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22 pags., 3 figs., 5 tabs., Aims. We aim to determine the abundances of SiO, CS, SiS, SO, and SO2 in a large sample of oxygen-rich asymptotic giant branch (AGB) envelopes covering a wide range of mass loss rates to investigate the potential role that these molecules could play in the formation of dust in these environments. Methods. We surveyed a sample of 30 oxygen-rich AGB stars in the λ 2 mm band using the IRAM 30m telescope. We performed excitation and radiative transfer calculations based on the large velocity gradient method to model the observed lines of the molecules and to derive their fractional abundances in the observed envelopes. Results. We detected SiO in all 30 targeted envelopes, as well as CS, SiS, SO, and SO2 in 18, 13, 26, and 19 sources, respectively. Remarkably, SiS is not detected in any envelope with a mass loss rate below 10-6 M⊙ yr-1, whereas it is detected in all envelopes with mass loss rates above that threshold. From a comparison with a previous, similar study on C-rich sources, it becomes evident that the fractional abundances of CS and SiS show a marked differentiation between C-rich and O-rich sources, being two orders of magnitude and one order of magnitude more abundant in C-rich sources, respectively, while the fractional abundance of SiO turns out to be insensitive to the C/O ratio. The abundance of SiO in O-rich envelopes behaves similarly to C-rich sources, that is, the denser the envelope the lower its abundance. A similar trend, albeit less clear than for SiO, is observed for SO in O-rich sources. Conclusions. The marked dependence of CS and SiS abundances on the C/O ratio indicates that these two molecules form more efficiently in C- than O-rich envelopes. The decline in the abundance of SiO with increasing envelope density and the tentative one for SO indicate that SiO and possibly SO act as gas-phase precursors of dust in circumstellar envelopes around O-rich AGB stars., We thank the IRAM 30m staff for their help during the observations. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. We acknowledge funding support from the European Research Council (ERC Grant 610256: NANOCOSMOS) and from Spanish MINECO through grant AYA2016-75066-C2-1-P. M.A. thanks Spanish MINECO for funding support through the Ramón y Cajal programme (RyC2014-16277). LVP acknowledges funding support from the Swedish Research Council and the European Research Council (ERC Consolidator Grant 614264)

12 pags., 8 figs., 8 tabs.-- Section: Letters to the Editor, Observations of IRC +10216 with the Yebes 40 m telescope between 31 and 50 GHz have revealed more than 150 unidentified lines. Some of them can be grouped into a new series of 26 doublets, harmonically related with integer quantum numbers ranging from Jup = 54 to 80. The separation of the doublets increases systematically with J, that is to say, as expected for a linear species in one of its bending modes. The rotational parameters resulting from the fit to these data are B = 290.8844 ± 0.0004 MHz, D = 0.88 ± 0.04 Hz, and q = 0.1463 ± 0.0001 MHz. The rotational constant is very close to that of the ground state of HC9N. Our ab initio calculations show an excellent agreement between these parameters and those predicted for the lowest energy vibrationally excited state, ν19 = 1, of HC9N. This is the first detection, and complete characterization in space, of vibrationally excited HC9N. An energy of 41.5 cm-1 is estimated for the ν19 state. In addition, 17 doublets of HC7N in the ν15 = 1 state, for which laboratory spectroscopy is available, were detected for the first time in IRC +10216. Several doublets of HC5N in its ν11 = 1 state were also observed. The column density ratio between the ground and the lowest excited vibrational states are ≈127, 9.5, and 1.5 for HC5N, HC7N, and HC9N, respectively. We find that these lowest-lying vibrational states are most probably populated via infrared pumping to vibrationally excited states lying at ≈600 cm-1. The lowest vibrationally excited states thus need to be taken into account to precisely determine absolute abundances and abundance ratios for long carbon chains. The abundance ratios N(HC5N)/N(HC7N) and N(HC7N)/N(HC9N) are 2.4 and 7.7, respectively., he Spanish authors thank Ministerio de Ciencia e Innovación for funding support through project AYA2016-75066-C2-1-P. We also thank ERC for funding through grant ERC-2013-Syg-610256-NANOCOSMOS. MA thanks Ministerio de Ciencia e Innovación for Ramón y Cajal grant RyC2014-16277. CB thanks Ministerio de Ciencia e Innovación for Juan de la Cierva grant FJCI-2016-27983. LVP acknowledges support from the Swedish Research Council and from the ERC through the consolidator

3 pags., 1 fig., Silicon carbide together with amorphous carbon are the main components of dust grains in the atmospheres of C-rich AGB stars. Small gaseous Si-C bearing molecules (such as SiC, SiCSi, and SiC2) are efficiently formed close to the stellar photosphere. They likely condense onto dust seeds owing to their highly refractory nature at the lower temperatures (i.e., below about 2500 K) in the dust growth zone which extends a few stellar radii from the photosphere. Beyond this region, the abundances of Si-C bearing molecules are expected to decrease until they are eventually reformed in the outer shells of the circumstellar envelope, owing to the interaction between the gas and the interstellar UV radiation field. Our goal is to understand the time-dependent chemical evolution of Si-C bond carriers probed by molecular spectral line emission in the circumstellar envelope of IRC+10216 at millimeter wavelengths., We thank funding support through ERC-2013-SyG-610256 (NANOCOSMOS), AYA2012-32032 and AYA2016-75066-C2-1-P grants.

