Detection of Water Vapor in the Photosphere of Arcturus

Abstract

We report detections of pure rotation lines of OH and H2O in the K1.5 III red-giant star Arcturus (alpha Bootis) using high-resolution, infrared spectra covering the regions 806-822 cm-1 (12.2-12.4 um) and 884-923 cm-1 (10.8-11.3 um). 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 H2O lines satisfactorily after lowering the temperature structure of the very outer parts of the photosphere (log tau_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 outer-most parts of the photosphere and the assumed break-down of the assumptions made in classical model-atmosphere codes are discussed.

arXiv commentTo appear in ApJ. See also http://www.astro.uu.se/~ryde/ART/

References in corpus (6)

• TEXES: A Sensitive High-Resolution Grating Spectrograph for the Mid-Infrared
• Water in Emission in the ISO Spectrum of the Early M Supergiant Star mu Cephei
• Water in K and M giant stars unveiled by ISO
• Spectral analysis of water vapour in cool stars
• Convective Wavelength Shifts in the Spectra of Late-Type Stars
• The 3 micron spectrum of R Doradus observed with the ISO-SWS

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