ABSTRACT A pair of 6.0 and 6.9 μm absorption features are frequently observed in Milky Way (MW) molecular-clouds and YSOs; they also occur in the z = 0.886 rest-frame of a molecule-rich spiral galaxy obscuring blazar PKS 1830–211. I calibrate χ2-fitting methods, which match observations with two or three laboratory spectra. The 6.0-μm component is dominated by H2O ice, as expected. Included MW sources were selected using opacity criteria which limit the range of explored H2O-ice column densities to 1.6–2.4 × 1018 molecules cm−2, while the H2O-ice density in the galaxy absorber is (2.7 ± 0.5) × 1018 molecules cm−2. CH3OH ice and / or small (< 0.1-μm-sized) Ca- and Mg-bearing carbonates contribute at 6.9 μm. The 41 per cent CH3OH:H2O molecular ratio in the PKS 1830–211 absorber is significantly higher than in the molecular cloud towards Taurus-Elias 16 (<7.5 per cent) and similar to the highest value in MW YSOs (35 per cent in AFGL 989). Fitted carbonate (-CO3):H2O ratios in the galaxy absorber of 0.091 per cent are low in comparison to most of the ratios detected in the MW sample (0.2 per cent–0.4 per cent; ∼0 per cent in AFGL 989). Inorganic carbonates could explain the increased oxygen depletion at the diffuse-medium-to-molecular-cloud transition, which Jones and Ysard associated with unobserved organic carbonates or materials with a C:O ratio of 1:3.

We present new room-temperature 1100 - 1800 cm^{-1} spectra of melilite silicates and 600 - 2000 cm^{-1} spectra of three randomly orientated fine-grained carbonates to determine the possible carrier(s) of a 6.9~micron absorption feature observed in a variety of dense astronomical environments including young stellar objects and molecular clouds. We focus on the low-mass post-AGB star Sakurai's Object which has been forming substantial quantities of carbonaceous dust since an eruptive event in the 1990s. Large melilite grains cannot be responsible for the 6.9-micron absorption feature because the similarly-shaped feature in the laboratory spectrum was produced by very low (0.1 per cent by mass) carbonate contamination which was not detected at other wavelengths. Due to the high band-strength of the 6.9-micron feature in carbonates, we conclude that carbonates carry the astronomical 6.9~micron feature. Replacement of melilite with carbonates in models of Sakurai's object improves fits to the 6 - 7-micron Spitzer spectra without significantly altering other conclusions of Bowey's previous models except that there is no link between the feature and the abundance of melilite in meteorites. With magnesite (MgCO3), the abundance of 25-micron-sized SiC grains is increased by 10 - 50 per cent and better constrained. The mass of carbonate dust is similar to the mass of PAH dust. Existing experiments suggest carbonates are stable below 700~K, however it is difficult to ascertain the applicability of these experiments to astronomical environments and more studies are required.

In this era of spatially resolved observations of planet forming disks with ALMA and large ground-based telescopes such as the VLT, Keck and Subaru, we still lack statistically relevant information on the quantity and composition of the material that is building the planets, such as the total disk gas mass, the ice content of dust, and the state of water in planetesimals. SPICA is an infrared space mission concept developed jointly by JAXA and ESA to address these questions. The key unique capabilities of SPICA that enable this research are (1) the wide spectral coverage 10-220 micron, (2) the high line detection sensitivity of (1-2) 10-19 W m-2 with R 2000-5000 in the far-IR (SAFARI) and 10-20 W m-2 with R 29000 in the mid-IR (SMI, spectrally resolving line profiles), (3) the high far-IR continuum sensitivity of 0.45 mJy (SAFARI), and (4) the observing efficiency for point source surveys. This paper details how mid- to far-IR infrared spectra will be unique in measuring the gas masses and water/ice content of disks and how these quantities evolve during the planet forming period. These observations will clarify the crucial transition when disks exhaust their primordial gas and further planet formation requires secondary gas produced from planetesimals. The high spectral resolution mid-IR is also unique for determining the location of the snowline dividing the rocky and icy mass reservoirs within the disk and how the divide evolves during the build-up of planetary systems. Infrared spectroscopy (mid- to far-IR) of key solid state bands is crucial for assessing whether extensive radial mixing, which is part of our Solar System history, is a general process occurring in most planetary systems and whether extrasolar planetesimals are similar to our Solar System comets/asteroids. ... (abbreviated)

