Analysis of normal and strong - lined K - type dwarf and giant stars

Citation

Oinas, Valdar (1972) Analysis of normal and strong - lined K - type dwarf and giant stars. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/HHGN-ZB70. https://resolver.caltech.edu/CaltechETD:etd-08212008-100608

Abstract

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In this work a detailed analysis is carried out for twenty-six normal and super-metal-rich (SMR) K dwarfs and giants in the solar neighborhood. The observational material consists of line measurements on tracings of high dispersion spectra along with photoelectric scans covering a wide range of wavelengths. The program Atlas was employed to construct the model atmospheres; the temperature fit was provided by a matching of the predicted continua to the de-blanketed scans. H[...] wing profiles were also used to obtain information on the temperatures. The major conclusions that were reached are the following:

1) A gravity defect sets in at about spectral type K2 in both dwarfs and giants; its nature is such that progressively lower gravities are required in order to obtain equal ion and neutral abundances as one goes to cooler stars. In the coolest stars the spectroscopic gravities imply masses lower than 0.1M[...]. It is suggested that the effect may be caused by a new opacity source that is acting to steepen the spectral gradient in the visual and near-infrared, thereby falsifying the temperatures. The dependence of the unknown absorber on the temperature and gravity. are discussed and a rough formula describing this dependence is given. It is shown that the new opacity also explains various discrepancies noted by other observers.

2) The SMR stars are generally overabundant by about 0.2 - 0.3 dex relative to the normal-abundance comparison stars of the same temperature. An overabundance of sodium by about 0.5 dex is found for all the SMR stars, with the exception of the dwarf 54 Psc, which is found to have essentially normal metal abundances. [...]UMi, the coolest giant in the program, is also the most super-metal-rich, with a general overabundance of about 0.4 dex and a sodium enhancement of 0.8 dex. The iron overabundance is rather marginal in most of the giants ([...]).

3) No correlation is found between metal abundance and turbulence. In particular, the SMR stars in this program are not found to possess high microturbulent velocities. The U-B deficiencies can be explained by the effects of a slight metal enhancement on the colors (Strom et al. 1971) and the line blocking due to the CN violet system.

4) The SMR dwarfs all lie high on the main sequence, in keeping with their derived metal abundances. It is not necessary to invoke substantial variations in helium content to account for their positions.

Thesis Files