Publications
of the
MPIfR Optical & Infrared Interferometry Group

Ohnaka, K.

Warm water vapor envelope in the supergiants α Ori and α Her and its effects on the apparent size from the near-infrared to the mid-infrared

Cool Stars, Stellar Systems and the Sun
Annual Scientific Meeting of the Astronomische Gesellschaft, July 5-9, 2004, Hamburg, Germany

ESA Special Publications Series (ESA-SP), v.560, p.849-852 (2005)

Abstract

We present a possible interpretation for the increase of the angular diameter of the supergiants α Ori and α Her from the K band to the 11 &microm region revealed by the recent interferometric observations using narrow bandpasses where no salient spectral feature is present (Werner et al. 2003a). Our simple model for the warm water vapor envelope can reproduce the angular diameters observed with Infrared Spatial Interferometer as well as the high-resoluion TEXES spectra obtained in the 11 &microm region. The warm water vapor layers are optically thick in the lines, and therefore, strong absorption due to H₂0 can be expected from such a dense water vapor envelope. However, the absorption lines are filled in by emission from the extended part of the envelope, and this results in the high-resolution 11 &microm spectra which exhibit only weak, fine spectral features, masking the spectroscopic fingerprints of the dense, warm water vapor envelope. On the other hand, the presence of the warm water vapor envelope manifests itself as the larger angular diameters in the 11 &microm region as compared to those measured in the near-infrared.

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