Context. Stars on the asymptotic giant branch (AGB) play important roles in a number of astronomical contexts. To quantify these roles, it is necessary to establish the mass-loss characteristics of stars as they evolve up and beyond the AGB. Aims. We used an equidistant sample of 77 AGB stars in the inner Galactic bulge, selected on the existence and strength of OH 1612 MHz maser emission, to obtain information on the mass loss of O-rich AGB stars, and on its transformations in geometry and kinematics that occur at the tip of the AGB. Methods. Observations of circumstellar lines from several rotational transitions of (CO)-C-12, (CO)-C-13, and (CO)-O-18 were performed with the Atacama Large Millimeter/submillimeter Array (ALMA), and, for a sub-sample, with the Atacama Pathfinder EXperiment telescope (APEX). The ALMA observations also provide continuum data. Existing infrared photometry was used to estimate colours and produce stellar light curves. Results. Based on mid-infrared colour, CO line, and near-infrared variability characteristics, the objects were divided into four categories of distinct stellar and/or circumstellar properties. Various circumstellar CO line characteristics are presented and compared between the categories, such as morphologies and extents of brightness distributions (BDs), line profiles (LPs), line intensity ratios, and kinematics. A majority of the objects form a homogenous group with sharply, centrally peaked BDs and LPs of the soft-parabola type, while the rest show extended and complex BDs and/or LPs with high-velocity wings. The (CO)-O-18 line and ALMA continuum detection rates vary significantly between the categories. CO line emission is also detected from interaction zones where the expanding circumstellar gas meets the interstellar medium. Conclusions. These data provide the foundation for more detailed studies, including radiative transfer analyses of the CO line and photometry data, on the evolution of stellar and circumstellar characteristics of O-rich stars on the upper AGB and beyond.

The present understanding of C-rich AGB chemistry largely relies on observations of the archetypal carbon star IRC+10216. Current molecular abundance estimates for carbon stars are based either on single-dish spectra sampling a range of excitation conditions, or on interferometric mapping of a few lines. We aim to estimate the circumstellar abundances of SiO, SiS, and their most abundant isotopologues (^29SiO, ^30SiO, ^29SiS, ^30SiS, and Si^34S) for a sample of five carbon stars. We derived molecular abundances using detailed 1D non-local thermodynamic equilibrium (non-LTE) radiative transfer (RT) modelling, constrained by both morphological and excitation information obtained from spatially resolved ALMA maps and single-dish observations. We further compared the derived abundances to chemical modelling results. We obtain good fits to the SiO and SiS line profiles, and derived well-constrained abundance profiles and reliable isotopic ratios for all sources except AFGL 3068. While the SiS peak abundances are very similar across the sample (2.0×10^-6-4.7×10^-6), we find that the SiO peak abundances of the rest of the stars are a factor of ∼5 larger than that of IRC+10216. The e-folding radii (R_e) are in the range 1.3×10^16-7.0×10^16 cm for SiO and 6.0×10^15-1.0×10^17 cm for SiS. The R_e increases with gas density for both SiO and SiS. Chemical models reproduce the derived SiO abundance profiles well, while over-predicting the SiS R_e values. Our models highlight the necessity of having spatially resolved observations across a broad range of excitation conditions, while also making evident the limitations inherent in 1D RT modelling using simplified (circum)stellar models. We find that the currently assumed SiS photodissociation rate in chemical models is underestimated.

