Using the Mid-infrared to Measure the Thermal Structure of M Supergiant Winds Where it Matters

The mid-IR lends itself to the study of the low temperatures found in the circumstellar envelopes of M supergiants, e.g., with the Kuiper Airborne Observatory. To make quantitative tests of  mass loss models requires us to probe the dynamics and thermodynamics within the first few stellar radii - where most of the energy is input into the wind. We describe our results of using forbidden Fe II diagnostics observed with the EXES and TEXES R=50,000 spectrographs on NASA-DLR's SOFIA and NASA IRTF, respectively. The spectra suggests that the envelope of Betelgeuse is cooler than expected based on previous multi-wavelength spatially resolved VLA maps. We explore some of the possible interpretations from the "Wiggle Room".