# The K2 Galactic Caps Project -- Going Beyond the \textit{Kepler} Field and Ageing the Galactic Disc

## TL;DR

This study uses asteroseismic data from K2 fields to analyze the age and chemical distribution of red giant stars, revealing bimodal age populations and vertical population transitions in the Galactic disc.

## Contribution

It extends the analysis of stellar populations beyond the Kepler field using K2 data, providing new insights into the age and chemical structure of the Galactic disc.

## Key findings

- Identification of two main age peaks at ~5 and ~12 Gyr.
- Detection of an [$eta$/Fe] dependence on the red clump position.
- Observation of a transition from young to old populations with increasing vertical distance.

## Abstract

Analyses of data from spectroscopic and astrometric surveys have led to conflicting results concerning the vertical characteristics of the Milky Way. Ages are often used to provide clarity, but typical uncertainties of $>$ 40\,\% restrict the validity of the inferences made. Using the \textit{Kepler} APOKASC sample for context, we explore the global population trends of two K2 campaign fields (3 and 6), which extend further vertically out of the Galactic plane than APOKASC. We analyse the properties of red giant stars utilising three asteroseismic data analysis methods to cross-check and validate detections. The Bayesian inference tool PARAM is used to determine the stellar masses, radii and ages. Evidence of a pronounced red giant branch bump and an [$\alpha$/Fe] dependence on the position of the red clump is observed from the radii distribution of the K2 fields. Two peaks in the age distribution centred at $\sim$5 and and $\sim$12 Gyr are found using a sample with $\sigma_{\rm{age}}$ $<$ 35\,\%. In a comparison with \textit{Kepler}, we find the older peak to be more prominent for K2. This age bimodality is also observed based on a chemical selection of low- ($\leq$ 0.1) and high- ($>$ 0.1) [$\alpha$/Fe] stars. As a function of vertical distance from the Galactic mid-plane ($|Z|$), the age distribution shows a transition from a young to old stellar population with increasing $|Z|$ for the K2 fields. Further coverage of campaign targets with high resolution spectroscopy is required to increase the yield of precise ages achievable with asteroseismology.