Previous measurements of stellar properties for K2 stars in the Ecliptic Plane Input Catalog \citep [ EPIC ; ] [ ] Huber2016 largely relied on photometry and proper motion measurements , with some added information from available spectra and parallaxes .
Combining Gaia DR2 distances with spectroscopic measurements of effective temperatures , surface gravities , and metallicities from the Large Sky Area Multi-Object Fibre Spectroscopic Telescope ( LAMOST ) DR5 , we computed updated stellar radii and masses for 26,838 K2 stars .
For 195,250 targets without a LAMOST spectrum , we derived stellar parameters using random forest regression on photometric colors trained on the LAMOST sample .
In total , we measured spectral types , effective temperatures , surface gravities , metallicities , radii , and masses for 222,088 A , F , G , K , and M-type K2 stars .
With these new stellar radii , we performed a simple reanalysis of 299 confirmed and 517 candidate K2 planet radii from Campaigns 1–13 , elucidating a distinct planet radius valley around 1.9 R _ { \oplus } , a feature thus far only conclusively identified with Kepler planets , and tentatively identified with K2 planets .
These updated stellar parameters are a crucial step in the process toward computing K2 planet occurrence rates .