bluuebunny/crossref_metadata_2025_split huggingface dataset:
Molecular spectral line surveys and the organic molecules in the interstellar molecular clouds
Authors: Ohishi Masatoshi 
Published: October 2008

AbstractIt is known that more than 140 interstellar and circumstellar molecules have so far been detected, mainly by means of the radio astronomy observations. Many organic molecules are also detected, including alcohols, ketons, ethers, aldehydes, and others, that are distributed from dark clouds and hot cores in the giant molecular clouds. It is believed that most of the organic molecules in space are synthesized through the grain surface reactions, and are evaporated from the grain surface when they are heated up by the UV radiation from adjacent stars.On the other hand the recent claim on the detection of glycine have raised an important issue how difficult it is to confirm secure detection of weak spectra from less abundant organic molecules in the interstellar molecular cloud.I will review recent survey observations of organic molecules in the interstellar molecular clouds, including independent observations of glycine by the 45 m radio telescope in Japan, and will discuss the procedure to securely identify weak spectral lines from organic molecules and the importance of laboratory measurement of organic species.
A confusion-limited spectral-line survey of Sgr B2(N) at 1, 2, and 3mm: Establishing the organic inventory in molecular clouds
Authors: Halfen DeWayne T. , Ziurys Lucy M. 
Published: October 2008

AbstractWe present preliminary results of an spectral-line survey at 1, 2, and 3 mm of the galactic center cloud Sgr B2(N). With the current data, several simple prebiotic molecules have been conclusively identified, while several more complex molecules have not. When complete, this survey will provide an accurate database of the gas-phase organic inventory in Sgr B2(N).
An ab-initio study of multiple conformers of glycine
Authors: Kaplan Dan , Recine Greg , Zhang H. 
Published: October 2008

AbstractThe recent combination of new computational chemistry techniques and high performance computational hardware is allowing unprecedented levels of accuracy in the calculations of physical quantities such as potential energy surfaces and rotational-vibrational spectra. Previous results exist in the literature for the first three most stable conformers of glycine at the aug-cc-pVDZ basis set. In this work, we extend the known results, presenting calculations of the four most stable conformers of glycine using the aug-cc-pVQZ basis set. We compare our calculations to experimental values and show that our current calculations differ by <2% from measured values, much better than results from previous years. When searching for molecules in the Interstellar Medium this small difference suggests that computational methods are becoming well-suited for the task. The natural question to ask is: at what point will the small deviation from experimental values render our computations just as reliable as experiments? We feel that the current results show that we are indeed close to this goal.
A Search for Interstellar CH2D+
Authors: Wootten Alwyn , Turner Barry E. 
Published: October 2008

AbstractWe report on a search for interstellar CH2D+. Four transitions occur in easily accessible portions of the spectrum; we report on emission at the frequencies of these transitions toward high column density star-forming regions. While the observations can be interpreted as being consistent with a detection of the molecule, further observations will be needed to secure its identification. The CH2D+ rotational spectrum has not been measured to high accuracy. Its lines are weak, as the dipole moment induced by the inclusion of deuterium in the molecule is small. Astronomical detection is favored by observations toward strongly deuterium-fractionated sources. However, enhanced deuteration is expected to be most significant at low temperatures. The sparseness of the available spectrum and the low excitation in regions of high fractionation make secure identification of CH2D+ difficult. Nonetheless, owing to the importance of CH3+ to interstellar chemistry, and the lack of rotational transitions of that molecule owing to its planar symmetric structure, a measure of its abundance would provide key data to astrochemical models.
Comparing ice composition in dark molecular clouds
Authors: Knez C. , Moore M. , Travis S. , Ferrante R. , Chiar J. , Boogert A. , Mundy L. , Pendleton Y. , Tielens A. , van Dishoeck E. , Evans N. 
Published: October 2008

