Previous abstract Next abstract

Session 103 - Cool Stars.
Display session, Thursday, January 18
North Banquet Hall, Convention Center

[103.11] M Stars Model Atmospheres: Spectra and Colors

F. Allard, T. Lawlor, D. R. Alexander (Wichita State U.), P. H. Hauschildt (Arizona State U.)

In this paper, we present new pressure-dependent line-by-line LTE model atmospheres for red giants in spherical geometry, computed using the multi-purpose atmospheric code Phoenix, which constitutes an extension of the existing cool dwarf grids of Allard amp; Hauschildt (1995) to the abundance and gravity regimes of cool M-S-C type giants. Departures from LTE in the Ti I lines is investigated for some selected models across the grid, but only modest NLTE effects are found in the abundance of the important absorber TiO. The combined dwarf and giant grid is compared to observations in the 8-colors Wing photometric sample of cool dwarfs and M-S-C giants of the Large Magellanic Clouds.

The Pheonix giant grid is also compared to results obtained with our version of the Atlas9 code. In particular, we investigate the failure of Atlas-family models to reproduce the Violet (2700 to 4000 Åenergy distribution of cool giants. Short amp; Lester (1994) suggested this may be due to a lack of molecular photo-dissociation opacities of hydrides. We find that Phoenix models computed with opacities similar to our Atlas9 opacities do not show this Violet discrepancy. We explore remaining opacity differences as well as differences in the treatment of radiative transfer.

Model atmospheres, synthetic spectra and colors presented here will be made available upon request. This research is partially supported by a grant AST-9217946 from the National Science Foundation.

Program listing for Thursday