Centroids
Use of Centroid Information
Given the very high precision of the Kepler photometry, tracking the photocenter of the photometric aperture is an effective means of identifying background eclipsing binaries (BGEB). The dimming of any object in the aperture will shift the measured photocenter since the photocenter is determined by the combination of the diffuse and discrete sources. The apparent change in the position of the target star due to a background eclipse event is dependent on the separation of the stars, their relative brightnesses, and the transit/eclipse depth. For example, if the Kepler aperture contains all the light from both the target star and a BGEB 5 magnitudes fainter and 1 pixel away with a 50% eclipse, the centroid of the target star will change by 5 millipixels. Thus, examining the centroid positions in and out of the transit event is important in evaluating the origin of the transit. For more information of the use of centroiding in vetting Kepler candidates, please see Batalha et al (2010), "Pre-spectroscopic False-positive Elimination of Kepler Planet Candidates".
Data Columns
The following table describes the data column names of centroids in the archive. The calculated centroids are flux-weighted.
| Column Name | Description |
|---|---|
| kepoi | Kepler object of interest unique identifier |
| cen_quarter | Quarter for flux weighted centroid shifts |
| cen_row_itr | In-transit image centroid row and uncertainty (pixels) |
| cen_col_itr | In-transit image centroid column and uncertainty (pixels) |
| cen_row_otr | Out-of-transit image centroid row and uncertainty (pixels) |
| cen_col_otr | Out-of-transit image centroid column and uncertainty (pixels) |
| cen_row_off | Row offset (Out-of-transit minus in-transit) and uncertainty (pixels) |
| cen_row_offosig | Ratio of row offset to sigma |
| cen_col_off | Column offset (Out-of-transit minus in-transit) and uncertainty (pixels) |
| cen_col_offosig | Ratio of column offset to sigma |
| cen_off_dist | Offset distance and uncertainty (pixels) |
| cen_distosig | Ratio of offset distance to sigma |
