Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

The shock-heated atmosphere of an asymptotic giant branch star resolved by ALMA

Abstract

Our current understanding of the chemistry and mass-loss processes in Sun-like stars at the end of their evolution depends critically on the description of convection, pulsations and shocks in the extended stellar atmosphere1. Three-dimensional hydrodynamical stellar atmosphere models provide observational predictions2, but so far the resolution to constrain the complex temperature and velocity structures seen in the models has been lacking. Here we present submillimetre continuum and line observations that resolve the atmosphere of the asymptotic giant branch star W Hydrae. We show that hot gas with chromospheric characteristics exists around the star. Its filling factor is shown to be small. The existence of such gas requires shocks with a cooling time longer than commonly assumed. A shocked hot layer will be an important ingredient in current models of stellar convection, pulsation and chemistry at the late stages of stellar evolution.

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Fig. 1: Brightness temperature map of the surface of the AGB star W Hya as observed with ALMA at 338 GHz.
Fig. 2: The residual map after subtracting the fitted uniform elliptical disk from the continuum image of W Hya.
Fig. 3: Spectra of the CO J = 3→2, v = 1 transition.

References

  1. 1.

    Habing, H. J. & Olofsson, H. Asymptotic Giant Branch Stars. (Springer, New York, Berlin, 2003).

    Google Scholar 

  2. 2.

    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).

    ADS  Article  Google Scholar 

  3. 3.

    Höfner, S. Winds of M-type AGB stars driven by micron-sized grains. Astron. Astrophys. 491, 1–4 (2008).

    Article  Google Scholar 

  4. 4.

    Woitke, P. 2D models for dust-driven AGB star winds. Astron. Astrophys. 452, 537–549 (2006).

    ADS  Article  Google Scholar 

  5. 5.

    Ireland, M. J., Scholz, M. & Wood, P. R. Dynamical opacity-sampling models of Mira variables—I. Modelling description and analysis of approximations. Mon. Not. R. Astron. Soc. 391, 1994–2002 (2008).

    ADS  Article  Google Scholar 

  6. 6.

    Bowen, G. H. Dynamical modeling of long-period variable star atmospheres. Astrophys. J. 329, 299–317 (1988).

    ADS  Article  Google Scholar 

  7. 7.

    Willacy, K. & Cherchneff, I. Silicon and sulphur chemistry in the inner wind of IRC + 10216. Astron. Astrophys. 330, 676–684 (1998).

    ADS  Google Scholar 

  8. 8.

    Cherchneff, I. I. A chemical study of the inner winds of asymptotic giant branch stars. Astron. Astrophys. 456, 1001–1012 (2006).

    ADS  Article  Google Scholar 

  9. 9.

    Agúndez, M. & Cernicharo, J. Oxygen chemistry in the circumstellar envelope of the carbon-rich star IRC + 10216. Astrophys. J. 650, 374–393 (2006).

    ADS  Article  Google Scholar 

  10. 10.

    L. A. Willson, & G. H. Bowen, In Cyclical Variability in Stellar Winds 294–305 (eds Kaper, L. & Fullerton, A. W.) (Springer, 1998).

  11. 11.

    Johnson, H. R. & Luttermoser, D. G. Ultraviolet spectra and chromospheres of cool carbon stars. Astrophys. J. 314, 329–340 (1987).

    ADS  Article  Google Scholar 

  12. 12.

    Montez, R., Ramstedt, S., Kastner, J. H., Vlemmings, W. & Sanchez, E. A catalog of GALEX ultraviolet emission from asymptotic giant branch stars. Astrophys. J. 841, 33 (2017).

    ADS  Article  Google Scholar 

  13. 13.

    Tuthill, P. G., Haniff, C. A. & Baldwin, J. E. Surface imaging of long-period variable stars. Mon. Not. R. Astron. Soc. 306, 353–360 (1999).

    ADS  Article  Google Scholar 

  14. 14.

    Ragland, S. et al. First surface-resolved results with the Infrared Optical Telescope Array Imaging Interferometer: detection of asymmetries in asymptotic giant branch stars. Astrophys. J. 652, 650–660 (2006).

