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1858 OH satellite line (1612 MHz) maser sources associated with the IRAS counterparts were assembled from the literature. Cross-correlation between collected OH/IR - IRAS sources and the recent catalogue of the IRAS LRS spectra (Kwok et al. 1997) allows us to subdivide 1024 of them (after excluding OH sources with uncertain IRAS associations) into 10 groups according to the Volk & Cohen (1989) classification scheme. We have found that sources with silicate emission form the largest group (about 57%), followed by the group with silicate absorption (only about 16%). For more sensitive individual OH maser surveys these numbers differentiate even more and the ratio between silicate emission and absorption sources reaches a value close to 6. Surprisingly, we found an association of OH maser emission with a small number of stars with carbon-rich atmospheres. The distribution of these subgroups of OH/IR stars in the IRAS colour-colour and the period-colour diagrams as well as histograms of some physical properties are presented. The galactic distribution of important parameters (periods, IRAS colours, expansion and stellar velocities) for different classes of OH/IR sources is analyzed from the point of view of the stars' evolutionary status. The correlations among the periods, colours, expansion and star velocities and the pumping efficiencies for selected subgroups of OH/IR stars are also investigated. These analyses allow us to demonstrate that a significant fraction of silicate emission group sources do not form an evolutionary sequence with the silicate absorption objects- as is suggested e.g. by the IRAS colour-colour diagram, but rather form a lower initial mass sequence, i.e. these sources will never develop sufficient mass loss to manifest silicate absorption.

Infrared Space Observatory (ISO )2 ¨45 km observations of seven protoplanetary nebulae (PPNs) and two other carbon-rich objects are presented. The unidenti—ed emission features at 21 and 30 km are detected in six sources, including four new detections of the 30 km feature. This previously unresolved 30 km feature is now resolved and found to consist of a broad feature peaking at 27.2 km (the ii 30 k mˇ ˇ feature) and a narrower feature at 25.5 km (the ii 26 km ˇˇ feature). This new 26 km feature is detected in eight sources and is particularly strong in IRAS Z02229)6208 and 16594(4656. The unidenti—ed infra- red (UIR) emission features at 3.3, 6.2, 7.7, and 11.3 km, which are commonly observed in planetary nebulae and H II regions, are also seen in these PPNs. However, their strengths relative to the contin- uum plateaus at 8 and 12 km are weaker than in planetary nebulae. The 6.9 km feature, seen almost exclusively in PPNs, is strong. New millimeter CO and HCN observations were made; they support the carbon-rich nature of the objects and yield the expansion velocities of the gaseous envelopes. The spec- tral energy distributions of these PPNs were —tted with a radiative-transfer model, taking into account the emission features at 21, 26, and 30 km. A signi—cant fraction of the total energy output is emitted in these features: as high as 20% in the 30 km feature and 8% in the 21 km feature. The fact that so much energy is carried in these features suggests that the material responsible for these features must be made of abundant elements and most likely involves carbon. appears to be ruled out as the emitter of the SiS 2 21 km feature due to the absence of a predicted companion feature. Subject headings: circumstellar matterinfrared: ISM: lines and bands ¨ planetary nebulae: generalradiative transferstars: AGB and post-AGB ¨ infrared: stars

In response to the recent molecular observations by ISO and millimeter-wave telescopes, we have developed a spherically symmetric, steady state chemical model for the planetary nebula NGC 7027. In our model, the neutral envelope consists of a geometrically thin, high-density shell of constant density and an outer stellar wind region with an inverse-square law density profile. The neutral envelope is subjected to ultraviolet (UV) radiation both from the central star and from the external interstellar field. Under an assumed visual extinction of 4 mag for the neutral envelope, the gas in our model is half molecular and half atomic. Simple molecules such as CH, CH+, OH are abundantly formed at an assumed gas temperature of 800 K in the partially molecular shell. The presence of molecular ions such as HCO+ and CO+ is well explained by photochemistry at high temperatures. The model CN/HCN ratio is almost constant at about 30 throughout the wind region and is 1-10 in the dense shell, comparable to observed values in planetary nebulae. Our model suggests that molecules are as efficiently formed with timescales shorter than 100 yr as they are photodissociated in the neutral envelope of NGC 7027 and probably in other young planetary nebulae.

