Query : 2002A&A...383..972M

2002A&A...383..972M - Astronomy and Astrophysics, volume 383, 972-986 (2002/3-1)

The time variation in infrared water-vapour bands in Mira variables.


Abstract (from CDS):

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 2.5-4.0µm region. All four stars show H2O bands in absorption around minimum in the visual light curve. At maximum, H2O emission features appear in the ∼3.5-4.0µm region, while the features at shorter wavelengths remain in absorption. These H2O bands in the 2.5-4.0µm 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 2000K and a ``cool'' layer with an excitation temperature of 1000-1400K. The column densities of the ``hot'' layer are 6x1020-3x1022cm–2, and exceed 3x1021cm–2 when the features are observed in emission. The radii of the ``hot'' layer (Rhot) are ∼1R* at visual minimum and 2R* at maximum, where R* is a radius of background source of the model, in practical, the radius of a 3000K black body. The ``cool'' layer has the column density (Ncool) of 7x1020-5x1022cm–2, and is located at 2.5-4.0R*. Ncool depends on the object rather than the variability phase. The time variation of Rhot/R* from 1 to 2 is attributed to the actual variation in the radius of the H2O layer, since the variation in Rhot far exceeds the variation in the ``continuum'' stellar radius. 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.

Abstract Copyright:

Journal keyword(s): stars: AGB and post-AGB - stars: atmospheres - stars: variables: general - infrared: stars - stars: late-type

Simbad objects: 7

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Number of rows : 7
N Identifier Otype ICRS (J2000)
ICRS (J2000)
Mag U Mag B Mag V Mag R Mag I Sp type #ref
1850 - 2022
1 * omi Cet Mi* 02 19 20.79210 -02 58 39.4956   7.63 6.53 5.03   M5-9IIIe+DA 1486 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 891 1
3 V* R Aql OH* 19 06 22.2510922392 +08 13 48.012661776 8.06 7.69 6.09     M6.5-9e 548 0
4 V* Z Cyg Mi* 20 01 27.5075704056 +50 02 32.634937212   11.12 7.10     M5.5-6.5e 158 0
5 V* T Cep Mi* 21 09 31.7834766408 +68 29 27.231070884 9.15 8.82 7.33     M6-9e 373 0
6 V* Z Cas Mi* 23 44 31.6014388200 +56 34 52.983926724     12.91     M7-e 76 1
7 V* R Cas Mi* 23 58 24.8682785040 +51 23 19.713029388 6.71 6.63 4.80     M6.5-9e 690 0

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