EDP Sciences
Free Access
Volume 447, Number 1, February III 2006
Page(s) 311 - 324
Section Stellar atmospheres
DOI https://doi.org/10.1051/0004-6361:20053359
Published online 27 January 2006
A&A 447, 311-324 (2006)
DOI: 10.1051/0004-6361:20053359

Amorphous alumina in the extended atmosphere of $\alpha$ Orionis

T. Verhoelst1, 2, L. Decin1, R. Van Malderen1, S. Hony1, J. Cami3, K. Eriksson4, G. Perrin2, P. Deroo1, B. Vandenbussche1 and L. B. F. M. Waters1, 5

1  Instituut voor Sterrenkunde, KU Leuven, Celestijnenlaan 200B, 3001 Leuven, Belgium
    e-mail: Tijl.Verhoelst@ster.kuleuven.ac.be
2  Observatoire de Paris-Meudon, LESIA, 5 place Jules Janssen, 92195 Meudon, France
3  NASA Ames Research Center, MS 245-6, Moffett Field, CA 94035, USA
4  Institute for Astronomy and Space Physics, Box 515, 75120 Uppsala, Sweden
5  Astronomical Institute "Anton Pannekoek", University of Amsterdam, Kruislaan 403, 1098 SJ Amsterdam, The Netherlands

(Received 3 May 2005 / Accepted 10 October 2005)

In this paper we study the extended atmosphere of the late-type supergiant $\alpha$ Orionis. Infrared spectroscopy of red supergiants reveals strong molecular bands, some of which do not originate in the photosphere but in a cooler layer of molecular material above it. Lately, these layers have been spatially resolved by near and mid-IR interferometry. In this paper, we try to reconcile the IR interferometric and ISO-SWS spectroscopic results on $\alpha$ Orionis with a thorough modelling of the photosphere, molecular layer(s) and dust shell. From the ISO and near-IR interferometric observations, we find that $\alpha$ Orionis has only a very low density water layer close above the photosphere. However, mid-IR interferometric observations and a narrow-slit N-band spectrum suggest much larger extra-photospheric opacity close to the photosphere at those wavelengths, even when taking into account the detached dust shell. We argue that this cannot be due to the water layer, and that another source of mid-IR opacity must be present. We show that this opacity source is probably neither molecular nor chromospheric. Rather, we present amorphous alumina (Al2O3) as the best candidate and discuss this hypothesis in the framework of dust-condensation scenarios.

Key words: techniques: high angular resolution -- techniques: spectroscopic -- stars: individual: $\alpha$ Orionis -- stars: atmospheres -- stars: supergiants -- stars: circumstellar matter

SIMBAD Objects

© ESO 2006

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.