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Atmospheric molecular blobs shape up circumstellar envelopes of AGB stars


During their thermally pulsing phase, asymptotic giant branch (AGB) stars eject material that forms extended dusty envelopes1. Visible polarimetric imaging found clumpy dust clouds within two stellar radii of several oxygen-rich stars2,3,4,5,6. Inhomogeneous molecular gas has also been observed in multiple emission lines within several stellar radii of different oxygen-rich stars, including W Hya and Mira7,8,9,10. At the stellar surface level, infrared images have shown intricate structures around the carbon semiregular variable R Scl and in the S-type star π1 Gru11,12. Infrared images have also shown clumpy dust structures within a few stellar radii of the prototypical carbon AGB star IRC+10°216 (refs. 13,14), and studies of molecular gas distribution beyond the dust formation zone have also shown complex circumstellar structures15. Because of the lack of sufficient spatial resolution, however, the distribution of molecular gas in the stellar atmosphere and the dust formation zone of AGB carbon stars is not known, nor is how it is subsequently expelled. Here we report observations with a resolution of one stellar radius of the recently formed dust and molecular gas in the atmosphere of IRC+10°216. Lines of HCN, SiS and SiC2 appear at different radii and in different clumps, which we interpret as large convective cells in the photosphere, as seen in Betelgeuse16. The convective cells coalesce with pulsation, causing anisotropies that, together with companions17,18, shape its circumstellar envelope.

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Fig. 1: Continuum emission of IRC+10°216 at 1 mm.
Fig. 2: Velocity-integrated maps of different emission lines.
Fig. 3: Velocity-integrated emission maps of the circumstellar environment of IRC+10°216 for different molecules.
Fig. 4: Analysis of intensity ratio of emission lines HCN ν3 = 1, J = 3–2 and SiS v = 3, J = 14–13.

Data availability

All the observational products used here are public and available through the ALMA, SMA and IRAM-30m archives:

Code availability

The 2012 version of the MADEX code, including spectroscopic information for approximately 3,500 species, is available as an executable in The chemical equilibrium and evolving envelope models are available on request. Enquiries about codes can be addressed to the corresponding authors and to the developers of the codes: M.A. for the chemical code, J.C. for the MADEX code and J.C. and J.P.F. for models of the evolving envelope.


  1. Habing, H. J. & Olofsson, H. Asymptotic Giant Branch Stars (Springer, 2004).

  2. Adam, C. & Ohnaka, K. Exploring the innermost dust formation region of the oxygen-rich AGB star IK Tauri with VLT/SPHERE-ZIMPOL and VLTI/AMBER. Astron. Astrophys. 628, A132 (2019).

    Article  ADS  Google Scholar 

  3. Khouri, T. et al. Study of the inner dust envelope and stellar photosphere of the AGB star R Doradus using SPHERE/ZIMPOL. Astron. Astrophys. 591, A70 (2016).

    Article  Google Scholar 

  4. Khouri, T. et al. Inner dusty envelope of the AGB stars W Hydrae, SW Virginis, and R Crateris using SPHERE/ZIMPOL. Astron. Astrophys. 635, A200 (2020).

    Article  CAS  Google Scholar 

  5. Ohnaka, K., Weigelt, G. & Hofmann, K.-H. Clumpy dust clouds and extended atmosphere of the AGB star W Hydrae revealed with VLT/SPHERE-ZIMPOL and VLTI/AMBER. Astron. Astrophys. 589, A91 (2016).

    Article  ADS  Google Scholar 

  6. Ohnaka, K., Weigelt, G. & Hofmann, K.-H. Clumpy dust clouds and extended atmosphere of the AGB star W Hydrae revealed with VLT/SPHERE-ZIMPOL and VLTI/AMBER. II. Time variations between pre-maximum and minimum light. Astron. Astrophys. 597, A20 (2017).

