Comparison of the temperature structure of the extended atmospheres of the early-M supergiants Antares and Betelgeuse. The filled red circles are the measurements summarized in this work for Antares, and the filled blue diamonds are the measurements for Betelgeuse (Lim et al. 1998; O’Gorman et al. 2017). The error bars in the gas temperature include the uncertainty in absolute flux density scale. The overlapping filled black circles at R_⋆ = 1 represent the photospheric effective temperatures of Antares and Betelgeuse. The solid black line is the temperature profile of the semiempirical model for the extended atmosphere of Betelgeuse discussed in Sect. 4.2 and Appendix B.