AbstractWe present 5–20 μm Spitzer/IRS spectroscopy toward stars behind dark molecular clouds. We present preliminary results from the Serpens dark cloud to show the variation between environments within a cloud. We are surveying 3 clouds with varying levels of star formation activity. Serpens has the highest level of activity from our 3 clouds. We show that location as well extinction can cause variations in ice composition. We also find that some lines of sight contain organic molecules such as methane and methanol, and the first detection of acetylene ice in the interstellar medium. We believe the high extinction lines of sight have been enriched by star formation activity near those lines of sight.
Fullerenes as carriers of extinction, diffuse interstellar bands and anomalous microwave emission
Authors: Iglesias-Groth Susana 
Published: October 2008

AbstractAccording to semiempirical models, photoabsorption by fullerenes (single and multishell) could explain the shape, width and peak energy of the most prominent feature of the interstellar absorption, the UV bump at 2175 Å. Other weaker transitions are predicted in the optical and near-infrared providing a potential explanation for diffuse interstellar bands. In particular, we find that several fullerenes could contribute to the well known strong DIB at 4430 Å. Comparing cross sections and available data for this DIB and the UV bump we estimate a density of fullerenes in the diffuse interstellar medium of 0.1–0.2 ppm. These molecules could then be a major reservoir for interstellar carbon. We also study the rotation rates and electric dipole emission of hydrogenated icosahedral fullerenes. We investigate these molecules as potential carriers of the anomalous (dust-correlated) microwave emission recently detected by several cosmic microwave background experiments.
Testing the attribution of selected DIBs to dehydrogenated coronene cations
Authors: Mulas G. , Malloci G. , Porceddu I. , Joblin C. 
Published: October 2008

AbstractDehydrogenated coronene molecules have been proposed as the source of the UV-bump in the interstellar extinction curve as well as of some of the diffuse interstellar bands (DIBs). To test this hypothesis we have recently undertaken a combined (a) modelling, and (b) observational work on the subject. (a) In the framework of a global approach to the photophysics of a PAH–like species in space, we used combined theoretical calculated properties, obtained with (time–dependent) density functional theory, and a Monte–Carlo model simulating the time evolution of the population of levels of a given molecule, to obtain the detailed ro–vibrational spectral structure of selected electronic transitions. (b) From the observational point of view, we compare our predictions with observations of the well–known λ6284 and λ5780 DIBs.
Depleted diffuse bands in circumstellar envelopes of post-AGB stars
Authors: Cox N. L. J. , Luna R. , Satorre M. A. , García Hernández D. A. , Suárez O. , García Lario P. 
Published: October 2008

AbstractWe report on new results in the search for diffuse bands, signatures of still unknown origin, in the circumstellar envelopes of evolved (post-AGB) stars.
On buckyonions as a carrier of the 2175 Å interstellar extinction feature
Authors: Chen Juhua , Li Moping , Li Aigen , Wang Yongjiu 
Published: October 2008

AbstractIn recent years buckyonions have been suggested as a carrier of the 2175 Å interstellar extinction feature, based on the close similarity between the electronic transition spectra of buckyonions and the 2175 Å interstellar extinction feature. We examine this hypothesis by calculating the interstellar extinction with buckyonions as a dust component. It is found that dust models containing buckyonions (in addition to amorphous silicates, PAHs, graphite or amorphous carbon) can closely reproduce the observed interstellar extinction curve. However, a more severe challenge to the buckyonion hypothesis is provided by the non-detection of the ~7–8 μm C–H stretching bands expected from buckyonions in the diffuse interstellar medium. This will allow us to place an upper limit on the abundance of buckyonions.
Organic molecules in protostellar environments
Authors: Ceccarelli Cecilia 
Published: October 2008

AbstractThe sequence that brings matter from a molecular cloud to a fully developed star plus planetary system seems to be a unique and rich chemistry laboratory where, step by step, molecular complexity increases. During the cold pre-collapse phase, atoms and simple molecules, like CO, freeze out onto the dust grains, forming icy mantles. Reactions on the grain surfaces likely form hydrogenated molecules (notably H2O, CH4, H2CO, CH3OH, and NH3) and perhaps even more complex organic molecules. The hallmark of this era is the super-deuteration phenomenon, i. e. the abnormal enhancement of molecules containing one or more D atoms instead of H atoms, by up to 13 orders of magnitude with respect to the cosmic elemental D/H ratio (~10−5). The frozen molecules are released into the gas upon warming by the forming star and undergo reactions which further increase the molecular complexity, leading to several complex organic molecules. Products of this efficient chemical factory are observed in the hot corinos, which are warm (~100 K), dense (~107–108 cm−3) solar-system-sized regions at the centre of the collapsing envelopes of solar type protostars. In this contribution, I review what is known about the organic molecules in protostellar environments, with emphasis on the hot corinos, and how possibly the organic molecules formed at this stage may constitute an heritage for the forming planetary system.
The birth and death of organic molecules in protoplanetary disks
Authors: Henning Thomas , Semenov Dmitry 
Published: October 2008

