Ultimately, all of the solids in the Solar System, including ourselves, consist of elements that were made in stars by stellar nucelosynthesis. However, most of the material from many different stellar sources that went into the making of the Solar System was thoroughly mixed, obliterating any information about its origin. An exception are tiny grains of preserved stardust found in primitive meteorites, micrometeorites, and interplanetary dust particles. These μm- and sub-μm-sized presolar grains are recognized as stardust by their isotopic compositions, which are completely different from those of the Solar System. They condensed in outflows from late-type stars and in SN ejecta and were included in meteorites, from which they can be isolated and studied for their isotopic compositions in the laboratory. Thus these grains constitute a link between us and our stellar ancestors. They provide new information on stellar evolution, nucleosynthesis, mixing processes in asymptotic giant branch (AGB) stars and supernovae, and galactic chemical evolution. Red giants, AGB stars, Type II supernovae, and possibly novae have been identified as stellar sources of the grains. Stardust phases identified so far include silicates, oxides such as corundum, spinel, and hibonite, graphite, silicon carbide, silicon nitride, titanium carbide, and Fe-Ni metal.

Measuring the deuterium fractionation in different molecules can allow one to determine the physical conditions in the gas and to differentiate between gas-phase and grain surface chemical processing. Observations of molecular D/H ratios in different species towards the dense gas surrounding low-mass protostars are presented and are compared with model simulations. These consider gas-phase chemistry, accretion and desorption, and reactions on grain surfaces during the initial stages of core collapse.

Anhydrous interplanetary dust particles (IDPs), which are the most mineralogically primitive extraterrestrial materials available for laboratory analysis, contain several percent organic matter. The high O:C and N:C ratios suggest the organic matter in the anhydrous IDPs is significantly less altered by thermal processing than the organic matter in meteorites. X-ray Absorption Near-Edge Structure (XANES) spectroscopy and infrared spectroscopy demonstrate the presence of C=C, most likely as C-rings, C=O, and aliphatic C-H2 and C-H3 in all the IDPs examined. A D-rich spot, containing material that is believed to have formed in a cold molecular cloud, has C-XANES and infrared spectra very similar to the organic matter in the anhydrous IDPs, possibly indicating a common formation mechanism. However the primitive organic matter in the IDPs differs from the interstellar/circumstellar organic matter characterized by astronomical infrared spectroscopy in the relative strengths of the asymmetric aliphatic C-H2 and C-H3 absorptions, with the IDP organic having a longer mean chain length. If both types of organic matter originated by the same process, this may indicate the interstellar organic matter has experienced more severe radiation processing than the organic matter in the primitive IDPs.

The mysterious 21 μm emission feature seen in only 12 C-rich proto-planetary nebulae (PPNe) remains unidentified since its discovery in 1989. Over a dozen materials have been suggested as the carrier candidates while none of them has received general acceptance. We investigate the inorganic carrier candidates by applying the observational constraints of the feature strength and associated features. It is found that: (1) three candidates, TiC clusters, fullerenes with Ti impurity atoms, and SiS2, are not abundant enough to account for the emission power of the 21 μm band, (2) five candidates, doped-SiC, SiO2-mantled SiC dust, carbon and silicon mixtures, Fe2O3, and Fe3O4, all show associated features which are either not detected in the 21 μm sources or detected but with a much lower strength, and (3) FeO, which satisfies the abundance constraints, does not display any associated features which are not seen in the 21 μm sources. Moreover, FeO is more likely to survive in the C-rich environment than Fe2O3 and Fe3O4. Thus FeO seems to be the most plausible one among the inorganic carrier candidates.

We are studying the Central Molecular Zone (CMZ) in the inner few degrees around the Galactic Centre, by mapping multiple 3-mm molecular lines, with the 22-m Mopra telescope. During 2006, we covered a 5 × 5 arcmin2 area of the Sagittarius B2 molecular cloud complex (Jones et al. 2008). We find substantial differences in chemical and physical conditions within the complex. We show some results here of Principal Component Analysis (PCA) of line features in this Sgr B2 area. During 2007 we covered the larger region of longitude −0.2 to 0.9 deg. and latitude -0.20 to 0.12 deg., including Sgr A and Sgr B2, in the frequency range 85.3 to 91.3 GHz. This includes lines of C3H2, CH3CCH, HOCO+, SO, H13CN, H13CO+, SO, H13NC, C2H, HNCO, HCN, HCO+, HNC, HC3N, 13CS and N2H+.