We present Infrared Space Observatory (ISO) SWS01 (2-43 μm) and LWS01 (43-195 μm) observations of five highly evolved carbon stars with extremely thick circumstellar envelopes. The unidentified 30 μm emission feature is detected in the SWS01 spectra of all five sources. This feature seems to be resolved into two subfeatures at 25.5 and 28.3 μm in two sources. These same two sources show a weak emission feature near 20 μm which may be the same as the 21 μm feature seen in carbon-rich proto-planetary nebulae. Absorption features at 13.7 μm attributed to C2H2 are also detected in four sources. No dust feature is detected in the LWS spectra. The only line present is the 157.74 μm line of C+, which could be interstellar in origin. We present radiative transfer models for the spectra of these five stars assuming that the dust is amorphous carbon. The derived optical depths at 11.2 μm range from 1.4 to 4.5, corresponding to optical depths at V = 190-600, making these stars among the asymptotic giant branch (AGB) stars with the most optically thick dust envelopes. From the model fittings, we found the 30 μm features to be optically thick with 5%-8% of the total stellar luminosities being emitted in the feature. For four of the five stars, the models also suggest that their mass-loss rates have been increasing rapidly over the last few 104 yr periods, with current mass-loss rates as high as 4 × 10-4 (D/kpc) M☉ yr-1. Such high mass-loss rates imply that these stars are in the final stages of AGB evolution. The observations of these extreme carbon stars therefore represent the best cases to study the transition from AGB to proto-planetary nebulae.

Baade-Wesselink analyses of this important Galactic classical Cepheid provide new values for the radius, luminosity, distance, and mass and show SU Cas likely to be pulsating in the first overtone. Application of a modified Baade-Wesselink technique and the maximum likelihood method, which we have previously applied to δ Scuti–type variables, yield values of = 33.0 ± 1.1 R⊙, L = 1536 ± 291 L⊙, = -3.28, r = 486 ± 52 pc, mass (from the Baade-Wesselink radius), M = 6.5 ± 0.6 M⊙ (assuming first-overtone pulsation), and evolutionary mass, Mev = 5.5 ± 0.3 M⊙. The results are consistent with the Hipparcos satellite parallax, 2.31 ± 0.58 mas (433 pc), providing further support for overtone pulsation of SU Cas. In the course of the analyses, a modification to the maximum likelihood method, devised by one of us (W. J. F. W.), is presented as an alternative to the modifications of Laney & Stobie and Coulson, Caldwell, & Gieren.

We present Infrared Space Observatory SWS06 mode observations of the 21 micron feature in eight sources, including a first "detection of the feature in IRAS Z02229+6208. The observed feature peak-to-continuum ratios range from 0.13 in IRAS Z02229+6208 to 1.30 in IRAS 07134+1005. The normalized spectra, obtained by the removal of the underlying continua and by scaling the features to the same peak flux value. show that all features have the same intrinsic profile and peak wavelength. There is no evidence for any discrete substructure due to molecular bands in the observed spectra, suggesting that the 21 micron feature is due to either a solid substance or a mixture of many similarly structured large molecules.

As we have noted before, the WG-IR was created following a Joint Commission Meeting at the IAU General Assembly in Baltimore in 1988, a meeting that provided both diagnosis and prescription for the perceived ailments of infrared photometry at the time. The results were summarized in Milone (1989). The challenges involve how to explain the failure to systematically achieve the milli-magnitude precision expected of infrared photometry and an apparent 3% limit on system transformability. The proposed solution was to re-define the broadband Johnson system, the passbands of which had proven so unsatisfactory that over time effectively different systems proliferated although bearing the same JHKLMNQ designations; the new system needed to be better positioned and centered in the atmospheric windows of the Earth's atmosphere, and the variable water vapour content of the atmosphere needed to be measured in real time to better correct for atmospheric extinction.

The unidentified emission feature at 21 μm is now observed in 12 sources, all being objects in transition between the asymptotic giant branch and planetary nebulae phases. The relations between the 21 μm and other emission features, such as the PAH features and the broad 30 μm feature, and the possible origins of the 21 μm feature are discussed.

We analyze the dust emission features seen in Spitzer Space Telescope Infrared Spectrograph (IRS) spectra of red supergiant (RSG) and oxygen-rich asymptotic giant branch (AGB) stars in the Large Magellanic Cloud and Small Magellanic Cloud galaxies and in various Milky Way globular clusters. The spectra come from the Spitzer Legacy program SAGE-Spectroscopy (PI: F. Kemper), the Spitzer program SMC-Spec (PI: G. Sloan), and other archival Spitzer-IRS programs. The broad 10 and 20 micron emission features attributed to amorphous dust of silicate composition seen in the spectra show evidence for systematic differences in the centroid of both emission features between O-rich AGB and RSG populations. Radiative transfer modeling using the GRAMS grid of models of AGB and RSG stars suggests that the centroid differences are due to differences in dust properties. We investigate differences in dust composition, size, shape, etc that might be responsible for these spectral differences. We explore how these differences may arise from the different circumstellar environments around RSG and O-rich AGB stars and assess effects of varying metallicity (LMC versus SMC versus Milky Way globular cluster) and other properties (mass-loss rate, luminosity, etc.) on the dust originating from these stars. BAS acknowledges funding from NASA ADAP grant NNX13AD54G.