AbstractThe most intriguing question related to the chemical evolution of protoplanetary disks is the genesis of pre-biotic organic molecules in the planet-forming zone. In this contribution we briefly review current observational knowledge of physical structure and chemical composition of disks and discuss whether organic molecules can be present in large amounts at the verge of planet formation. We predict that some molecules, including CO-bearing species such as H2CO, can be underabundant in inner regions of accreting protoplanetary disks around low-mass stars due to the high-energy stellar radiation and chemical processing on dust grain surfaces. These theoretical predictions are further compared with high-resolution observational data and the limitations of current models are discussed.
Precursors of complex organic molecules: NH3 and CH3OH in the ices surrounding low-mass protostars
Authors: Bottinelli Sandrine , Boogert Adwin C. A. , van Dishoeck Ewine F. , Beckwith Martha , Bouwman Jordy , Linnartz Harold , Öberg Karin I. 
Published: October 2008

AbstractNH3 and CH3OH are key molecules in the chemical networks leading to the formation of complex N- and O-bearing organic molecules. However, despite a number of recent studies, there is still a lot to learn about their abundances in the solid state and how they relate to those of other N/O-bearing organic molecules or to NH3 and CH3OH abundances in the gas phase. This is particularly true in the case of low-mass young stellar objects (YSOs), for which only the recent advent of the Spitzer Space Telescope has allowed high sensitivity observations of the ices in their enveloppes. We present a combined study of Spitzer data (obtained within the Legacy program “From Molecular Cores to Planet-Forming Disks”, c2d) and laboratory spectra, leading to the detections of NH3 and CH3OH in the ices of low-mass protostars. We investigate correlations with other ice features and conclude with prospects on further studies linking these two precursors of complex organic molecules with their gas-phase products.
Chemical changes during transport from cloud to disk
Authors: Visser Ruud , van Dishoeck Ewine F. , Doty Steven D. 
Published: October 2008

AbstractWe present the first semi-analytical model that follows the chemical evolution during the collapse of a molecular cloud and the formation of a low-mass star and the surrounding disk. It computes infall trajectories from any starting point in the cloud and it includes a full time-dependent treatment of the temperature structure. We focus here on the freeze-out and desorption of CO and H2O. Both species deplete towards the centre before the collapse begins. CO evaporates during the infall phase and re-adsorbs when it enters the disk. H2O remains in the solid phase everywhere, except within a few AU of the star. Material that ends up in the planet- and comet-forming zones is predicted to spend enough time in a warm zone during the collapse to form complex organic species.
High-resolution observations of CH3CN in the hot corino of NGC1333-IRAS4A
Authors: Bottinelli Sandrine , Ceccarelli Cecilia , Neri Roberto , Williams Jonathan P. 
Published: October 2008

AbstractThe formation and evolution of complex organic molecules in the early stages of solar-type protostars (Class 0 objects) is crucial as it sets the stage for the content in pre-biotic molecules of the subsequent proto-planetary nebula. In order to understand the chemistry of these Class 0 objects, it is necessary to perform interferometric observations which allow us to resolve the hot corino, that is the warm, dense inner region of the envelope of a Class 0 object, where the complex organic molecules are located. Such observations exist for only two objects so far, IRAS16293-2422 and NGC1333-IRAS2A and we present here Plateau de Bure interferometric maps of a third hot corino, NGC1333-IRAS4A, which show emission of the complex organic molecule CH3CN arising from a region of size ~0.8″/175 AU, that is, of the order of the size of the Solar System. Combining these high-angular resolution maps with prior single-dish observations of the same transitions of CH3CN indicates that extended emission is also present, and we investigate the implications for organic chemistry in hot corinos.
Complex organic molecules in the intermediate mass protostar OMC2-FIR4
Authors: Crimier Nicolas , Ceccarelli Cecilia , Lefloch Bertrand , Faure Alex 
Published: October 2008