    ADS  Article  Google Scholar 

  15. 15.

    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).

    ADS  Article  Google Scholar 

  16. 16.

    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 

  17. 17.

    Tsuji, T., Ohnaka, K., Aoki, W. & Yamamura, I. Warm molecular envelope of M giants and Miras: a new molecule forming region unmasked by the ISO SWS. Astron. Astrophys. 320, L1–L4 (1997).

    ADS  Google Scholar 

  18. 18.

    Khouri, T. et al. The wind of W Hydrae as seen by Herschel. II. The molecular envelope of W Hydrae. Astron. Astrophys. 570, A67 (2014).

    Article  Google Scholar 

  19. 19.

    Woodruff, H. C. et al. The Keck Aperture Masking Experiment: spectro-interferometry of three Mira variables from 1.1 to 3.8 μm. Astrophys. J. 691, 1328–1336 (2009).

    ADS  Article  Google Scholar 

  20. 20.

    Zhao-Geisler, R., Quireenbach, A., Köhler, R., Lopez, B. & Leinert, C. The mid-infrared diameter of W Hydrae. Astron. Astrophys. 530, A120 (2011).

    ADS  Article  Google Scholar 

  21. 21.

    Vlemmings, W. H. T., van Langevelde, H. J., Diamond, P. J., Habing, H. J. & Schilizzi, R. T. VLBI astrometry of circumstellar OH masers: proper motions and parallaxes of four AGB stars. Astron. Astrophys. 407, 213–224 (2003).

    ADS  Article  Google Scholar 

  22. 22.

    Reid, M. J. & Menten, K. M. Imaging the radio photospheres of Mira variables. Astrophys. J. 671, 2068–2073 (2007).

    ADS  Article  Google Scholar 

  23. 23.

    Reid, M. J. & Menten, K. M. Radio photospheres of long-period variable stars. Astrophys. J. 476, 327–346 (1997).

    ADS  Article  Google Scholar 

  24. 24.

    Lim, J., Carilli, C. L., White, S. M., Beasley, A. J. & Marson, R. G. Large convection cells as the source of Betelgeuse’s extended atmosphere. Nature 392, 575–577 (1998).

    ADS  Article  Google Scholar 

  25. 25.

    Harper, G. M., O’Riain, N. & Ayres, T. R. Chromospheric thermal continuum millimetre emission from non-dusty K and M red giants. Mon. Not. R. Astron. Soc. 428, 2064–2073 (2012).

    ADS  Article  Google Scholar 

  26. 26.

    Landau, L. D. & Lifshitz, E. M. Fluid Mechanics (Pergamon Press, Oxford, 1959).

    MATH  Google Scholar 

  27. 27.

    Khouri, T. et al. ALMA observations of the vibrationally excited rotational CO transition v = 1, J = 3 - 2 towards five AGB stars. Mon. Not. R. Astron. Soc. 463, L74–L78 (2016).

    ADS  Article  Google Scholar 

  28. 28.

    Hinkle, K. H. Infrared spectroscopy of Mira variables. I. R Leonis: the CO and OH vibration-rotation overtone bands. Astrophys. J. 220, 210–228 (1978).

    ADS  Article  Google Scholar 

  29. 29.

    Danilovich, T. et al. Water isotopologues in the circumstellar envelopes of M-type AGB stars. Astron. Astrophys. 602, A14 (2017).

    Article  Google Scholar 

  30. 30.

    Lèbre, A. et al. Search for surface magnetic fields in Mira stars. First detection in χ Cygni. Astron. Astrophys. 561, A85 (2014).

    Article  Google Scholar 

  31. 31.

    Vlemmings, W. H. T., van Langevelde, H. J. & Diamond, P. J. The magnetic field around late-type stars revealed by the circumstellar H2O masers. Astron. Astrophys. 434, 1029–1038 (2005).

    ADS  Article  Google Scholar 

  32. 32.

