  High-resolution ground-based optical speckle and near-infrared adaptive
optics images are taken to search for stars in close angular proximity to host
stars of candidate planets identified by the NASA Kepler Mission. Neighboring
stars are a potential source of false positive signals. These stars also blend
into Kepler light curves, affecting estimated planet properties, and are
important for an understanding of planets in multiple star systems. Deep images
with high angular resolution help to validate candidate planets by excluding
potential background eclipsing binaries as the source of the transit signals. A
study of 18 Kepler Object of Interest stars hosting a total of 28 candidate and
validated planets is presented. Validation levels are determined for 18 planets
against the likelihood of a false positive from a background eclipsing binary.
Most of these are validated at the 99% level or higher, including 5
newly-validated planets in two systems: Kepler-430 and Kepler-431. The stellar
properties of the candidate host stars are determined by supplementing existing
literature values with new spectroscopic characterizations. Close neighbors of
7 of these stars are examined using multi-wavelength photometry to determine
their nature and influence on the candidate planet properties. Most of the
close neighbors appear to be gravitationally-bound secondaries, while a few are
best explained as closely co-aligned field stars. Revised planet properties are
derived for each candidate and validated planet, including cases where the
close neighbors are the potential host stars.