ABSTRACT 6–14 μm Spitzer spectra obtained at 6 epochs between 2005 April and 2008 October are used to determine temporal changes in dust features associated with Sakurai’s Object (V4334 Sgr), a low mass post-AGB star that has been forming dust in an eruptive event since 1996. The obscured carbon-rich photosphere is surrounded by a 40-milliarcsec torus and 32 arcsec PN. An initially rapid mid-infrared flux decrease stalled after 2008 April 21. Optically thin emission due to nanometre-sized SiC grains reached a minimum in 2007 October, increased rapidly between 2008 April 21–30 and more slowly to 2008 October. 6.3-μm absorption due to PAHs increased throughout. 20 μm-sized SiC grains might have contributed to the 6–7 μm absorption after 2007 May. Mass estimates based on the optically thick emission agree with those in the absorption features if the large SiC grains formed before 1999 May and PAHs formed in 1999 April–June. Estimated masses of PAH and large-SiC grains in 2008 October, were 3 × 10−9 M⊙ and 10−8 M⊙, respectively. Some of the submicron-sized silicates responsible for a weak 10 μm absorption feature are probably located within the PN because the optical depth decreased between 2007 October and 2008 October. 6.9-μm absorption assigned to ∼10 μm-sized crystalline melilite silicates increased between 2005 April and 2008 October. Abundance and spectroscopic constraints are satisfied if $\lesssim$2.8 per cent of the submicron-sized silicates coagulated to form melilites. This figure is similar to the abundance of melilite-bearing calcium–aluminium-rich inclusions in chondritic meteorites.

Crystals of pyroxene are common in meteorites but few compositions have been recognized in astronomical environments due to the limited chemistries included in laboratory studies. We present quantitative room-temperature spectra of 17 Mg-, Fe-, and Ca-bearing ortho- and clinopyroxenes, and a Ca-pyroxenoid in order to discern trends indicative of crystal structure and a wide range of composition. Data are produced using a diamond anvil cell: our band strengths are up to six times higher than those measured in KBr or polyethylene dispersions, which include variations in path length (from grain size) and surface reflections that are not addressed in data processing. Pyroxenes have varied spectra: only two bands, at 10.22 and 15.34 mu m in enstatite (En(99)), are common to all. Peak wavelengths generally increase as Mg is replaced by Ca or Fe. However, two bands in MgFe-pyroxenes shift to shorter wavelengths as the Fe component increases from 0 to 60 per cent. A high-intensity band shifts from 11.6 to 11.2 mu m and remains at 11.2 mu m as Fe increases to 100 per cent; it resembles an astronomical feature normally identified with olivine or forsterite. The distinctive pyroxene bands between 13 and 16 mu m show promise for their identification in Mid-Infrared-Instrument spectra obtained with the James Webb Space Telescope. The many pyroxene bands between 40 and 80 mu m could be diagnositic of silicate mineralogy if data were obtained with the proposed Space Infrared Telescope for Cosmology and Astrophysics. Our data indicate that comparison between room-temperature laboratory bands for enstatite and cold similar to 10 - K astronomical dust features at wavelengths greater than or similar to 28 mu m can result in the identification of (Mg,Fe)- pyroxenes that contain 7-15 per cent less Fe-than their true values because some temperature shiftsmimic some compositional shifts. Therefore some astronomical silicates may contain more Fe, and less Mg, than previously thought.