Aims. We investigate how the presence of a binary companion appears to affect dust and molecule formation in the circumstellar environment of a star on the asymptotic giant branch (AGB). Methods.L- and N-band observations obtained over the course of one month with the multi aperTure mid-infrared spectroScopic experiment instrument (MATISSE) at the very large telescope interferometer (VLTI) were used to constrain the distribution of dust and molecules in the close environment of π1 Gru through image reconstruction. The reconstructed images were fit to the interferometric observables, that is, the visibilities and closure phases, using the two Python-based tools Python for MiRA (PYRA) and mean astrophysical images with PYRA (MYTHRA) built around the multi-aperture image reconstruction algorithm (MiRA). Results. Our observations support (i) a wind Roche-lobe overflow (WRLOF) scenario, where mass transfer from the AGB star to its companion produces a possible circumcompanion disk in the L band around π1 Gru C, with a central cavity that likely traces dust sublimation and a circumcompanion envelope in the N band. (ii) A main-sequence nature for the companion: Because both Atacama large millimeter/submillimeter array (ALMA) and the VLTI/MATISSE N-band observations show emission, we favor a thermal infrared emission from the main-sequence star over free-free emission from a with dwarf companion. Finally, (iii) a plume-like structure extending from π1 Gru C, likely marking the onset of the spiral observed at larger scales. Together, this provides direct evidence that links small-scale mass transfer and disk formation through WRLOF to the global circumstellar morphology. Conclusions. These results highlight the atmospheric deformation induced by the companion, reveal ongoing mass transfer between the evolved star and its companion, and indicate a circumcompanion disk-like structure.

Context. Stars on the asymptotic giant branch (AGB) play important roles in a number of astronomical contexts. To quantify these roles, it is necessary to establish the mass-loss characteristics of stars as they evolve up and beyond the AGB. Aims. We used an equidistant sample of 77 AGB stars in the inner Galactic bulge, selected on the existence and strength of OH 1612 MHz maser emission, to obtain information on the mass loss of O-rich AGB stars, and on its transformations in geometry and kinematics that occur at the tip of the AGB. Methods. Observations of circumstellar lines from several rotational transitions of 12CO, 13CO, and C18O were performed with the Atacama Large Millimeter/submillimeter Array (ALMA), and, for a sub-sample, with the Atacama Pathfinder EXperiment telescope (APEX). The ALMA observations also provide continuum data. Existing infrared photometry was used to estimate colours and produce stellar light curves. Results. Based on mid-infrared colour, CO line, and near-infrared variability characteristics, the objects were divided into four categories of distinct stellar and/or circumstellar properties. Various circumstellar CO line characteristics are presented and compared between the categories, such as morphologies and extents of brightness distributions (BDs), line profiles (LPs), line intensity ratios, and kinematics. A majority of the objects form a homogenous group with sharply, centrally peaked BDs and LPs of the soft-parabola type, while the rest show extended and complex BDs and/or LPs with high-velocity wings. The C18O line and ALMA continuum detection rates vary significantly between the categories. CO line emission is also detected from interaction zones where the expanding circumstellar gas meets the interstellar medium. Conclusions. These data provide the foundation for more detailed studies, including radiative transfer analyses of the CO line and photometry data, on the evolution of stellar and circumstellar characteristics of O-rich stars on the upper AGB and beyond.

Context. The circumstellar envelopes of AGB stars are sites of rich molecular chemistry. The present understanding of C-rich AGB chemistry largely relies on observations of the archetypal carbon star IRC+10 216. Current molecular abundance estimates for carbon stars are based either on single-dish spectra sampling a range of excitation conditions, or on interferometric mapping of a few lines. Aims. We aim to estimate the circumstellar abundances of SiO, SiS, and their most abundant isotopologues (29SiO, 30SiO, 29SiS, 30SiS, and Si34S) for a sample of five carbon stars. This study compares molecular abundances across the sources, tests chemical modelling predictions, and examines whether IRC+10 216 is representative of the broader carbon star population. Methods. We derived molecular abundances using detailed 1D non-local thermodynamic equilibrium (non-LTE) radiative transfer (RT) modelling, constrained by both morphological and excitation information obtained from spatially resolved ALMA maps and single-dish observations. We further compared the derived abundances to chemical modelling results. Results. We obtain good fits to the SiO and SiS line profiles, and derived well-constrained abundance profiles and reliable isotopic ratios for all sources except AFGL 3068. While the SiS peak abundances are very similar across the sample (2.0 × 10−6–4.7 × 10−6), we find that the SiO peak abundances of the rest of the stars are a factor of ~5 larger than that of IRC +10 216. The e-folding radii (Re) are in the range 1.3 × 1016 − 7.0×1016cm for SiO and 6.0 × 1015 − 1.0×1017 cm for SiS. The Re increases with gas density for both SiO and SiS. Our RT models cannot simultaneously fit the low- and high-J SiO lines of IRC+10216. Chemical models reproduce the derived SiO abundance profiles well, while over-predicting the SiS Re values. Conclusions. Our models highlight the necessity of having spatially resolved observations across a broad range of excitation conditions to robustly constrain molecular abundance profiles, while also making evident the limitations inherent in 1D RT modelling using simplified (circum)stellar models. We find that the currently assumed SiS photodissociation rate in chemical models is underestimated.