    Article  ADS  Google Scholar 

  7. Takigawa, A., Kamizuka, T., Tachibana, S. & Yamamura, I. Dust formation and wind acceleration around the aluminum oxide-rich AGB star W Hydrae. Sci. Adv. 3, eaao2149 (2017).

    Article  PubMed  PubMed Central  Google Scholar 

  8. Vlemmings, W. et al. The shock-heated atmosphere of an asymptotic giant branch star resolved by ALMA. Nat. Astron. 1, 848–853 (2017).

    Article  ADS  Google Scholar 

  9. Khouri, T. et al. High-resolution observations of gas and dust around Mira using ALMA and SPHERE/ZIMPOL. Astron. Astrophys. 620, A75 (2018).

    Article  CAS  Google Scholar 

  10. Gottlieb, C. A. et al. ATOMIUM: ALMA tracing the origins of molecules in dust forming oxygen rich M-type stars. Astron. Astrophys. 660, A94 (2022).

    Article  CAS  Google Scholar 

  11. Wittkowski, M. et al. Aperture synthesis imaging of the carbon AGB star R Sculptoris. Detection of a complex structure and a dominating spot on the stellar disk. Astron. Astrophys. 601, A3 (2017).

    Article  Google Scholar 

  12. Paladini, C. et al. Large granulation cells on the surface of the giant star π1 Gruis. Nature 553, 310–312 (2018).

    Article  CAS  PubMed  ADS  Google Scholar 

  13. Leão, I. C., de Laverny, P., Mékarnia, D., de Medeiros, J. R. & Vandame, B. The circumstellar envelope of IRC+10216 from milli-arcsecond to arcmin scales. Astron. Astrophys. 455, 187–194 (2006).

    Article  ADS  Google Scholar 

  14. Stewart, P. N. et al. The weather report from IRC+10216: evolving irregular clouds envelop carbon star. Mon. Not. R. Astron. Soc. 455, 3102–3109 (2016).

    Article  CAS  ADS  Google Scholar 

  15. Siebert, M. A., Van de Sande, M., Millar, T. J. & Remijan, A. J. Investigating anomalous photochemistry in the inner wind of IRC+10216 through interferometric observations of HC3N. Astrophys. J. 941, 90 (2022).

    Article  ADS  Google Scholar 

  16. Montargès, M. et al. A dusty veil shading Betelgeuse during its Great Dimming. Nature 594, 365–368 (2021).

    Article  PubMed  ADS  Google Scholar 

  17. Ramstedt, S. et al. The circumstellar envelope around the S-type AGB star W Aql. Astron. Astrophys. 605, A126 (2017).

    Article  PubMed  PubMed Central  Google Scholar 

  18. Decin, L. et al. (Sub)stellar companions shape the winds of evolved stars. Science 369, 1497–1500 (2020).

    Article  CAS  PubMed  ADS  Google Scholar 

  19. Freytag, B., Liljegren, S. & Höfner, S. Global 3D radiation-hydrodynamics models of AGB stars. Effects of convection and radial pulsations on atmospheric structures. Astron. Astrophys. 600, A137 (2017).

    Article  ADS  Google Scholar 

  20. Cernicharo, J., Marcelino, N., Agúndez, M. & Guélin, M. Molecular shells in IRC+10216: tracing the mass loss history. Astron. Astrophys. 575, A91 (2015).

    Article  PubMed  PubMed Central  ADS  Google Scholar 

  21. Sozzetti, A., Smart, R. L., Drimmel, R., Giacobbe, P. & Lattanzi, M. G. Evidence for orbital motion of CW Leonis from ground-based astrometry. Mon. Not. R. Astron. Soc. 471, L1–L5 (2017).

    Article  ADS  Google Scholar 

  22. Menten, K. M., Reid, M. J., Kamiński, T. & Claussen, M. J. The size, luminosity, and motion of the extreme carbon star IRC+10216 (CW Leonis). Astron. Astrophys. 543, A73 (2012).