Post-AGB stars are key objects for the study of the dramatic morphological changes of low- to intermediate-mass stars on their evolution from the Asymptotic Giant Branch (AGB) towards the planetary nebula stage. There is growing evidences that binary interaction processes may very well have a determining role in the shaping process of many objects, but so far direct evidence is still weak. We aim at a systematic study of the dust distribution around a large sample of post-AGB stars as a probe of the symmetry breaking in the nebulae around these systems. We used imaging in the mid-infrared to study the inner part of these evolved stars to probe direct emission from dusty structures in the core of post-AGB stars in order to better understand their shaping mechanisms. We imaged a sample of 93 evolved stars and nebulae in the mid-infrared using VISIR/VLT, T-Recs/Gemini South and Michelle/Gemini North. We found that all the the proto-planetary nebulae we resolved show a clear departure from spherical symmetry. 59 out of the 93 observed targets appear to be non resolved. The resolved targets can be divided in two categories. The nebulae with a dense central core, that are either bipolar and multipolar. The nebulae with no central core have an elliptical morphology. The dense central torus observed likely host binary systems which triggered fast outflows that shaped the nebulae.

cumstellar material in either a dusty torus or a disc. Our team has discovered some discs/tori in the heart of PNe (Lagadec et al., 2006; Chesneau et al., 2006; Matsuura et al., 2006; Chesneau et al., 2007) using adaptive optics on ESO’s Very Large Telescope (VLT) and midinfrared (MIR) interferometry at the Very Large Telescope Interferometer (VLTI). But the role of these discs/tori in the shaping of the nebulae is still unclear, as we know neither the fraction of the total dust mass that is present in these central cores, nor the fraction of objects exhibiting such a disc/torus structure.

Post-asymptotic giant branch (post-AGB) stars are key objects for the study of the dramatic morphological changes of low-to intermediate-mass stars on their evolution from the AGB towards the planetary nebula stage. There is growing evidence that binary interaction processes may very well have a determining role in the shaping process of many objects, but so far direct evidence is still weak. We aim at a systematic study of the dust distribution around a large sample of post-AGB stars as a probe of the symmetry breaking in the nebulae around these systems. We used imaging in the mid-infrared to study the inner part of these evolved stars to probe direct emission from dusty structures in the core of post-AGB stars in order to better understand their shaping mechanisms. We imaged a sample of 93 evolved stars and nebulae in the mid-infrared using VLT spectrometer and imager for the mid-infrared (VISIR)/VLT, T-Recs/Gemini-South and Michelle/Gemini-North. We found that all the proto-planetary nebulae we resolved show a clear departure from spherical symmetry. 59 out of the 93 observed targets appear to be non-resolved. The resolved targets can be divided into two categories. (i) The nebulae with a dense central core, that are either bipolar and multipolar and (ii) the nebulae with no central core, with an elliptical morphology. The dense central torus observed likely hosts binary systems which triggered fast outflows that shaped the nebulae.

Stars form in the densest, coldest, most quiescent regions of molecular clouds. Molecules provide the only probes which can reveal the dynamics, physics, chemistry and evolution of these regions, but our understanding of the molecular inventory of sources and how this is related to their physical state and evolution is rudimentary and incomplete. The Spectral Legacy Survey (SLS) is one of seven surveys recently approved by the JCMT Board. Starting in 2007, the SLS will produce a spectral imaging survey of the content and distribution of all the molecules detected in the 345 GHz atmospheric window (between 332 GHz and 373 GHz) towards a sample of 5 sources. Our intended targets are: a low mass core (NGC1333 IRAS4), 3 high mass cores spanning a range of star forming environments and evolutionary states (W49, AFGL2591, and IRAS20126), and a PDR (the Orion Bar). The SLS will use the unique spectral imaging capabilities of HARP-B/ACSIS to study the molecular inventory and the physical structure of these objects, which span different evolutionary stages and physical environments, to probe their evolution during the star formation process. As its name suggests, the SLS will provide a lasting data legacy from the JCMT that is intended to benefit the entire astronomical community. As such, the entire data set (including calibrated spectral datacubes, maps of molecular emission, line identifications, and calculations of the gas temperature and column density) will be publicly available.