5 pags., 2 figs., We report on the detection of calcium isocyanide, CaNC, in the carbon-rich evolved star IRC+10216. We derived a column density for this species of (2 ± 0.5) × 1011 cm−2 . Based on the observed line profiles and the modelling of its emission through the envelope, the molecule has to be produced in the intermediate and outer layers of the circumstellar envelope where other metal-isocyanides have previously been found in this source. The abundance ratio of CaNC relative to MgNC and FeCN is '1/60 and '1, respectively. We searched for the species CaF, CaCl, CaC, CaCCH, and CaCH3 for which accurate frequency predictions are available. Only upper limits have been obtained for these molecules., The Spanish authors thank the Ministerio de Ciencia Innovación y Universidades for funding support from the CONSOLIDER-Ingenio program “ASTROMOL” CSD 2009-00038, AYA2012-32032, AYA2016-75066- C2-1-P. We also thank the ERC for funding through grant ERC-2013-Syg610256-NANOCOSMOS. MA thanks the Ministerio de Ciencia Innovación y Universidades for the Ramón y Cajal grant RyC-2014-16277. CB thanks the Ministerio de Ciencia Innovación y Universidades for the Juan de la Cierva grant FJCI-2016-27983. LVP acknowledges support from the Swedish Research Council and ERC consolidator grant 614264.

We report the detection and investigate the properties of high-excitation lambda-doubling line emission of hydroxyl (OH) detected towards three asymptotic giant branch (AGB) stars (W Hya, R Dor, and IK Tau) using ALMA. The OH lines are produced very close to the central stars and seem optically thin and with no maser effect. We analyse the molecular excitation using population diagrams and find rotational temperatures of $\sim 2500$ K and column densities of $\sim 10^{19}$ cm$^{-2}$ for both W Hya and R Dor. For W Hya, we observe emission from vibrationally excited H2O arising from the same region as the OH emission. Moreover, CO $v = 1; J = 3 - 2$ emission also shows a brightness peak in the same region. Considering optically thin emission and the rotational temperature derived for OH, we find a CO column density $\sim 15$ times higher than that of OH, within an area of ($92 \times 84$) mas$^2$ centred on the OH emission peak. These results should be considered tentative because of the simple methods employed. The observed OH line frequencies differ significantly from the predicted transition frequencies in the literature, and provide the possibility of using OH lines observed in AGB stars to improve the accuracy of the Hamiltonian used for the OH molecule. We predict stronger OH lambda-doubling lines at millimetre wavelengths than those we detected. These lines will be a good probe of shocked gas in the extended atmosphere and are possibly even suitable as probes of the magnetic field in the atmospheres of close-by AGB stars through the Zeeman effect., Published in Astronomy and Astrophysics Letters

5 pags., 3 figs., 1 tab., We present new interferometer molecular observations of R Leo taken at 1.2 mm with the Atacama Large Millimeter Array with an angular resolution up to 0'. 026. These observations permitted us to resolve the innermost envelope of this star, which revealed a complex structure that involves extended continuum emission and molecular emission showing a non-radial gas velocity distribution. This molecular emission displays prominent red-shifted absorptions located immediately in front of the star, which are typical footprints of material infall. This emission also shows lateral gas motions compatible with a torus-like structure., We thank the European Research Council (ERC Grant 610256: NANOCOSMOS) and the Spanish MINECO/MICINN for funding support through grant AYA2016-75066-C-1-P and the ASTROMOL Consolider project CSD2009-00038. MA acknowledges funding support from the Ramón y Cajal program of Spanish MINECO (RyC-2014-16277).

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

10 pags., 5 figs., 7 tabs., 5 apps., We report on the detection of two series of harmonically related doublets in IRC+10216. From the observed frequencies, the rotational constant of the first series is B = 1380.888 MHz and that of the second series is B = 1381.512 MHz. The two series correspond to two species with a 2Σ electronic ground state. After considering all possible candidates, and based on quantum chemical calculations, the first series is assigned to MgC3N and the second to MgC4H. For the latter species, optical spectroscopy measurements support its identification. Unlike diatomic metal-containing molecules, the line profiles of the two new molecules indicate that they are formed in the outer layers of the envelope, as occurs for MgNC and other polyatomic metal-cyanides. We also confirm the detection of MgCCH that was previously reported from the observation of two doublets. The relative abundance of MgC3N with respect to MgNC is close to one while that of MgC4H relative to MgCCH is about ten. The synthesis of these magnesium cyanides and acetylides in IRC+10216 can be explained in terms of a two-step process initiated by the radiative association of Mg+ with large cyanopolyynes and polyynes followed by the dissociative recombination of the ionic complexes., The Spanish authors thank the Ministerio de Ciencia Innovación y Universidades for funding support from the CONSOLIDER-Ingenio program “ASTROMOL” CSD 2009-00038, AYA2012-32032, AYA2016-75066-C2-1-P. We also thank ERC for funding through grant ERC-2013-Syg610256-NANOCOSMOS. MA thanks the Ministerio de Ciencia Innovación y Universidades for the Ramón y Cajal grant RyC-2014-16277. CB thanks the Ministerio de Ciencia Innovación y Universidades for the Juan de la Cierva grant FJCI-2016-27983. LVP acknowledges support from the Swedish Research Council and from ERC consolidator grant 614

