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ABSTRACT: We present ESO - Very Large Telescope and ESA - Infrared Space Observatory 3 to 4 $\mu$m spectra of Seyfert 2 nuclei as compared to our galactic center lines of sight. The diffuse interstellar medium probed in both environments displays the characteristic 3.4 $\mu$m aliphatic CH stretch absorptions of refractory carbonaceous material. The profile of this absorption feature is similar in all sources, indicating the CH$_2$/CH$_3$ ratios of the carbon chains present in the refractory components of the grains are the same in Seyfert 2 inner regions. At longer wavelengths the circumstellar contamination of most of the galactic lines of sight precludes the identification of other absorption bands arising from the groups constitutive of the aliphatics seen at 3.4 $\mu$m. The clearer continuum produced by the Seyfert 2 nuclei represents promising lines of sight to constrain the existence or absence of strongly infrared active chemical groups such as the carbonyl one, important to understand the role of oxygen insertion in interstellar grains. The Spitzer Space Telescope spectrometer will soon allow one to investigate the importance of aliphatics on a much larger extragalactic sample. Comment: 10 pages. Accepted for publication on April 30th 2004 in Astronomy and Astrophysics
05/2004;
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02/2004; 545:239-240.
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ABSTRACT: We review the recent detections of amino acids following the recreation
of the conditions on interstellar grains in the laboratory.
10/2002; -1:217.
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ABSTRACT: Amino acids are the essential molecular components of living organisms on Earth, but the proposed mechanisms for their spontaneous generation have been unable to account for their presence in Earth's early history. The delivery of extraterrestrial organic compounds has been proposed as an alternative to generation on Earth, and some amino acids have been found in several meteorites. Here we report the detection of amino acids in the room-temperature residue of an interstellar ice analogue that was ultraviolet-irradiated in a high vacuum at 12 K. We identified 16 amino acids; the chiral ones showed enantiomeric separation. Some of the identified amino acids are also found in meteorites. Our results demonstrate that the spontaneous generation of amino acids in the interstellar medium is possible, supporting the suggestion that prebiotic molecules could have been delivered to the early Earth by cometary dust, meteorites or interplanetary dust particles.
Nature 04/2002; 416(6879):403-6. · 36.28 Impact Factor
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ABSTRACT: The L723 low mass class 0 protostellar object has been observed with the IRS low resolution spectrometer onboard Spitzer Space Telescope. A huge CO$_2$ ice column density of 6.3 $\pm$ 1 $\times$ 10$^{18}$ cm$^{-2}$ is detected toward this extremely red object. We constructed the spectral energy distribution (SED) of L723 by combining the Spitzer spectral data with Infrared Space Observatory (ISO) camera extracted fluxes, IRAS points, ISO long wavelength spectrometer (LWS) observations and millimeter ground based observations. A self consistent 1D model was developed to fit the SED. We show that, besides the high CO$_2$ column density, the abundance ratio of CO$_2$ ice to silicates grain cores is similar to other lines-of-sight.
http://dx.doi.org/10.1051/0004-6361:200500211.
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ABSTRACT: Aims.Two irradiation experiments on interstellar ice analogs at 80 K under interstellar-like conditions were performed with the LURE SU5 synchrotron beamline to assess, for the first time, the photochemical effect of circularly polarized ultraviolet light (UV CPL) at 167 nm (7.45 eV) with right and left polarizations on such ice mixtures.Methods.This effect was measured by determining the enantiomeric excesses (e.e.s) for two amino acids formed in the solid organic residues produced during the subsequent warm-up of the irradiated samples to room temperature: alanine, the most abundant chiral proteinaceous amino acid produced (both polarizations) and 2,3-diaminopropanoic acid (DAP), a non-proteinaceous amino acid (right-polarization experiment). These excesses were compared to those measured for the same amino acids produced after unpolarized UV irradiation of the same ice mixtures (expected to be zero), in order to determine the contribution of CPL only. A careful estimate of all the associated uncertainties (statistical and systematic errors) was also developed.Results.It appears that the enantiomeric photochemical effect at this wavelength is weak, since both alanine and DAP e.e.s were found to be small, at most of the order of 1% in absolute values, and tends to be inconclusive since the effects obtained for both amino acids and both polarizations are not those expected. In light of these results, the hypothesis that CPL may be one source responsible for the e.e.s measured for such amino acids in some meteorites and, more generally, that CPL may be directly related to the origin of biomolecular homochirality on Earth is discussed.
http://dx.doi.org/10.1051/0004-6361:20042018.