A major discovery by the ISO satellite was the presence, in the spectra of many evolved stars, of an array of narrow emission features that could be attributed to crystalline silicate grains in their envelopes (Molster et al. 2002). As the circumstellar envelope is formed from the continuous mass loss of the object during the AGB stage, it is natural to suppose that the central star would share its chemical properties. Thus, one would expect a star surrounded by silicate-rich material to be oxygen-rich. However, crystalline silicates are frequently associated with carbon-rich central objects. These dual chemistry objects present an opportunity to investigate the mechanisms of mass ejection that forms the circumstellar envelope during and after the AGB stage and that also contribute to the enrichment of the interstellar medium. We are modeling the dust envelope of Roberts 22, a post-AGB star with dual chemistry, using a Monte Carlo simulation method to describe the radiative transfer in its circumstellar dust envelope.

This paper describes a James Clerk Maxwell Telescope (JCMT) legacy survey that has been awarded roughly 500 hr of observing time to be carried out from 2007 to 2009. In this survey, we will map with SCUBA‐2 (Submillimetre Common‐User Bolometer Array 2) almost all of the well‐known low‐mass and intermediate‐mass star‐forming regions within 0.5 kpc that are accessible from the JCMT. Most of these locations are associated with the Gould Belt. From these observations, we will produce a flux‐limited snapshot of star formation near the Sun, providing a legacy of images, as well as point‐source and extended‐source catalogs, over almost 700 deg2 of sky. The resulting images will yield the first catalog of prestellar and protostellar sources selected by submillimeter continuum emission, and should increase the number of known sources by more than an order of magnitude. We will also obtain with the array receiver HARP (Heterodyne Array Receiver Program) CO maps, in three CO isotopologues, of a large typical sample of prestellar and protostellar sources. We will then map the brightest hundred sources with the SCUBA‐2 polarimeter (POL‐2), producing the first statistically significant set of polarization maps in the submillimeter. The images and source catalogs will be a powerful reference set for astronomers, providing a detailed legacy archive for future telescopes, including ALMA, Herschel, and JWST.

We present mid-infrared spectra from individual enstatite silicate grains separated from primitive type 3 chondritic meteorites. The 2–16 μm transmission spectra were taken with microspectroscopic Fourier-transform infrared (FT-IR) techniques as part of a project to produce a data base of infrared spectra from minerals of primitive meteorites for comparison with astronomical spectra. In general, the wavelength of enstatite bands increases with the proportion of Fe. However, the wavelengths of the strong En100 bands at 10.67 and 11.67 decrease with increasing Fe content. The 11.67-μm band exhibits the largest compositional wavelength shift (twice as large as any other). Our fits of the linear dependence of the pyroxene peaks indicate that crystalline silicate peaks in the 10-μm spectra of Herbig AeBe stars, HD 179218 and 104237, are matched by pyroxenes of En90−92 and En78−80, respectively. If these simplistic comparisons with the astronomical grains are correct, then the enstatite pyroxenes seen in these environments are more Fe-rich than are the forsterite (Fo100) grains identified in the far-infrared which are found to be Mg end-member grains. This differs from the general composition of type 3 chondritic meteoritic grains in which the pyroxenes are more Mg-rich than are the olivines from the same meteorite.

Identification of astronomical dust composition rests on comparison of Infrared (IR) spectra with standard laboratory spectra; frequently, however, a single mineralogical composition is assumed for spectral matching. Advances in laboratory instrumentation have enabled very precise IR spectra to be measured on single grains and zones within grains; with a more complete set of spectral data for planetary dust, better compositional matches will be achieved for astronomical dust. We have compared several FT–IR spectroscopy techniques (open path transmission spectroscopy and diffuse reflectance spectroscopy of powders; microspectroscopy of single grains and powders and ATR spectroscopy of thin sections) to determine their utility for the direct measurement of the mid-IR spectra of small amounts of extraterrestrial grains. We have focussed our investigation on the spectra of the olivine series of silicates, (Mg,Fe)2SiO4, a species frequently identified as one of the major constituents of interstellar dust. The positions of three characteristic SiO4 stretching bands at ∼10.4, 11.3 and 12μm were measured for comparison of the techniques. All methods gave satisfactory results, although care must be taken to guard against artefacts from sample thickness and orientation effects. Single grains hand-picked from meteorites can be analysed, but results are inaccurate if the grain size is too large (>1–10μm). Spectra for single grains also show variations that arise from sample orientation effects. Once the analytical artefacts are taken into account, we found that measurement of powder with a diamond compression cell is best suited for the analysis of small amounts of materials.