33 pags., 21 figs., 4 tabs., 2 apps., We present continuum and molecular line emission ALMA observations of OH 231.8+4.2, a well studied bipolar nebula around an asymptotic giant branch (AGB) star. The high-angular resolution (~0.¿¿2¿0.¿¿3) and sensitivity of our ALMA maps provide the most detailed and accurate description of the overall nebular structure and kinematics of this object to date. We have identified a number of outflow components previously unknown. Species studied in this work include 12CO, 13CO, CS, SO, SO2, OCS, SiO, SiS, H3O+, Na37Cl, and CH3OH. The molecules Na37Cl and CH3OH are first detections in OH 231.8+4.2, with CH3OH being also a first detection in an AGB star. Our ALMA maps bring to light the totally unexpected position of the mass-losing AGB star (QX Pup) relative to the large-scale outflow. QX Pup is enshrouded within a compact (¿60 AU) parcel of dust and gas (clump S) in expansion (Vexp ~ 5¿7 km s¿1) that is displaced by ~ 0.¿¿6 to the south of the dense equatorial region (or waist) where the bipolar lobes join. Our SiO maps disclose a compact bipolar outflow that emerges from QX Pup¿s vicinity. This outflow is oriented similarly to the large-scale nebula but the expansion velocities are about ten times lower (Vexp ¿ 35 km s¿1). We deduce short kinematical ages for the SiO outflow, ranging from ~50¿80 yr, in regions within ~150 AU, to ~400¿500 yr at the lobe tips (~3500 AU). Adjacent to the SiO outflow, we identify a small-scale hourglass-shaped structure (mini-hourglass) that is probably made of compressed ambient material formed as the SiO outflow penetrates the dense, central regions of the nebula. The lobes and the equatorial waist of the mini-hourglass are both radially expanding with a constant velocity gradient (Vexp ¿ r). The mini-waist is characterized by extremely low velocities, down to ~1 km s¿1 at ~150 AU, which tentatively suggest the presence of a stable structure. The spatio-kinematics of the large-scale, high-velocity lobes (HV lobes), and the dense equatorial waist (large waist) known from previous works are now precisely determined, indicating that both were shaped nearly simultaneously about ~800¿900 yr ago. We report the discovery of two large (~8¿¿ × 6¿¿), faint bubble-like structures (fish bowls) surrounding the central parts of the nebula. These are relatively old structures, although probably slightly (~100¿200 yr) younger than the large waist and the HV lobes. We discuss the series of events that may have resulted in the complex array of nebular components found in OH 231.8+4.2 as well as the properties and locus of the central binary system. The presence of ¿80 yr bipolar ejections indicate that the collimated fast wind engine is still active at the core of this outstanding object., This paper makes use of the following ALMA data: ADS/JAO.ALMA#2015.1.00256.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), NSC and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO, and NAOJ. The data here presented have been reduced by CASA (ALMA default calibration software; https://casa.nrao.edu); data analysis was made using the GILDAS software (http://www.iram. fr/IRAMFR/GILDAS). This work has been partially supported by the Spanish MINECO through grants AYA2012-32032, AYA2016-75066-C2-1-P, and AYA2016-78994-P and by the European Research Council through ERC grant 610256: NANOCOSMOS. This research has made use of the The JPL Molecular Spectroscopy catalog, The Cologne Database for Molecular Spectroscopy, the SIMBAD database operated at CDS (Strasbourg, France), the NASA’s Astrophysics Data System and Aladin.

Context. The variability in IRC+10216, the envelope of the asymptotic giant branch (AGB) star CW Leo, has attracted increasing attention in recent years. Studying the details of this variability in the molecular emission required a systematic observation program. Aims. We aim to reveal and characterize the periodical variability of the rotational lines from several molecules and radicals in IRC+10216, and to compare it with previously reported IR variability. Methods. We carried out systematic monitoring within the ~80–116 GHz frequency range with the IRAM 30 m telescope. Results. We report on the periodical variability in IRC+10216 of several rotational lines from the following molecules and radicals: HC3N, HC5N, CCH, C4H, C5H, and CN. The analysis of the variable molecular lines provides periods that are consistent with previously reported IR variability, and interesting phase lags are revealed that point toward radiative transfer and pumping, rather than chemical effects. Conclusions. This study indicates that observations of several lines of a given molecule have to be performed simultaneously or at least at the same phase in order to avoid erroneous interpretation of the data. In particular, merging ALMA data from different epochs may prove to be difficult, as shown by the example of the variability we studied here. Moreover, radiative transfer codes have to incorporate the effect of population variability in the rotational levels in CW Leo.