The bipolar proto-planetary nebula IRAS 17441-2411 (the "Silkworm Nebula") was observed with the Hubble Space Telescope. By fitting the observed spectral energy distribution and the V-band image by a two-dimensional radiation transfer model, we derive the properties of the circumstellar wind and a proposed circumstellar "disk." We suggest that bipolar structures are probably more common than actually observed, because objects with similar intrinsic structures may simply appear stellar because of their orientation in the sky.

IRAS low-resolution spectra were extracted for 11,224 IRAS sources. These spectra were classified into astrophysical classes, based on the presence of emission and absorption features and on the shape of the continuum. Counterparts of these IRAS sources in existing optical and infrared catalogs are identified, and their optical spectral types are listed if they are known. The correlations between the photospheric/optical and circumstellar/infrared classification are discussed.

A model to simulate the entire spectrum (1000 A to 1 cm) of the high-excitation young planetary nebula NGC 7027 is presented. The ionized, dust, and molecular components of the object are modeled using geometric parameters obtained from visible, radio, infrared, and CO data. The physical processes considered include recombination lines of H and He, collisional excited lines of metals, bf and ff continuum radiations, two-photon radiation, dust continuum radiation, and molecular rotational and vibrational transitions. The dust component is assumed to be heated by a combination of direct starlight and the line and continuum radiation from the ionized nebula. The molecular component of the nebula is coupled to the dust component through the stimulated absorption of the dust continuum radiation. Specifically, we compare the predicted fluxes of the CO rotational lines and the 179.5 μm water rotational line to those observed by the Infrared Space Observatory satellite (Liu et al. 1996, A&A in press).

We present an analysis and comparison of the 30 µm dust feature in the spectra of carbon-rich objects located in the Milky Way, Magellanic Clouds and the Sagittarius dwarf spheroidal galaxy. These spectra were collected by Spitzer Space Telescope. All of these galaxies are characterized by the different metallicities. We expect that some physical and chemical processes related to the formation of the feature are a function of the metallicity. Our study should allow us to better understand the mass loss process and thus late stages of stellar evolution of carbon-rich stars in these four galaxies. Our analysis uses the "Manchester method" as a basis of estimating the temperature of dust for the carbon-rich stars and the planetary nebulae in our sample. In the case of post-AGB objects we changed the spectral ranges used for the temperature estimation, because of the presence of the 21 µm feature. We used a blackbody function with a single temperature deduced from the Manchester method to approximate the continuum under the 30 µm feature. We have produced on-line catalogues of photometric and Spitzer IRS spectra for all objects that show the 30 µm feature. These resources are available on-line for use by the community.

The Fine Guidance Sensor (FGS) is one of the four science instruments on board the JamesWebb Space Telescope (JWST). FGS features two modules: an infrared camera dedicated to fine guiding of the observatory and a science camera module, the Near-Infrared Imager and Slitless Spectrograph (NIRISS) covering the wavelength range between 0.7 and 5.0 μm with a field of view of 2.2'×2.2'. NIRISS has four observing modes: 1) broadband imaging featuring seven of the eight NIRCam broadband filters, 2) wide-field slitless spectroscopy at a resolving power of ̃150 between 1 and 2.5 μm, 3) single-object cross-dispersed slitless spectroscopy enabling simultaneous wavelength coverage between 0.7 and 2.5 μm at R ̃ 660, a mode optimized for transit spectroscopy of relatively bright (J > 7) stars and, 4) sparse aperture interferometric imaging between 3.8 and 4.8 μm enabling high- contrast (̃ 10-4) imaging of M < 8 point sources at angular separations between 70 and 500 milliarcsec. This paper presents an overview of the FGS/NIRISS design with a focus on the scientific capabilities and performance offered by NIRISS. © 2012 SPIE., Space Telescopes and Instrumentation 2012: Optical, Infrared, and Millimeter Wave, July 1-6, 2012, Amsterdam, The Netherlands, Series: Proceedings of SPIE; no. 8442

High-resolution HST imaging of the compact planetary nebula NGC 6644 has revealed two pairs of bipolar lobes and a central ring lying close to the plane of the sky. From mid-infrared imaging obtained with the Gemini Telescope, we have found a dust torus which is oriented nearly perpendicular to one pair of the lobes. We suggest that NGC 6644 is a multipolar nebula and have constructed a 3-D model which allows the visualization of the object from different lines of sight. These results suggest that NGC 6644 may have similar intrinsic structures as other multipolar nebulae and the phenomenon of multipolar nebulosity may be more common than previously believed., 31 pages, 13 figures, accepted for publication in ApJ