Three-millimeter-wavelength spectra of a number of nearby galaxies have been obtained at the Five College Radio Astronomy Observatory (FCRAO) using a new, very broadband receiver. This instrument, which we call the Redshift Search Receiver, has an instantaneous bandwidth of 36 GHz and operates from 74 to 110.5 GHz. The receiver has been built at UMass/FCRAO to be part of the initial instrumentation for the Large Millimeter Telescope (LMT) and is intended primarily for determination of the redshift of distant, dust-obscured galaxies. It is being tested on the FCRAO 14 m by measuring the 3 mm spectra of a number of nearby galaxies. There are interesting differences in the chemistry of these galaxies.

A long-standing problem in interstellar chemistry is how molecules can be maintained in the gas phase at the extremely low temperatures in space. Photodesorption has been suggested to explain the observed cold gas in cloud cores and disk mid-planes. We are studying the UV photodesorption of ices experimentally under ultra high vacuum and at astrochemically relevant temperatures (15 – 27 K) using a hydrogen discharge lamp (7-10.5 eV). The ice desorption during irradiation is monitored using reflection absorption infrared spectroscopy and the desorbed species using mass spectrometry. We find that both the UV photodesorption rates and mechanisms are highly molecule specific. CO photodesorbs without dissocation from the surface layer of the ice. N2, which lacks dipole allowed electronic transitions in the range of the lamp, does not photodesorb. CO2 desorbs through dissociation and subsequent recombination from the top few layers of the ice. At low temperatures (15 – 18 K) the derived photodesorption rates are ~ 10−3 for CO and CO2 and < 2 × 10−4 for N2 ice per incident photon.

Carbonaceous materials have been prepared in the laboratory by laser-induced pyrolysis of a mixture of hydrocarbons under different conditions and laser ablation of graphite in reactive gas atmospheres. We have investigated the soluble and insoluble parts of the condensed carbon powders with several spectroscopic and chromatographic methods in order to obtain information on the composition of the condensate. The results of these experiments have demonstrated that, at temperatures lower than 1700 K, the pyrolysis by-products are mainly PAHs, whereas at higher temperatures fullerenes and polyyne-based compounds are formed. The experimental findings point to different soot formation mechanisms with variable intermediates and end products. It has been found that soot extracts can contain more than 65 different polycyclic aromatic hydrocarbons (PAHs). Eventually, the study of the condensation pathways of soot particles and their precursors and by-products will permit the prediction of the spectral properties of carbonaceous matter in space.

We report on new results in the search for diffuse bands, signatures of still unknown origin, in the circumstellar envelopes of evolved (post-AGB) stars.

The possibility of an extraterrestrial origin of biomolecule building blocks has been a subject of intense discussions for many years. The detection of amino acids in meteorites opens the possibility of a delivery of biomolecules synthesized in the interstellar medium or star-forming regions to the primeval Earth. Whereas it can be doubted if more complex species like amino acids can survive the strong UV radiation in the early Solar System, this does not necessary hold for more primitive precursor molecules like nitriles. These compounds can also be synthesized very efficiently in methane-nitrogen dominated atmospheres like the one present on Titan and the early ages of Earth. This Contribution focuses on the formation and degradation processes of nitriles in interstellar clouds and planetary atmospheres and on their possible role in the generation of biomolecules.

Although unidentified infrared bands (UIBs) have been observed in many astrophysical environments, there is one notable exception: carbon (C) stars. Only a handful of C stars have been shown to emit UIBs and most have hot companions. This makes C stars with hot companions an ideal location to investigate the emitters of the UIBs. PAHs are excited by absorption of single photons whose energy is then distributed over the whole molecule. These molecules then emit the energy at the characteristic wavelengths, but the precise wavelengths and strength ratios depend on the size, composition and charge state of the individual PAHs. Furthermore, the wavelength of photons needed to excite PAHs depends on their size and charge state. While small PAHs undoubtedly need higher energy (UV) photons, it has been suggested that large or ionized PAHS (>100 C atoms) can be excited by visible or even near-IR photons. The lack of PAH emission from single carbon stars suggests that either PAHs do not form around C stars or that only small neutral grains form, which cannot be excited by a C star's radiation field.

