| 1. |
- Buckle, J. V., et al.
(författare)
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Observations of chemical differentiation in clumpy molecular clouds
- 2006
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Ingår i: Faraday Discussions. - : Royal Society of Chemistry (RSC). - 1359-6640 .- 1364-5498. ; 133, s. 63 - 82
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Tidskriftsartikel (refereegranskat)abstract
- We have extensively mapped a sample of dense molecular clouds (L1512, TMC-1C, L1262, Per7, L1389, L1251E) in lines of HC 3 N, CH 3 OH, SO and C 18 O. We demonstrate that a high degree of chemical differentiation is present in all of the observed clouds. We analyse the molecular maps for each cloud, demonstrating a systematic chemical differentiation across the sample, which we relate to the evolutionary state of the cloud. We relate our observations to the cloud physical, kinematical and evolutionary properties, and also compare them to the predictions of simple chemical models. The implications of this work for understanding the origin of the clumpy structures and chemical differentiation observed in dense clouds are discussed. © The Royal Society of Chemistry 2006.
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| 2. |
- Olofsson, Henrik, 1972, et al.
(författare)
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A spectral line survey of Orion KL in the bands 486-492 and 541-577 GHz with the Odin satellite. I. The observational data
- 2007
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 476:number 2, December III, s. 791-806
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Tidskriftsartikel (refereegranskat)abstract
- Aims.Spectral line surveys are useful since they allow identification of new molecules and new lines in uniformly calibrated data sets. The subsequent multi-transition analysis will provide improved knowledge of molecular abundances, cloud temperatures and densities, and may also reveal previously unsuspected blends of molecular lines, which otherwise may lead to erroneous conclusions. Nonetheless, large portions of the sub-millimetre spectral regime remain unexplored due to severe absorptions by H2O and O2 in the terrestrial atmosphere. The purpose of the measurements presented here is to cover wavelength regions at and around 0.55 mm - regions largely unobservable from the ground.Methods.Using the Odin astronomy/aeronomy satellite, we performed the first spectral survey of the Orion KL molecular cloud core in the bands 486-492 and 541-576 GHz with rather uniform sensitivity (22-25 mK baseline noise). Odin's 1.1 m size telescope, equipped with four cryo-cooled tuneable mixers connected to broad band spectrometers, was used in a satellite position-switching mode. Two mixers simultaneously observed different 1.1 GHz bands using frequency steps of 0.5 GHz (25 h each). An on-source integration time of 20 h was achieved for most bands. The entire campaign consumed ~1100 orbits, each containing one hour of serviceable astro-observation.Results.We identified 280 spectral lines from 38 known interstellar molecules (including isotopologues) having intensities in the range 80 to 0.05 K. An additional 64 weak lines remain unidentified. Apart from the ground state rotational 11,0-10,1 transitions of ortho-H2O, H218O and H217O, the high energy 62,4-71,7 line of para-H2O (Eu=867$\,$K) and the HDO(20,2-11,1) line have been observed, as well as the 10-01 lines from NH3 and its rare isotopologue 15NH3. We suggest assignments for some unidentified features, notably the new interstellar molecules ND and SH-. Severe blends have been detected in the line wings of the H218O, H217O and 13CO lines changing the true linewidths of the outflow emission.
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| 3. |
- Persson, Carina, 1964, et al.
