  Data from the Kepler space telescope have led to the discovery of thousands
of planet candidates. Most of these candidates are likely to be real
exoplanets, but a significant number of false positives still contaminate the
sample, especially in candidate lists from the K2 mission. Identifying and
rejecting the false positives lurking in the planet candidates sample is
important for prioritizing follow-up resources and measuring the most accurate
population statistics. Here, we identify false positives in the K2 planet
candidate sample using a technique called "ephemeris matching," in which we
compare the period and transit time of different signals. When signals from
different stars show the same period and time of transit, we can conclude that
at least one of the two signals is contamination. We identify 43 false
positives among published K2 planet candidates (nearly 2% of the complete
list), one of which (K2-256 b) was previously validated as genuine exoplanet.
This work increases the reliability of the K2 planet sample and helps boost
confidence in the surviving planet candidates.