We present late-time optical and mid-infrared observations of the Type II supernova 2003gd in the galaxy NGC 628. Mid-infrared excesses consistent with cooling dust in the ejecta are observed 499 to 678 days after outburst and are accompanied by increasing optical extinction and growing asymmetries in the emission-line profiles. Radiative-transfer models show that up to 0.02 solar masses of dust has formed within the ejecta, beginning as early as 250 days after outburst. These observations show that dust formation in supernova ejecta can be efficient and that massive-star supernovae could have been major dust producers throughout the history of the universe.

Absorption coefficients associated with atomic motions of species expected in astronomical environments are determined from infrared measurements of various hydrosilicates, hydrated magnesium oxide, and the Al-bearing chain silicate, sapphirine. Band types measured include O—H stretching modes near 3 μm, Si—O stretching motions near 10 μm, Si—O—Si bends near 14 μm, O—Si—O bends near 20 μm, and tra...

Infrared spectra of mineral grains from primitive meteorites could be useful for comparison with astronomical infrared spectra since some of their grains might be similar to those formed in the planet-forming disks around young stars or in the envelopes surrounding late-type stars. To assess the usefulness of meteorite spectra, olivine grains separated from primitive meteorites have been analyzed using FTIR microscope techniques in the 2-16 mu m wavelength range. The sub-micron sizes of the grains made a complex preparation process necessary.Five characteristic bands were measured near 11.9, 11.2, 10.4, 10.1, and 10.0 mu m. The results of 59 analyses allow the calculation of band positions for meteoritic olivines as a function of their iron and magnesium contents. Comparison of the meteoritic results with astronomical data for comets and dust around young and old stars, which exhibit bands similar to the strongest infrared bands observed in the grains (at 11.2 mu m), show that the spectral resolution of the astronomical observations is too low to ascertain the exact iron and magnesium (Mg:Fe) ratio of the dust in the 8-13 mu m wavelength range.

Dust emission from the Type II supernova SN 2002hh in NGC 6946 has been detected at mid-infrared wavelengths by the Spitzer Space Telescope from 590 to 758 days after outburst and confirmed by higher angular resolution Gemini-N mid-IR observations. The day-600 5.8 − 24-μm emission can be fit by a 290-K blackbody having a luminosity of 1.6×10 L⊙. The minimum emitting radius of 1.1×10 cm is too large for the emitting dust to have been formed in the supernova ejecta. Using radiative transfer models and realistic dust grain parameters, fits to the observed flux distribution could be obtained with an optically thick dust shell having a mass of 0.10-0.15 M⊙, corresponding to a total dust+gas mass in excess of 10 M⊙, suggesting a massive M supergiant or luminous blue variable precursor to this self-obscured object. Subject headings: dust, extinction — supernovae: general — supernovae: individual(SN 2002hh) — galaxies: individual(NGC 6946) Dept. of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, UK Space Telescope Science Institute, 3700 San Martin Drive Baltimore, MD 21218 Gemini Observatory, Northern Operations Center, 670 North A’ohoku Place, Hilo, HI 96720 Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803 Radio Astronomy Laboratory, University of California at Berkeley, Berkeley, CA 94720 Department of Physics, Astronomy & Maths, University of Hertfordshire, College Lane, Hatfield AL10 9AB, UK Steward Observatory, University of Arizona, Tucson, Arizona 85721 Kapteyn Astronomical Institute, P.O. Box 800, 9700 AV Groningen, The Netherlands School of Physics & Astronomy, University of Manchester, PO Box 88, Manchester M60 1QD