We present a 2Dust model for the dust shell around a LMC long-period variable (LPV) previously studied as part of the OGLE survey. OGLE LMC LPV 28579 (SAGE J051306.40-690946.3) is a carbon-rich asymptotic giant branch (AGB) star for which we have photometry and spectra from the Spitzer SAGE and SAGE-Spec programs along with UBVIJHK_s photometry. By modeling this source, we obtain a baseline set of dust properties to be used in the construction of a grid of models for carbon stars. We reproduce its spectral energy distribution using a mixture of AmC and SiC (15% by mass). The grain sizes are distributed according to the KMH model. The best-fit model has an optical depth of 0.28 for the shell at the peak of the SiC feature, with R_in~1430 R_sun or 4.4 R_star. The temperature at this inner radius is 1310 K. Assuming an expansion velocity of 10 km s^-1, we obtain a dust mass-loss rate of 2.5x10^-9 M_sun yr-1. We calculate a 15% variation in this rate by testing the fit sensitivity against variation in input parameters. We also present a simple model for the molecular gas in the extended atmosphere that could give rise to the 13.7 \mu m feature seen in the spectrum. We find that a combination of CO and C_2H_2 gas at an excitation temperature of about 1000 K and column densities of 3x10^21 cm^-2 and 10^19 cm^-2 respectively are able to reproduce the observations. Given that the excitation temperature is close to T_dust(R_in), most of the molecular contribution probably arises from the inner shell region. The luminosity corresponding to the first epoch of SAGE observations is 6580 L_sun. For an effective temperature of about 3000 K, this implies a stellar mass of 1.5-2 M_sun and an age of 1-2.5 Gyr. For a gas:dust ratio of 200, we obtain a gas mass-loss rate of 5.0x10^-7 M_sun yr^-1, consistent with the gas mass-loss rates estimated from the period, color and 8 \mu m flux of the source., Comment: 14 pages, 5 figures, accepted for publication in Astronomy & Astrophysics

The Fine Guidance Sensor (FGS) of the James Webb Space Telescope (JWST) features a tunable filter imager (TFI) module covering the wavelength range from 1.5 to 5.0 μm at a resolving power of ~100 over a field of view of 2.2'×2.2'. TFI also features a set of occulting spots and a non-redundant mask for high-contrast imaging. This paper presents the current status of the TFI development. The instrument is currently under its final integration and test phase.

The SAGE-Spec Spitzer Legacy program is a spectroscopic follow-up to the SAGE-LMC photometric survey of the Large Magellanic Cloud carried out with the Spitzer Space Telescope. We present an overview of SAGE-Spec and some of its first results. The SAGE-Spec program aims to study the life cycle of gas and dust in the Large Magellanic Cloud, and to provide information essential to the classification of the point sources observed in the earlier SAGE-LMC photometric survey. We acquired 224.6 hours of observations using the InfraRed Spectrograph and the SED mode of the Multiband Imaging Photometer for Spitzer. The SAGE-Spec data, along with archival Spitzer spectroscopy of objects in the Large Magellanic Cloud, are reduced and delivered to the community. We discuss the observing strategy, the specific data reduction pipelines applied and the dissemination of data products to the scientific community. Initial science results include the first detection of an extragalactic "21 um" feature towards an evolved star and elucidation of the nature of disks around RV Tauri stars in the Large Magellanic Cloud. Towards some young stars, ice features are observed in absorption. We also serendipitously observed a background quasar, at a redshift of z~0.14, which appears to be host-less., 33 pages, 12 figures, 8 tables; accepted for publication by PASP

The goal of this paper is to present the results of a preliminary analysis of the extended infrared (IR) emission by dust in the interstellar medium (ISM) of the Large Magellanic Cloud (LMC). We combine Spitzer Surveying the Agents of Galaxy Evolution (SAGE) and Infrared Astronomical Satellite (IRAS) data and correlate the infrared emission with gas tracers of H I, CO, and Hα. We present a global analysis of the infrared emission as well as detailed modeling of the spectral energy distribution (SED) of a few selected regions. Extended emission by dust associated with the neutral, molecular, and diffuse ionized phases of the ISM is detected at all IR bands from 3.6 μm to 160 μm. The relative abundance of the various dust species appears quite similar to that in the Milky Way (MW) in all the regions we have modeled. We construct maps of the temperature of large dust grains. The temperature map shows variations in the range 12.1-34.7 K, with a systematic gradient from the inner to outer regions, tracing the general distribution of massive stars and individual H II regions as well as showing warmer dust in the stellar bar. This map is used to derive the far-infrared (FIR) optical depth of large dust grains. We find two main departures in the LMC with respect to expectations based on the MW: (1) excess mid-infrared (MIR) emission near 70 μm, referred to as the 70 μm excess, and (2) departures from linear correlation between the FIR optical depth and the gas column density, which we refer to as FIR excess emission. The 70 μm excess increases gradually from the MW to the LMC to the Small Magellanic Cloud (SMC), suggesting evolution with decreasing metallicity. The excess is associated with the neutral and diffuse ionized gas, with the strongest excess region located in a loop structure next to 30 Dor. We show that the 70 μm excess can be explained by a modification of the size distribution of very small grains with respect to that in the MW, and a corresponding mass increase of ≃13% of the total dust mass in selected regions. The most likely explanation is that the 70 μm excess is due to the production of large very small grains (VSG) through erosion of larger grains in the diffuse medium. This FIR excess could be due to intrinsic variations of the dust/gas ratio, which would then vary from 4.6 to 2.3 times lower than the MW values across the LMC, but X_(CO) values derived from the IR emission would then be about three times lower than those derived from the Virial analysis of the CO data. We also investigate the possibility that the FIR excess is associated with an additional gas component undetected in the available gas tracers. Assuming a constant dust abundance in all ISM phases, the additional gas component would have twice the known H I mass. We show that it is plausible that the FIR excess is due to cold atomic gas that is optically thick in the 21 cm line, while the contribution by a pure H_2 phase with no CO emission remains a possible explanation.

