SIMBAD references

We present an update to the EVEREST K2 pipeline that addresses various limitations in the previous version and improves the photometric precision of the light curves. We develop a fast regularization scheme for pixel-level decorrelation (PLD) and adapt the algorithm to include the PLD vectors of other stars to enhance the predictive power of the model and minimize overfitting, particularly for faint stars. We also modify PLD to work for saturated stars and improve its performance on variable stars, although some high-frequency variables may still suffer from overfitting. On average, EVEREST 2.0 light curves have 10-20% higher photometric precision than those in version 1, yielding the highest-precision light curves at all Kp magnitudes of any publicly available K2 catalog. For most K2 campaigns, we recover the original Kepler precision to at least Kp = 14, and to at least Kp = 15 for campaigns 1, 5, 6, and 13. We also detrend most short-cadence targets observed by K2, obtaining even higher photometric precision for these stars. Like all aggressive, flexible models, EVEREST is prone to overfitting, and may cause a decrease in transit depths by ∼10%; we urge users to mask signals of interest using our open-source software, which we show removes this bias. Light curves for campaigns 0-8 and 10-13 are available online in the EVEREST catalog, which will be updated with future campaigns. EVEREST 2.0 is open source and is coded in a framework that can be adapted to other photometric surveys, including Kepler and the upcoming TESS mission.