AbstractWe present the physical structure (density and temperature profiles) and the distribution of formaldehyde and methanol in intermediate mass protostar OMC2-FIR4 in the Orion molecular cloud complex.
Methanol formation: A Monte Carlo study
Authors: Das Ankan , Acharyya Kinsuk , Chakrabarti Sonali , Chakrabarti Sandip K. 
Published: October 2008

AbstractWe carry out a Monte-Carlo simulation to study the formation of methanol on the grain surfaces. We found that the recombination efficiencies are strongly dependent on the extrinsic properties of the grain, such as the number of sites on the grain surface and the flux of the accreting matter. This uses the concept of effective grain surface (denoted through a factor α) area which changes as the grain is populated.
Solid CH4 toward low-mass protostars: How much is there to build complex organics?
Authors: Öberg Karin I. , Boogert A. C. Adwin , Pontoppidan Klaus M. , Blake Geoffrey A. , Evans Neal J. , Lahuis Fred , van Dishoeck Ewine F. 
Published: October 2008

AbstractWe use Spitzer IRS spectra to determine the solid CH4 abundance toward a large sample (52 sources) of low mass protostars. 50% of the sources have an absorption feature at 7.7 μm, attributed to solid CH4. The solid CH4/H2O abundances are 2–13%, but toward sources with H2O column densities above 2 × 1018 cm−2, the CH4 abundances (20 out of 25) are nearly constant at 4.7 ± 1.6%. Correlations with CO2 and H2O together with the inferred abundances are consistent with CH4 formation through sequential hydrogenation of C on grain surfaces, but not with formation from CH3OH and formation in gas phase with subsequent freeze-out.
Collisional excitation of complex organic molecules
Authors: Faure Alexandre , Josselin Eric , Wiesenfeld Laurent , Ceccarelli Cecilia 
Published: October 2008

AbstractA major difficulty in modelling the infrared and (sub)millimeter spectra of gas-phase complex organic molecules is the lack of state-to-state collisional rate coefficients. Accurate quantum or classical scattering calculations for large polyatomic species are indeed computationally highly challenging, particularly when both rotation and low frequency vibrations such as bending and torsional modes are involved. We briefly present here an approximate approach to estimate and/or extrapolate rotational and rovibrational rates for polyatomic molecules with many degrees of freedom.
Ion chemistry in the interstellar medium
Authors: Martinez Oscar , Snow Theodore P. , Bierbaum Veronica M. 
Published: October 2008

AbstractWithout accurate data on reaction rates and branching ratios, models of interstellar chemistry are unreliable. Recent research has identified a number of reactions of unusual importance because the rates and branching ratios are unknown or poorly known. Efforts to expand and improve on current databases are underway using a flowing afterglow-selected ion flow tube (FA-SIFT) coupled to a quadrupole mass spectrometer. Our current focus is on the reactions of C+, a major cation in the interstellar medium, with the neutrals O2, H2O, CH4, NH3 and C2H2. Future planned work includes studies of polycyclic aromatic hydrocarbons (PAHs), developing comprehensive pathways for their formation, and identification of those PAHs important to interstellar chemistry. The recent discovery of ISM anions has highlighted the importance of examining mechanisms of anionic chemistry in the interstellar medium, and we plan to obtain data relevant to the formation and destruction processes of molecular anions in space.
Molecular collisions : State-of-the-art calculations of inelastic collisions
Authors: Wiesenfeld Laurent , Faure Alexandre , Troscompt Nicolas , Wernli Michael , Ceccarelli Cecilia , Valiron Pierre 
Published: October 2008