Ground-based mid-infrared (mid-IR) observations appear to be widely perceived as esoteric and demanding, and very sensitive to observing conditions. Although the principles of observing in the background-limited regime are well-known, it is difficult for the non-specialist to find specific information on exactly how mid-IR data can be affected by environmental conditions. Understanding these effects is important for the efficiency of mid-IR queue observing, the ability of classical observers to adapt their programs to the prevailing conditions, and the standard of data being delivered. Through operating mid-IR instruments in the queue at Gemini we have amassed a considerable database of standard star observations taken under a wide range of atmospheric conditions and in a variety of instrumental configurations. These data can be used to illustrate the effect of factors such as water vapour column, airmass, cloud cover, etc. on observed quantities like raw sky background, residual background, atmospheric transmission and image FWHM. Here we present some preliminary results from this study, which we hope to be of use to observatory users and staff as a guide to which environmental conditions are truly important to mid- IR imaging observations, and which can safely be neglected.

Computer simulations of the atmospheric extinction are presented for the JHK filters. Comparison with observations show that the deviations from linearity in a magnitude/air mass plot are small even though the linear extrapolation to zero air mass produces a value much different than the models predict. The cause of this effect is discussed. It appears that direct verification of the non-linearity predicted by the models will be difficult to obtain.

The evolution of the IR spectra of asymptotic giant branch (AGB) stars has been obtained by time-dependent radiative transfer models. These models are compared with IRAS photometric and spectroscopic observations. Extrapolation of the models to beyond the AGB lead to predictions of the spectra of proto-planetary nebulae. Candidates of protoplanetary nebulae have been successfully found from these predictions.

We have mapped [Ne II] (12.8um) and [S IV] (10.5um) emission from W51 IRS 2 with TEXES on Gemini North, and we compare these data to VLA free-free observations and VLT near-infrared images. With 0.5" spatial and 4 km/s spectral resolution we are able to separate the ionized gas into several components: an extended H II region on the front surface of the molecular cloud, several embedded compact H II regions, and a streamer of high velocity gas. We interpret the high velocity streamer as a precessing or fan-like jet, which has emerged from the molecular cloud into an OB star cluster where it is being ionized., Comment: 3 pages, 4 figures, 2 movies

Molecular oxygen, O2 has been expected historically to be an abundant component of the chemical species in molecular clouds and, as such, an important coolant of the dense interstellar medium. However, a number of attempts from both ground and from space have failed to detect O2 emission. The work described here uses heterodyne spectroscopy from space to search for molecular oxygen in the interstellar medium. The Odin satellite carries a 1.1 m sub-millimeter dish and a dedicated 119 GHz receiver for the ground state line of O2. Starting in 2002, the star forming molecular cloud core rho Oph A was observed with Odin for 34 days during several observing runs. We detect a spectral line at v(LSR) = 3.5 km/s with dv(FWHM) = 1.5 km/s, parameters which are also common to other species associated with rho Ohp A. This feature is identified as the O2 (N_J = 1_1 - 1_0) transition at 118 750.343 MHz. The abundance of molecular oxygen, relative to H2,, is 5E-8 averaged over the Odin beam. This abundance is consistently lower than previously reported upper limits., Comment: 10 pages, 11 figures, accepted for publication in A&A

TEXES is a versatile mid-infrared spectrograph, which has been used on the NASA IRTF since 2000. It is capable of high spectral resolution (R ≈ 100,000), which is well suited for observations of interstellar and circumstellar molecules and ions, as well as molecules in planetary and stellar atmospheres. It has been installed on Gemini North where its point source sensitivity is expected to improve by a factor of 7, and its angular resolution will improve by 8/3.