(författare)
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A spectral line survey of Orion KL in the bands 486-492 and 541-577 GHz with the Odin satellite. II. Data analysis
- 2007
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 476:2, December III, s. 807-827
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Tidskriftsartikel (refereegranskat)abstract
- Aims.We investigate the physical and chemical conditions in a typical star forming region, including an unbiased search for new molecules in a spectral region previously unobserved.Methods.Due to its proximity, the Orion KL region offers a unique laboratory of molecular astrophysics in a chemically rich, massive star forming region. Several ground-based spectral line surveys have been made, but due to the absorption by water and oxygen, the terrestrial atmosphere is completely opaque at frequencies around 487 and 557 GHz. To cover these frequencies we used the Odin satellite to perform a spectral line survey in the frequency ranges 486-492 GHz and 541-577 GHz, filling the gaps between previous spectral scans. Odin's high main beam efficiency, $\eta_{{\rm mb}}$ = 0.9, and observations performed outside the atmosphere make our intensity scale very well determined.Results.We observed 280 spectral lines from 38 molecules including isotopologues, and, in addition, 64 unidentified lines. A few U-lines have interesting frequency coincidences such as ND and the anion SH-. The beam-averaged emission is dominated by CO, H2O, SO2, SO, 13CO and CH3OH. Species with the largest number of lines are CH3OH, (CH3)2O, SO2, 13CH3OH, CH3CN and NO. Six water lines are detected including the ground state rotational transition 11,0-10,1 of o-H2O, its isotopologues o-H218O and o-H217O, the Hot Core tracing p-H2O transition 62,4-71,7, and the 20, 2-11,1 transition of HDO. Other lines of special interest are the 10-0$_$ transition of NH3 and its isotopologue 15NH3. Isotopologue abundance ratios of D/H, 12C/13C, 32S/34S, 34S/33S, and 18O/17O are estimated. The temperatures, column densities and abundances in the various subregions are estimated, and we find very high gas-phase abundances of H2O, NH3, SO2, SO, NO, and CH3OH. A comparison with the ice inventory of ISO sheds new light on the origin of the abundant gas-phase molecules.
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| 4. |
- Wirström, Eva, 1977, et al.
(författare)
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A search for pre-biotic molecules in hot cores
- 2007
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 473, s. 177-180
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Tidskriftsartikel (refereegranskat)abstract
- Aims. Our aim is to better understand the complex chemistry of organic molecules in the interstellar medium, leading to the formation of pre-biotic molecules such as amino acids.Methods. We have performed a search for the pre-biotic molecules amino acetonitrile (H2N CH2 CN) and vinyl acetylene (C2H3 CCH) towards four northern hot core sources using the Onsala 20 m telescope.Results. We have determined upper limits to the column density of amino acetonitrile (1-4*10^13 cm^-2) and vinyl acetylene (2-7*10^14 cm^-2) in the observed sources. In addition, from the absence of other lines within the observed frequency band, we have further constrained the column density of oxiranecarbonitrile (c-C3H3 NO) and amino-ethanol (NH2 CH2 CH2 OH) in these sources.
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| 5. |
- Wirström, Eva, 1977
(författare)
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Astrochemistry at Millimetre and Submillimetre Wavelengths
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The focus of this thesis is a series of observational tests, aiming to clarify the chemical and physical origin of interstellar molecules. Spectral lines at millimetre and submillimetre wavelengths, caused by rotational transitions in CO, H2O, NH3, CH3OH, CH3SH, C2H3CN, and several of their isotopologues, have been observed towards regions of star-formation in the Galaxy. Maps of extended H2O and CO emission from the Orion nebula demonstrate that the water probably is localised to the photon-dominated region at the surface of the molecular cloud, at higher abundances than previously thought. Water is also observed in absorption from its ground-state towards the massive star-forming region Sgr B2. Curiously enough, a water abundance similar to the one reported for Orion is found in the low-excitation gas in one of the Galactic spiral arms. Ammonia absorption was also observed from diffuse spiral arm clouds along the same line-of-sight, but at about an order of magnitude lower abundance. The observed water and ammonia absorptions caused by the Sgr B2 cloud itself are successfully modelled without invoking a morphological component of hot gas.Two independent methods of analysis are applied to observations of methanol (CH3OH) and its 13C isotopologue in the cold envelopes of young stellar objects. Both methods indicate that methanol is mainly formed by hydrogenation of CO on cold dust grains. A study comparing the interstellar abundances of CH3SH (methyl mercaptan) and CH3OH unveil a possible trend of lower relative CH3SH abundances in more evolved objects. However, the significance of this trend, in relation to the chemical origin of these molecules, needs to be further investigated.In addition, searches for two pre-biotic molecules, namely vinyl acetylene (C2H3CCH) and amino acetonitrile (H2NCH2CN), resulting in improved upper abundance limits are presented.A comprehensive conclusion of this thesis is that in order to exploit the full capacity of high-quality observations there is a serious need for additional theoretical and laboratory investigations of processes like proton-exchange reactions, collision rates, freeze-out and desorption, all taking into account different isotopologues and spin-types.