    Article  ADS  Google Scholar 

  23. Weigelt, G. et al. 76mas Speckle-masking interferometry of IRC+10216 with the SAO 6m telescope: Evidence for a clumpy shell structure. Astron. Astrophys. 333, L51–L54 (1998).

    ADS  Google Scholar 

  24. Chiavassa, A. & Freytag, B. 3D hydrodynamical simulations of evolved stars and observations of stellar surfaces. In Proc. of a Conference at University Campus, Vienna, Austria on why galaxies care about AGB stars III: a closer look in space and time (eds. by Kerschbaum, F. et al.) (Astronomical Society of the Pacific, 2015).

  25. Höfner, S. & Freytag, B. Exploring the origin of clumpy dust clouds around cool giants. A global 3D RHD model of a dust-forming M-type AGB star. Astron. Astrophys. 623, A158 (2019).

    Article  ADS  Google Scholar 

  26. Martínez, L. et al. Prevalence of non-aromatic carbonaceous molecules in the inner regions of circumstellar envelopes. Nat. Astron. 4, 97–105 (2020).

    Article  PubMed  ADS  Google Scholar 

  27. Cernicharo, J. et al. Discovery of SiCSi in IRC+10216: a missing link between gas and dust carriers of Si-C bonds. Astrophys. J. Lett. 806, L3 (2015).

    Article  PubMed  PubMed Central  ADS  Google Scholar 

  28. Decin, L. et al. ALMA data suggest the presence of spiral structure in the inner wind of CW Leonis. Astron. Astrophys. 574, A5 (2015).

    Article  Google Scholar 

  29. Guélin, M. et al. IRC+10216 in 3D: morphology of a TP-AGB star envelope. Astron. Astrophys. 610, A4 (2018).

    Article  PubMed  PubMed Central  Google Scholar 

  30. Ireland, M. J. & Scholz, M. Observable effects of dust formation in dynamic atmospheres of M-type Mira variables. Mon. Not. R. Astron. Soc. 367, 1585–1593 (2006).

    Article  CAS  ADS  Google Scholar 

  31. Norris, B. R. M. et al. A close halo of large transparent grains around extreme red giant stars. Nature 484, 220–222 (2012).

    Article  CAS  PubMed  ADS  Google Scholar 

  32. Van de Sande, M. et al. Determining the effects of clumping and porosity on the chemistry in a non-uniform AGB outflow. Astron. Astrophys. 616, A106 (2018).

    Article  Google Scholar 

  33. Ridgway, S. & Keady, J. J. The IRC+10216 circumstellar envelope. II. Spatial measurements of the dust. Astrophys. J. 326, 843 (1988).

    Article  ADS  Google Scholar 

  34. Men’shchikov, A. B., Balega, Y., Blöcker, T., Osterbart, R. & Weigelt, G. Structure and physical properties of the rapidly evolving dusty envelope of IRC+10216 reconstructed by detailed two-dimensional radiative transfer modeling. Astron. Astrophys. 368, 497–526 (2001).

    Article  ADS  Google Scholar 

  35. McMullin, J. P., Waters, B., Schiebel, D., Young, W. & Golap, K. CASA architecture and applications. Publ. Astron. Soc. Pac. 376, 127 (2007).

  36. Högbom, J. A. Aperture synthesis with a non-regular distribution of interferometer baselines. Astron. Astrophys. Suppl. 15, 417 (1974).

    ADS  Google Scholar 

  37. Steer, D. G., Dewdney, P. E. & Ito, M. R. Enhancements to the deconvolution algorithm ‘CLEAN’. Astron. Astrophys. 137, 159–165 (1984).

    ADS  Google Scholar 

  38. Reid, M. J. et al. The distance to the center of the galaxy: H 2O maser proper motions in Sagittarius B2(N). Astrophys. J. 330, 809 (1988).

