Properties of simulated cosmic matters after gamma-ray and neutron irradiation

Interstellar and circumstellar matter is known to be strongly irradiated by cosmic radiation and several types of cosmic ray particles. The effects of irradiation on simulated interstellar and circumstellar matter such as CaCO₃, MgCO₃, SiO₂ and Al₂O₃ are investigated. Especially, thermoluminescence (TL) spectra after γ-ray and neutron irradiation are compared carefully. It is shown that the thermoluminescence after neutron irradiation appears significantly in the wavelength of blue region. On the reflectance in infrared region, the irradiation effect appears scarcely.     

Stars with discrepant v sin i as derived from Ca II λ 3933 Å and Mg II λ 4481 Å lines. III. Stars with v sin i (λ 3933 Å) < v sin i (λ 4481 Å)

Axial rotation of a star plays an important role in its evolution, physical conditions in its atmosphere and the appearance of its spectrum. We analyzed CCD spectra of nine stars for which the projected rotational velocity derived from the Ca II line at λ 3933 Å was remarkably lower than the one derived from the MgII line at λ 4481 Å. We derived effective temperatures and surface gravities using published uvbyβ photometries, and computed synthetic spectra. Comparing the observed line profiles of the two lines with the computed ones, we estimated the values of v sin i. One of the stars, HD44783, is a Be-star which, besides the narrow absorptions in the spectrum originating in its circumstellar envelope, also has lines of interstellar origin. We also found indications of circumstellar matter in the spectrum of HD25152. In the spectra of the remaining seven stars the narrow components in the Ca II λ 3933 Å line as well as narrow absorptions in the Na I λ 5889.951 Å (D1) and λ 5895.924 Å (D2) lines are of interstellar origin. In HD114376 there are two systems of interstellar components, thus disclosing two different interstellar clouds in the direction of the star. In the spectrum of HD138527 signs of a possible companion were detected, the emission of which contributes 15% to the total light of the system.     

3-D Structure of the Galactic Interstellar Matter: A Contribution from GAIA

We investigate the possibilities for tracing interstellar extinction with the ESA's astrometric space mission GAIA. The analysis is based on detailed simulations of the GAIA photometry, which are used to derive the distribution of interstellar matter in a modelled Galaxy. We find that `small' diffuse clouds (diameter D = 4 pc, E <sub>B-V</sub> = 0.06) will be easily traced with GAIA up to the distances of ∼ 800 pc. `Large' diffuse interstellar clouds (D = 10 pc, E _B-V = 0.13) will be located up to the distances of ∼ 2.5 kpc. This holds for the reddening tracers of spectral types O – K2 brighter than V = 17. Inmost cases, due to their low spatial density, the early type stars (O– A2) cannot provide reliable information about the distribution of interstellar matter. None of the reddening tracers measured by GAIA will provide reliable identification of the individual interstellar clouds beyond the distances of ∼ 3 kpc. Therefore, we conclude that the information available from photometric observations will be not sufficient for the detailed reconstruction of the 3-D distribution of Galactic interstellar matter. It is therefore extremely important to define the new strategies which would allow to combine all the available information, including the earlier space- and/or ground-based investigations, together with the information which will be provided by GAIA itself (parallaxes, E _B-V etc.). This revised version was published online in July 2006 with corrections to the Cover Date.     

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.     

A classification of the available astrophysica data of particularHii regions

We have calculated the energy spectra of cosmic ray secondary antiprotons and positrons using the latest available data on inclusive reactions. Using the measured positron spectrum, we have found that the amount of matter traversed by the cosmic rays in the few GeV region to bem≈4.7±1.5 g cm^?2 of interstellar hydrogen. The computed antiproton to proton ratio is about 4×10^?4 for energies 5–10 GeV. This is sufficient to make observations of antiprotons feasible from balloon flights. We have also pointed out the type of information that can be obtained if accurate information of the spectra of these two components becomes available.     

Peculiarities of the abundance of chemical elements in the atmosphere of PMMR23-red supergiant in the Small Magellanic Cloud due to interstellar gas accretion

The chemical composition of the PMMR23 red supergiant located in the Small Magellanic Cloud (SMC) is analyzed. The abundance of 35 chemical elements and the upper limits of abundance for Tl and U are found. The relative abundance of heavy elements is higher by 0.6–1.0 dex with respect to iron peak elements. The spectra of several SMC red supergiants PMMR27, PMMR28, and PMMR144—located in the region where the velocities of stars and interstellar gas are quite high— show the emission components in the wings of the hydrogen line. This emission is not detected for PMMR23. A possibility of interstellar gas accretion on the atmospheres of PMMR23 and other supergiants in Magellanic Clouds is discussed. The analysis is carried out using spectra measured at ESO 3.6 m telescope with the spectral resolving power R = 30000.     