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| 6. |
- Wirström, Eva, 1977, et al.
(författare)
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Observational constraints on the formation of interstellar methanol
- 2008
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Ingår i: in Proceedings of "Organic Matter in Space", Hong Kong Feb. 18-22, 2008, IAU symposium 251, eds. S. Kwok, S. Sandfjord, Cambridge University Press. - 9780521889827 ; , s. 143-144
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The processes by which methanol, one of the most abundant interstellar organics, is formed in the interstellar medium are not yet accurately known. Pure gas-phase chemistry models fail to reproduce observed abundances by orders of magnitude, pointing to formation on grains and subsequent desorption.Observations of methanol and its isotopologue 13CH3OH in several sources have been used to trace the origin, and thus the formation routes of methanol on interstellar grains, by means of isotope labelling a posteriori.
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| 7. |
- Wirström, Eva, 1977, et al.
(författare)
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Odin * CO and 13CO J=5-4 mapping of Orion KL - a step towards accurate water abundances
- 2006
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Ingår i: Astronomy & Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 453, s. 979-987
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Tidskriftsartikel (refereegranskat)abstract
- Aims. The very high main beam efficiency (90%) of the telescope on the sub-millimetre wave satellite Odin, in combination with the small calibration errors in the absence of atmospheric attenuation, assures that observed line brightness temperatures are very accurately determined. Based on this, we attempt to determine the column density distribution of H-2, and the ortho-water abundance, in the Orion KL region.Methods. We have, for the first time, mapped the (CO)-C-12 J = 5-4 emission in a 7' x 7' region covering Orion KL, observed simultaneously with a (CO)-C-13 J = 5-4 map. Also presented are (CO)-O-18 J = 5-4 emission data at four different positions and a (CO)-O-17 J = 5-4 emission spectrum detected towards the Orion KL position. The Odin mapping was performed at 1' spacing ( beam full width at half maximum 126'' at 557 GHz).Results. The CO J = 5-4 narrow line emission from this region mainly arises in the warm, dense gas at the interface ( the photon-dominated region) between the M42 HII region and the Orion A molecular cloud, the Orion PDR. The (CO)-C-12 and (CO)-C-13 J = 5-4 emission maps have been used to determine the column density distribution of H-2 gas across the Orion KL region. The results have been verified by comparing to column densities obtained using the decidedly optically thin (CO)-O-18 emission as input to the RADEX radiative transfer code. We find H-2 column densities ranging from 5 x 10(21) cm(-2) at map edges to 7 x 10(22) cm(-2) at the molecular ridge. The mass of the gas in the mapped region is estimated to be 480 M-circle dot, of which 320 M-circle dot is situated towards the molecular ridge. We estimate that about half of this mass belongs to the warm Orion PDR interface layer. Finally, based on data from the positions where (CO)-O-18 J = 5-4 has been observed, we estimate the ortho-water abundance in the Orion PDR layer to be >= 8 x 10(-8), higher than previously estimated.
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| 8. |
- Wirström, Eva, 1977
(författare)
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Studies in Molecular Astrophysics and Astrobiology
- 2006
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The molecules of the interstellar medium (ISM) can be used as probes of the physical conditions in a range of different types of interstellar environment, for example star forming regions. The first chapters of this thesis describe the theory and the observational techniques used to study the rotational transition emission from, and the present knowledge of, these molecules. In particular, models and observations of prebiotic molecules, like the simplest amino acid glycine, have become increasingly interesting in the light of a possible connection to the beginning of life on Earth. Searches for two prebiotic molecules, vinyl acetylene (C2H3 CCH) and amino acetonitrile (H2N CH2 CN), towards hot star-forming cores with the Onsala 20 metre radio telescope are presented. Neither of the molecules has been detected, but towards the richest molecular-line source observed, Orion KL, the upper column density limits are determined to N(C2H3 CCH) 5x10-8.Footnote 1: Odin is a Swedish-led satellite project funded jointly by the Swedish National Space Board (SNSB), the Canadian Space Agency (CSA), the National Technology Agency of Finland (Tekes), and the Centre National d'Etudes Spatiales (CNES, France). The Swedish Space Corporation (SSC) was the industrial prime contractor and is also responsible for the satellite operation.
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