clouds. The ultimate product of photoprocessing of grain material in the laboratory is a complex nonvolatile residue which is yellow in color and soluble in water and methanol. The molecular weight is greater than the mid-hundreds. The infrared absorption spectra indicate the presence of carboxylic acid and amino groups resembling those of other molecules of presumably prebiological significance produced by more classical methods. One of our residues, when subjected to high resolution mass spectroscopy gave a mass of 82 corresponding to C4H6H2 after release of CO2 and trace ammounts of urea suggesting amino pyroline rings. The deposit of prebiotic dust molecules occurred as many as 5 times in the first 500-700 million years on a primitive Earth by accretion during the passage of the solar system through a dense interstellar cloud. The deposition rate during each passage is estimated to be between 10(9) and 10(10) g per year during the million or so years of each passage; i.e., a total deposition of 1O(9)-10(10) metric tons of complex organic material per passage.     

Chemical evolution and the origin of life.

During the last three decades major advances have been made in our understanding of the formation of carbon compounds in the universe and of the occurence of processes of chemical evolution. 1) Carbon and other biogenic elements (C,H,N,O,S and P) are some of the most abundant in the universe. 2) The interstellar medium has been found to contain a diversity of molecules of these elements. 3) Some of these molecules have also been found in comets which are considered the most primordial bodies of the solar system. 4) The atmospheres of the outer planets and their satellites, for example, Titan, are actively involved in the formation of organic compounds which are the precursors of biochemical molecules. 5) Some of these biochemical molecules, such as amino acids, purines and pyrimidines, have been found in carbonaceous chondrites. 6) Laboratory experiments have shown that most of the monomers and oligomers necessary for life can be synthesized under hypothesized but plausible primitive Earth conditions from compounds found in the above cosmic bodies. 7) It appears that the primitive Earth had the necessary and sufficient conditions to allow the chemical synthesis of biomacromolecules and to permit the processes required for the emergence of life on our planet. 8) It is unlikely that the emergence of life occurred in any other body of the solar system, although the examination of the Jovian satellite Europa may provide important clues about the constraints of this evolutionary process. Some of the fundamental principles of chemical evolution are briefly discussed.     

EUVITA — An extreme UV imaging telescope array with spectral capability

EUVITA is a set of 8 extreme UV normal incidence imaging telescopes, each of them sensitive in a narrow band (λ/Δλ = 15 to 80), centered at wavelengths between 50 and 175 Å. Each telescope has an effective area of a few cm²; a field of view of 1.2° and a spatial resolution of 10 arcsec.

EUVITA will be flown on the Russian mission SPECTRUM X-G. This satellite will be launched in a highly eccentric orbit with a period of 4 days, allowing long, uninterrupted observations (e.g. 10⁵ seconds). EUVITA's narrow spectral bands allow the measurement of source parameters such as temperature or power law index as well as interstellar absorption, and will resolve groups of strong lines emitted by optically thin hot plasmas.     

Chemical interactions of solar wind with cometary nuclei and comae

Solar wind particles, especially H, C, N, O, S, and P-ions, may undergo specific chemical reactions with gaseous or solid matter of comets when in the energy region of a few 10 to some eV. Each component of the solar wind, even if not chemically reactive itself, creates a multiplicity of energetic secondary particles by knock-on processes with the cometary matter. These are responsible for the majority of the so called “hot” chemical processes. Endothermic reactions with high activation energy and atom molecule interactions are possible and may add to the classical exothermic ion-molecule or radical reactions. Other sources of hot atoms or ions in comets are: cosmic rays, acceleration or pick-up processes and turbulences in comae and gas or dust tails, and photon absorption induced dissociation. The products of hot chemical reactions, short period comets experience on their orbits, add to those formed in the individual component ice or dust grains by strong fluxes of energetic particles in times prior to the accretion to a comet.     

Ion production and ionization effect in the atmosphere during the Bastille day GLE 59 due to high energy SEPs

The influence of high energy particles, specifically cosmic rays, on atmospheric physics and chemistry is highly discussed. In most of the proposed models the role of ionization in the atmosphere due to cosmic rays is not negligible. Moreover, effect(s) on minor constituents and aerosols are recently observed, specifically over the polar regions during strong solar particle events. According to the recent findings for such effects it is necessary an essential increase of ion production, specifically during the winter period. The galactic cosmic rays are the main source of ionization in the Earth’s stratosphere and troposphere. Occasionally, the atmospheric ionization is significantly enhanced during strong solar energetic particles events, specifically over the polar caps. During the solar cycle 23 several strong ground level enhancements were observed. One of the strongest was the Bastille day event occurred on 14 July 2000. Using a full Monte Carlo 3-D model, we compute the atmospheric ionization, considering explicitly the contribution of cosmic rays with galactic and solar origin, focusing on high energy particles. The model is based on atmospheric cascade simulation with the PLANETOCOSMICS code. The ion production rate is computed as a function of the altitude above the sea level. The ion production rate is computed on a step ranging from 10 to 30?min throughout the event, considering explicitly the spectral and angular characteristics of the high energy part of solar protons as well as their time evolution. The corresponding event averaged ionization effect relative to the average due to galactic cosmic rays is computed in lower stratosphere and upper troposphere at various altitudes, namely 20?km, 15?km, 12?km and 8?km above the sea level in a sub-polar and polar regions. The 24^h and the weekly ionization effects are also computed in the troposphere and low stratosphere. Several applications are discussed.     

L'interaction entre le flot d'helium neutre d'origine interstellaire et l'heliosphere

Elastic collisions between neutral helium atoms from interstellar origin and protons from both the interstellar plasma in the heliospheric interface and the solar wind inside the heliosphere modify parameters of the helium gas. Upstream the heliopause, the helium atoms release momentum to the plasma, which results in a decrease of their bulk velocity, and remove energy from the plasma, which results in an increase of their temperature. Inside the heliosphere, the major part of the energy communicated by solar wind protons to helium atoms is transferred through scarce frontal collisions, which results in the creation of a hot tenuous He component in the downstream (with respect to the sun) region. The modification of the spatial He distribution function near the sun due to slightly deflected atoms is negligible in first approximation. Lastly, we emphasize that the collisional effect is probably insufficient to explain the high temperature of helium derived from photometric measurements of the interplanetary medium at 58.4 nm (16 000 K). By taking into account two other effects which are the light transfer in the He resonance line inside the focusing cone and a possible latitudinal anisotropy of the solar ionizing EUV flux, leading both to a lowering of the contrast of the cone, we show that the temperature discrepancy between H (8 000 K : spectral measurements : line width, Doppler shift) and He (16 000 K : photometric measurements) can be reasonably explained by the combined actions of these three effects : elastic collisions, light transfer at 58.4 nm inside the focusing cone, solar EUV flux latitudinal anisotropy.