[4] The first public release of a list of KOIs was on 15 June 2010 and contained 306 stars suspected of hosting exoplanets, based on observations taken between 2 May 2009 and 16 September 2009.
[5] On February 1, 2011, a second release of observations made during the same time frame contained improved date reduction and listed 1235 transit signals around 997 stars.
[6] Stars observed by Kepler that are considered candidates for transit events are given the designation "KOI" followed by an integer number.
[6] Once a transit candidate is verified to be a planet (see below), the star is designated "Kepler" followed by a hyphen and an integer number.
These quantities are derived from photometric observations taken prior to Kepler's launch at the 1.2 m reflector at Fred Lawrence Whipple Observatory.
On the other hand, statistical fluctuations in the data are expected to contribute less than one false positive event in the entire set of 150,000 stars being observed by Kepler.
[6] In addition to false positives, a transit signal can be due to a planet that is substantially larger than what is estimated by Kepler.
[6] Additional observations are necessary in order to confirm that a KOI actually has the planet that has been predicted, instead of being a false positive or misidentification.
The most well-established confirmation method is to obtain radial velocity measurements of the planet acting on the KOI.
Six transit signals released in the February 1, 2011 data are indicative of planets that are both "Earth-like" (less than 2 Earth radii in size) and located within the habitable zone of the host star.
[18] A 2011 list of Kepler candidates also lists KOI-959 as hosting a transiting white dwarf,[6] but this is actually a transiting brown dwarf known as LHS 6343 C.[19] KOI-54 is believed to be a binary system containing two A-class stars in highly eccentric orbits with a semi-major axis of 0.4 AU.
In addition, these tidal forces induce resonant pulsations in one (or both) of the stars, making it only the 4th known stellar system to exhibit such behavior.