Visions for Infrared Astronomy location:Paris, France date:March 20-22, 2006
We present a study of the extended atmosphere of the late-type supergiant Betelgeuse. From near-IR observations, we find that Betelgeuse has only a very low density water layer just above the photosphere. However, mid-IR observations suggest a much larger opacity source close to the photosphere, which can not be due to the water layer. We show that amorphous alumina grains are the most likely source of this opacity and discuss this hypothesis in the context of dust-condensation scenarios.