Issue |
EAS Publications Series
Volume 60, 2013
Betelgeuse Workshop 2012 The Physics of Red Supergiants: Recent Advances and Open Questions
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Page(s) | 131 - 136 | |
Section | Atmospheric Structure and Dynamics | |
DOI | https://doi.org/10.1051/eas/1360014 | |
Published online | 23 May 2013 |
P. Kervella, T. Le Bertre and G. Perrin (eds) EAS Publications Series, 60 (2013) 131-136
Turbulent Structure in the Upper Chromospheres of Cool Supergiants
DAO, Victoria, Canada
Although the contribution of a chromosphere to the total flux may be small, it plays a vital role as the interface between the star and interstellar space, as it is where the stellar wind originates. The very outermost layers of a star are expected to be turbulent. Images of the solar chromosphere and corona reveal both small-scale inhomogeneities (prominences and spaces) and large-scale variability (polar plumes near sunspot minima, streamers near sunspot maxima), and something similar but more exaggerated can be expected in cool supergiants. Samplings of the high chromosphere in late-K supergiants show extreme variability in both density and velocity, and can be thought of as analogues of the solar case. Series of chromospheric-eclipse spectra of the Ca ii K line in 31 Cyg, 32 Cyg and ζAur demonstrate (a) the presence in the high chromosphere of discrete, rapidly-moving clumps of gas, (b) that structures are not stable or symmetrical, either from eclipse to eclipse or from ingress to egress in the same eclipse, (c) plenty of empty space, and (d) huge differences between one late-K supergiant and another. What information can this evidence offer as regards the outer structure and wind of Betelgeuse?
© EAS, EDP Sciences 2013