Context. The circumstellar envelopes of AGB stars are sites of rich molecular chemistry. The present understanding of C-rich AGB chemistry largely relies on observations of the archetypal carbon star IRC+10 216. Current molecular abundance estimates for carbon stars are based either on single-dish spectra sampling a range of excitation conditions, or on interferometric mapping of a few lines. Aims. We aim to estimate the circumstellar abundances of SiO, SiS, and their most abundant isotopologues ((SiO)-Si-29, (SiO)-Si-30, (SiS)-Si-29, (SiS)-Si-30, and (SiS)-S-34) for a sample of five carbon stars. This study compares molecular abundances across the sources, tests chemical modelling predictions, and examines whether IRC+10 216 is representative of the broader carbon star population. Methods. We derived molecular abundances using detailed 1D non-local thermodynamic equilibrium (non-LTE) radiative transfer (RT) modelling, constrained by both morphological and excitation information obtained from spatially resolved ALMA maps and single-dish observations. We further compared the derived abundances to chemical modelling results. Results. We obtain good fits to the SiO and SiS line profiles, and derived well-constrained abundance profiles and reliable isotopic ratios for all sources except AFGL 3068. While the SiS peak abundances are very similar across the sample (2.0 x 10(-6) - 4.7 x 10(-6)), we find that the SiO peak abundances of the rest of the stars are a factor of similar to 5 larger than that of IRC +10 216. The e-folding radii (R-e) are in the range 1.3 x 10(16) - 7.0 x 10(16)cm for SiO and 6.0 x 10(15) - 1.0 x 10(17) cm for SiS. The R-e increases with gas density for both SiO and SiS. Our RT models cannot simultaneously fit the low- and high-J SiO lines of IRC+10216. Chemical models reproduce the derived SiO abundance profiles well, while over-predicting the SiS R-e values. Conclusions. Our models highlight the necessity of having spatially resolved observations across a broad range of excitation conditions to robustly constrain molecular abundance profiles, while also making evident the limitations inherent in 1D RT modelling using simplified (circum)stellar models. We find that the currently assumed SiS photodissociation rate in chemical models is underestimated.

Aims. We investigate how the presence of a binary companion appears to affect dust and molecule formation in the circumstellar environment of a star on the asymptotic giant branch (AGB). Methods.L- and N-band observations obtained over the course of one month with the multi aperTure mid-infrared spectroScopic experiment instrument (MATISSE) at the very large telescope interferometer (VLTI) were used to constrain the distribution of dust and molecules in the close environment of π1 Gru through image reconstruction. The reconstructed images were fit to the interferometric observables, that is, the visibilities and closure phases, using the two Python-based tools Python for MiRA (PYRA) and mean astrophysical images with PYRA (MYTHRA) built around the multi-aperture image reconstruction algorithm (MiRA). Results. Our observations support (i) a wind Roche-lobe overflow (WRLOF) scenario, where mass transfer from the AGB star to its companion produces a possible circumcompanion disk in the L band around π1 Gru C, with a central cavity that likely traces dust sublimation and a circumcompanion envelope in the N band. (ii) A main-sequence nature for the companion: Because both Atacama large millimeter/submillimeter array (ALMA) and the VLTI/MATISSE N-band observations show emission, we favor a thermal infrared emission from the main-sequence star over free-free emission from a with dwarf companion. Finally, (iii) a plume-like structure extending from π1 Gru C, likely marking the onset of the spiral observed at larger scales. Together, this provides direct evidence that links small-scale mass transfer and disk formation through WRLOF to the global circumstellar morphology. Conclusions. These results highlight the atmospheric deformation induced by the companion, reveal ongoing mass transfer between the evolved star and its companion, and indicate a circumcompanion disk-like structure.

