Query : 2004A&A...424.1011O

2004A&A...424.1011O - Astronomy and Astrophysics, volume 424, 1011-1024 (2004/9-4)

Warm water vapor envelope in Mira variables and its effects on the apparent size from the near-infrared to the mid-infrared.


Abstract (from CDS):

We present a possible interpretation for the increase of the angular diameter of the Mira variables {omi} Cet, R Leo, and χ Cyg from the K band to the 11µm region revealed by the recent interferometric observations using narrow bandpasses where no salient spectral feature is present (Weiner et al., 2003ApJ...588.1064W and 2003ApJ...589..976W). A simple two-layer model consisting of hot and cool H2O layers for the warm water vapor envelope, whose presence in Mira variables was revealed by previous spectroscopic observations, can reproduce the angular diameters observed with Infrared Spatial Interferometer as well as the high-resolution TEXES spectra obtained in the 11µm region. The warm water vapor layers are optically thick in the lines, and therefore, strong absorption due to H2O 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 11µm spectra which exhibit only weak, fine spectral features, masking the spectroscopic evidences 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 11µm region as compared to those measured in the near-infrared. Furthermore, comparison of the visibilities predicted in the near-infrared (1.5-3.8µm) with observational results available in the literature demonstrates that our two-layer model for the warm water vapor envelope can also reproduce the observed near-infrared visibilities and angular diameters, and suggests that the wavelength dependence of the angular size of Mira variables in the infrared largely reflects the H2O opacity. The radii of the hot H2O layers in the three Mira variables are derived to be 1.5-1.7 R* with temperatures of 1800-2000K and H2O column densities of (1-5)x1021cm–2, while the radii of the cool H2O layers are derived to be 2.2-2.5R* with temperatures of 1200-1400K and H2O column densities of (1-7)x1021cm–2.

Abstract Copyright:

Journal keyword(s): infrared: stars - molecular processes - techniques: interferometric - stars: late-type - stars: AGB and post-AGB - stars: individual: o Cet, R Leo, χ Cyg

Simbad objects: 3

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Number of rows : 3
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2023
1 * omi Cet Mi* 02 19 20.79210 -02 58 39.4956   7.63 6.53 5.03   M5-9IIIe+DA 1497 0
2 V* R Leo Mi* 09 47 33.4839808805 +11 25 43.823283729 9.22 8.94 7.53 3.39 0.12 M7-9e 897 1
3 * chi Cyg S* 19 50 33.9213430345 +32 54 50.575531294 7.02 6.06 4.24 1.81 -0.01 S6-9/1-2e 685 0

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