Kepler Object of Interest (KOI) Catalog - Q1-Q16

First delivery date: 2013 Dec 18
Last delivery date: 2014 Dec 18
Status: Done

Contents

  1. Summary of Q1-Q16 KOI Activity Table
  2. Triage of TCEs to create new KOIs
  3. Dispositioning Q1-Q16 KOIs
  4. Stellar Parameters
  5. Planetary Parameters
  6. Errata

1. Summary of the Q1-Q16 KOI Activity Table

The Q1-Q16 Kepler light curves were searched for transit-like signatures, otherwise known as Threshold Crossing Events (TCEs). The Q1-Q16 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 TCEs that are likely caused by planetary transits or eclipsing binaries are included in the KOI table. For all KOIs new to the Q1-Q16 table, each is given a disposition of CANDIDATE or FALSE POSITIVE. A TCE is deemed a FALSE POSITIVE if the team finds evidence that the TCE is an eclipsing binary, background eclipsing binary or an instrumental artifact. The catalog uses the stellar parameters published by Huber et al. (2014) for the observed Kepler targets. The transit parameters for most KOIs have been obtained from a Markov chain Monte Carlo analysis (see Rowe et al. 2014) using the entire Q1-Q17 data set (Data Releases 21-23).

More details about this catalog, the vetting procedures, and the candidates it contains are available in Mullally et al. (2015).

2. Triage of TCEs to create new KOIs

The Kepler pipeline (release SOC 9.1) was run on the Q1-Q16 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. 2014). All TCEs found by this pipeline run are available in the Q1-Q16 TCE table. For the Q1-Q16 pipeline run, 16,285 TCEs were generated. A majority of these TCEs are not valid planet candidates; most are induced by uncorrected instrumental signatures, 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, and is described in detail in Mullally et al. (2015)).

The triage process consists of a number of discrete steps:

  1. Identification of TCEs that correspond to previously known KOIs.
  2. Elimination of obvious instrumental artifacts by rule.
  3. Manual triage of the remainding TCEs.
  4. Checks that the TCE is not an artifact of detrending.

During Step 3, human vetters (i.e., TCERT) identified and eliminated obvious false positives by examining the DV one-page summary for each TCE. Step 4 uses an alternate detrending, available in the TCERT companion documentation.

TCEs that survive triage are given KOI numbers, and passed on to the next stage, dispositioning.

3. Dispositioning Q1-Q16 KOIs

KOIs found by the pipeline, both new and previously known are posted to the KOI table. The next step is to separate out signals that are not caused by transiting planets (e.g., eclipsing binaries, events caused by events on background stars, variability or artifacts not identified during triage). Not all KOIs were vetted in Q16; we focused on three populations:
  1. KOIs newly discovered during triage,
  2. Known KOIs with periods > 50 days, and
  3. KOIs identified as ephemeris matches (e.g., a TCE with the same period and epoch as a known eclipsing binary (Coughlin et al., 2014).
A small number of other previously known KOIs with P < 50 days were also vetted, most of them in multiple KOI systems.

KOIs clearly identified as not being due to planets are labeled FALSE POSITIVE in the "Disposition Using Kepler Data" column of the KOI table. The forms used during vetting are described in the TCERT companion documentation

The reasons a KOI was marked as FALSE POSITIVE are recorded using four false positive flag columns. Briefly, these flags indicate that a KOI is:

  • Not Transit Like: A KOI whose light curve is not consistent with that of a transiting planet. This includes, but is not limited to, instrumental artifacts, non-eclipsing variable stars and spurious detections.
  • Significant Secondary: A KOI that is observed to have a significant secondary event, meaning that the transit event is most likely caused by an eclipsing binary.
  • Centroid Offset: The source of the transit was on a nearby star, not the target KOI
  • Ephemeris Match Indicates Contamination: The KOI shares the same period and epoch as another system (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. (2014) characterized the entire sample of stars observed by Kepler. This KOI catalog uses the stellar parameters in the Q1-Q17 stellar table (set the search field "st_delivname" to q1_q17_dr24_stellar), 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 model 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 Rowe et al. (2013). To summarize, the procedure assumes a circular orbit and fits for the stellar density, impact parameter, radius ratio, period and epoch. To best estimate the posterior distribution on each fitted parameter, a MCMC approach was used to account for strong correlations between variables (especially stellar density, impact parameter and radius ratio). The error bars reported for these values encompass 68% of the posterior distribution, emulating 1-sigma error bars.

For some very low signal-to-noise false positives, the above fitting procedure was unsuccessful. In these cases the catalog contains the period, epoch and transit duration as given for the original TCE, with no error bars.

The MCMC chains used to compute the planetary parameters are also available. Note that the parameters given in the table are based on the best fit model, not the median value of the MCMC chains as reported in the catalog paper (Mullally et al. 2015).

6. Errata

The stellar parameters for four KOIs are reported incorrectly as having Solar properties in the Q1-Q16 KOI activity table. Nevertheless, the planetary parameters derived using the stellar parameters (such as semi major axis) are calculated correctly using the stellar parameters listed in the Q1-Q16 stellar table. The four KOIs with incorrect stellar parameters are:

  • K01818.01
  • K03554.01
  • K04163.01
  • K05713.01