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ABSTRACT: Aims. We attempt to ellucidate the structure and chemical composition of the carbon bulk detected in cometary Stardust particles. We determine if the carbon material observed spectroscopically is of true cometary origin and whether or not it was formed by direct UV-photoprocessing of icy grain mantles in the local dense cloud and/or the solar nebula.Methods. We acquire infrared spectroscopy of ten Stardust cometary particles from track 35 and the aerogel inside and outside the particle track. Using infrared and Raman spectroscopy, the dominant carbon component in cometary Stardust particles was compared to IDPs and organics made from UV-photoprocessing of interstellar/circumstellar ice analogs in the laboratory. The Raman spectra of Stardust particles used in this comparison are adapted from the literature.Results. As indicated in previous works, it is found that the collecting aerogel medium, processed during particle impact, poses serious problems for the infrared analysis of the Stardust cometary particles reported in this paper. We identify the structure of the carbon bulk of the organic material retrieved from the aerogel with a form of (hydrogenated) amorphous carbon. It is found that this material is not a direct product of ice photoprocessing.
http://dx.doi.org/10.1051/0004-6361:20078879.
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ABSTRACT: Aims.The available ground- and space-based spectroscopic capabilities of observatories now allow us to extend Galactic interstellar medium composition studies to extragalactic cases. Absorptions in the mid-infrared shows evidence for silicate and carbonaceous grains in other galaxies.Methods.A set of extragalactic spectra of luminous infrared galaxies (LIRGs) has been extracted from the Spitzer database and compared to the spectra of laboratory-produced interstellar carbon dust analogues.Results.These highly obscured lines-of-sight display the characteristic absorptions at ~6.85 and 7.25 $\mu$m of the CH$_3$/CH$_2$ deformation modes of hydrogenated amorphous carbon (a-C:H) grains. They are compared to laboratory-produced a-C:H and imply carbon atom column densities in the solid phase exceeding ~10$^{18}$ cm$^{-2}$.Conclusions.These observations further demonstrate the ubiquitousness of a-C:H in the diffuse interstellar medium (DISM) of galaxies, for a long time almost only observed in the Milky-Way ISM lines-of-sights. Whereas PAH emission lines trace the re-processing of energetic young stellar radiation, the observed a-C:H features underline the existence of large masses of amorphous carbon dust in (extra-)galactic dust budgets. The difficulty in observing such an interstellar component in the mid-infrared is linked to its low absorption contrast $(A_{\rm V}/\tau(6.85)\approx 625 \pm 40)$ for the strongest band, which therefore requires high column densities to detect a-C:H grains. Such carbon grains might be present but spectroscopically hidden in many other galactic environments.
http://dx.doi.org/10.1051/0004-6361:20077798.
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ABSTRACT: The production of a hydrogenated amorphous carbon polymer (a-C:H) via the photolysis of a series of organic molecule precursors at low temperature is described. Such amorphous material is synthesised under interstellar conditions (10 K and Lyman-$\alpha$ photons) and represents the best candidate to explain the Diffuse Interstellar Medium absorption observed in our Galaxy and in other galaxies. We perform a series of laboratory analyses (Infrared spectroscopy, $\mu$spectroscopy, Raman, Photoluminescence and UV-visible spectroscopy) which allow a full characterisation of such polymers. This allows us to assess the importance of the polymer and possible scenarios for its role in crucial aspects of the lifecycle of dust. Such material has implications for the carbon budget at galactic scales, hydrogen formation, extended red emission, as a PAH precursor, and in explaining the 2175 $\AA$ extinction bump.
http://dx.doi.org/10.1051/0004-6361:20042094.
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ABSTRACT: Experiments simulating the processing of various hydrocarbon species under diffuse and dense cloud conditions by UV irradiation were performed. The results indicate that such molecules will be efficiently dehydrogenated in interstellar space. It is argued that the presence of hydrogen in the aliphatic grain material in diffuse clouds results from an equilibrium between dehydrogenation by UV processing and re-hydrogenation by the impinging atomic gas. In dense clouds, the presence of the ice layer will prevent the re-hydrogenation process, causing the carbonaceous grain material to be gradually de-hydrogenated if UV photons are able to penetrate into the dense medium. The implications of this study for the evolution of the carbonaceous component of dust in the interstellar medium are discussed.
http://dx.doi.org/10.1051/0004-6361:20000341.