There are two competing formation mechanisms for PAHs around C stars: (1) “bottom-up” where acetylene molecules react to form aromatic rings, building up to PAHs; or (2) “top-down”, where small carbon grains react with H atoms and desorb PAHs

Using spatially resolved spectroscopic observations from Gemini/Michelle, of five carbon stars with hot companions, we investigate the circumstance under which PAH emission occurs and try to discriminate between formation mechanisms.

We use discrete dipole approximation (DDA) to study the scattering properties of composite grains made up of host silicate spheroids and graphite inclusions. We calculate the extinction cross sections of the composite grains in the wavelength region 0.20–0.55 μm and study the extinction of the composite grains as a function of graphite inclusions. We present the composite grain model and discuss the results.

We made near- to mid-infrared imaging and spectroscopic observations of the dwarf galaxy NGC 1569 with the Infrared Camera (IRC) on board AKARI. The unidentified infrared (UIR) band features at 6.2, 7.7, and 11.2 μm, which are generally attributed to polycyclic aromatic hydrocarbons (PAHs), are clearly detected in a structure associated with an Hα filament. The filament is filled with X-ray emission and is thought to be formed by outflow from the galaxy. Since PAHs are destroyed rapidly in hot plasma, it is most likely that PAHs in the filament are produced from fragmentation of large carbonaceous grains in the shock. We also detect excess emission in 2–5 μm in the filament, which may come from very small grains.

The idea that some nitrogen bases, such as adenine and guanine, are easily formed and can be found in interstellar space is should not be rejected. In fact, they have been found in the soluble fraction of some ancient meteors. It is possible that the “seed” of life had its origin in space, and thanks to Earth conditions, a synergistic interaction ocurred and allowed life to spring forth on our planet.

NH3 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.

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.

Edge 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 of n(H2) ~ 104 cm−3. Based on our CO maps, we estimate the mass of EC2 at around 104 M⊙, 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.

As the number of detections of complex molecules keeps increasing, answering the question about their formation becomes more pressing. Many of the saturated organic molecules are found to have a very low gas phase formation rate and are therefore thought to be formed on the icy surfaces of dust grains. In the Sackler Laboratory for Astrophysics we started a systematic study of the surface reaction routes that have been suggested over the years. Here we present the experimental results on the formation of methanol and ethanol by hydrogenation reactions of carbon monoxide and acetaldehyde ice. Computer simulations of the surface processes under similar conditions using the continuous-time random-walk Monte Carlo technique reveal some of the underlying physical processes. A better understanding of the physical conditions in which these molecules are formed can help in the interpretation of the observational results. The CO hydrogenation results will appear in detail in Fuchs et al. (2008). For more details on ethanol formation we refer to Bisschop et al. (2007).

We have performed a study of 3.3 micron PAH emission in planetary nebulae using ground-based observations with FLITECAM, one of a suite of instruments designed for airborne astronomy aboard SOFIA, NASA's Stratospheric Observatory for Infrared Astronomy. The survey was performed on the Shane 3 meter telescope at Lick Observatory as part of the ground-based commissioning of the FLITECAM grism spectroscopy mode. Spectral resolution of R ~ 1700 was obtained with direct-ruled KRS-5 grisms. Targets included AGB stars and sources showing PAH emission in KAO, ISO or IRAS observations. Additionally, several oxygen-rich nebulae were observed in order to test methodology. Twenty objects were surveyed, of which 11 showed PAH emission. In objects exhibiting PAH emission, the relationship between the nebular C/O ratio and PAH equivalent width was found, showing a detectable PAH emission cutoff at a nebular C/O ratio of 0.65 ± 0.28. Selected objects with detected PAH emission were further investigated to trace PAH emission spectral variation within individual nebulae.

A 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.