Abstract
ABSTRACT We present an analysis of the starspot evolution, the surface differential rotation (SDR), the correlation between chromospheric activity indicators and the spatial connection between chromospheric and photospheric activities on the active star Kepler-411, using time-series photometry over four years from Kepler, and spectroscopic data from Keck I 10-m and Lijiang 2.4-m telescopes. We constructed the light curve (LC) by re-performing photometry and reduction from the Target Pixel Files and Cotrending Basis Vectors with a manually redefined aperture using the software pyke3. An efficient program, gemc_lcm, was developed to apply a two-spots model to chosen LC segments with three spot groups at fixed latitudes (30○, 45○), (30○, 60○) and (45○, 60○). We found a periodic variation of the starspots at the period of about 660 d which independs on spot latitudes, and estimated the lower limit of SDR rate α = 0.1016(0.0023) and equatoral rotation period Peq = 9.7810(0.0169) d. Simultaneously, the relative variations of chromospheric activity indicators were derived by subtracting the overall mean spectrum from individual spectrum. It is found that Ca ii H and K emissions are strongly correlated with each other, and there also exists a correlation between Hα and Ca ii H & K emissions, with large dispersion, in accordance with previous results. Furthermore, we find the correlation between Ca ii H and K emissions is different in 2011 and 2012. The chromospheric emission variation shows a highly spatial anticorrelation with the LC, suggesting a spatial connection between the chromospheric active region and spot region.
Highlights
Starspots are surface manifestations of tubes of magnetic flux, where the magnetic fields are strong enough to suppress the overturning convection and block the energy from the stellar interior to the surface, causing the spots to remain cooler than surrounding photosphere (Bouvier et al 1986; Strassmeier 2009; Walkowicz et al 2013)
We present an analysis of the starspot evolution, the surface differential rotation (SDR), the correlation between chromospheric activity indicators and the spatial connection between chromospheric and photospheric activities on the active star Kepler-411, using time series photometry over 4 years from Kepler, and spectroscopic data from Keck I 10-m and Lijiang 2.4-m telescopes
In this paper we present a detailed analysis of surface inhomogeneities on the K2-type main sequence star Kepler-411 (KIC 11551692), using high-precision Kepler light curve (LC) spanning over four years, to derive starspots and their evolution, and SDR at different epochs
Summary
Starspots are surface manifestations of tubes of magnetic flux, where the magnetic fields are strong enough to suppress the overturning convection and block the energy from the stellar interior to the surface, causing the spots to remain cooler (and darker) than surrounding photosphere (Bouvier et al 1986; Strassmeier 2009; Walkowicz et al 2013). One interesting technique based on analysis of spot-crossing events where spot is occulted by transiting planet was proven to be capable of solving this issue (e.g. Désert et al 2011; Llama et al 2012; Sanchis-Ojeda et al 2013) This phenomenon was mentioned on Kepler-411 by Sun et al (2019) and such an analysis is beyond the scope of this paper. One can try to exploit Kepler LCs for inversing the spot distributions at different observing time, and to estimate the potential temporal evolution of SDR. This provides us the opportunity for the investigation of such kind of phenomenon on more active stars other than the Sun, AB Dor, etc.
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