We present high spectral resolution mid-IR observations of SiS towards the C-rich AGB star IRC+10216 carried out with the Texas Echelon-cross-Echelle Spectrograph mounted on the NASA Infrared Telescope Facility. We have identified 204 ro-vibrational lines of 28Si32S, 26 of 29Si32S, 20 of 28Si34S, and 15 of 30Si32S in the frequency range 720–790 cm−1. These lines belong to bands v = 1–0, 2–1, 3–2, 4–3, and 5–4, and involve rotational levels with Jlow ≲ 90. About 30 per cent of these lines are unblended or weakly blended and can be partially or entirely fitted with a code developed to model the mid-IR emission of a spherically symmetric circumstellar envelope composed of expanding gas and dust. The observed lines trace the envelope at distances to the star ≲35R⋆ (≃0.7 arcsec). The fits are compatible with an expansion velocity of 1 + 2.5(r/R⋆ − 1) km s−1 between 1 and 5R⋆, 11 km s−1 between 5 and 20R⋆, and 14.5 km s−1 outwards. The derived abundance profile of 28Si32S with respect to H2 is 4.9 × 10−6 between the stellar photosphere and 5R⋆, decreasing linearly down to 1.6 × 10−6 at 20R⋆ and to 1.3 × 10−6 at 50R⋆. 28Si32S seems to be rotationally under local thermodynamic equilibrium (LTE) in the region of the envelope probed with our observations and vibrationally out of LTE in most of it. There is a red-shifted emission excess in the 28Si32S lines of band v = 1−0 that cannot be found in the lines of bands v = 2−1, 3–2, 4–3, and 5–4. This excess could be explained by an enhancement of the vibrational temperature around 20R⋆ behind the star. The derived isotopic ratios 28Si/29Si, and 32S/34S are 17 and 14, compatible with previous estimates., JPF was supported during part of this study by the UNAM through a postdoctoral fellowship. We thank the Spanish MINECO/MICINN for funding support through grants AYA2009-07304, AYA2012-32032, the ASTROMOL Consolider project CSD2009-00038 and the European Research Council (ERC Grant 610256: NANOCOSMOS). MJR is supported by grant AST 03-07497. Development of TEXES was supported by grants from the NSF and USRA. MJR, JHL, and others want to thank IRTF, which is operated by the University of Hawaii under Cooperative Agreement NCC 5-538 with the National Aeronautics and Space Administration, Office of Space Science, Planetary Astronomy Program.

18 pags., 11 figs., 3 tabs., 2 apps., We present new high angular resolution interferometer observations of the v = 0 J = 14-13 and 15-14 SiS lines toward IRC+10216, carried out with the Combined Array for Research in Millimeter-wave Astronomy and the Atacama Large Millimeter Array. The maps, with angular resolutions of ≃0.″25 and 0.″55, reveal (1) an extended, roughly uniform, and weak emission with a size of ≃0.″5; (2) a component elongated approximately along the east-west direction peaking at ≃0.″13 and 0.″17 at both sides of the central star; and (3) two blue- and redshifted compact components peaking around 0.″07 to the NW of the star. We have modeled the emission with a 3D radiation transfer code, finding that the observations cannot be explained only by thermal emission. Several maser clumps and one arc-shaped maser feature arranged from 5 to 20 from the central star, in addition to a thin shell-like maser structure at ≃13 , are required to explain the observations. This maser-emitting set of structures accounts for 75% of the total emission, while the other 25% is produced by thermally excited molecules. About 60% of the maser emission comes from the extended emission, and the rest comes from the set of clumps and the arc. The analysis of a time monitoring of these and other SiS and SiS lines carried out with the IRAM 30 m telescope from 2015 to present suggests that the intensity of some spectral components of the maser emission strongly depends on the stellar pulsation, while other components show a mild variability. This monitoring evidences a significant phase lag of ≃0.2 between the maser and near-IR light curves., During the first part of this work, J.P.F. was supported by the UNAM through a postdoctoral fellowship. J.C., M.A., L.V.P., G.Q.-L., M.S.-G., J.R.P., and J.P.F. thank the Spanish MINECO/MICINN for funding support through grants AYA2009-07304, AYA2012-32032, AYA2016-75066-C-1-P, the ASTROMOL Consolider project CSD2009-00038, and the European Research Council (ERC Grant 610256: NANOCOSMOS). M.A. also acknowledges funding support from the Ramón y Cajal program of Spanish MINECO (RyC-2014- 16277).

[Context] ALMA is providing us essential information on where certain molecules form. Observing where these molecules emission arises from, the physical conditions of the gas, and how this relates with the presence of other species allows us to understand the formation of many species, and to significantly improve our knowledge of the chemistry that occurs in the space., [Aims] We studied the molecular distribution of NaCN around IRC +10216, a molecule detected previously, but whose origin is not clear. High angular resolution maps allow us to model the abundance distribution of this molecule and check suggested formation paths., [Methods] We modeled the emission of NaCN assuming local thermal equilibrium (LTE) conditions. These profiles were fitted to azimuthal averaged intensity profiles to obtain an abundance distribution of NaCN., [Results] We found that the presence of NaCN seems compatible with the presence of CN, probably as a result of the photodissociation of HCN, in the inner layers of the ejecta of IRC +10216. However, similar as for CHCN, current photochemical models fail to reproduce this CN reservoir. We also found that the abundance peak of NaCN appears at a radius of 3 × 10 cm, approximately where the abundance of NaCl, suggested to be the parent species, starts to decay. However, the abundance ratio shows that the NaCl abundance is lower than that obtained for NaCN. We expect that the LTE assumption might result in NaCN abundances higher than the real ones. Updated photochemical models, collisional rates, and reaction rates are essential to determine the possible paths of the NaCN formation., 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 No. 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. M.A. also ackowledges funding support from the Ramón y Cajal programme of Spanish MINECO (RyC-2014-16277).

19 pags., 24 figs., 3 tabs., Low-mass evolved stars are major contributors to interstellar medium enrichment as a consequence of the intense mass-loss process these stars experience at the end of their lives. 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-30 m data, of several lines of SiO, SiS, and CS towards the best-studied AGB circumstellar envelope, IRC + 10°216. 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 H2, which on average are equal to f(SiO) 10-7, f(SiS) 10-6, and f(CS) 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 ( 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 + 10°216, on timescales of hundreds of years., Our team acknowledges the support given by ERC through the grant ERC-2013-Syg-610256 “NANOCOSMOS”, the Spanish MINECO through the grants AYA2012-32032 and AYA2016-75066-C2-1-P and the CONSOLIDERIngenio program “ASTROMOL” CSD 2009-00038. LVP acknowledges support from the Swedish Research Council and the ERC consolidator grant 614264. This work is based on observations carried out under projects numbers 014-13 and 055-15 with the IRAM-30 m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). This paper makes use of the following ALMA data: ADS/JAO.ALMA#2013.1.00432.S. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada) and NSC and ASIAA (Taiwan), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. This research has made use of NASA’s Astrophysics Data System. This work has made use of GILDAS2 and CASA3 softwares to reduce and analyse data.

