2002/07/17 by N. Ryde, D. L. Lambert, M. J. Richter +1 · 11 citations
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/343040
published as Astrophys.J. 580 (2002) 447-458 · To appear in ApJ. See also http://www.astro.uu.se/~ryde/ART/
arxiv created 2002/07/17 · openalex publication_date 2002/11/20 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/07/31
We report detections of pure rotation lines of OH and H 2 O in the K1.5 III red giant star Arcturus (α Bootis) using high-resolution, infrared spectra covering the regions 806-822 cm -1 (12.2-12.4 μm) and 884-923 cm -1 (10.8-11.3 μm). Arcturus is the hottest star yet to show water vapor features in its disk-averaged spectrum. We argue that the water vapor lines originate from the photosphere, albeit in the outer layers. We are able to predict the observed strengths of OH and H 2 O lines satisfactorily after lowering the temperature structure of the outermost parts of the photosphere (log τ 500 = -3.8 and beyond) compared to a flux-constant, hydrostatic, standard MARCS model photosphere. Our new model is consistently calculated including chemical equilibrium and radiative transfer from the given temperature structure. Possible reasons for a temperature decrease in the outermost parts of the photosphere and the assumed breakdown of the assumptions made in classical model atmosphere codes are discussed.