    Martí-Vidal, I., Vlemmings, W. H. T., Muller, S. & Casey, S. UVMULTIFIT: a versatile tool for fitting astronomical radio interferometric data. Astron. Astrophys. 563, A136 (2014).

    ADS  Article  Google Scholar 

  33. 33.

    Magnum J.The Relationship Between Flux Density and Brightness Temperature (National Radio Astronomy Observatory, 2015); https://safe.nrao.edu/wiki/pub/Main/RadioTutorial/flux-to-brightness.pdf.

  34. 34.

    Condon, J. J. Errors in elliptical Gaussian fits. Publ. Astron. Soc. Pacific 109, 166–172 (1997).

    ADS  Article  Google Scholar 

  35. 35.

    Gendriesch, R. et al. Accurate laboratory rest frequencies of vibrationally excited CO up to v = 3 and up to 2 THz. Astron. Astrophys. 497, 927–930 (2009).

    ADS  Article  Google Scholar 

  36. 36.

    Höfner, S., Bladh, S., Aringer, B. & Ahuja R., Dynamic atmospheres and winds of cool luminous giants. I. Al2O3 and silicate dust in the close vicinity of M-type AGB stars. Astron. Astrophys. 594, A108 (2016).

    Article  Google Scholar 

  37. 37.

    Woitke, P., Helling, Ch, Winters, J. M. & Jeong, K. S. On the formation of warm molecular layers. Astron. Astrophys. 348, L17–L20 (1999).

    ADS  Google Scholar 

  38. 38.

    Tsuji, T. High resolution spectroscopy of CO in the infrared spectra of cool stars—turbulent velocities and carbon abundance in M-giant stars. Astron. Astrophys. 156, 8–21 (1986).

    ADS  Google Scholar 

  39. 39.

    Humphreys, E. M. L. et al. Simultaneous 183 GHz H2O Maser and SiO observations towards evolved stars using APEX SEPIA Band 5. Astron. Astrophys. 603, A77 (2017).

    Article  Google Scholar 

  40. 40.

    Remijan, A. J., Markwick-Kemper, A., ALMA Working Group on Spectral Line Frequencies. Splatalogue; Database for Astronomical Spectroscopy. Bull. Am. Astron. Soc. 39, 963 (2007).

    Article  Google Scholar 

  41. 41.

    Underwood, D. S. et al. ExoMol molecular line lists – XIV. The rotation–vibration spectrum of hot SO2. Mon. Not. R. Astron. Soc. 459, 3890–3899 (2016).

    ADS  Article  Google Scholar 

Download references

Acknowledgements

Support for this work was provided by the European Research Council (ERC) through the ERC consolidator grant number 614264, and by the Swedish Research Council (VR). E.D.B. further acknowledges support from the Swedish National Space Board. We are also indebted to the staff of the Nordic ALMA regional centre node, and in particular I. Martí-Vidal, for developments of the tools used in the data analysis and plotting. ALMA is a partnership of the European Southern Observatory (ESO, representing its member states), the National Science Foundation (United States) and the National Institutes of Natural Sciences (NINS, Japan), together with the National Research Council (Canada), the National Science Council (Taiwan), the NINS in collaboration with the Academia Sinica (Taiwan) and the Korea Astronomy and Space Science Institute (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, Associated Universities Inc./National Radio Astronomy Observatory and the National Astronomical Observatory of Japan.

Author information

Affiliations

Authors

Contributions

W.V. reduced and analysed the data and wrote most of the manuscript. T.K. performed the radiative-transfer modelling and wrote the modelling section of the Methods. E.D.B. and B.L. analysed the unidentified line and provided the relevant text. A.T. obtained the ALMA data. All authors contributed with comments on the manuscript and data interpretation.

Corresponding author

Correspondence to Wouter Vlemmings.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Electronic supplementary material

Supplementary Information

Supplementary Figures 1–6 and Supplementary Table 1

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Vlemmings, W., Khouri, T., O’Gorman, E. et al. The shock-heated atmosphere of an asymptotic giant branch star resolved by ALMA. Nat Astron 1, 848–853 (2017). https://doi.org/10.1038/s41550-017-0288-9

Download citation

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing