Editorial Dear Colleagues, It is our pleasure to present you the 124 issue of the AGB Newsletter, with 25 refereed journal articles, numerous conference papers and two job opportunities in Hong Kong. This issue covers AGB-related research in an especially diverse range of stellar systems: the Milky Way disc and halo, ω Centauri, the Magellanic Clouds, other Local Group dwarf galaxies Fornax, Sgr dIrr, DDO210 and NGC 3109, to as far as the z = 0.0237 Scd galaxy IC 1277. We also wish to draw your attention in particular to the review paper on AGB nucleosynthesis by Amanda Karakas and John Lattanzio. The next issue will be distributed on the 1 of November; the deadline for contributions is the 31 of October.

In this paper we study the extended atmosphere of the late-type supergiant α Orionis. Infrared spectroscopy of red supergiants reveals strong molecular bands, some of which do not originate in the photosphere but in a cooler layer of molecular material above it. Lately, these layers have been spatially resolved by near and mid-IR interferometry. In this paper, we try to reconcile the IR interferometric and ISO-SWS spectroscopic results on α Orionis with a thorough modelling of the photosphere, molecular layer(s) and dust shell. From the ISO and near-IR interferometric observations, we find that α Orionis has only a very low density water layer close above the photosphere. However, mid-IR interferometric observations and a narrow-slit N-band spectrum suggest much larger extra-photospheric opacity close to the photosphere at those wavelengths, even when taking into account the detached dust shell. We argue that this cannot be due to the water layer, and that another source of mid-IR opacity must be present. We show that this opacity source is probably neither molecular nor chromospheric. Rather, we present amorphous alumina (Al2O3) as the best candidate and discuss this hypothesis in the framework of dust-condensation scenarios.

We report the detection of strong absorption and weak emission features in the 4--27 micron Spitzer-IRS spectrum of the distant ultraluminous infrared galaxy (ULIRG) IRAS F00183--7111 (z=0.327). The absorption features of CO2 and CO gas, water ice, hydrocarbons and silicates are indicative of a strongly obscured (A[9.6]>=5.4; A[V]>=90) and complex line of sight through both hot diffuse ISM and shielded cold molecular clouds towards the nuclear power source. From the profile of the 4.67 micron CO fundamental vibration mode we deduce that the absorbing gas is dense (n~10^6 cm^-3) and warm (720 K) and has a CO column density of ~10^19.5 cm^-2, equivalent to N[H]~10^23.5 cm^-2. The high temperature and density, as well as the small infered size (<0.03pc), locates this absorbing gas close to the power source of this region. Weak emission features of molecular hydrogen, PAHs and Ne+, likely associated with star formation, are detected against the 9.7 micron silicate feature, indicating an origin away from the absorbing region. Based on the 11.2 micron PAH flux, we estimate the star formation component to be responsible for up to 30% of the IR luminosity of the system. While our mid-infrared spectrum shows no tell-tale signs of AGN activity, the similarities to the mid-infrared spectra of deeply obscured sources (e.g. NGC4418) and AGN hot dust (e.g. NGC1068), as well as evidence from other wavelength regions, suggest that the power source hiding behind the optically thick dust screen may well be a buried AGN.

We report the detection of strong absorption and weak emission features in the 4-27 mum Spitzer Infrared Spectrograph (IRS) spectrum of the distant ultraluminous infrared galaxy IRAS F00183-7111 (z = 0.327). The absorption features of CO2 and CO gas, water ice, hydrocarbons, and silicates are indicative of a strongly obscured (A(9.6) greater than or equal to 5.4; A(V) greater than or equal to 90) and complex line of sight through both the hot diffuse interstellar medium and shielded cold molecular clouds toward the nuclear power source. From the profile of the 4.67 mum CO fundamental vibration mode, we deduce that the absorbing gas is dense (n similar to 10(6) cm(-3)) and warm ( 720 K) and has a CO column density of similar to10(19.5) cm(-2), equivalent to N-H similar to 10(23.5) cm(-2). The high temperature and density, as well as the small inferred size (<0.03 pc), locates this absorbing gas close to the power source of this region. Weak emission features of molecular hydrogen, polycyclic aromatic hydrocarbons (PAHs), and Ne+, likely associated with star formation, are detected against the 9.7 mu m silicate feature, indicating an origin away from the absorbing region. Based on the 11.2 mu m PAH flux, we estimate the star formation component to be responsible for up to 30% of the IR luminosity of the system. While our mid-infrared spectrum shows no telltale signs of active galactic nucleus (AGN) activity, the similarities to the mid-infrared spectra of deeply obscured sources ( e. g., NGC 4418) and AGN hot dust (e.g., NGC 1068), as well as evidence from other wavelength regions, suggest that the power source hiding behind the optically thick dust screen may well be a buried AGN.

We present submillimeter observations of rotational transitions of carbon monoxide from J = 2→ 1 up to 7→ 6 for a sample of Asymptotic Giant Branch stars and red supergiants. It is the first time that the high transitions J = 6 → 5 and 7→ 6 are included in such a study. With line radiative transfer calculations, we aim to determine the mass-loss history of these stars by fitting the CO line intensities. We find that the observed line intensities of the high transitions, including the J = 4→ 3 transition, are significantly lower than the predicted values. We conclude that the physical structure of the outflow of Asymptotic Giant Branch stars is more complex than previously thought. In order to understand the observed line intensities and profiles, a physical structure with a variable mass-loss rate and /or a gradient in stochastic gas velocity is required. A case study of the AGB star WX Psc is performed. We find that the CO line strengths may be explained by variations in mass-loss on time scales similar to those observed in the separated arc-like structures observed around post-AGB stars. In addition, a gradient in the stochastic velocity may play a role. Until this has been sorted out fully, any mass loss determinations based upon single CO lines will remain suspect.