Evidence for Metallicity-Dependant Spin Evolution in the Kepler field

TL;DR

This study finds that metallicity significantly influences stellar rotation rates in the Kepler field, with higher metallicity stars generally rotating more slowly, supported by observational data and theoretical models.

Contribution

It demonstrates a clear correlation between metallicity and stellar rotation, integrating observational data with models to explain the rotation period distribution in the Kepler field.

Findings

Higher metallicity stars tend to rotate more slowly.

Theoretical models predict a metallicity-rotation correlation matching observations.

Metallicity is a key parameter in stellar rotational evolution.

Abstract

A curious rotation period distribution in the Color-Magnitude-Period Diagram (CMPD) of the Kepler field was recently revealed, thanks to data from Gaia and Kepler spacecraft. It was found that redder and brighter stars are spinning slower than the rest of the main sequence. On the theoretical side, it was demonstrated that metallicity should affect the rotational evolution of stars as well as their evolution in the Hertzprung-R\"ussel or Color-Magnitude diagram. In this work we combine this dataset with medium and high resolution spectroscopic metallicities and carefully select main sequence single stars in a given mass range. We show that the structure seen in the CMPD also corresponds to a broad correlation between metallicity and rotation, such that stars with higher metallicity rotate on average more slowly than those with low metallicity. We compare this sample to theoretical rotational evolution models that include a range of different metallicities. They predict a correlation between rotation rate and metallicity that is in the same direction and of about the same magnitude as that observed. Therefore metallicity appears to be a key parameter to explain the observed rotation period distributions. We also discuss a few different ways in which metallicity can affect the observed distribution of rotation period, due to observational biases and age distributions, as well as the effect on stellar wind torques.