Kepler Object of Interest (KOI) Catalog - Q1-Q12

First delivery date: May 28, 2013
Last delivery date: December 4, 2014
Status: Done

Summary of Q1-Q12 KOI Activity Table
Triage of TCEs to create new KOIs
Vetting of Q1-Q12 KOIs
Stellar Parameters
Planetary Parameters

1. Summary of the Q1-Q12 KOI Activity Table

The Q1-Q12 Kepler light curves were searched for transit-like signatures, otherwise known as Threshold Crossing Events (TCEs). The Q1-Q12 catalog of Kepler Objects of Interest described here are the result of an extensive examination of these events by the group known as TCERT (Threshold Crossing Event Review Team). Those targets that are likely caused by planetary transits or eclipsing binaries are included in the KOI table. For all KOIs new to the Q1-Q12 table, each is given a disposition of CANDIDATE or FALSE POSITIVE. A target is deemed a FALSE POSITIVE if the team finds evidence that the target is an eclipsing binary, background eclipsing binary or an instrumental artifact. The catalog uses the stellar parameters published by Huber et al. (2013) for the observed Kepler targets. The transit parameters for all KOIs have been updated using the entire Q1-Q17 data set (Data Releases 21-23) and fit using a Markov chain Monte Carlo analysis (see Rowe et al. (2014).

More details about this catalog and the candidates it contains are available in Rowe et al. (2015).

2. Triage of TCEs to create new KOIs

The Kepler pipeline (release SOC 9.0) was run on the Q1-Q12 data set to search for potential planet candidates (Jenkins 2002). Potential planet candidates delivered by the Kepler pipeline are called Threshold Crossing Events (TCEs; Tenenbaum et al. 2013). All TCEs found by this pipeline run are available in the Q1-Q12 TCE table. For the Q1-Q12 pipeline run, 18,406 TCEs were generated on 11,087 different Kepler targets. A majority of the TCEs are not valid planet candidates; most are induced by uncorrected instrumental instabilities, eclipsing binaries or astrophysical variability. The triage step of the vetting procedure quickly culls the obviously non-credible TCEs from those that look like transits.

Of the 18,406 TCEs in Q1-Q12, four were observed only in the partial quarter known as Q1, and thus were not considered for review. We also identified 3,482 that federated to previously identified KOIs via their periods, epochs and KIC numbers. This left 14,920 TCEs that required vetting.

In the triage process, human vetters (i.e. TCERT) were given the DV one-page summary for each TCE. By looking at the folded and binned light curves, the vetters were asked to classify the TCE as belonging to one of four categories: New Candidate, Instrumental, Variable Star, or Low SNR. A minimum of two independant human vetters examined each TCE and chose a category. In the event of disagreement between the first two vetters, examination by at least one additional, independant vetter was preformed. The 3,616 TCEs designated as new candidates were subjected to an additional level of scrutiny that required the transit to be 1) visible in a different detrending than that utilized by the pipeline and 2) not be the secondary eclipse of a binary system. Additionally, several additional TCEs were identified in a non-delivered Q1-Q10 transit search. These TCEs were triaged and subjected to the same vetting process as the Q1-Q12 TCEs. In the end 2,011 new KOIs were created; the details of the process will be fully described in Rowe et al. (2015).

3. Vetting of Q1-Q12 KOIs

The purpose of vetting is to disposition KOIs into CANDIDATES and FALSE POSITIVES using diagnostic information extracted from the Kepler data. In general, KOI vetting examines the Kepler flux time series data for consistency with the expectation of a transiting planet signal and the Kepler pixel-level time series data for consistency with the expectation that the signal originates from the target of interest in the aperture.

More specifically, the review of the data involves answering the following questions about the observed event:

Does the phase-folded transit indeed look transit shaped? Variable stars, instrumental effects and heartbeat stars are sometimes found in the KOI list.
Are there differences in the depth between the odd- and even-numbered transits? If so this is an eclipsing binary found at the wrong period.
Is there a significant secondary event? If so, this is most likely an eclipsing binary. For the smallest, short period events, this determination is overturned if a planet model interpretation can produce a credible occultation event.
Is this transit event unique? The DV-generated transit model was used as a template to measure the amplitude of other transit-like events at all phases and is called the Model-Shift test. The amplitude was measured by effectively fitting the depth of the transit model centered at the phases of all data points. If many other transit signals of similar depth were found with statistical significance, the transit was said to fail because it was likely instrumental in nature.
Does the transit event originate from the specified target? This test was preformed by measuring the difference between the flux in the pixel mask both in and out of the transit on a quarterly basis. A significant shift in the location usually indicates the transit is due to a background eclipsing binary.
Does the ephemeris match a known variable star or eclipsing binary? If so, then this transit event is likely due to contamination via one of the mechanisms discussed in Coughlin et al. (2014).

TCERT answers most of these questions by using a multi-page vetting form with check-boxes to summarize their decisions and a comment box to give reasons and point-out unusal cases. At least two individuals evaluated every KOI. For difficult cases, and cases of disagreement, a third or fourth, knowledgeable person helped determine the disposition.

In Q1-Q12, false positive flags are provided to indicate the likely reason(s) a target was designated a false positive. The false positive flags closely map to the questions described above and are as follows: 1) Not transit like (this includes both whether the transit is unique and if it is transit shaped), 2) Significant Secondary, 3) Centroid Offset and 4) Ephemeris Match Indicates Contamination. These flags can be added to the online KOI table by selecting the columns under the section Transit and Disposition Parameters.

All KOIs that are new to the Q1-Q12 table were given dispositions. No effort was made to re-disposition objects from previous KOI Activity Tables, though some were automatically re-dispositioned as part of the ephemeris matching activity (Coughlin et al. 2014).

4. Stellar Parameters

Understanding the stellar population is required in order to understand the planet population found in this transit survey. By combining the works of many published sources, Huber et al. (2013), characterized the entire sample of stars observed by Kepler. This KOI catalog uses these stellar parameters, which were also used to create the DV reports and one-page summaries. A few tens of KOIs have no published stellar information; for these, solar parameters are reported in the KOI table.

5. Planetary Parameters

Planetary parameters for the majority of KOIs are based upon fitting the Mandel & Agol (2002) transit model to the Q1-Q17 Kepler flux time series data. The data was fit to the light curves available at the MAST on September 1, 2014 (Data Releases 21-23).

The fitting procedure is the same as that described in the beginning of Rowe et al. (2013). To summarize, the procedure assumes a circular orbit and fits for the stellar density. To best estimate the posterior distribution on each fitted parameters, a MCMC approach was used to account for strong correlations between varaibles (especially stellar density, impact parameter and radius ratio). The error bars reported for these values are given to encompass 68% of the posterior distribution, emulating 1-sigma error bars.