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Session 96 - Cepheids and Supergiant Variable Stars.
Display session, Thursday, January 16
We probe the atmospheres of Mira variables as observed from 7000 Å\ to 8000 Å\ The spectra are dominated by the TiO \gamma -system and void of any intense hydrogen-series emission lines. \ The TiO features may be produced in a layer somewhat far from the photosphere. \ Haniff et al. (1992, AJ, 103, 1662) present optical aperture synthetic images of Mira's photosphere at 6500 ÅÅand within a TiO bandhead at 7099 Åwith the star phase 0.94. \ They find asymmetry in the images, with the TiO image one and a half times larger than the photospheric images. \ Also, narrowband speckle interferometric measurements taken in the TiO 7120 Å\ bandhead and outside at 7400 Å\ by Labeyrie et al. (1977, ApJ Letters, 218, L75) shows that the diameters of R Leo and Mira are twice as large in the TiO feature than outside of it. \ So, a model atmosphere, based on the spectra observed between 7000 Å\ to 8000 Åprovides parameters such as T_eff and g in an atmospheric layer far from the photosphere.
The primary aim of this paper is to present model atmosphere parameters calculated for synthetic spectra modeling new low resolution spectra (120 Åmm) taken over the spectral range from 7,000 Å\ to 8,000 Å\ of three Mira variables. \ Spectra were taken at two different phases. \ By taking spectra at different phases we can further probe the effects the pulsation mechanism has on the atmosphere parameters. \ For example, Wing (1967, unpublished Ph.D. Thesis, University of California, Berkley)\ found the TiO bands strengthen as the temperature decreases.\ Model atmosphere parameters are compared at the two phases.
The authors gratefully acknowledge support from NSF grant AST-9500756 and an NSF REU Supplement grant.
Program listing for Thursday