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ABSTRACT: We simulate experimentally the physical conditions present in dense clouds by means of a high vacuum experimental setup at low temperature $T$ $\approx$ 12 K. The accretion and photoprocessing of ices on grain surfaces is simulated in the following way: an ice layer with composition analogous to that of interstellar ices is deposited on a substrate window, while being irradiated by ultraviolet (UV) photons. Subsequently the sample is slowly warmed up to room temperature; a residue remains containing the most refractory products of photo- and thermal processing. In this paper we report on the Fourier transform-infrared (FT-IR) spectroscopy of the refractory organic material formed under a wide variety of initial conditions (ice composition, UV spectrum, UV dose and sample temperature). The refractory products obtained in these experiments are identified and the corresponding efficiencies of formation are given. The first evidence for carboxylic acid salts as part of the refractory products is shown. The features in the IR spectrum of the refractory material are attributed to hexamethylenetetramine (HMT, [ (CH$_2$)$_6$N$_4$] ), ammonium salts of carboxylic acids [ (R–COO$^-$)(NH$^+_4$)] , amides [ H$_2$NC(=O)–R] , esters [ R–C(=O)–O–R$'$] and species related to polyoxymethylene (POM, [ (–CH$_2$O–)$_n$] ). Furthermore, evidence is presented for the formation of HMT at room temperature, and the important role of H$_2$O ice as a catalyst for the formation of complex organic molecules. These species might also be present in the interstellar medium (ISM) and form part of comets. Ongoing and future cometary missions, such as Stardust and Rosetta, will allow a comparison with the laboratory results, providing new insight into the physico-chemical conditions present during the formation of our solar system.
http://dx.doi.org/10.1051/0004-6361:20031408.
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ABSTRACT: Aims.Interplanetary dust particle (IDP) matter probably evolved under irradiation in the interstellar medium (ISM) and the solar nebula. Currently IDPs are exposed to irradiation in the Solar System. Here the effects of UV and proton processing on IDP matter are studied experimentally. The structure and chemical composition of the bulk of carbon matter in IDPs is characterized.Methods.Several IDPs were further irradiated in the laboratory using ultraviolet (UV) photons and protons in order to study the effects of such processing. By means of infrared and Raman spectroscopy, IDPs were also compared to different materials that serve as analogs of carbon grains in the dense and diffuse ISM.Results.The carbonaceous fraction of IDPs is dehydrogenated by exposure to hard UV photons or 1 MeV protons. On the other hand, proton irradiation at lower energies (20 keV) leads to an efficient hydrogenation of the carbonaceous IDP matter. The dominant type of carbon in IDPs, observed with Raman and infrared spectroscopy, is found to be either a form of amorphous carbon ($a$-C) or hydrogenated amorphous carbon ($a$-C:H), depending on the IDP, consisting of aromatic units with an average domain size of 1.35 nm (5-6 rings in diameter), linked by aliphatic chains.Conclusions.The D- and $^{15}$N-enrichments associated to an aliphatic component in some IDPs are probably the result of chemical reactions at cold temperatures. It is proposed that the amorphous carbon in IDPs was formed by energetic processing (UV photons and cosmic rays) of icy grains, maybe during the dense cloud stage, and more likely on the surface of the disk during the T Tauri phase of our Sun. This would explain the isotopic anomalies and morphology of IDPs. Partial annealing, 300-400 $^{\circ}$C, is required to convert an organic residue from ice photoprocessing into the amorphous carbon with low heteroatom content found in IDPs. Such annealing might have occurred as the particles approached the Sun and/or during atmospheric entry heating.
http://dx.doi.org/10.1051/0004-6361:20042571.
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ABSTRACT: We present the results of a laboratory program aimed at studying the effects induced by energetic UV photons on hydrogenated carbon particles. Experiments have been performed under simulated diffuse and dense interstellar medium conditions. To monitor the effects of UV irradiation on grains IR spectroscopy has been used. In both circumstances UV photons lead to a reduction of the aliphatic 3.4 $\mu$m band. An estimation of the destruction cross section by UV photons for the hydrogenated carbon particles has been derived from the reduction of the 3.4 $\mu$m intensity band as a function of the UV fluence. The results of the present work, together with previous laboratory data, can shed light on the enigmatic difference observed for the 3.4 $\mu$m band between dense and diffuse interstellar medium clouds. This difference is compatible with the transformation of hydrogenated carbon particles produced by UV photons and hydrogen atoms and with the changes of the grain properties in the two environments.
http://dx.doi.org/10.1051/0004-6361:20000340.