We report the discovery in space of methyl silane, CHSiH, from observations of ten rotational transitions between 80 and 350 GHz (J from 4 to 16) with the IRAM 30 m radio telescope. The molecule was observed in the envelope of the C-star IRC +10216. The observed profiles and our models for the expected emission of methyl silane suggest that the it is formed in the inner zones of the circumstellar envelope, 1-40 R, with an abundance of (0.5-1) × 10 relative to H. We also observed several rotational transitions of silyl cyanide (SiHCN), confirming its presence in IRC +10216 in particular, and in space in general. Our models indicate that silyl cyanide is also formed in the inner regions of the envelope, around 20 R, with an abundance relative to H of 6 × 10. The possible formation mechanisms of both species are discussed. We also searched for related chemical species but only upper limits could be obtained., We acknowledge funding support from Spanish MINECO under grants AYA2012-32032, AYA2016-75066-C2-1-P, and CSD2009-00038, and from the European Research Council under grant ERC-2013-SyG 610256 (NANOCOSMOS).

During their late pulsating phase, AGB stars expel most of their mass in the form of massive dusty envelopes, an event that largely controls the composition of interstellar matter. The envelopes, however, are distant and opaque to visible and NIR radiation: Their structure remains poorly known and the mass-loss process poorly understood. Millimeter-wave interferometry is the optimal investigative tool for this purpose. The circumstellar envelope IRC +10 216 and its central star, the C-rich TP-AGB star closest to the Sun, are the best objects for such an investigation. Two years ago, we reported on IRAM 30-m telescope CO(2-1) line emission observations in that envelope (HPBW 11"). We now report much higher angular resolution observations of CO(2-1), CO(1-0), CN(2-1) and C$_4$H(24-23) made with the SMA, PdB and ALMA interferometers (with synthesized half-power beamwidths of 3", 1" and 0.3", respectively). Although the envelope appears more intricate at high resolution, its prevailing structure remains a pattern of thin, nearly concentric shells. Outside the small (r, 22 pages, 28 figures. Accepted for publication in A&A

[Aims] We aim to investigate the physical and chemical properties of the molecular envelope of the oxygen-rich AGB star IK Tau., [Methods] We carried out a millimeter wavelength line survey between ∼79 and 356 GHz with the IRAM-30 m telescope. We analysed the molecular lines detected in IK Tau using the population diagram technique to derive rotational temperatures and column densities. We conducted a radiative transfer analysis of the SO lines, which also helped us to verify the validity of the approximated method of the population diagram for the rest of the molecules., [Results] For the first time in this source we detected rotational lines in the ground vibrational state of HCO, NS, NO, and HCO, as well as several isotopologues of molecules previously identified, namely, CO, SiO, SiO, SiS, SiS, SiS, HCN, CS, CS, H S, SO, and SO. We also detected several rotational lines in vibrationally excited states of SiS and SiO isotopologues, as well as rotational lines of HO in the vibrationally excited state ν = 2. We have also increased the number of rotational lines detected of molecules that were previously identified toward IK Tau, including vibrationally excited states, enabling a detailed study of the molecular abundances and excitation temperatures. In particular, we highlight the detection of NS and HCO with fractional abundances of f(NS)∼10 and f(HCO) ∼ [10-10]. Most of the molecules display rotational temperatures between 15 and 40 K. NaCl and SiS isotopologues display rotational temperatures higher than the average (∼65 K). In the case of SO a warm component with T∼ 290 K is also detected., [Conclusions] With a total of ∼350 lines detected of 34 different molecular species (including different isotopologues), IK Tau displays a rich chemistry for an oxygen-rich circumstellar envelope. The detection of carbon bearing molecules like HCO, as well as the discrepancies found between our derived abundances and the predictions from chemical models for some molecules, highlight the need for a revision of standard chemical models. We were able to identify at least two different emission components in terms of rotational temperatures. The warm component, which is mainly traced out by SO, is probably arising from the inner regions of the envelope (at ≤ 8 R) where SO has a fractional abundance of f(SO) ∼ 10. This result should be considered for future investigation of the main formation channels of this, and other, parent species in the inner winds of O-rich AGB stars, which at present are not well reproduced by current chemistry models., We acknowledge the Spanish MICINN/MINECO for funding support through grants AYA2009-07304, AYA2012-32032, the ASTROMOL Consolider project CSD2009-00038 and also the European Research Council funding support (ERC grant 610256: NANOCOSMOS). L.V.P. also acknowledges the support of the Universidad Complutense de Madrid Ph.D. programme.

