Computer Science – Numerical Analysis
Scientific paper
Apr 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...284..179j&link_type=abstract
Astronomy and Astrophysics (ISSN 0004-6361), vol. 284, no. 1, p. 179-186
Computer Science
Numerical Analysis
82
Atmospheric Models, Excitation, Stellar Atmospheres, Stellar Models, Titanium Oxides, Giant Stars, M Stars, Numerical Analysis, Stellar Spectrophotometry, Stellar Structure
Scientific paper
We have computed the frequencies, the gf values, and the excitation energy of the lower level for 12 million lines from 5 isotopes of titanium oxide. The data are collected onto a tape which is offered to the community. By treating the lines in the opacity sampling (OS) approximation, we have computed model atmospheres for M type giant stars. We analyze the effects, on the structure of these models, of TiO in general as well as of various parts of the computed TiO opacity. Our computation is an extension of, and based on, the thesis work by Collins (1975a). The extension includes evaluation of the opacity due to all relevant isotopes of TiO and due to the epsilon system. Line frequencies and excitation energies of lines in the epsilon-system as well as the f-value were computed based on recently determined values from laboratory experiments. We find that the epsilon-system contributes a significant fraction of the heating caused by TiO in stellar atmospheres, whereas a detailed treatment of all the isotopic systems were found to be of less importance for the stellar structure. On the other hand, the isotopes affect the synthetic spectra, and their main importance is for such calculations. We find that TiO heats the surface layers of a Teff = 3500 K model by approximately equals 500 K, a 3100 K model with approximately equals 300 K, and a 2800 K model with approximately equals 150 K. The amount of heating is relatively insensitive to the gravity. The decreasing effect of TiO for the coolest stars reflects the increase of the partial pressure of water vapor relative to TiO.
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