Comparing Kepler’s 29 star clusters

[christinahedges]

Star clusters provide the opportunity to study stars that can be assumed to have the same age, composition, and formation history. We can use them as laboratories for understanding stellar evolution and planet formation under controlled conditions. Kepler and K2 have observed two star forming associations (<10 Myr old), 17 open clusters (1 Myr to 8 Gyr), and nine globular clusters ('11 Gyr). Of these, only 7 have been analyzed by 5 or more scientific publications to date (see Cody et al. 2018, for an overview). Notable clusters which appear to have been under-utilized are the young Lagoon nebula region (M8), the intermediate-age M35 cluster, and the young Taurus star forming region.

Several methods exist to analyze the properties of stellar clusters, including asteroseismic analyses (e.g. Stello et al. 2016), the identification of eclipsing binary systems to derive benchmark radii and masses (e.g. Gillen et al. 2017; Kraus et al. 2017; Kepler’s discoveries will continue 11 Sandquist et al. 2018; Torres et al. 2018), and rotation rate studies as a function of age and mass.

Recent analyses of young clusters by K2 have already revealed that late M-type dwarf stars shed angular momentum after star formation in a way that is significantly slower than their earlier-type counterparts (e.g. Douglas et al. 2017; Rebull et al. 2018). At this time it remains unclear what explains this difference in stellar evolution.

[joshuawallace]

I've used K2 data of the globular cluster M4 (the closest GC to Earth) to discover a new type of variable star: horizontal branch stars just outside the instability strip that have RR1 Lyrae-like variability but at ~1 mmag amplitudes instead of ~300 mmag or so for actual RR1 Lyrae. Just goes to show what kind of discoveries may still be waiting in the data.

I would love to hear any ideas, feedback, or additional vetting anyone has on these new variables.

Paper can be found here: http://iopscience.iop.org/article/10.3847/2041-8213/aaf8ac/meta