    Article  CAS  ADS  Google Scholar 

  39. Lucas, R. 1.3 MM Plateau de Bure observations of IRC+10216. Astrophys. Space Sci. 251, 247–250 (1997).

    Article  CAS  ADS  Google Scholar 

  40. Fonfría, J. P. et al. The complex dust formation zone of the AGB star IRC+10216 probed with CARMA 0.25 arcsec angular resolution molecular observations. Mon. Not. R. Astron. Soc. 445, 3289–3308 (2014).

    Article  ADS  Google Scholar 

  41. Groenewegen, M. A. T. et al. An independent distance estimate to CW Leonis. Astron. Astrophys. 543, L8 (2012).

    Article  ADS  Google Scholar 

  42. Freytag, B., Holweger, H., Steffen, M. & Ludwig, H.-G. On the scale of photospheric convection. In Proc. of the ESO workshop: Science with the VLT Interferometer 316 (Springer, 1997).

  43. Weigelt, G. et al. Bispectrum speckle interferometry of IRC+10216: the dynamic evolution of the innermost circumstellar environment from 1995 to 2001. Astron. Astrophys. 392, 131–141 (2002).

    Article  ADS  Google Scholar 

  44. Monnier, J. D. et al. Mid-infrared interferometry on spectral lines. II. Continuum (dust) emission around IRC+10216 and VY Canis Majoris. Astrophys. J. 543, 861–867 (2000).

    Article  CAS  ADS  Google Scholar 

  45. Tuthill, P. G., Monnier, J. D., Danchi, W. C. & Lopez, B. Smoke signals from IRC+10216. I. Milliarcsecond proper motions of the dust. Astrophys. J. 543, 284–290 (2000).

    Article  ADS  Google Scholar 

  46. Leão, I. C., de Laverny, P., Mekarnia, D., de Medeiros, J. R. & Vandame, B. Observations of the AGB star IRC+10216 from milliarcsec to arcmin spatial scales. Publ. Astron. Soc. Pac. 378, 309 (2007).

  47. Kim, H. et al. Multiepoch optical images of IRC+10216 tell about the central star and the adjacent environment. Astrophys. J. 914, 35 (2021).

    Article  CAS  ADS  Google Scholar 

  48. Kim, H., Lee, H.-G., Mauron, N. & Chu, Y.-H. HST images reveal dramatic changes in the core of IRC+10216. Astrophys. J. Lett. 804, L10 (2015).

    Article  ADS  Google Scholar 

  49. Agúndez, M., Martínez, J. I., de Andres, P. L., Cernicharo, J. & Martín-Gago, J. A. Chemical equilibrium in AGB atmospheres: successes, failures, and prospects for small molecules, clusters, and condensates. Astron. Astrophys. 637, A59 (2020).

    Article  PubMed  PubMed Central  Google Scholar 

  50. Cernicharo, J. Laboratory astrophysics and astrochemistry in the Herschel/ALMA era. EAS Publ. Ser. 58, 251–261 (2012).

  51. Cherchneff, I. The inner wind of IRC+10216 revisited: new exotic chemistry and diagnostic for dust condensation in carbon stars. Astron. Astrophys. 545, A12 (2012).

    Article  ADS  Google Scholar 

  52. Soker, N. Binary progenitor models for bipolar planetary nebulae. Astrophys. J. 496, 833–841 (1998).

    Article  ADS  Google Scholar 

  53. Guelin, M., Lucas, R. & Cernicharo, J. MgNC and the carbon-chain radicals in IRC+10216. Astron. Astrophys. 280, L19–L22 (1993).

    CAS  ADS  Google Scholar 

  54. Velilla-Prieto, L. et al. IRC+10°216 mass loss properties through the study of λ 3 mm emission. Large spatial scale distribution of SiO, SiS, and CS. Astron. Astrophys. 629, A146 (2019).

    Article  CAS  Google Scholar 

  55. Mastrodemos, N. & Morris, M. Bipolar preplanetary nebulae: hydrodynamics of dusty winds in binary systems. I. Formation of accretion disks. Astrophys. J. 497, 303–329 (1998).