Ever since the pioneering study of Spitzer, it has been widely recognized that grains play an important role in the heating and cooling of photo-ionized environments. A detailed code is necessary to model grains in a photo-ionized medium. In this paper we will use the spectral synthesis code Cloudy for this purpose. The grain model of this code has recently undergone a comprehensive upgrade. Part of this is the newly developed hybrid grain charge model, which will be described in detail. This model allows discrete charge states of very small grains to be modelled accurately while simultaneously avoiding the overhead of fully resolving the charge distribution of large grains, thus making the model both accurate and computationally efficient. A comprehensive comparison with the fully resolved charge state models of Weingartner & Draine (2001) shows that the agreement is very satisfactory for realistic size distributions. The effect of the grain size distribution on the line emission from photo-ionized regions is studied by taking standard models for an H II region and a planetary nebula and adding a dust component to the models with varying grain size distributions. A comparison of the models shows that varying the size distribution has a dramatic effect on the emitted spectrum, and affects the ionization balance as well. These results clearly demonstrate that the grain size distribution is an important parameter in photo-ionization models., 12 pages, 3 figures, 8 tables, minor typographical corrections wrt v1

The Odin satellite has been used to detect emission and absorption in the 557-GHz H2O line in the Galactic Centre towards the Sgr A* Circumnuclear Disk (CND), and the Sgr A +20 km/s and +50 km/s molecular clouds. Strong broad H2O emission lines have been detected in all three objects. Narrow H2O absorption lines are present at all three positions and originate along the lines of sight in the 3-kpc Spiral Arm, the -30 km/s Spiral Arm and the Local Sgr Spiral Arm. Broad H2O absorption lines near -130 km/s are also observed, originating in the Expanding Molecular Ring. A new molecular feature (the ``High Positive Velocity Gas'' - HPVG) has been identified in the positive velocity range of ~ +120 to +220 km/s, seen definitely in absorption against the stronger dust continuum emission from the +20 km/s and +50 km/s clouds and possibly in emission towards the position of Sgr A* CND. The 548-GHz H2_18O isotope line towards the CND is not detected at the 0.02 K (rms) level., 5 pages, 3 figures, accepted by A&A, special Odin Letters issue

Odin has successfully observed three regions in the Orion A cloud, i.e. Ori KL, Ori S and the Orion Bar, in the 572.5 GHz rotational ground state line of ammonia, ortho-NH3 (J,K) = (1,0) -> (0,0), and the result for the Orion Bar represents the first detection in an ammonia line. Several velocity components are present in the data. Specifically, the observed line profile from the Orion Bar can be decomposed into two components, which are in agreement with observations in high-J CO lines by Wilson et al. 2001. Using the source model for the Orion Bar by these authors, our Odin observation implies a total ammonia abundance of NH3/H2 = 5E-9., 4 pages with 2 figures, accepted for publication in A&A

We have mapped the submillimeter emission from the 1(10)-1(01) transition of ortho-water in the W3 star-forming region. A 5'x5' map of the W3 IRS4 and W3 IRS5 region reveals strong water lines at half the positions in the map. The relative strength of the Odin lines compared to previous observations by SWAS suggests that we are seeing water emission from an extended region. Across much of the map the lines are double-peaked, with an absorption feature at -39 km/s; however, some positions in the map show a single strong line at -43 km/s. We interpret the double-peaked lines as arising from optically thick, self-absorbed water emission near the W3 IRS5, while the narrower blue-shifted lines originate in emission near W3 IRS4. In this model, the unusual appearance of the spectral lines across the map results from a coincidental agreement in velocity between the emission near W3 IRS4 and the blue peak of the more complex lines near W3 IRS5. The strength of the water lines near W3 IRS4 suggests we may be seeing water emission enhanced in a photon-dominated region., Accepted to A&A Letters as part of the special Odin issue; 4 pages

Some characteristics of the 21 and 30 μm features observed in carbon star dust shells are briefly discussed.

K-band spectra are presented for a sample of 39 Spitzer Infrared Spectrograph (IRS) SAGE-Spec sources in the Large Magellanic Cloud. The spectra exhibit characteristics in very good agreement with their positions in the near-infrared—Spitzer color-magnitude diagrams and their properties as deduced from the Spitzer IRS spectra. Specifically, the near-infrared spectra show strong atomic and molecular features representative of oxygen-rich and carbon-rich asymptotic giant branch stars, respectively. A small subset of stars was chosen from the luminous and red extreme ''tip'' of the color-magnitude diagram. These objects have properties consistent with dusty envelopes but also cool, carbon-rich ''stellar'' cores. Modest amounts of dust mass loss combine with the stellar spectral energy distribution to make these objects appear extreme in their near-infrared and mid-infrared colors. One object in our sample, HV 915, a known post-asymptotic giant branch star of the RV Tau type, exhibits CO 2.3 μm band head emission consistent with previous work that demonstrates that the object has a circumstellar disk.

