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Statement on Kepler Timing Error


The barycenteric times currently reported in the TIME columns and the headers of all Kepler data products have an error. The times are reported in the UTC (Coordinated Universal Time) system, not in TDB (Barycentric Dynamical Time) as the headers of the files state. As a result the time stamps are incorrect by approximately one minute: the sum of the number of leap seconds and the offset between Atomic Time (TAI) and Terrestrial Time (TT). Except for the addition of one leap second in Q14, the reported times are internally consistent and this error is only apparent when comparing Kepler times to other observations with timing accuracies better than a couple of minutes. However, all Kepler results that report an absolute barycentric time (e.g., the epoch of a planet transit) have this error, including those reported in published papers and in the Kepler archives (i.e., NExScI, MAST and KSAS).

The following data file types are affected: ffi_cal, ffi_uncert, lpd-targ, spd-targ, llc, slc, and bkg. The Kepler times can be corrected to the TDB system by adding 66.184 seconds to the reported barycentric times for all cadence numbers less than or equal to 57139 in LC (1702663 in SC). For times after this cadence, add 67.184 seconds. This cadence was taken during the first month of Q14 at the time of the most recent leap second, UTC 2012-06-30 23:59:60. This simple additive correction does not account for the relativistic correction between the UTC and TDB systems, which is of order 1.6 ms and significantly less than the 50 ms precision of the Kepler clock.

The Kepler project will correct this error during a future reprocessing effort in mid 2013. Meanwhile, Kepler will continue reporting all epochs and periods in the current time system until the data files at MAST can be uniformly corrected. When the Kepler times have been corrected, users will be alerted via data release notes, this web site, and statements in published papers.