Observational analysis of 21 giant stars shows Fe I+Fe II blend emission proportional to Ca II K with matching Teff power-law exponent and a slope break in the flux ratio at log g ≈ 2.5.
The [Fe/H] Dependence on the Ca {\sc ii}-$M_V$ Relationship
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abstract
We examined the Wilson-Bappu effect, a relationship between the absolute magnitude of the star, $M_V$, and the logarithm of the Ca {\sc ii} emission width, $W_0$, over the largest $M_V$ range to date, +13 to -5, covering M-dwarfs to type Ia supergiants. We used an extensive literature, the latest Hipparcos reduction, data from two globular clusters, and new observations from Apache Point Observatory to compile a sample that allowed us to study the effect of [Fe/H] on the Wilson-Bappu relationship. Our results include reporting the deviations from linearity and demonstrating that the Wilson-Bappu relationship is insensitive to metallicity.
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On the stellar parameter dependence of the combined Fe I and Fe II chromospheric emission-line in the wings of the Ca II K line
Observational analysis of 21 giant stars shows Fe I+Fe II blend emission proportional to Ca II K with matching Teff power-law exponent and a slope break in the flux ratio at log g ≈ 2.5.