The [Fe/H] Dependence on the Ca {\sc ii}-$M_V$ Relationship

TL;DR

This study investigates the Wilson-Bappu effect across a wide range of stellar types and finds that the relationship between Ca II emission width and absolute magnitude is unaffected by metallicity variations.

Contribution

It provides the largest analysis to date of the Wilson-Bappu effect, incorporating extensive data and demonstrating its insensitivity to [Fe/H] metallicity.

Findings

Wilson-Bappu relationship is linear over a broad magnitude range.

The effect is insensitive to metallicity variations.

Deviations from linearity are reported.

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.