Infrared spectra of carbon-rich objects which have evolved off the asymptotic giant branch reveal a range of dust properties, including fullerenes, polycyclic aromatic hydrocarbons (PAHs), aliphatic hydrocarbons, and several unidentified features, including the 21 um emission feature. To test for the presence of fullerenes, we used the position and width of the feature at 18.7-18.9 um and examined other features at 17.4 and 6-9 um. This method adds three new fullerene sources to the known sample, but it also calls into question three previous identifications. We confirm that the strong 11 um features seen in some sources arise primarily from SiC, which may exist as a coating around carbonaceous cores and result from photo-processing. Spectra showing the 21 um feature usually show the newly defined Class D PAH profile at 7-9 um. These spectra exhibit unusual PAH profiles at 11-14 um, with weak contributions at 12.7 um, which we define as Class D1, or show features shifted to ~11.4, 12.4, and 13.2 um, which we define as Class D2. Alkyne hydrocarbons match the 15.8 um feature associated with 21 um emission. Sources showing fullerene emission but no PAHs have blue colors in the optical, suggesting a clear line of sight to the central source. Spectra with 21 um features and Class D2 PAH emission also show photometric evidence for a relatively clear line of sight to the central source. The multiple associations of the 21 um feature to aliphatic hydrocarbons suggest that the carrier is related to this material in some way., 30 pages, 30 figures, ApJ, in press

We discuss the results of analysis of Infrared Space Observatory spectra of PPN candidates. In particular for the carbon-rich PPNs in our sample we have analysis of the 21 and 30 μm features as well as the UIR features and plateaus. The 30 μm feature appears to have two sub-components, at about 27 and about 34 μm, which vary from source to source (Hrivnak, Volk, & Kwok, 2000). Based upon dust radiative transfer models we are able to fit the underlying continuum and so compare feature strengths and shapes for different objects The UIR features appear to vary somewhat from source to source, whereas the broad features seem to be the same in all sources. We also briefly discuss the galactic distribution of the PPNs

Aromatic features at 3.3, 6.2, 7.7, 8.6, 11.3 μm are observed in proto-planetary nebulae (PPNe) as well as in PNe and H ii regions. Aliphatic features at 3.4 and 6.9 μm are also observed; however, these features are often stronger in PPNe than in PNe. These observations suggest an evolution in the features from simple molecules (C2H2) in AGB stars to aliphatics in PPNe to aromatics in PNe. In the same carbon-rich PPNe, a strong, broad, unidentified 21 μm emission feature has been found. We will present recent observations of the aromatic, aliphatic, and 21 μm emission features, along with C2H2 (13.7 μm) and a new feature at 15.8 μm, and discuss correlations among them and other properties of these PPNe.

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 PAHsUsing 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 have constructed a detailed model for the infrared (IR) point source sky that comprises geometrically and physically realistic representations of the galactic disk, bulge, stellar halo, spiral arms (including the “local arm”), molecular ring, and the extragalactic sky. We represent each of the distinct galactic components by up to 87 types of galactic source, each fully characterized by scale heights, space densities, and absolute magnitudes at BVJHK, 12, and 25 μm, and a spectrum from the IRAS Low Resolution Spectrometer (LRS). Our model has been guided by a parallel Monte Carlo simulation of the Galaxy at 12 μm. The content of our galactic source table constitutes an excellent match to the 12 μm luminosity function in the simulation, as well as to the luminosity functions at V and K. We are able to predict differential and cumulative IR source counts for any bandpass lying fully within the IRAS LRS range (7.7–22.7 μm) as well as for the IRAS 12 and 25 μm bands. These source counts match the IRAS observations extremely well. The model can be used to predict the character of the point source sky expected for observations from future IR space experiments (e.g., ISO, SIRTF, LDR).

The WG-IR was created following a Joint Commission Meeting at the IAU General Assembly in Baltimore in 1988, a meeting that provided both diagnosis and prescription for the perceived ailments of infrared photometry at the time. The results were summarized in Milone (1989). The challenges involve how to explain the failure to systematically achieve the milli-magnitude precision expected of infrared photometry and an apparent 3% limit on system transformability. The proposed solution was to redefine the broadband Johnson system, the passbands of which had proven so unsatisfactory that over time effectively different systems proliferated although bearing the sameJHKLMNQdesignations; the new system needed to be better positioned and centered in the atmospheric windows of the Earth's atmosphere, and the variable water vapour content of the atmosphere needed to be measured in real time to better correct for atmospheric extinction.

We are obtaining low- (SWS01) and medium-resolution (SWS06) spectra of PPNe to investigate spectral features arising in these transitional objects. Three sources with the 21 µm feature have been confirmed, one new source found, and evidence of some substructure seen.

