2001A&A...376L...1T

Based on the spectra obtained with Infrared Space Observatory, ISO, we detected the 6.3µm bands of water in the late K giant Aldebaran (α Tau) and several early M giant stars (between M0 and M3.5), which have been deemed to be too warm for tri-atomic H₂O molecule to reside in their photospheres. The water column densities range (0.2-2)x10¹⁸molecules/cm² in our sample of K and M giant stars and the excitation temperatures are 1500K or higher. Thus, the water bands are not originating in cool stellar winds either. The presence of water in the K and early M giant stars was quite unexpected from the traditional picture of the atmosphere of the red giant star consisting of the photosphere, hot chromosphere, and cool wind. We confirm that a rather warm molecule forming region should exist as a new component of the atmosphere of red giant stars and that this should be a general phenomenon in late-type stars.