Mass loss during the advanced evolutionary stages of low- and intermediate-mass stars is traditionally attributed to dust-driven winds, whereas the influence of magnetic fields remains poorly constrained. However, recent observations show massive directional mass ejections from the nearby asymptotic giant branch (AGB) star Mira A that appear not to be driven by radiation pressure on the dust. We observationally investigate whether magnetic fields are responsible for the mass loss ejections from Mira A. We obtained full-polarisation ALMA observations of the SiO v=1, J=5→4 maser transition at 215 GHz with angular resolutions of 1.5-2.6 au. The observations reveal a highly magnetized loop-like mass ejection traced by strongly polarised SiO masers extending to approximately eight stellar radii. The morphology, polarisation pattern, energetics, and kinematics indicate a magnetically driven eruption analogous to a stellar coronal mass ejection. The observations demonstrate that magnetic eruptions can dominate mass loss from evolved stars and imply that magnetic fields must become an integral component of future models of AGB, and potentially other cool giant, winds.

Context. Supernova observations imply the presence of a dense and asymmetric circumstellar environment around SN Type II progenitors, whereas the mass loss from these progenitors, namely, red supergiants, is still poorly constrained. Aims. We aim to characterise the dust and gas in the circumstellar environment of the extreme Galactic red supergiant NML Cyg in terms of mass, morphology, and kinematics. Methods. Based on interferometric observations with NOEMA at 230 GHz, we estimated the dust masses and temperatures, and measured the extent and morphological complexity of the circumstellar environment. Results. We detected two strong continuum components, amounting to an estimated total dust mass of similar to 2 x 10-3 M circle dot located out to similar to 2000 AU from the star, largely beyond the dust detected at optical/infrared wavelengths. The extent of the detected CO emission supports the notion that the outflow is formed by a mass-loss rate of several 10-4 M circle dot yr-1 and that it is not primarily shaped by extreme irradiation from the Cyg OB2 cluster the star has been associated with. We have detected, but not resolved, previously unseen highvelocity components close to the star. The observations reveal a very complex circumstellar morphology and we propose that some of the detected components could be the imprint of a hitherto unknown binary companion.

Atacama Large Millimeter/submillimeter Array (ALMA) observations at 1.3 mm have recently revealed surprising complexity in the circumstellar environment of DFK 52, a red supergiant (RSG) located in the Stephenson 2 massive open cluster. We provide an initial characterisation of the star's mass-loss properties by studying its circumstellar emission in continuum, (CO)-C-12, (CO)-C-13, and SiO rotational lines. We find that DFK 52 is surrounded by an extremely large outflow (up to 50 000 au in radius) that shows complex morphologies in both its molecular and dust emission. The size of the circumstellar medium is unprecedented, even when compared with other known extreme RSGs, and its lower luminosity indicates that its mass ejection mechanism may be unique among this population. The molecular emission can be partially reproduced by a two-component model consisting of a fast (27 km s(-1)) detached equatorial component with M similar to 0.05 M-circle dot and a slow (10 km s(-1)) spherical envelope with M similar to 3 x 10(-6) M-circle dot yr(-1). This suggests that DFK 52 underwent a dramatic mass-loss event similar to 4000 years ago, but has since transitioned into having a slower more symmetric mass loss. We conservatively estimate a total mass of 0.1 - 1 M-circle dot in the complex extended regions of the outflow. The uncertain nature of the dramatic mass loss warrants extensive follow-up of this likely supernova progenitor.

