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26 April 2024 |
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The time variation in infrared water-vapour bands in Mira variables | | M. Matsuura
; I. Yamamura
; J. Cami
; T. Onaka H. Murakami
; | | Date: |
7 Dec 2001 | | Subject: | astro-ph | | Affiliation: | ISAS, Japan, University of Tokyo, UMIST, UK), I. Yamamura (ISAS, Japan), J. Cami (University of Amsterdam, SRON-Groningen, the Netherlands), T. Onaka (University of Tokyo) H. Murakami (ISAS, Japan | | Abstract: | The time variation in the water-vapour bands in oxygen-rich Mira variables has been investigated using multi-epoch ISO/SWS spectra of four Mira variables in the 2.5-4.0 micron region. All four stars show H2O bands in absorption around minimum in the visual light curve. At maximum, H2O emission features appear in the ~3.5-4.0 micronm region, while the features at shorter wavelengths remain in absorption. These H2O bands in the 2.5-4.0 micron region originate from the extended atmosphere. The analysis has been carried out with a disk shape, slab geometry model. The observed H2O bands are reproduced by two layers; a `hot’ layer with an excitation temperature of 2000 K and a `cool’ layer with an excitation temperature of 1000-1400 K. The radii of the `hot’ layer (R_hot) are ~1 R_* at visual minimum and 2 R_* at maximum, where R_* is a radius of background source of the model. The time variation of R_hot/R_* from 1 to 2 is attributed to the actual variation in the radius of the H2O layer. A high H2O density shell occurs near the surface of the star around minimum, and moves out with the stellar pulsation. This shell gradually fades away after maximum, and a new high H2O density shell is formed in the inner region again at the next minimum. Due to large optical depth of H2O, the near-infrared variability is dominated by the H2O layer, and the L’-band flux correlates with the area of the H2O shell. The infrared molecular bands trace the structure of the extended atmosphere and impose appreciable effects on near-infrared light curve of Mira variables. | | Source: | arXiv, astro-ph/0201084 | | Services: | Forum | Review | PDF | Favorites | |
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