An explanation of the super-metal-rich phenomenon in field K giants as an effect of a difference in surface temperature.
Abstract
The super-metal-rich (SMR) phenomenon in K giants is investigated by comparing the atomic line strengths on the weak and flat parts of the curve of growth in three field K giants of the same type and (R - I) color: kappa Oph, iota Dra (both relatively normal), and mu Leo (SMR). The relative metal abundance is determined directly from the ratios of weak lines of selected elements, and it is shown that every element for which unblended lines weaker than 100 mA are present has the same abundance to 10% in all three stars. This demonstrates that a uniform metal-abundance enhancement cannot be the cause of the strong-lined phenomenon in such stars. An alternative explanation is developed in which the strong-lined giants are cooled, relative to normal giants, in atmospheric layers just above the continuum-forming region. Such cooling is shown to increase the strengths of certain classes of lines, but not to affect (R - I) color or spectral type. It is found that cooling is definitely present in mu Leo and that cyanogen is overabundant due to an increase in nitrogen abundance; it is suggested that the cyanogen overabundance is responsible for the atmospheric cooling. Application of these results to stellar populations of external galaxies is briefly discussed.
- Publication:
-
The Astrophysical Journal Supplement Series
- Pub Date:
- January 1976
- DOI:
- 10.1086/190357
- Bibcode:
- 1976ApJS...30...61P
- Keywords:
-
- Giant Stars;
- K Stars;
- Late Stars;
- Metallic Stars;
- Stellar Spectra;
- Stellar Temperature;
- Abundance;
- Galactic Structure;
- Star Distribution;
- Stellar Atmospheres;
- Astrophysics