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Issue A&A Volume 376, Number 1, September II 2001 Page(s) L1 - L4 Section Letters DOI 10.1051/0004-6361:20011012

A&A 376, L1-L4 (2001)
DOI: 10.1051/0004-6361:20011012

Water in K and M giant stars unveiled by ISO

T. Tsuji

Institute of Astronomy, The University of Tokyo, Mitaka, Tokyo 181-0015, Japan

(Received 29 May 2001 / Accepted 11 July 2001 )

Abstract
Based on the spectra obtained with Infrared Space Observatory, ISO, we detected the 6.3 m bands of water in the late K giant Aldebaran ( 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 molecules cm^-2 in our sample of K and M giant stars and the excitation temperatures are 1500 K 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.

Key words: infrared: stars -- molecular processes -- stars: atmospheres -- stars: chromospheres -- stars: individual: Tau, And, Cet, Peg, Cru -- stars: late-type

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© ESO 2001

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