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ABSTRACT: We have analyzed seven interplanetary dust particles (IDPs) using an infrared microscope with the aim of comparing the 3.4 $\mu$m feature to the same feature observed in the diffuse interstellar medium (DISM) and of searching for additional absorption features due to organic matter. We have developed an in situ extraction method based on the etching of the silicate phases with hydrofluoric acid, which allowed a better detection of the organic fraction. Six out of the seven particles studied present a well resolved 3.4 $\mu$m feature corresponding to aliphatic chains. Some of these particles also present a carbonyl group around 1700 cm$^{-1}$ due to ketone and, probably also, carboxylic acid compounds. Here we report the first determination of the column densities of the aliphatic and aromatic fractions in IDPs, as well as other functional groups. With the asymmetric CH$_{3}$ and CH$_{2}$ column densities we calculated the CH$_2$/CH$_3$ ratios of the IDPs. The average ratio (CH$_2$/CH$_3 = 3.7 \pm 0.9$) is clearly larger than the one measured for the DISM (2.2), indicating that the aliphatic chains in IDPs are longer (or less ramified) than in the DISM. The 3.4 $\mu$m feature of IDPs is significantly narrower than in the DISM, which suggests that the aliphatic fraction in IDPs is made of relatively simpler and less ramified compounds. We conclude that the carbonaceous compounds found in these IDPs have been formed or evolved in a different environment from the DISM.
http://dx.doi.org/10.1051/0004-6361:20041605.
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ABSTRACT: Irradiation of interstellar/circumstellar ice analogs by ultraviolet (UV) light followed by warm up in the laboratory leads to the formation of complex organic molecules, stable at room temperature. Hydrolysis of the room temperature residue releases amino acids, the building blocks of proteins. These amino acids exist in two different forms (l and d), but proteins encountered in living beings consist exclusively of l enantiomers. The origin of this property, called homochirality, is still unknown. Amino acids can be detected and quantified by chemical techniques such as chiral gas chromatography coupled with mass spectrometry (GC-MS). Enantiomers of chiral organics are also known to interact selectively with circularly polarized light (CPL), leading to a selective production or destruction of the final compounds. This paper describes how we settled an experiment where amino acids are formed by irradiation of interstellar/circumstellar ice analogs with ultraviolet (UV) CPL, produced by a synchrotron radiation beamline, which allowed us to quantify the effect of such polarized light on the production of amino acids. These results can be compared to the enantiomeric excesses measured in primitive meteorites such as Murchison.
Advances in Space Research.
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Astronomy and Astrophysics, 367, 355 - 361 (2001).
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Astronomy and Astrophysics, 367, 347 - 354 (2001).
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Astronomy and Astrophysics, 413, 209 - 216 (2004).
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Astronomy and Astrophysics, 444, L57 - L60 (2005).
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ABSTRACT: The Cometary Sampling and Composition Experiment on board of European space Agency's cornerstone mission ROSETTA is designed to identify organic molecules in cometary matter in situ by a combined pyrolysis gas chromatographic and mass spectrometric technique. Its capillary columns coated with chiral stationary phases received considerable attention, because they are designed for separations of non-complex enantiomers to allow the determination of enantiomeric ratios of cometary chiral organic compounds and consequently to provide information about the origin of molecular parity violation in biomolecules. To get gas chromatographic access to organic compounds on the comet, where macromolecules and complex organic polymers of low volatility are expected to make up the main organic ingredients, the combination of two injection techniques will be applied. The pyrolysis technique performed by heating cometary samples stepwise to defined temperatures in specific ovens resulting in thermochemolysis reactions of polymers and a chemical derivatization technique, in which the reagent dimethylformamide dimethylacetal assists pyrolysis derivatization reactions in producing methyl esters of polar monomers. The combination of the reagent assisted pyrolysis gas chromatographic technique with enantiomer separating chromatography was tested with laboratory-produced simulated cometary matter.
Advances in Space Research.