This work presents a detailed analysis of the laboratory and astrophysical spectral data available for 28SiC2, 29SiC2, 30SiC2, Si13CC, and Si2C. New data on the rotational lines of these species between 70 and 350 GHz have been obtained with high spectral resolution (195 kHz) with the IRAM 30 m telescope in the direction of the circumstellar envelope IRC +10216. Frequency measurements can reach an accuracy of 50 kHz for features observed with a good signal to noise ratio. From the observed astrophysical lines and the available laboratory data new rotational and centrifugal distortion constants have been derived for all the isotopologues of SiC2, allowing us to predict their spectrum with an estimated accuracy better than 50 kHz below 500 GHz and around 50–100 kHz for the strong lines above 500 GHz. Improved rotational and centrifugal distortion constants have also been obtained for disilicon carbide, Si2C. This work shows that observations of IRC +10216 taken with the IRAM 30 m telescope, with a spectral resolution of 195 kHz, can be used for any molecular species detected in this source to derive, or improve, its rotational constants. Hence, IRC +10216 in addition to be one the richest sources in molecular species in the sky, can also be used as a spectroscopy laboratory in the millimetre and submillimetre domains.

Silicon carbide dust is ubiquitous in circumstellar envelopes around C-rich AGB stars. However, the main gas-phase precursors leading to the formation of SiC dust have not yet been identified. The most obvious candidates among the molecules containing an Si--C bond detected in C-rich AGB stars are SiC2, SiC, and Si2C. We aim to study how widespread and abundant SiC2, SiC, and Si2C are in envelopes around C-rich AGB stars and whether or not these species play an active role as gas-phase precursors of silicon carbide dust in the ejecta of carbon stars. We carried out sensitive observations with the IRAM 30m telescope of a sample of 25 C-rich AGB stars to search for emission lines of SiC2, SiC, and Si2C in the 2 mm band. We performed non-LTE excitation and radiative transfer calculations based on the LVG method to model the observed lines of SiC2 and to derive SiC2 fractional abundances in the observed envelopes. We detect SiC2 in most of the sources, SiC in about half of them, and do not detect Si2C in any source, at the exception of IRC +10216. Most of these detections are reported for the first time in this work. We find a positive correlation between the SiC and SiC2 line emission, which suggests that both species are chemically linked, the SiC radical probably being the photodissociation product of SiC2 in the external layer of the envelope. We find a clear trend in which the denser the envelope, the less abundant SiC2 is. The observed trend is interpreted as an evidence of efficient incorporation of SiC2 onto dust grains, a process which is favored at high densities owing to the higher rate at which collisions between particles take place. The observed behavior of a decline in the SiC2 abundance with increasing density strongly suggests that SiC2 is an important gas-phase precursor of SiC dust in envelopes around carbon stars., Comment: Published in A&A. 16 pages and 10 figures

The Atacama Large Millimeter/submillimeter Array is allowing us to study the innermost regions of the circumstellar envelopes of evolved stars with unprecedented precision and sensitivity. Key processes in the ejection of matter and dust from these objects occur in their inner zones. In this work, we present sub-arcsecond interferometric maps of transitions of metal-bearing molecules toward the prototypical C-rich evolved star IRC +10216. While Al-bearing molecules seem to be present as a roughly spherical shell, the molecular emission from the salts NaCl and KCl presents an elongation in the inner regions with a central minimum. In order to accurately analyze the emission from the NaCl rotational lines, we present new calculations of the collisional rates for this molecule based on new spectroscopic constants. The most plausible interpretation for the spatial distribution of the salts is a spiral with a NaCl mass of 0.08 $;{M}_{odot }$. Alternatively, a torus of gas and dust would result in structures similar to those observed. From the torus scenario we derive a mass of ~1.1 × 10−4$;{M}_{odot }$. In both cases, the spiral and the torus, the NaCl structure presents an inner minimum of 27 AU. In the case of the torus, the outer radius is 73 AU. The kinematics of both the spiral and the torus suggests that they are slowly expanding and rotating. Alternative explanations for the presence of the elongation are explored. The presence of these features only in KCl and NaCl might be a result of their comparatively high dipole moment with respect to the Al-bearing species.

We report the detection of SiS rotational lines in high-vibrational states as well as SiO and SiC2 lines in their ground vibrational state toward IRC+10216 during the Atacama Large Millimeter Array Cycle 0. The spatial distribution of these molecules shows compact emission for SiS and a more extended emission for SiO and SiC2 and also proves the existence of an increase in the SiC2 emission at the outer shells of the circumstellar envelope (CSE). We analyze the excitation conditions of the vibrationally excited SiS using the population diagram technique, and we use a large velocity gradient model to compare with the observations. We found moderate discrepancies between the observations and the models that could be explained if SiS lines detected are optically thick. Additionally, the line profiles of the detected rotational lines in the high-energy vibrational states show a decreasing linewidth with increasing energy levels. This may be evidence that these lines could be excited only in the inner shells, i.e., the densest and hottest, of the CSE of IRC+10216., We thank the Spanish MINECO/MICINN for funding support through grants AYA2009-07304 and AYA2012-32032, the ASTROMOL Consolider project CSD2009-00038, and the European Research Council (ERC grant 610256: NANOCOSMOS).