Chemodynamical Modelling of Galaxy Formation and Evolution

We present our recently developed 3-dimensional chemodynamical code for galaxy evolution. This code follows the evolution of different galactic components like stars, dark matter and different components of the interstellar medium (ISM), i.e. a diffuse gaseous phase and the molecular clouds. Stars and dark matter are treated as collisionless N-body systems. The ISM is numerically described by a smoothed particle hydrodynamics (SPH) approach for the diffuse gas and a sticky particle scheme for the molecular clouds. Additionally, the galactic components are coupled by several phase transitions like star formation, stellar death or condensation and evaporation processes within the ISM. As an example we show the dynamical and chemical evolution of a star forming dwarf galaxy with a total baryonic mass of 2 ċ 10⁹ M_⊙. After a moderate collapse phase the stars and the molecular clouds follow an exponential radial distribution, whereas the diffuse gas shows a central depression as a result of stellar feedback. The metallicities of the galactic components behave quite differently with respect to their temporal evolution as well as their radial distribution. Especially, the ISM is at no stage well mixed. This revised version was published online in September 2006 with corrections to the Cover Date.     

Laboratory set-up for studying ices at the MIR and FIR region

H₂O, CO and CO₂ ices are condensed on carbonaceous and silicate dust grains in dense interstellar clouds and circumstellar environments. The presence of these ices is inferred by analysing their infrared (IR) spectra. The upcoming Herschel space observatory (HERSCHEL) and ground-based astronomy project (ALMA) will provide new spectral data in the unexplored far infrared (FIR) and sub-millimetre range. In our laboratory we are developing instrumentation to study ices at IR region. One of the key components of our laboratory is a silicon composite bolometer in our IFS. This detector allows us to obtain spectra with a sensitivity much greater than that obtained with a standard deuterated triglycine sulphate (DTGS) detector working at room temperature and under vacuum conditions. We plan to collect mid infrared (MIR) and FIR spectra of simple ices and their mixtures and compare these with observational data. It is also planned to do a systematic laboratory study of the effects that ultraviolet (UV) photolysis and thermal annealing have on the ice band profiles and their structure.     

Far UV radiation transfer and H2CO lifetime in dense interstellar clouds

The UV radiation transfer within spherical interstellar dust clouds is analyzed using the method of successive scatterings. The results are used to determine the lifetime of interstellar H₂CO against photo-destruction. The effectiveness of this process is compared with those of chemical mechanisms.     

Zur Struktur der interstellaren Materie bei Zeta Persei

The region around ξ Persei is qualified for an extended investigation of the interstellar matter in a limited volume because of its position in the Galaxy and the high brightness of ξ Persei. The basis for this analysis were spectra of high dispersion, 21 cm line profiles, photoelectric UBV measurements, measurements of star light polarization, and a photographic three colour photometry. The total numbers of absorbers per cm² for Ca II and Na I were evaluated by the dublet ratio method. The adaption of observations to models for the distribution of the interstellar gas yielded the abundances of Ca and Na. Ca is deficient by about a factor 150. The total number of H I atoms per cm² followed from a gaussian analysis of 21 cm lines. The results of the analysis can be best described by a model consisting of a dense H I layer with a density of 20 to 140 cm⁻³ situated 10 to 30 pc in front of ξ Persei. The interstellar reddening is not uniform in this region; the extension of this cloud in the line of sight is about 100 pc. The structure analysis of reddening provided micro-scales of 0.4 and 4.5 pc for the fluctuations in density of interstellar absorbing matter. On the assumption that the interstellar dust consists of silicate grains the density ratio between interstellar gas and dust amounts to nearly 35. The total mass of the interstellar matter in the analysed region is ≤ 1100 z.dstR;⊙. The direction and strength of the magnetic field were estimated from the star light polarization; according to that the field strength is about 8 · 10⁻⁶G. It is likely that the interstellar matter around ξ Persei is connected with the evolution of the association II Persei.     