Atacama Large Millimeter/submillimeter Array (ALMA) observations at 1.3 mm have recently revealed surprising complexity in the circumstellar environment of DFK 52, a red supergiant (RSG) located in the Stephenson 2 massive open cluster. We provide an initial characterisation of the star’s mass-loss properties by studying its circumstellar emission in continuum, 12 CO, 13 CO, and SiO rotational lines. We find that DFK 52 is surrounded by an extremely large outflow (up to 50 000 au in radius) that shows complex morphologies in both its molecular and dust emission. The size of the circumstellar medium is unprecedented, even when compared with other known extreme RSGs, and its lower luminosity indicates that its mass ejection mechanism may be unique among this population. The molecular emission can be partially reproduced by a two-component model consisting of a fast (27 km s −1 ) detached equatorial component with M ∼ 0.05 M ⊙ and a slow (10 km s −1 ) spherical envelope with Ṁ ∼ 3 × 10 −6 M ⊙ yr −1 . This suggests that DFK 52 underwent a dramatic mass-loss event ∼4000 years ago, but has since transitioned into having a slower more symmetric mass loss. We conservatively estimate a total mass of 0.1 − 1 M ⊙ in the complex extended regions of the outflow. The uncertain nature of the dramatic mass loss warrants extensive follow-up of this likely supernova progenitor.

Strong laser emission from hydrogen cyanide (HCN) at 805 and 891 GHz has been discovered towards carbon-rich (C-rich) AGB stars, originating from the Coriolis-coupled system between two (1,1^{1e},0) and (0,4^0,0) vibrational states. However, other lines (at 894, 964, 968 and 1055 GHz) in this system remained unexplored due to observational challenges. Using SOFIA/4GREAT observations and Herschel/HIFI archival data, we analyzed the six HCN transitions in eight C-rich AGB stars. We report new HCN transitions show laser action at 964, 968, and 1055 GHz. The 805, 891, and 964 GHz lasers were detected in seven C-rich stars, the 968 GHz laser in six, and the 1055 GHz laser in five, while the 894 GHz line was not detected in any target. Among the detected lasers, the 891 GHz laser is always the strongest, and the 964 GHz laser, like a twin of the 891 GHz line, is the second strongest. Towards IRC+10216, all five HCN laser transitions were observed in six to eight epochs and exhibited significant variations in line profiles and intensities. The cross-ladder lines at 891 and 964 GHz exhibit similar variations, and their intensity changes do not follow the near-infrared light curve (i.e. non-periodic variations). In contrast, the variations of the rotational lines at 805, 968, and 1055 GHz appear to be quasi-periodic, with a phase lag of 0.1 - 0.2 relative to the near-infrared light curve. A comparative analysis indicates that these HCN lasers may be seen as analogues to vibrationally excited SiO and water masers in oxygen-rich stars. We suggest chemical pumping and radiative pumping could play an important role in the production of the cross-ladder HCN lasers, while the quasi-periodic behavior of the rotational HCN laser lines may be modulated by additional collisional and radiative pumping driven by periodic shocks and variations in infrared luminosity. [abridged]