We report the discovery in space of a disilicon species, SiCSi, from observations between 80 and 350 GHz with the IRAM 30m radio telescope. Owing to the close coordination between laboratory experiments and astrophysics, 112 lines have now been detected in the carbon-rich star CWLeo. The derived frequencies yield improved rotational and centrifugal distortion constants up to sixth order. From the line profiles and interferometric maps with the Submillimeter Array, the bulk of the SiCSi emis- sion arises from a region of 6 arcseconds in radius. The derived abundance is comparable to that of SiC2. As expected from chemical equilibrium calculations, SiCSi and SiC2 are the most abundant species harboring a SiC bond in the dust formation zone and certainly both play a key role in the formation of SiC dust grains., To be published in the Astrophysical Journal Letters; Accepted May 6 2015

OH 231.8+4.2, a bipolar outflow around a Mira-type variable star, displays a unique molecular richness amongst circumstellar envelopes (CSEs) around O-rich AGB and post-AGB stars. We report line observations of the HCO+ and H13CO+ molecular ions and the first detection of SO+, N2H+, and (tentatively) H3O+ in this source. SO+ and H3O+ have not been detected before in CSEs around evolved stars. These data have been obtained as part of a full mm-wave and far-IR spectral line survey carried out with the IRAM 30 m radio telescope and with Herschel/HIFI. Except for H3O+, all the molecular ions detected in this work display emission lines with broad profiles (FWHM ~ 50−90 km s-1), which indicates that these ions are abundant in the fast bipolar outflow of OH 231.8. The narrow profile (FWHM ~ 14 km s-1) and high critical densities (>106 cm-3) of the H3O+ transitions observed are consistent with this ion arising from denser, inner (and presumably warmer) layers of the fossil remnant of the slow AGB CSE at the core of the nebula. From rotational diagram analysis, we deduce excitation temperatures of Tex~ 10−20 K for all ions except for H3O+, which is most consistent with Tex≈ 100 K. Although uncertain, the higher excitation temperature suspected for H3O+ is similar to that recently found for H2O and a few other molecules, which selectively trace a previously unidentified, warm nebular component. The column densities of the molecular ions reported here are in the range Ntot≈ [1−8] × 1013 cm-2, leading to beam-averaged fractional abundances relative to H2 of X(HCO+) ≈ 10-8, X(H13CO+) ≈2 × 10-9, X(SO+) ≈4 × 10-9, X(N2H+) ≈2 × 10-9, and X(H3O+) ≈7 × 10-9 cm-2. We have performed chemical kinetics models to investigate the formation of these ions in OH 231.8 as the result of standard gas phase reactions initiated by cosmic-ray and UV-photon ionization. The model predicts that HCO+, SO+, and H3O+ can form with abundances comparable to the observed average values in the external layers of the slow central core (at ~[3−8] × 1016 cm); H3O+ would also form quite abundantly in regions closer to the center (X(H3O+) ~ 10-9 at ~1016 cm). For N2H+, the model abundance is lower than the observed value by more than two orders of magnitude. The model fails to reproduce the abundance enrichment of HCO+, SO+, and N2H+ in the lobes, which is directly inferred from the broad emission profiles of these ions. Also, in disagreement with the narrow H3O+ spectra, the model predicts that this ion should form in relatively large, detectable amounts (≈10-9) in the external layers of the slow central core and in the high-velocity lobes. Some of the model-data discrepancies are reduced, but not suppressed, by lowering the water content and enhancing the elemental nitrogen abundance in the envelope. The remarkable chemistry of OH 231.8 probably reflects the molecular regeneration process within its envelope after the passage of fast shocks that accelerated and dissociated molecules in the AGB wind ~800 yr ago., This work has been partially supported by the Spanish MINECO through grants CSD2009-00038, AYA2009-07304, and AYA2012-32032.

Linear carbon chains are common in various types of astronomical molecular sources. Possible formation mechanisms involve both bottom-up and top-down routes. We have carried out a combined observational and modeling study of the formation of carbon chains in the C-star envelope IRC+10216, where the polymerization of acetylene and hydrogen cyanide induced by ultraviolet photons can drive the formation of linear carbon chains of increasing length. We have used ALMA to map the emission of 3 mm rotational lines of the hydrocarbon radicals C2H, C4H, and C6H, and the CN-containing species CN, C3N, HC3N, and HC5N with an angular resolution of 1". The spatial distribution of all these species is a hollow, 5-10" wide, spherical shell located at a radius of 10-20" from the star, with no appreciable emission close to the star. Our observations resolve the broad shell of carbon chains into thinner sub-shells which are 1-2" wide and not fully concentric, indicating that the mass loss process has been discontinuous and not fully isotropic. The radial distributions of the species mapped reveal subtle differences: while the hydrocarbon radicals have very similar radial distributions, the CN-containing species show more diverse distributions, with HC3N appearing earlier in the expansion and the radical CN extending later than the rest of the species. The observed morphology can be rationalized by a chemical model in which the growth of polyynes is mainly produced by rapid gas-phase chemical reactions of C2H and C4H radicals with unsaturated hydrocarbons, while cyanopolyynes are mainly formed from polyynes in gas-phase reactions with CN and C3N radicals., Accepted for publication in A&A

We report on the discovery of strong intensity variations in the high rotational lines of abundant molecular species towards the archetypical circumstellar envelope of IRC+10216. The observations have been carried out with the HIFI instrument on board \textit{Herschel}\thanks{\textit{Herschel} is an ESA space observatory with science instruments provided by European-led Principal Investigator consortia and with important participation from NASA} and with the IRAM\thanks{This work was based on observations carried out with the IRAM 30-meter telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain)} 30-m telescope. They cover several observing periods spreading over 3 years. The line intensity variations for molecules produced in the external layers of the envelope most probably result from time variations in the infrared pumping rates. We analyze the main implications this discovery has on the interpretation of molecular line emission in the envelopes of Mira-type stars. Radiative transfer calculations have to take into account both the time variability of infrared pumping and the possible variation of the dust and gas temperatures with stellar phase in order to reproduce the observation of molecular lines at different epochs. The effect of gas temperature variations with stellar phase could be particularly important for lines produced in the innermost regions of the envelope. Each layer of the circumstellar envelope sees the stellar light radiation with a different lag time (phase). Our results show that this effect must be included in the models. The sub-mm and FIR lines of AGB stars cannot anymore be considered as safe intensity calibrators.

