Evidence for Metallicity-Dependant Spin Evolution in the Kepler field
  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.