Context. Strong laser emission from hydrogen cyanide (HCN) at 805 and 891 GHz has been discovered towards carbon-rich (C-rich) asymptotic giant branch (AGB) stars. Both lines belong to the Coriolis-coupled system between the (1,11e,0) and (0,40,0) vibrational states, which has been extensively studied in early molecular spectroscopy in the laboratory. However, the other lines in this system with frequencies above similar to 900 GHz, which are challenging to observe with ground-based telescopes, have remained unexplored in astronomical contexts. Aims. We aim to (1) search for new HCN transitions that show laser activity in the (0,40,0), J = 10-9 line at 894 GHz, the (1,11e,0)-(0,40,0), J = 11-10 line at 964 GHz, the (1,11e,0), J = 11-10 at 968 GHz, and the (1,11e,0), J = 12-11 line at 1055 GHz towards C-rich AGB stars; (2) study the variability of multiple HCN laser lines, including the two known lasers at 805 and 891 GHz; and (3) construct a complete excitation scenario to the Coriolis-coupled system. Methods. We conducted SOFIA/4GREAT observations and combined our data with Herschel/HIFI archival data to construct a sample of eight C-rich AGB stars, covering six HCN transitions (i.e. the 805, 891, 894, 964, 968, and 1055 GHz lines) in the Coriolis-coupled system. Results. We report the discovery of HCN lasers at 964, 968, and 1055 GHz towards C-rich AGB stars. Laser emission in the 805, 891, and 964 GHz HCN lines was detected in seven C-rich stars, while the 968 GHz laser was detected in six stars and the 1055 GHz laser in five stars. Notably, the 894 GHz line emission was not detected in any of the targets. Among the detected lasers, the emission of the cross-ladder line at 891 GHz is always the strongest, with typical luminosities of a few 1044 photons s-1. The cross vibrational state 964 GHz laser emission, which is like a twin of the 891 GHz line, is the second strongest. The 1055 GHz laser emission always has a stronger 968 GHz counterpart. Towards IRC+10216, all five HCN laser transitions were observed in six to eight epochs and exhibited significant variations in line profiles and intensities. The 891 and 964 GHz lines exhibit similar variations, and their intensity changes do not follow the near-infrared light curve (i.e. they have non-periodic variations). In contrast, the variations in the 805, 968, and 1055 GHz lines appear to be quasi-periodic, with a phase lag of 0.1-0.2 relative to the near-infrared light curve. A comparative analysis indicates that these HCN lasers may be seen as analogues to vibrationally excited SiO and H2O masers in oxygen-rich stars. Conclusions. We suggest that chemical pumping and radiative pumping could play an important role in the production of the cross-ladder HCN lasers, while the quasi-periodic behaviour of the rotational HCN laser lines may be modulated by additional collisional and radiative pumping driven by periodic shocks and variations in infrared luminosity.

Context. The circumstellar envelopes (CSEs) of asymptotic giant branch (AGB) stars harbour a rich variety of molecules and are sites of complex chemistry. Our current understanding of the circumstellar chemical processes of carbon-rich AGB stars is predominantly based on observations of a single star, IRC +10 216, often regarded as an archetypical carbon star. Aims. We aim to estimate stellar and circumstellar properties for five carbon stars, and constrain their circumstellar CS abundances. This study compares the CS abundances among the sources, informs circumstellar chemical models, and helps to assess if IRC+10 216 is a good representative of the physics and chemistry of carbon star CSEs. Methods. We modelled the spectral energy distributions (SEDs) and CO line emission to derive the stellar and outflow properties. Using these, we then retrieved CS abundance profiles with detailed radiative transfer modelling, imposing spatial and excitation constraints from ALMA and single-dish observations. Results. We obtain good fits to the SEDs and CO lines for all sources and reproduce the CS line emission across various transitions and apertures, yielding robust estimates of the CS abundance profiles. Peak CS fractional abundances range from 1x10(-6)-4x10(-6), with e-folding radii of 1.8x10(16)-6.8x10(16) cm. We also derive reliable C-12/(13C) and S-32/S-34 ratios from CS isotopologue modelling. Conclusions. Our results refine previous single-dish CS abundance estimates and improve the relative uncertainty on the CS e-folding radius for IRAS 07454-7112 by a factor of similar to 2.5. Chemical models reproduce our estimates of the CS radial extent, corroborating the CS photodissociation framework used therein. We find no significant differences between the derived CS abundance profiles for IRC +10 216 and the rest of the sample, apart from the expected density-driven variations.