AbstractWe set up a framework for calculating in a precise and controlled way the collisional properties of several molecules of astrophysical meaning. The quantities that are relevant for astrophysics are rotational and vibrational quenching/excitation rates by means of collisions of H2 with water and some organic molecules (HC3N, H2CO). We calculate those rates by means of successively determining a intermolecular potential energy surface and calculating inelastic cross sections and rates classically and/or quantum mechanically. These calculations are part of the European Union FP6 Molecular Universe program.
Observational constraints on the formation of interstellar methanol
Authors: Wirström E. S. , Persson C. M. , Hjalmarson Å. , Black J. H. , Bergman P. , Geppert W. D. , Hamberg M. , Vigren E. 
Published: October 2008

AbstractThe 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.
Molecular line observations and chemical modelling of galactic edge clouds
Authors: Ruffle Paul , Millar Tom , Roberts Helen , Lubowich Don , Henkel Christian 
Published: October 2008

AbstractEdge Clouds 1 and 2 (EC1 and EC2) are large molecular clouds with the largest galactocentric distances known to exist in the Milky Way. We present observations of these clouds and use them to determine physical characteristics. For EC2 we calculate a gas temperature of 20 K and a density ofn(H2) ~ 104cm−3. Based on our CO maps, we estimate the mass of EC2 at around 104M⊙, and continuum observations suggest a dust-to-gas mass ratio as low as 0.001. Chemical models have been developed to reproduce the abundances in EC2 and they indicate that: heavy element abundances may be reduced by a factor of five relative to the solar neighbourhood (similar to dwarf irregular galaxies and damped Lyman alpha systems); very low extinction (AV< 4 mag) due to a very low dust-to-gas ratio; an enhanced cosmic ray ionisation rate; and a higher UV field compared to local interstellar values. The reduced abundances may be attributed to the low level of star formation in this region and are probably also related to the continuing infall of low metallicity halo gas since the Milky Way formed. We find that shocks from an old supernova remnant may have determined the morphology and dynamics of EC2, including the recently discovered star clusters embedded in the northern and southern cores. However, compared to EC2, EC1 appears to be a chemically less varied environment. The apparent molecule-poor nature of EC1 demonstrates the characteristics of clouds that have not had the benefit of SN shocks to stimulate an active cloud chemistry and star formation.
Ethylene in the circumstellar envelope of IRC+10216
Authors: Hinkle K. H. , Wallace L. , Richter M. J. , Cernicharo J. 
Published: October 2008

AbstractEthylene (C2H4) is a symmetric molecule that is best detected using mid-infrared transitions. We report on observations of the 10.5 μm ν7 band using the cryogenic grating spectrograph TEXES. These confirm the previous ethylene detection in the IRC+10216 circumstellar shell. We detect 18 ethylene lines. The lines are both narrow and weak with depths of no more than ~2%. The ethylene lines suggest an excitation temperature of ~80 K.
Molecular line observations of the SiO maser source IRAS 19312+1950
Authors: Nakashima J. , Deguchi S. , Imai H. , Kemball A. 
Published: October 2008

AbstractIRAS 19312+1950 is a unique SiO maser source, exhibiting a rich set of molecular radio lines, although SiO maser sources are usually identified as oxygen-rich evolved stars, in which chemistry is relatively simple comparing with carbon-rich environments. The rich chemistry of IRAS 19312+1950 has raised a problem in circumstellar chemistry if this object is really an oxygen-rich evolved star, but its evolutional status is still controversial. In this paper, we briefly review the previous observations of IRAS 19312+1950, as well as presenting preliminary results of recent VLBI observations in maser lines. PDF file of the poster is available from http://www.geocities.jp/nakashima_junichi/
The physics and chemistry of circumstellar envelopes of S-stars on the AGB
Authors: Ramstedt Sofia , Schöier Fredrik L. , Olofsson Hans 
Published: October 2008

AbstractPresented here are the preliminary results of a long-term study of S-stars on the AGB. S-stars are important as possible transition objects between oxygen-rich M-stars and carbon stars. The aim of the study is to compare results from our newly gathered observational database for the S-stars with those already obtained for the M- and carbon stars. We can thus follow the changes as the stars evolve along the AGB and more firmly establish the suggested M-MS-S-SC-C evolutionary sequence. It will also allow us to determine the relative importance of processes such as non-equilibrium chemistry, grain formation, and photodissociation in regulating the chemistry in circumstellar envelopes of AGB stars.