Kepler Light Curves Optimized For Asteroseismology ("KEPSEISMIC")

KEPSEISMIC light curves are obtained from Kepler pixel-data files using large custom apertures that produce more stable light curves on longer time scales for seismic studies. For each pixel in the pixel-data file, a reference weighted flux value is computed as the 99.9th percentile of the flux divided by its error representing a measure of the signal-to-noise ratio. Starting from the center of the point-spread function of the target star pixels, new pixels are added in one direction of the mask if two conditions are fulfilled: i) the reference weighted flux of the pixel is higher than a threshold of 100; ii) the weighted flux is smaller than the value of the previous pixel within a small tolerance. In most cases, this second condition allows the team to remove the pixels corresponding to a second star present in the aperture.

The resultant light curve is processed through the implementation of the Kepler Asteroseismic Data Analysis and Calibration Software (KADACS, García et al. 2011). KADACS corrects for outliers, jumps, and drifts, properly concatenates the independent Kepler Quarters in a star-by-star basis. It also fills the gaps shorter than 20 days in long cadence data following in-painting techniques based on a multi-scale cosine transform (García et al. 2014, Pires et al. 2015). The resulting light curves are high-pass filtered at 20, 55 days (quarter by quarter) and 80 days (using the full light curve at once) yielding three different light curves for each target. This ensures the homogeneity of the treatment done to the light curves when a single filter is used (e.g. for studies of the stellar convective background). For light curves longer than one month, KADACS corrects for discontinuities at the edges of the Kepler Quarters.