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The mechanisms responsible for heating the extended atmospheres of early-Mspectral-type supergiants are poorly understood. So too is the subsequent rolethese mechanisms play in driving the large mass-loss rates of these stars. Herewe present ALMA long (i.e., $\sim$16 km) baseline 338 GHz (0.89 mm) continuumobservations of the free-free emission in the extended atmosphere of the M2spectral-type supergiant Betelgeuse. The spatial resolution of 14 masexquisitely resolves the atmosphere, revealing it to have a mean temperature of2760 K at $\sim$1.3 R$_{\star}$, which is below both the photospheric effectivetemperature ($T_{\textrm{eff}} = 3690$ K) and the temperatures at $\sim$$2$R$_{\star}$. This is unambiguous proof for the existence of an inversion ofthe mean temperature in the atmosphere of a red supergiant. The emission isclearly not spherically symmetric with two notable deviations from a uniformdisk detected in both the images and visibilities. The most prominent asymmetryis located in the north-east quadrant of the disk and is spatially resolvedshowing it to be highly elongated with an axis-ratio of 2.4 and occupying$\sim$$5\%$ of the disk projected area. Its temperature is approximately 1000 Kabove the measured mean temperature at 1.3 R$_{\star}$. The other mainasymmetry is located on the disk limb almost due east of the disk center andoccupies $\sim$$3\%$ of the disk projected area. Both emission asymmetries areclear evidence for localized heating taking place in the atmosphere ofBetelgeuse. We suggest that the detected localized heating is related tomagnetic activity generated by large-scale photospheric convection.

The inhomogeneous sub-millimeter atmosphere of Betelgeuse