The [Fe/H] Dependence on the Ca ii- M_V Relationship

Abstract

We have examined the Wilson-Bappu effect, a relationship between the absolute magnitude of the star, M_V, and the logarithm of the Ca ii emission width, W₀, 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.