    Article  CAS  ADS  Google Scholar 

  56. Mastrodemos, N. & Morris, M. Bipolar pre-planetary nebulae: hydrodynamics of dusty winds in binary systems. II. Morphology of the circumstellar envelopes. Astrophys. J. 523, 357–380 (1999).

    Article  ADS  Google Scholar 

  57. De Nutte, R. et al. Nucleosynthesis in AGB stars traced by oxygen isotopic ratios. I. Determining the stellar initial mass by means of the 17O/18O ratio. Astron. Astrophys. 600, A71 (2017).

    Article  Google Scholar 

  58. Kim, H. & Taam, R. E. Wide binary effects on asymmetries in asymptotic giant branch circumstellar envelopes. Astrophys. J. 759, 59 (2012).

    Article  ADS  Google Scholar 

  59. Malfait, J. et al. SPH modelling of wind-companion interactions in eccentric AGB binary systems. Astron. Astrophys. 652, A51 (2021).

    Article  Google Scholar 

  60. Maes, S. et al. Route towards complete 3D hydro-chemical simulations of companion-perturbed AGB outflows. In Proc. of the International Astronomical Union on the Origin of Outflows in Evolved Stars (eds. Decin, L. et al.) (Cambridge Univ. Press, 2021).

  61. Aydi, E. & Mohamed, S. 3D models of the circumstellar environments of evolved stars: formation of multiple spiral structures. Mon. Not. R. Astron. Soc. 513, 4405–4430 (2022).

    Article  CAS  ADS  Google Scholar 

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This publication is part of project ‘I+D+i’ (research, development and innovation, nos. PID2020-117034RJ-I00, PID2019-107115GB-C21, PID2019-106110GB-I00 and PID2019-105203GB-C22) supported by the Spanish Ministerio de Ciencia e Innovación (MCIN/AEI/10.13039/501100011033). This work was also supported by the European Research Council under Synergy Grant ERC-2013-SyG, G.A. 610256 (NANOCOSMOS). This work is based on observations carried out with the IRAM, SMA and ALMA telescopes. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). SMA is a joint project between the Smithsonian Astrophysical Observatory (USA) and the Academia Sinica Institute of Astronomy and Astrophysics (Taiwan) and is funded by the Smithsonian Institution and Academia Sinica. This paper makes use of the following ALMA data: ADS/JAO.ALMA#2013.1.01215.S, ADS/JAO.ALMA#2013.1.00432.S and ADS/JAO.ALMA#2018.1.01485. ALMA is a partnership that includes 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. We made use of CASA software ( The GILDAS package was used to reduce and analyse data ( We acknowledge the GILDAS software team, in particular S. Bardeau, for their help and assistance. We also thank IRAM staff, who provided relevant information for flux calibration from the Northern Extended Millimetre Array observatory database.

Author information

Authors and Affiliations



L.V.-P. led this publication, analysed and interpreted data, wrote the article and created all the figures except for the Extended data Fig. 3 and Extended data Fig. 4. J.P.F. delivered the method used to produce input data for the radiative transfer models from shock model output, and developed and produced the models of the evolving envelope. M.A. created the chemical code and associated images (Extended data Fig. 3 and Extended data Fig. 4). A.C.-C. calibrated and reduced the ALMA data. M.G. contributed subtantially to revision of the literature and detailed revision of the text. I.C. provided the input abundances that were used to produce the shock models. J.C. developed the MADEX and evolving envelope codes, led the ALMA proposal and contributed to the overall analysis of this work. All authors contributed to the conception, design and writing of the ALMA proposal and to discussion and revisions of the article.

Corresponding authors

Correspondence to L. Velilla-Prieto or J. Cernicharo.

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Extended data figures and tables

Extended Data Fig. 1 Velocity-integrated emission maps of SiS isotopologues in different vibrationally excited states.

