The height of convective plumes in the red supergiant $\mu$ Cep

Abstract

Aims. We seek to understand convection in red supergiants and the mechanisms that trigger the mass loss from cool evolved stars. Methods. Linear spectropolarimetry of the atomic lines of the spectrum of $\mu$ Cep reveals information well outside the wavelength range expected from previous models. This is interpreted as structures in expansion that are visible in the front hemisphere and sometimes also in the back hemisphere. We model the plasma distribution together with its associated velocities through an inversion algorithm to fit the observed linear polarization. Results. We find that supposing the existence of plasma beyond the limb rising high enough to be visible above it can explain the observed linear polarization signatures as well as their evolution in time. From this we are able to infer the geometric heights of the convective plumes and establish that this hot plasma rises to at least 1.1 R*. Conclusions. $\mu$ Cep appears to be in an active phase in which plasma rises often above 1.1 R* . We generalize this result to all red supergiants in a similarly evolved stage, which at certain epochs may easily send plasma to greater heights, as $\mu$ Cep appears to be doing at present. Plasma rising to such heights can easily escape the stellar gravity.

Accepted for publication in A&A

References in corpus (4)

• Probing the mass-loss history of AGB and red supergiant stars from CO rotational line profiles I. Theoretical model -- Mass-loss history unravelled in VY CMa
• A dusty veil shading Betelgeuse during its Great Dimming
• NOEMA maps the CO $J=2-1$ environment of the red supergiant $\mu$ Cep
• Three-dimensional imaging of convective cells in the photosphere of Betelgeuse

Cited by in corpus (4)

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• Stellar evolution through the Red Supergiant phase
• Making sense of the spectral line profiles of Betelgeuse and other Red SuperGiants
• The variability of Betelgeuse explained by surface convection