ALMA interferometer is providing us molecular maps with unprecedent precision and sensitivity, Key processes in the ejection of matter and dust from these objects occur in their inner zones. We have obtained sub-arcsecond interferometric maps of rotational transitions of metal-bearing molecules towards the prototypical C-rich evolved star IRC+ 10216. While Al- bearing molecular emission presents a roughly spherical shell, the molecular emission from NaCl and KCl presents an elongation in the inner regions, with a central minimum. The presence of the observed features only in KCl and NaCl might be a direct result of their comparatively high dipole moment with respect to the Al-bearing species. The most plausible interpretation for the spatial distribution of the salts is a spiral with a NaCl mass of 0.08 M ⊙ with an inner radius of 27 AU. The gas kinematics suggests that it is slowly expanding and rotating. Alternative gas distributions which could result in the presence of the elongation are also explored.

IRC +10216 is a circumstellar envelope around a carbon-rich evolved star which contains a large variety of molecules. According to interferometric observations, molecules are distributed either concentrated around the central star or as a hollow shell with a radius of ~15''. We present ALMA Cycle 0 band 6 observations of the J = 14 – 13 rotational transition of CH3CN in IRC +10216, obtained with an angular resolution of 0farcs76 × 0farcs61. The bulk of the emission is distributed as a hollow shell located at just ~2'' from the star, with a void of emission in the central region up to a radius of ~1''. This spatial distribution is markedly different from those found to date in this source for other molecules. Our analysis indicates that methyl cyanide is not formed in either the stellar photosphere or far in the outer envelope, but at radial distances as short as 1''–2'', reaching a maximum abundance of ~0.02 molecules cm−3 at 2'' from the star. Standard chemical models of IRC +10216 predict that the bulk of CH3CN molecules should be present at a radius of ~15'' where other species such as polyyne radicals and cyanopolyynes are observed, with an additional inner component within 1'' from the star. The non-uniform structure of the circumstellar envelope and grain surface processes are discussed as possible causes of the peculiar distribution of methyl cyanide in IRC +10216., We thank funding support from the European Research Council (ERC grant 610256: NANOCOSMOS) and from Spanish MINECO through grants CSD2009-00038, AYA2009-07304, and AYA2012-32032.

Circumstellar envelopes (CSEs) around asymptotic giant branch (AGB) stars are the main sites of molecular formation. OH 231.8+4.2 is a well studied oxygen-rich CSE around an intermediate-mass evolved star that, in dramatic contrast to most AGB CSEs, displays bipolar molecular outflows accelerated up to ~400 km s-1. OH 231.8+4.2 also presents an exceptional molecular richness probably due to shock-induced chemical processes. We report the first detection in this source of four nitrogen-bearing species, HNCO, HNCS, HC3N, and NO, which have been observed with the IRAM-30 m radiotelescope in a sensitive mm-wavelength survey towards this target. HNCO and HNCS are also first detections in CSEs. The observed line profiles show that the emission arises in the massive (~0.6 M⊙) central component of the envelope, expanding with low velocities of Vexp~ 15–30 km s-1, and at the base of the fast lobes. The NO profiles (with FWHM~ 40–50 km s-1) are broader than those of HNCO, HNCS, and HC3N and, most importantly, broader than the line profiles of 13CO, which is a good mass tracer. This indicates that the NO abundance is enhanced in the fast lobes relative to the slow, central parts. From LTE and non-LTE excitation analysis, we estimate beam-average rotational temperatures of Trot~ 15–30 K (and, maybe, up to ~55 K for HC3N) and fractional abundances relative to H2 of X(HNCO) ~ [0.8–1] × 10-7, X(HNCS) ~ [0.9–1] × 10-8, X(HC3N) ~ [5–7] × 10-9, and X(NO) ~ [1–2] × 10-6. NO is, therefore, amongst the most abundant N-bearing species in OH 231.8+4.2. We performed thermodynamical chemical equilibrium and chemical kinetics models to investigate the formation of these N-bearing species in OH 231.8+4.2. The model underestimates the observed abundances for HNCO, HNCS, and HC3N by several orders of magnitude, which indicates that these molecules can hardly be products of standard UV-photon and/or cosmic-ray induced chemistry in OH 231.8+4.2 and that other processes (e.g. shocks) play a major role in their formation. For NO, the model abundance, ≈10-6, is compatible with the observed average value; however, the model fails to reproduce the NO abundance enhancement in the high-velocity lobes (relative to the slow core) inferred from the broad NO profiles. The new detections presented in this work corroborate the particularly rich chemistry of OH 231.8+4.2, which is likely to be profoundly influenced by shock-induced processes, as proposed in earlier works., We acknowledge the Spanish MICINN/MINECO for funding support through grants AYA2009-07304, AYA2012-32032, and the ASTROMOL Consolider project CSD2009-00038. L.V. acknowledges the Spanish MINECO for funding support through FPI2012 short stay programme (ref. EEBB-I-13-06211) and the Laboratoire D’Astrophysique de Bordeaux (LAB-CNRS) for hosting this stay under the supervision of Dr. Marcelino Agúndez. L.V. also acknowledges the support of the Universidad Complutense de Madrid through the Ph.D. programme. M.A. acknowledges the support from the European Research Council (ERC Grant 209622: E3 ARTHS).