Starspot Evolution on stellar surface on a F-type star constructed from Kepler observations



The F-type star KIC 6791060 was observed for four years from 13 December 2009 to 13 December 2013 by the Kepler satellite. The Kepler data consist of practically continuous photometry for that period. The data were taken in two different modes. In eighteen quarters, data were taken with 30-min exposures (long-cadence; LC mode) and in one quarter only it was observed with 1-min exposures (short-cadence; SC mode). For our analysis we used the pre-search data conditioning simple aperture photometry (PDCSAP) data in which instrumental effects are removed. The raw PDCSAP light curve obtained in LC mode. For further analysis, we have subtracted a linear fit from the light curve of each individual quarter to remove any long-term calibration errors and normalized it to its average flux.


Dark spots move across the stellar disk due to the stellar rotation and thus modulate the total brightness with the rotational period of the star. In order to determine locations of spots on the stellar surface, we have performed inversion of the phased light curves into stellar images using the light curve inversion code (iPH; see Savanov & Strassmeier 2008; Karmakar et al. 2016; Savanov et al. 2016). The model assumes that, due to the low spatial resolution, the local intensity of the stellar surface always has a contribution from the photosphere (IP ) and from cool spots (IS ) weighted by the fraction of the surface covered by spots, i.e., the spot filling factor f by the following relation: I = f × IP + (1−f)× IS; with 0 < f < 1. The inversion of a light curve results in a distribution of the spot filling factor (f) over the visible stellar surface. We could make 3899 time-intervals as each interval corresponds to a single rotation of the star. Individual light curves were analyzed using the iPH code. In our modeling, the surface of the star was divided into a grid of 6◦ × 6◦ pixels.


In the above video, 1 ms corresponds to 2 solar day.

[Image Credit: Karmakar et al. (2018)]