NanoSIMS analysis of organic carbon from the Tissint Martian meteorite: Evidence for the past existence of subsurface organic‐bearing fluids on Mars

Two petrographic settings of carbonaceous components, mainly filling open fractures and occasionally enclosed in shock‐melt veins, were found in the recently fallen Tissint Martian meteorite. The presence in shock‐melt veins and the deuterium enrichments (δD up to +1183‰) of these components clearly indicate a pristine Martian origin. The carbonaceous components are kerogen‐like, based on micro‐Raman spectra and multielemental ratios, and were probably deposited from fluids in shock‐induced fractures in the parent rock of Tissint. After precipitation of the organic matter, the rock experienced another severe shock event, producing the melt veins that encapsulated a part of the organic matter. The C isotopic compositions of the organic matter (δ¹³C = ?12.8 to ?33.1‰) are significantly lighter than Martian atmospheric CO₂ and carbonate, providing a tantalizing hint for a possible biotic process. Alternatively, the organic matter could be derived from carbonaceous chondrites, as insoluble organic matter from the latter has similar chemical and isotopic compositions. The presence of organic‐rich fluids that infiltrated rocks near the surface of Mars has significant implications for the study of Martian paleoenvironment and perhaps to search for possible ancient biological activities on Mars.     

Time dependent chemical study of contracting interstellar clouds. II. abundances of oxygen- and sulphur-bearing molecules

Abstract. We have constructed a chemical reaction system in a contracting interstellar cloud. In paper (I) we have presented the details of the physical and chemical scheme and the method of solution. The results of our chemical model produce fractional abundances of H₂CO, CO, OH, H₂O, SO and OCS which are in good agreement with the results of observations. On the other hand, the results of chlorine-bearing species are not in agreement with those of the observations. The calculated abundances of H₂CO, CO, OH, H₂O, SO, OCS and Cl⁺ are in agreement with the results of previous theoretical studies.     

Comparison of the Raman spectra of ion irradiated soot and collected extraterrestrial carbon

We use a low pressure flame to produce soot by-products as possible analogues of the carbonaceous dust present in diverse astrophysical environments, such as circumstellar shells, diffuse interstellar medium, planetary disks, as well as in our own Solar System. Several soot samples, displaying an initial chemical diversity from aromatic to aliphatic dominated material, are irradiated with 200-400 keV H⁺, He⁺, and Ar⁺⁺ ions, with fluences comprised between 10¹⁴ and 10¹⁶ ions/cm², to simulate expected radiation induced modification on extraterrestrial carbon. The evolution of the samples is monitored using Raman spectroscopy, before, during, and after irradiation. A detailed analysis of the first- and second-order Raman spectra is performed, using a fitting combination of Lorentzian and/or Gaussian-shaped bands. Upon irradiation, the samples evolve toward an amorphous carbon phase. The results suggest that the observed variations are more related to vacancy formation than ionization processes. A comparison with Raman spectra of extraterrestrial organic matter and other irradiation experiments of astrophysically relevant carbonaceous materials is presented. The results are consistent with previous experiments showing mostly amorphization of various carbonaceous materials. Irradiated soots have Raman spectra similar to those of some meteorites, IDPs, and Comet Wild 2 grains collected by the Stardust mission. Since the early-Sun expected irradiation fluxes sufficient for amorphization are compatible with accretion timescales, our results support the idea that insoluble organic matter (IOM) observed in primitive meteorites has experienced irradiation-induced amorphization prior to the accretion of the parent bodies, emphasizing the important role played by early solar nebula processing.     

On the presence of phyllosilicate minerals in the interstellar grains

The composition of the interstellar silicate dust is investigated. Condensation or alteration of silicate grains at temperatures of a few hundred degrees, in the presence of H₂O, would result in hydrous or phyllosilicates, the silicate type most abundant in the type I carbonaceous chondrites. Infrared spectra of small particles (～0.1 μ) of the high temperature condensates, olivine and pyroxene, at 300 K and 4 K do not give a good match to the interstellar absorption band near 9.8 μ. Laboratory spectra of several phyllosilicates give better agreement as does the spectrum of a carbonaceous chondrite. We propose that the silicates in the interstellar grains are predominantly phyllosilicates and suggest additional spectral tests for this hypothesis.     

The distribution of interstellar matter in NGC 654

The young cluster NGC 654 is studied using UBV photographic photometry with a view to determining the distribution of interstellar matter in a region where star formation recently occurred.NGC 654 is found to be enclosed in a shell of interstellar matter of mass 1500M . The mass of all stars in the cluster is 4000M .     