Under nebular conditions it is expected that the [CaII] lines at 7291.470 and 7323.880 A should be among the strongest emission lines in the red part of the optical spectrum unless the nebula is matter bounded. The lines are observed in novae, supernovae and some symbiotic systems but the only observation of these lines in planetary nebulae (PN) is for AFGL 618 where the lines are thought to be shock-excited. While higher ionization states of Ca do produce some lines observed in a few high-excitation PN, from which gas-phase Ca abundances averaging to about 5% of solar are found, the CaII lines are not observed even in PN with massive neutral envelopes such as NGC 7027. If the Ca is depleted onto dust grains it would explain the absence of the CaII lines. However it is thought that the dust is destroyed with time in the ionized region. Any observation of the CaII lines would produce better abundance estimates and would test the extent of dust destruction that is taking place in the outer parts of the PN.

Some carbon-rich evolved stars exhibit a very prominent spectral feature at {approx}{sup 3}0 {mu}m''. The C-rich nature of these objects suggests that the carrier is a sulfide, carbide, or other substance apt to form in a reducing environment. However, the carrier of this spectral feature remains disputed, with magnesium sulfide (MgS) as the most favored candidate. In order to investigate the carrier of the {sup 3}0 {mu}m'' feature further, we have taken a dual approach, studying both laboratory and observational data. In order to obtain a homogeneous sample, we studied the {sup 3}0 {mu}m'' feature observed in the spectra of galactic extreme carbon stars that exhibit the 11 {mu}m SiC absorption feature. Thus, we avoid potential differences in the target objects that could contribute to the observed differences in the shape, position, and strength of the {sup 3}0 {mu}m'' feature. In addition, we analyzed the shape and position of the {sup 3}0 {mu}m'' features for a range of sulfide minerals for which laboratory data exist. Our study of observed astronomical features shows a range of shapes and positions for the {sup 3}0 {mu}m'' feature despite similarities in the source objects. The nature of our sample argues against grain processing ormore » temperature differences due to hardening of the stellar radiation field with evolution. While there are very few correlations between spectral parameters for our sample, the peak positions of the {approx}11 {mu}m absorption and 30 {mu}m emission features do correlate, and these peak positions correlate with the modeled optical depth. These correlations suggest that the carriers of the observable spectral features are closely related to one another and to the density/pressure in the dust formation zone. Furthermore, we suggest that the blue-broadening of the 11 {mu}m feature cannot be attributed to SiS{sub 2} based on existing laboratory spectra, but further lab work is needed to investigate the effect of increasing oxidation.« less

We present fits to the spectral energy distributions of two post-AGB sources with the 21 µm feature: IRAS 222724–5435, where the 30 µm band was also detected, and IRAS 05113+1347, where observations around 30 µm are not yet available. Results of modeling suggest that all 21 µm emitters also have the 30 µm band. We show that magnesium sulfide could be responsible for the observed 30 µm feature. We also find that the stellar effective temperatures necessary for modeling of post-AGB objects are rather higher than those inferred from the spectral classification.

Carbon-rich AGB stars, protoplanetary nebulae (PPNe), and PNe show a variety of dust features attributed to carbon-based compounds. Of particular interest are the three dust features peaking near 21, 26 and 33 μm. The 26 and 33 μm features (collectively the “30 μm feature”; see Volk et al. 2002) are always observed together. The 21 μm feature is weak in the AGB phase and becomes more prominent in the PPN phase, which implies carrier evolution. We wish to see how this evolution continues into the PN phase from detailed modelling of the infrared spectra of PNe.

It has been well known since the IRAS mission that dust emission represents a significant fraction of the energy output from PNe (Zhang & Kwok 1991). Although the dust component in PNe was long thought to be due to the remnants of the envelopes of AGB stars (Kwok 1982), we now know that dust in PNe has a much richer chemical composition. In addition to amorphous silicates and SiC features commonly seen in AGB stars, PNe have been found to have strong aromatic infrared features (Russell et al. 1977), crystalline silicate features (Waters et al. 1997), and an unidentified emission feature at 30 μm (Forrest et al. 1981). In this paper, we show the ISO spectra of a number of PNe illustrating the diverse dust chemistry in PNe.

Many carbon-rich PNe show strong emission features due to various stretching and bending modes of aromatic hydrocarbon bonds (AHB). Comparisons between ISO spectra of evolved carbon stars, proto-planetary nebulae (PPNe), and PNe have shown that the AHB features develop late in the PPN phase (Kwok et al. 1999). In order to test the formation history of this carbonaceous component, it would be desirable to image the spatial distributions of the dust components. The Gemini Telescopes, optimized for infrared observations with adaptive optics capabilities, offer the unique opportunity for such observations. In this paper, we present the preliminary results of imaging of NGC 7027 and BD+30°3639 with the OSCIR mid-infrared camera at Gemini North.