The velocity-integrated emission maps are shown in colour scale. Note that the intensity scale varies within boxes for improved visualisation. The grey contours correspond to 10, 30, 50, 100, 200, 300, 400, 500, and 600 σ of the r.m.s. of the noise of the continuum emission, which is equal to 92 μJy beam−1. The cyan dashed contour represents the radio photosphere22. The shape of the synthetic beam is shown in the bottom-left corner of each box. North is up, and East to he left.

Extended Data Fig. 2 Velocity-integrated emission maps of HCN isotopologues in different vibrationally excited states.

The colour scale, contours, beam, and orientation are defined as in Extended Data Fig. 1.

Extended Data Fig. 3 Results from the chemical equilibrium models for C2, SiC2, HCN, and SiS.

The colour scale map represents the logarithm of the mole fraction of the given molecule as a function of the kinetic temperature and the logarithm of the pressure of the gas.

Extended Data Fig. 4 Fractional abundance profiles.

The abundance profiles are shown as a function of temperature for a fixed pressure of 5  ×  10−5 bar, which should be close to the gas pressure at the photosphere of IRC+10°216 ref. 49.

Extended Data Fig. 5 Predicted line profiles of the J = 14–13 SiS line in different vibrational states as a function of the pulsation phase.

a–b: density and temperature profiles, where oscillating lines represent the phases ϕ = 0 (black), ϕ = 0.25 (red), ϕ = 0.5 (green), and ϕ = 0.75 (blue). An additional model with no stellar pulsation using density and temperature profiles that falls as r−2 and r−0.7, respectively, is shown as a pink (non-oscillating) solid line. c–f: Emergent line profiles where the coloured lines, which follow the colour code mentioned before, represent the predictions for an angular resolution of \(0\,.\,\,{\rm{{\prime\prime} }}\,2\). g–h: Velocity profile of the gas following also this colour code.

Extended Data Fig. 6 Line profiles of the ν = 2 J = 14–13 SiS line as observed at different locations in the plane of the sky.

The lines have been obtained by averaging the spectra in an area of 10 mas surrounding each selected position. The different numbered offset positions are shown and numbered in the total intensity map to the right. Each corresponding position number is shown in red at the bottom-left corner of the boxes displaying the plots of the spectra.

Extended Data Fig. 7 Line profiles of the HCN 3\({{\boldsymbol{\nu }}}_{{\bf{2}}}^{{\bf{e}}}\)J = 3–2 line as observed at different locations in the plane of the sky.

Details of this figure are defined as in Extended Data Fig. 6.

Extended Data Fig. 8 Spectra in velocity units at different offsets from the source of the SiS ν = 2 J = 14–13 line.

The velocity range shown for each spectrum is ±  15 km s−1 with respect to the systemic velocity of the source, from negative (left) to positive (right). The intensity scale, in Jy beam−1, ranges between -0.03 and 0.06. The red circle represents the stellar disk in the IR (radius equal to 19 mas)33, while the blue circle correspond to the radio photosphere (radius equal to 40.5 mas)22.

Extended Data Fig. 9 Spectra in velocity units at different offsets from the source of the HCN 3\({{\boldsymbol{\nu }}}_{{\bf{2}}}^{{\bf{e}}}\) line.

Details of this figure are defined as in Extended Data Fig. 8.

Extended Data Fig. 10 Results from the growing envelope model.

Three cases are presented: a) control case of an isolated AGB star without formation of blobs, b) AGB steady wind in a binary system with an inclination of 60° separated by 25 AU, and c) as in b but for a closer companion located at 10 AU and including the randomly generated blobs at the AGB stellar photosphere. The maps are in normalised intensity units to their respective maximum intensity.

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Velilla-Prieto, L., Fonfría, J.P., Agúndez, M. et al. Atmospheric molecular blobs shape up circumstellar envelopes of AGB stars. Nature 617, 696–700 (2023).

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