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Spectral line observations encode a wealth of information. A key challenge, therefore, lies in the interpretation of these observations in terms of models to derive the physical and chemical properties of the astronomical environments from which they arise. In this paper, we present pomme, an open-source Python package that allows users to retrieve 1D or 3D models of physical properties, such as chemical abundance, velocity, and temperature distributions of (optically thin) astrophysical media, based on spectral line observations. We discuss how prior knowledge, for instance, in the form of a steady-state hydrodynamics model, can be used to guide the retrieval process, and we demonstrate our methods on both synthetic and real observations of cool stellar winds.

Turbulence is expected to transport angular momentum and drive mass accretion in protoplanetary disks. One way to directly measure turbulent motion in disks is through molecular line broadening. DM Tau is one of only a few disks with claimed detection of nonthermal line broadening of 0.25cs–0.33cs, where cs is the sound speed. Using the radiative transfer code mcfost within a Bayesian inference framework that evaluates over five million disk models to efficiently sample the parameter space, we fit high-resolution ( 0.″15 , 28 m s−1) 12CO J = 3–2 observations of DM Tau from the exoALMA Large Program. This approach enables us to simultaneously constrain the disk structure and kinematics, revealing a significant nonthermal contribution to the line width of ∼0.4cs, inconsistent with purely thermal motions. Using the CO-based disk structure as a starting point, we reproduce the CS J = 7–6 emission well, demonstrating that the CS (which is more sensitive to nonthermal motions than CO) agrees with the turbulence inferred from the CO fit. Establishing a well-constrained background disk model further allows us to identify residual structures in the moment maps that deviate from the expected emission, revealing localized perturbations that may trace forming planets. This framework provides a powerful general approach for extracting disk structure and nonthermal broadening directly from molecular line data and can be applied to other disks with high-quality observations.

We present the first hydrodynamical simulations of common envelope evolution that include the formation of dust and the effect of radiation pressure on dust grains. We performed smoothed particle hydrodynamics simulations of the CE evolution for two systems made of a 1.7 M⊙ and 3.7 M⊙ AGB star primary with a 0.6 M⊙ binary companion. The results of our calculations indicate that dust formation has a negligible impact on the gas dynamics essentially because dust forms in the already unbound material. The expansion and cooling of the envelope yield very early and highly efficient production of dust. In our formalism, which does not consider dust destruction, almost 100% of the available carbon that is not locked in CO condensates in dust grains. This massive dust production, thus, strongly depends on the envelope mass and composition, in particular, its C/O ratio, and has a considerable impact on the observational aspect of the object, resulting in a photospheric radius that is approximatively one order of magnitude larger than that of a non-dusty system.

For the first time in 2024, the Astronomical Society of Australia Annual Scientific Meeting was held as an online-first conference, incorporating unprecedented use of immersive spatial venues. This Comment presents findings from this experiment in accessible conferencing and reflects on their implications in the current academic climate.

The modern era of highly sensitive telescopes is enabling the detection of more and more molecular species in various astronomical environments. Many of these are now being carefully examined for the first time. However, to move beyond detection to more detailed analysis such as radiative transfer modelling, certain molecular properties need to be properly measured and calculated. The importance of contributions from vibrationally excited states or collisional (de-)excitations can vary greatly, depending on the specific molecule and the environment being studied. Here, we discuss the present molecular data needs for detailed radiative transfer modelling of observations of molecular rotational transitions, primarily in the (sub-)millimetre and adjacent regimes, and with a focus on the stellar winds of AGB stars.

There are clear differences in what sulphur molecules form in AGB circumstellar envelopes (CSEs) across chemical types. CS forms more readily in the CSEs of carbon stars, while SO and SO 2 have only been detected towards oxygen-rich stars. However, we have also discovered differences in sulphur chemistry based on the density of the CSE, as traced by mass-loss rate divided by expansion velocity. For example, the radial distribution of SO is drastically different between AGB stars with lower and higher density CSEs. H 2 S can be found in high abundances towards higher density oxygen-rich stars, whereas SiS accounts for a significant portion of the circumstellar sulphur for higher density carbon stars.

We performed numerical simulations of the common envelope (CE) interaction between two intermediate-mass asymptotic giant branch (AGB) stars and their low-mass companions. For the first time, formation and growth of dust in the envelope is calculated explicitly. We find that the first dust grains appear as early as ∼1–3 yrs after the onset of the CE, and are smaller than grains formed later. As the simulations progress, a high-opacity dusty shell forms, resulting in the CE photosphere being up to an order of magnitude larger than it would be without the inclusion of dust. At the end of the simulations, the total dust yield is ∼8.2×10−3 M⊙ (∼2.2×10−2 M⊙) for a CE with a 1.7 M⊙ (3.7 M⊙) AGB star. Dust formation does not substantially lead to more mass unbinding or substantially alter the orbital evolution.

ALMA observations with angular resolution in the range ∼20–200 mas demonstrate that emission at 268.149 and 262.898 GHz in the (0,2,0) and (0,1,0) vibrationally excited states of water are widespread in the inner envelope of O-rich AGB stars and red supergiants. These transitions are either quasi-thermally excited, in which case they can be used to estimate the molecular column density, or show signs of maser emission with a brightness temperature of ∼103–107 K in a few stars. The highest spatial resolution observations probe the inner few stellar radii environment, up to ∼10–12 R* in general, while the mid resolution data probe more thermally excited gas at larger extents. In several stars, high velocity components are observed at 268.149 GHz which may be caused by the kinematic perturbations induced by a companion. Radiative transfer models of water are revisited to specify the physical conditions leading to 268.149 and 262.898 GHz maser excitation.

Sulfur and its isotopic ratios play a crucial role in understanding astrophysical environments, providing insights into nucleosynthesis, ISM processes, star formation, planetary evolution, and galactic chemistry. We investigate the distribution of sulfur bearing species \\(\\rm{SO_2}\\), \\(\\rm{^{34}SO_2}\\), SO, and \\(\\rm{^{34}SO}\\) towards five oxygen rich Asymptotic Giant Branch (AGB) stars (\\(o\\) Ceti, R Dor, W Hya, R Leo, and EP Aqr), along with their excitation temperatures, column densities, and isotopic ratios. Using ALMA Band 6,7,8 data and CASSIS, we detect these species and estimate excitation temperature and column density via the rotational diagram and MCMC methods under LTE. Line imaging of various transitions is used to infer spatial distributions. The excitation temperatures of \\(\\rm{SO_2}\\) range from \\(\\sim\\)200-600 K with column densities of \\(\\rm{1-7\\times10^{16}\\ cm^{-2}}\\), while \\(\\rm{^{34}SO_2}\\) shows comparable or slightly lower values and about an order of magnitude lower column densities. The \\(\\rm{^{32}S/^{34}S}\\) ratios for R Dor and W Hya are near solar, slightly higher for \\(o\\) Ceti, and lower for EP Aqr and R Leo. Most detected lines exhibit centralized emission: high excitation \\(\\rm{SO_2}\\) traces compact hot gas in inner CSEs, whereas low-excitation lines trace more extended structures. Morphological differences, irregular emission in \\(o\\) Ceti, circular in R Leo and W Hya, clumpy in R Dor, and unresolved in EP Aqr may arise from variations in physical conditions, multiplicity, outflows, rotation, desorption processes, UV or cosmic ray effects, or observational resolution. Overall, the centralized SO and \\(\\rm{SO_2}\\) emissions support previous findings for low mass-loss rate AGB stars, and the \\(\\rm{^{32}S/^{34}S}\\) ratios likely reflect natal cloud composition, with deviations linked to metallicity or excitation conditions.

Low- and intermediate-mass stars will all eventually enter the asymptotic giant branch (AGB) phase. AGB stars experience intense mass-loss, generating a significant fraction of the dust and molecular matter that enrichesthe ISM. AGB stars are also responsible for a the production of about half of all elements heavier than iron.AGB stars can be classified into two broad categories: oxygen-rich M stars and carbon-rich C stars. When a star leaves the main sequence and ascends the AGB, it will initially be oxygen-rich. Over time, for a particular subset of AGB stars, enough carbon will be dredged up fromtheir interiors to enrich their atmospheres and, eventually, turn them into carbon-rich stars. S-type AGB stars are believed to be an intermediate evolutionary stage between M and C stars, with a C/O ratio close to 1.As transition objects they provide a unique window into the mass-loss mechanism(s) and chemistry of AGB stars.W Aql is an S-type AGB star with a binary companion. In this thesis we examine its mass-loss properties through a detailed analysis of the molecular emission in its circumstellar envelope (CSE). With new Herschel/HIFI observations which probe areas of the CSE closer to the star, we are able to better constrain mass-loss and CSE properties than previously possible. We detect molecular emission lines of CO, H2O, SiO, HCN and NH3, the latter for the first time in an S star. We find a mass-loss rate for W Aql of 3.5E-6 Msun/yr and present abundances of each molecular species.We also use optical observations of W Aql to determine the spectral type, and hence constrain the mass and temperature, of the fain companion to the AGB star. Our spectroscopic analysis puts the companion in the range F8V–G0V. Our photometric observations broadly agree with this result and indicate that the companion undergoes extensive extinction, most likely due to dust produced by the AGB star.