Our purpose is to study the effect of binary companions located within the first 10 stellar radii from the primary AGB star. In this work, we target the mass-losing carbon star V Hydrae (V Hya), looking for signatures of its companion in the dust forming region of the atmosphere. The star was observed in the L- and N-bands with the VLTI/MATISSE instrument at low spectral resolution. We reconstructed images of V Hya's photosphere and surroundings using the two bands and compared our interferometric observables with VLTI/MIDI and VISIR archival data. To constrain the dust properties, we used DUSTY to model the spectral energy distribution. The star is dominated by dust emission in the L- and N- bands. The VISIR image confirms the presence of a large-scale dusty circumstellar envelope surrounding V Hya. The MATISSE reconstructed images show asymmetric and elongated structures in both infrared bands. In the L-band, we detected an elongated shape of approximately 15 mas, likely to be of photospheric origin. In the N-band, we found a 20 mas extension North-East from the star, and perpendicular to the L-band elongated axis. The position angle and the size of the N-band extension match the prediction of the companion position at MATISSE epoch. By comparing MATISSE N-band with MIDI data, we deduce that the elongation axis in the N-band has rotated since the previous interferometric measurements 13 years ago, supporting the idea that the particle enhancement is related to the dusty clump moving along with the companion. The MATISSE images unveil the presence of a dust enhancement at the companion position, opening new doors for further analysis on the binary interaction with an AGB component.

The transport of energy through convection is important during many stages of stellar evolution1,2, and is best studied in our Sun3 or giant evolved stars4. Features that are attributed to convection are found on the surface of massive red supergiant stars5-8. Also for lower-mass evolved stars, indications of convection are found9-13, but convective timescales and sizes remain poorly constrained. Models indicate that convective motions are crucial to produce strong winds that return the products of stellar nucleosynthesis into the interstellar medium14. Here we report a series of reconstructed interferometric images of the surface of the evolved giant star R Doradus. The images reveal a stellar disk with prominent small-scale features that provide the structure and motions of convection on the stellar surface. We find that the dominant structure size of the features on the stellar disk is 0.72 ± 0.05 astronomical units. We measure the velocity of the surface motions to vary between -18 and +20 km s-1, which means that the convective timescale is approximately one month. This indicates a possible difference between the convection properties of low-mass and high-mass evolved stars.

AGB stars are major contributors to the chemical enrichment of the ISM through nucleosynthesis and extensive mass loss. Most of our current knowledge of AGB atmospheric and circumstellar chemistry, in particular in a C-rich environment, is based on observations of the carbon star IRC+10216. We aim to obtain a more generalised understanding of the chemistry in C-rich AGB CSEs by studying a sample of three carbon stars, IRAS15194-5115, IRAS15082-4808, and IRAS07454-7112, and test the archetypal status often attributed to IRC+10216. We performed spatially resolved, unbiased spectral surveys in ALMA Band 3. We identify a total of 132 rotational transitions from 49 molecular species. There are two main morphologies of the brightness distributions: centrally-peaked (e.g. HCN) and shell-like (e.g. C$_2$H). We estimated the sizes of the molecular emitting regions using azimuthally-averaged radial profiles of the line brightness distributions, and derived abundance estimates. Of the shell distributions, the cyanopolyynes peak at slightly smaller radii than the hydrocarbons, and CN and HNC show the most extended emission. The emitting regions for each species are the smallest for IRAS07454-7112. We find that, within the uncertainties of the analysis, the three stars present similar abundances for most species, also compared to IRC+10216. We find that SiO is more abundant in our three stars compared to IRC+10216. Our estimated isotopic ratios match well the literature values for the sources. The observed circumstellar chemistry appears very similar across our sample and compared to that of IRC+10216, both in terms of the relative location of the emitting regions and molecular abundances. This implies that, to a first approximation, the chemical models tailored to IRC+10216 are able to reproduce the observed chemistry in C-rich envelopes across roughly an order of magnitude in wind density.

