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Large convection cells as the source of Betelgeuse's extended atmosphere

Nature volume 392, pages 575–577 (1998)Cite this article

Abstract

Supergiant stars such as Betelgeuse have very extended atmospheres, the properties of which are poorly understood. Alfvén waves1,2,3,4, acoustic waves1,2,5,6,7 and radial pulsations8 have all been suggested as likely mechanisms for elevating these atmospheres and driving the massive outflows of gas seen in these stars: such mechanisms would heat the atmosphere from below, and there are indeed observations showing that Betelgeuse's extended atmosphere is hotter than the underlying photosphere9,10. Here we report radio observations of Betelgeuse that reveal the temperature structure of the extended atmosphere from two to seven times the photospheric radius. Close to the star, we find that the atmosphere has an irregular structure, and a temperature (3,450 ± 850 K) consistent with the photospheric temperature but much lower than that of gas in the same region probed by optical and ultraviolet observations10. This cooler gas decreases steadily in temperature with radius, reaching 1,370 ± 330 K by seven stellar radii. The cool gas coexists with the hot chromospheric gas, but must be much more abundant as it dominates the radio emission. Our results suggest that a few inhomogeneously distributed large convective cells (which are widely believed11,12,13,14,15,16 to be present in such stars) are responsible for lifting the cooler photospheric gas into the atmosphere; radiation pressure on dust grains that condense from this gas may then drive Betelgeuse's outflow.

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Figure 1: An image of Betelgeuse's atmosphere observed at a wavelength of 7 mm with the VLA.
Figure 2: The temperature profile of Betelgeuse's atmosphere measured at the radio wavelengths indicated below each point.

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Acknowledgements

The VLA is a facility of the National Radio Astronomy Observatory, which is operated by Associated Universities, Inc., under cooperative agreement with the National Science Foundation. We thank B. Butler for providing us with the ellipse-fitting algorithm.

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Authors and Affiliations

  1. Academia Sinica Institute of Astronomy & Astrophysics, PO Box 1-87, Nankang, 115, Taipei, Taiwan

    Jeremy Lim

  2. National Radio Astronomical Observatory, Socorro, 87801, New Mexico, USA

    Chris L. Carilli, Anthony J. Beasley & Ralph G. Marson

  3. Department of Astronomy, University of Maryland, College Park, 20742, Maryland, USA

    Stephen M. White

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Correspondence to Jeremy Lim.

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Lim, J., Carilli, C., White, S. et al. Large convection cells as the source of Betelgeuse's extended atmosphere. Nature 392, 575–577 (1998). https://doi.org/10.1038/33352

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