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Models of the chemical evolution of the interstellar medium, galaxies, and the Universe rely on our understanding of the amounts and chemical composition of the material returned by stars and supernovae. Stellar yields are obtained from stellar-evolution models, which currently lack predictive prescriptions of stellar mass loss, although it significantly affects stellar lifetimes, nucleosynthesis, and chemical ejecta. Galaxy properties are derived from observations of the integrated light of bright member stars. Stars in the late stages of their evolution are among the infrared-brightest objects in galaxies. An unrealistic treatment of the mass-loss process introduces significant uncertainties in galaxy properties derived from their integrated light. We describe current efforts and future needs and opportunities to characterize AGB outflows: driving mechanisms, outflow rates, underlying fundamental physical and chemical processes such as dust grain formation, and dependency of these on metallicity., Submitted to Astro2020 decadal survey; 8 pages, 2 figures

The study of the gas in the envelopes surrounding asymptotic giant branch (AGB) stars through observations in the millimetre wavelength range provides information about the history and nature of these molecular factories. Here we present ALMA observations at subarsecond resolution, complemented with IRAM-30m data, of several lines of SiO, SiS, and CS towards the best-studied AGB circumstellar envelope, IRC+10216. We aim to characterise their spatial distribution and determine their fractional abundances mainly through radiative transfer and chemical modelling. The three species display extended emission with several enhanced emission shells. CS displays the most extended distribution reaching distances up to approximately 20''. SiS and SiO emission have similar sizes of approximately 11'', but SiS emission is slightly more compact. We have estimated fractional abundances relative to H$_2$, which on average are equal to f(SiO)$\sim$10$^{-7}$, f(SiS)$\sim$10$^{-6}$, and f(CS)$\sim$10$^{-6}$ up to the photo-dissociation region. The observations and analysis presented here show evidence that the circumstellar material displays clear deviations from an homogeneous spherical wind, with clumps and low density shells that may allow UV photons from the interstellar medium (ISM) to penetrate deep into the envelope, shifting the photo-dissociation radius inwards. Our chemical model predicts photo-dissociation radii compatible with those derived from the observations, although it is unable to predict abundance variations from the starting radius of the calculations ($\sim$10$R_{*}$), which may reflect the simplicity of the model. We conclude that the spatial distribution of the gas proves the episodic and variable nature of the mass loss mechanism of IRC+10216, on timescales of hundreds of years., 21 pages, 24 figures. Accepted for publication in A&A

Chemical evolution of the ISM and galaxies depends critically on stellar mass loss. We describe current efforts and future needs and opportunities to characterize AGB outflows: driving mechanisms, outflow rates, underlying fundamental physical and chemical processes such as dust grain formation, and dependency of these on metallicity.

ALMA 2019, Cagliari, Italy 14–18 October 2019, Asymptotic Giant Branch stars (AGBs) display roughly spherically symmetric circumstellar envelopes (CSEs) composed of expanding molecular gas and dust. Nevertheless, several AGB stars have been found so far showing a set of concentric arcs or spiral-like structures (e.g., IRC+10216, CRL3068, R Scl). The formation of spirals can be explained by the effect of the orbital movement of binary systems on the ejected gas. They are easily noticeable if the binary systems are face-on but a different spatial orientation blurs the structures showing patterns that comprise many concentric arcs. However, the concentric arcs can be explained also by gas instabilities occurring in the winds of single AGB stars. The matter ejection process involve two mechanisms: (1) the stellar pulsation, that could include episodic (and anisotropic) matter ejection, and (2) the gas acceleration, based on dust and the related gas-phase chemistry. These mechanisms, along with the formation of arcs or spirals, could result in very complex structures difficult to understand and analyze. Hence, exploring the inner layers of the CSEs is crucial to understand the matter ejection and the structures in them. R Leo is a close O-rich low mass-loss rate AGB star where a complex structure in the maser SiO(v=1,J=2-1) has been detected (Cernicharo et al. 1994). This structure could be interpreted as a developing bipolar outflow or a rotating torus in the inner CSE. Additional asymmetries found at larger scales by Plez et al. (1994) suggest that this structure could be part of a larger one covering a significant fraction of the envelope. We present new interferometer molecular observations of R Leo taken at 1.2 mm with ALMA with a HPBW~0.025>. Short-spacings derived from on-the-fly observations acquired with the IRAM 30m telescope were added to recover the filtered emission. These data probe a complex structure that involves extended continuum and molecular emission which imply material infall onto the star. Lateral gas motions compatible with the presence of a torus-like structure have been also observed. At larger scales, the envelope also shows a remarkable red-shifted shell-like structure with a very bright spot in the CO(2-1) emission linked to the gas in the vicinity of the star. The rest of the envelope is still quite complex showing arcs and different elongations that suggest an irregular mass-loss. The maps also reveal significant asymmetries in the molecular abundance distributions.

The Atacama Large Millimeter/Submillimeter Array (ALMA), Cagliari, Italy 14–18 October 2019, ALMA has allowed us to study the ejecta around evolved stars with unprecedented resolution. This extremely high resolution at the millimeter domain provides a unique tool to study the processes taking place in the innermost regions of these evolved stars. In particular, the processes leading to the mass ejections of the Red Supergiant stars are unknown. The pulsation process responsible for mass ejection in the intermediate mass AGB phase does not work in the high mass evolved stars. Therefore, studying the characteristics of the mass ejections near the photosphere of the massive stars is essential to constrain the processes leading to the observed gas ejection. In this sense, we have obtained interferometric maps in the range 231.7 ¿ 235.3 GHz of the ejecta around the Red Supergiant star VY CMa with an spatial resolution of 0.02>. These maps revealed a level of complexity higher than previously anticipated from previous observations. The complexity seems to be due both to structural and chemical processes. The molecular lines covered within these maps range from upper energies 19 up to 3400 K, tracing different excitation conditions. We will present a global view of the different structures observed, The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement n. 610256 (NANOCOSMOS). We would also like to thank the Spanish MINECO for funding support from grants CSD2009-00038, AYA2012-32032, AYA2016-75066-C2-1-P & AYA2016-78994-P. M.A. also thanks for funding support from the Ramón y Cajal programme of Spanish MINECO (RyC-2014- 16277).

These tables include the energy levels and polynomial coefficients needed to derive the rate coefficients of SO2. Each energy level in so2level.dat is uniquely identified by a identifier number used in the file so2pcoef.dat. File so2pcoef.dat contains polynomial coefficients that fit the decimal logarithm of the collisional rates between two levels computed by Balanca et al. (2016MNRAS.460.3766B). A sixth order polynomial reproduces with a relative error below 30% all rates between 20 and 1000K for the 410 energy levels used in the calculations. (4 data files).

International audience; During the late phases of low-intermediate mass (0.1 to 8 solar masses) stars, a significant mass loss is produced creating a gas and dust envelope surrounding the central star. Due to the physical conditions in the envelope, gas is primarily molecular, placing these objects as efficient molecular factories that will enrich the interstellar medium. Observation and study of molecular emission allows deriving physical and chemical properties of these envelopes. As far as today, Oxygen rich objects are not so well studied as their Carbon counterparts, because Carbon chemistry is much more active than Oxygen chemistry. Importance of this work is that the Oxygen rich envelopes are not completely characterized yet. We present preliminary results from our on-going milimiter wavelength survey with the EMIR receivers of the IRAM 30 meters radiotelescope towards the envelopes of two evolved Oxygen rich objects: IK Tauri and OH231.8+4.2. We detect a wealth of lines ranging from few mK to K (with rms ranging from 1 to 3 mK in best cases). Both objects present significant differences in their molecular emission features due to contrast of evolutionary stage and physical properties and both show evidences of different chemical formation processes. Some of the molecules identified are CO, SiO, H_{2}O, NS, HCO^{+}, SO, SO_{2}, SH_{2}, OCS, HCN, HNC, CN, HC_{3}N, CS, H_{2}CO, HNCO, HNCS, SiS, N_{2}H^{+} and a number of isotopologues (bearing ^{13}C, ^{33}S, ^{34}S, ^{17}O, ^{18}O, ^{28}Si, ^{29}Si, ^{30}Si and ^{15}N atoms). Some of the molecules identified represent first detections in Oxygen rich AGB stars. We expect to get a better understanding of the chemistry and structure of these objects, in particular how interaction between AGB (Asymptotic Giant Branch) envelopes and post-AGB winds influences chemistry producing a reformation of molecules through shocked gas reactions. held in Valencia, July 9 - 13, 2012, Eds.: J.C. Guirado, L.M. Lara, V. Quilis, and J. Gorgas.

10 pags., 8 figs., 1 tab., 1 app., We aim to study the properties of a particular type of evolved stars, C-rich evolved stars with high expansion velocities. For this purpose we have focused on the two best studied objects within this group, IRC+10401 and AFGL 2233. We focused on determining their luminosity by studying their spectral energy distribution. Also, we have obtained single-dish line profiles and interferometric maps of the CO J = 1-0 and J = 2-1 emission lines for both objects. We have modeled this emission using a LVG radiative transfer code to determine the kinetic temperature and density profiles of the gas ejected by these stars. We have found that the luminosities obtained for these objects (log(L/L ) = 4.1 and 5.4) locate them in the domain of the massive asymptotic giant branch stars (AGBs) and the red supergiant stars (RSGs). In addition, the mass-loss rates obtained (1.5 × 10-6 ×10 M yr) suggest that while IRC+10401 might be an AGB star, AFGL 2233 could be an RSG star. All these results, together with those from previous works, suggest that both objects are massive objects, IRC+10401 a massive evolved star with M ∼ 5-9 M which could correspond to an AGB or an RSG and AFGL 2233 an RSG with M ∼ 20 M , which would confirm the existence of massive C-rich evolved stars. Two scenarios are proposed to form these types of objects. The first one is capable of producing high-mass AGB stars up to ∼8 M and the second one is capable of forming C-rich RSGs like AFGL 2233., The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013)/ ERC grant Agreement n. 610256 (NANOCOSMOS). We would also like to thank the Spanish MINECO for funding support from grants CSD2009-00038, AYA2012-32032, AYA2016- 75066-C2-1-P and AYA2016-78994-P. M.A. also thanks for funding support from the Ramón y Cajal programme of Spanish MINECO (RyC-2014-16277). This work has made use of data from the European Space Agency (ESA) mission Gaia, processed by the Gaia Data Processing and Analysis Consortium (DPAC. Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement

12 pags., 10 figs. 2 tabs., Red supergiant stars (RSGs, Minit = 10-40Msun) are known to eject large amounts of material, as much as half of their initial mass during this evolutionary phase. However, the processes powering the mass ejection in low- and intermediate-mass stars do not work for RSGs and the mechanism that drives the ejection remains unknown. Different mechanisms have been proposed as responsible for this mass ejection but so far little is known about the actual processes taking place in these objects. Here we present high angular resolution interferometric ALMA maps of VY CMa continuum and molecular emission, which resolve the structure of the ejecta with unprecedented detail. The study of the molecular emission from the ejecta around evolved stars has been shown to be an essential tool in determining the characteristics of the mass loss ejections. Our aim is thus to use the information provided by these observations to understand the ejections undergone by VY CMa and to determine their possible origins. We inspected the kinematics of molecular emission observed. We obtained position-velocity diagrams and reconstructed the 3D structure of the gas traced by the different species. It allowed us to study the morphology and kinematics of the gas traced by the different species surrounding VY CMa. Two types of ejecta are clearly observed: extended, irregular, and vast ejecta surrounding the star that are carved by localized fast outflows. The structure of the outflows is found to be particularly flat. We present a 3D reconstruction of these outflows and proof of the carving. This indicates that two different mass loss processes take place in this massive star. We tentatively propose the physical cause for the formation of both types of structures. These results provide essential information on the mass loss processes of RSGs and thus of their further evolution., The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (FP/2007-2013) / ERC Grant Agreement n. 610256 (NANOCOSMOS). We would also like to thank the Spanish MINECO for funding support from grants CSD2009-00038, AYA2012-32032. M.A. also thanks for funding support from the Ramón y Cajal programme of Spanish MINECO (RyC2014-16277). This publication is part of the “I+D+i” (research, development, and innovation) projects PID2019-107115GB-C21, and PID2019-106110GBI00, and PID2020-117034RJ-I00, supported by the Spanish “Ministerio de Ciencia e Innovación” MCIN/AEI/10.13039/501100011033.