Context. Asymptotic giant branch (AGB) stars enrich the interstellar medium through their mass loss. The mechanism(s) shaping the circumstellar environment of mass-losing stars is not clearly understood so far. Aims. Our purpose is to study the effect of binary companions located within the first 10 stellar radii from the primary AGB star. In this work, we target the mass-losing carbon star V Hydrae (V Hya) and search for signatures of its companion in the dust-forming region of the atmosphere. Methods. The star was observed in the L and N bands with the VLTI/MATISSE instrument at low spectral resolution. We reconstructed images of the photosphere and surroundings of V Hya using the two bands and compared our interferometric observables with VLTI/MIDI and VISIR archival data. To constrain the dust properties, we used the 1D radiative transfer code DUSTY to model the spectral energy distribution. Results. The star is dominated by dust emission in the L- and N-bands. The MATISSE reconstructed images show asymmetric and elongated structures in both infrared bands. In the L band, we detected an elongated shape of approximately 15 mas that likely is of photospheric origin. In the N band, we found a 20 mas extension northeast from the star and perpendicular to the L-band elongated axis. The position angle and the size of the N-band extension match the prediction of the companion position at the MATISSE epoch. By comparing MATISSE N-band with MIDI data, we deduce that the elongation axis in the N-band has rotated since the previous interferometric measurements 13 yr ago, supporting the idea that the particle enhancement is related to the dusty clump moving along with the companion. The VISIR image confirms the presence of a large-scale dusty circumstellar envelope surrounding V Hya. Conclusions. The MATISSE images unveil the presence of a dust enhancement at the position of the companion. This opens new doors for further analyses of the binary interaction with an AGB component.

The mass loss experienced on the asymptotic giant branch (AGB) at the end of the lives of low- and intermediate-mass stars is widely accepted to rely on radiation pressure acting on dust grains formed in the extended AGB atmospheres. The interaction of convection, stellar pulsation, and heating and cooling processes cause the density, velocity and temperature distributions in the inner regions of the envelope to be complex, making the dust-formation process difficult to calculate. Hence, characterising the extended atmospheres and inner outflow empirically is paramount to advance our understanding of the dust-formation and wind-driving processes. To this end, we observe the AGB star R Dor using ALMA and modelled the $^{12}$CO $v=0, J=2-1$, $v=1, J=2-1$ and $3-2$ and $^{13}$CO $v=0, J=3-2$ lines using the 3D radiative transfer code LIME up to a distance of $\sim 4$ times the radius of the star at sub-mm wavelengths. We find a complex velocity field with structure down to scales at least equal to the resolution of the observations. The observed maps are well reproduced assuming spherical symmetry for the gas temperature and density distributions. We find the radial profiles of these two quantities to be very steep close to the star and shallower for radii larger than $\sim 1.6$ times the stellar sub-mm radius. This change is consistent with the transition between extended atmosphere and outflow. We constrain the standard deviation of the stochastic velocity distribution in the large-scale outflow to be $\lesssim 0.4$ km/s. We observe two emission blobs in the CO $v=0, J=2-1$ line and find their gas densities and radial velocities to be substantially larger than those of the surrounding gas. Monitoring the evolution of these blobs will lead to a better understanding of the role of these structures in the mass-loss process of R Dor.

Binary interactions have been proposed to explain a variety of circumstellar structures seen around evolved stars, including asymptotic giant branch (AGB) stars and planetary nebulae. Studies resolving the circumstellar envelopes of AGB stars have revealed spirals, disks and bipolar outflows, with shaping attributed to interactions with a companion. Here we use a combined chemical and dynamical analysis to reveal a highly eccentric and long-period orbit for W Aquilae, a binary system containing an AGB star and a main-sequence companion. Our results are based on anisotropic SiN emission, the detections of irregular NS and SiC emission towards the S-type star, and density structures observed in the CO emission. These features are all interpreted as having formed during periastron interactions. Our astrochemistry-based method can yield stringent constraints on the orbital parameters of long-period binaries containing AGB stars, and will be applicable to other systems. When stars like our Sun die, they expel their outer layers in a dramatic stellar wind. This study of an unusual chemical signature in one particular stellar wind reveals that the signature is due to the presence of a binary system whose components had a close approach around 200 years ago.