Initial data release of the Kepler-INT Survey
  This paper describes the first data release of the Kepler-INT Survey (KIS),
that covers a 116 deg2 region of the Cygnus and Lyra constellations. The Kepler
field is the target of the most intensive search for transiting planets to
date. Despite the fact that the Kepler mission provides superior time series
photometry, with an enormous impact on all areas of stellar variability, its
field lacks optical photometry complete to the confusion limit of the Kepler
instrument necessary for selecting various classes of targets. For this reason,
we follow the observing strategy and data reduction method used in the IPHAS
and UVEX galactic plane surveys in order to produce a deep optical survey of
the Kepler field. This initial release concerns data taken between May and
August 2011, using the Isaac Newton Telescope on the island of La Palma. Four
broadband filters were used, U, g, r, i, as well as one narrowband one, Halpha,
reaching down to a 10-sigma limit of around 20th mag in the Vega system.
Observations covering around 50 deg2, thus about half of the field, passed our
quality control thresholds and constitute this first data release. We derive a
global photometric calibration by placing the KIS magnitudes as close as
possible to the Kepler Input Catalog (KIC) photometry. The initial data release
catalogue containing around 6 million sources from all the good photometric
fields is available for download from the KIS webpage, as well as via MAST.
