NLTE model atmospheres for M dwarfs and giants
Abstract
The atmospheres of M stars are dominated by a small number of very strong molecular compounds (H$_2$O, TiO, H$_2$, CO, VO). Most of the hydrogen is locked in molecular H$_2$, most of the carbon in CO; and H$_2$O, TiO and VO opacities define a pseudo-continuum covering the entire flux distribution of these stars. The optical ``continuum'' is due to TiO vibrational bands which are often used as temperature indicators for these stars. These may be the depth of the bands relative to the troughs in between them; or the depth of the VO bands; or of the atomic lines relative to the local ``continuum''; or even the strength of the infrared water bands; all of these depend on the strength of the TiO bands and the amount of flux-redistribution to longer wavelengths exerted by them. Departures from LTE of the Ti I atom, and thus the concentration of the important TiO molecule, could, therefore, have severe and measurable consequences on the atmospheric structure and spectra of these stars. In this paper we discuss NLTE effects of Ti I in fully self-consistent models for a few representative M/Brown dwarf and M giant model atmospheres and spectra.
- Publication:
-
Stellar Surface Structure
- Pub Date:
- 1996
- DOI:
- 10.48550/arXiv.astro-ph/9601155
- arXiv:
- arXiv:astro-ph/9601155
- Bibcode:
- 1996IAUS..176..539H
- Keywords:
-
- Astrophysics
- E-Print:
- 27 pages, latex, crckapb style, figures 1-3 not included, complete text with figures available via http://brian.la.asu.edu/ or at ftp://brian.la.asu.edu/NLTE-dwarfs+giants.tar.gz, to appear in Proc. of IAU Symp 176 'Stellar Surface Structure'