Low‐energy helium ion irradiation‐induced amorphization and chemical changes in olivine: Insights for silicate dust evolution in the interstellar medium

Abstract— We present the results of irradiation experiments aimed at understanding the structural and chemical evolution of silicate grains in the interstellar medium. A series of He+ irradiation experiments have been performed on ultra‐thin olivine, (Mg,Fe)₂SiO₄, samples having a high surface/volume (S/V) ratio, comparable to the expected S/V ratio of interstellar dust. The energies and fluences of the helium ions used in this study have been chosen to simulate the irradiation of interstellar dust grains in supernovae shock waves. The samples were mainly studied using analytical transmission electron microscopy. Our results show that olivine is amorphized by low‐energy ion irradiation. Changes in composition are also observed. In particular, irradiation leads to a decrease of the atomic ratios O/Si and Mg/Si as determined by x‐ray photoelectron spectroscopy and by x‐ray energy dispersive spectroscopy. This chemical evolution is due to the differential sputtering of atoms near the surfaces. We also observe a reduction process resulting in the formation of metallic iron. The use of very thin samples emphasizes the role of surface/volume ratio and thus the importance of the particle size in the irradiation‐induced effects. These results allow us to account qualitatively for the observed properties of interstellar grains in different environments, that is, at different stages of their evolution: chemical and structural evolution in the interstellar medium, from olivine to pyroxene‐type and from crystalline to amorphous silicates, porosity of cometary grains as well as the formation of metallic inclusions in silicates.     

O VI in the local interstellar medium

We report preliminary results of a search for O VI absorption in the spectra of ～100 hot DA white dwarfs observed by the FUSE satellite. We have carried out a detailed analysis of the radial velocities of interstellar and (where present) stellar absorption lines for the entire sample of stars. In many cases, the velocity differences between the interstellar and photospheric components are below the resolution of the FUSE spectrographs. However, in a significant number of cases the interstellar and photospheric contributions can be separated. In the majority of stars where we find O VI absorption lines, the material is clearly associated with the stellar photosphere and not the interstellar medium. There are a small number of lines-of-sight where the gas is interstellar in nature but the stars are located beyond the boundaries of the local cavity.     

Interstellar gas depletion and dust parameters

It is shown that on theoretical grounds the relative abundances of the elements in the interstellar gas phase should be correlated with the wavelength of maximum interstellar polarization _max. If these correlations can be determined by observations, then there is the possibility to determine the relative abundances of the heavier elements within the mantles as well as within the cores of interstellar dust grains, at least in principle.The observational data available up to now confirm the existence of such correlations between _max and the interstellar gas phase abundances of titanium, iron, magnesium, and carbon. Statements about the chemical composition of the dust particles are not yet possible. For this there are observations of the interstellar gas depletion needed, especially in such lines of sight where _max has extreme values.Paper presented at a Workshop on The Role of Dust in Dense Regions of Interstellar Matter, held at Georgenthal, G.D.R., in March 1986.     

Interstellar water and interstellar ice

There are two ways that water ice can form in the interstellar medium: H₂O molecules can form in the gas phase and then freeze out onto dust grain surfaces, or O and OH can be converted at the surfaces of grains to form H₂O, which is then retained. Bergin et al. (1998) have recently shown that shocks passing through interstellar clouds sufficiently frequently can make the first method effective. However, we present results from a similar chemical model which indicate that this requires significant optical shielding because of the high ionization fraction in regions exposedto a high UV flux. We deduce, therefore, that grain surface reactions probably represent the main source of H₂O ice on lines of sight with visual extinction up to about 6 magnitudes to an embedded source or 12 magnitudes to a background object. This revised version was published online in July 2006 with corrections to the Cover Date.     

Protosolar nebula and composition of comets

Comets seem to be composed of matter, which is supposed to have the same molecular composition as protosolar nebula. Although there are no unbiased evidence that cometary nuclei retain the molecular composition inherited from the protosolar cloud, the observed properties of comets indicate that there is at least a resemblance between cometary composition and the material properties of dense interstellar clouds. Therefore the origin of comets could be searched in the cold stages of the protosolar nebula and molecular abundances of grain mantles in this nebula may be similar to those in the cometary dust. It is suggested that comets may contain pristine, virtually unaltered protosolar material and their study might be very relevant way to more information about processes in early stages of the solar nebula. Our knowledge about composition of the cometary nucleus is still relatively scarce, but we can partly deduce it from data obtained either by ground-based spectroscopy or by in situ mass spectrometry from space experiments. Most important were the discovery of fluffy CHON particles composed partly or even completely from compounds containing light elements. No consensus concerning the presence of interstellar pristine matter in comet has been reached from various approaches to determine the relationship between comets and interstellar grains. Most of these studies are based on infrared spectroscopy. Another method is the comparison on the chemical models of the protosolar nebula with the volatile compounds of the cometary nuclei. Both gas-phase and grain-surface chemistry are considered and initial gas-phase atomic abundances are assumed to be protosolar. The cometary matter is certainly not identical with the typical material of dense interstellar cool dense clouds, but it is closer to it than any other type of matter in solar system so far accessible to us. The data from comets combined with models of chemical evolution of matter in environment similar as prevailed the early stage of presolar nebula may at least impose constrains on the condition for comet formation. Here presented study is a preliminary contribution to such studies.