Starspot evolution, differential rotation, and correlation between chromospheric and photospheric activities on Kepler-411

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.

Stellar Chromospheric Variability

“…As a star rotates and its spots and associated plages rotate into view, one would expect the S MW index to increase and the continuum flux to decrease simultaneously. However, for a number of their sample G and K stars, Morris et al [190] pointed out that as the dark spots rotate out of view, we continue to see evidence of chromospheric emission (see also [179]). This suggests that the network of plages on those stars is more extensive than the distribution of the dark starspots.…”

“…Both phenomena are associated with magnetic activity. The latitude dependencies of plages and sunspots are similar, whereas the largest solar plages are typically associated spatially with dark sunspots [163,[177][178][179]. Lorenzo-Oliveira et al [26] established a robust and reproducible mean relationship between solar chromospheric activity and the international sunspot number, 1 N (see Figure 9, right): S MW = (3.12 ± 0.28) × 10 −5 N + (0.1667 ± 0.0003).…”

“…This type of chromospheric variability reflects a star's rotational modulation. In turn, this can be used to compute the minimum spot covering fraction via the so-called 'flux deficit' [190] (see also [179]),…”

Stellar rotation and its connection to the evolution of hydrogen-dominated atmospheres of exoplanets

“…It allows reproducing parameters of the planet at the given age of the system (D. Kubyshkina & Vidotto, 2021). Despite the host star being young (212 ± 31 Myr) and active ( XUV ∼ 9.35 × 10 28 erg/s, which corresponds to XUV ∼ 427 erg/s/cm 2 at the planetary orbit; see Johnstone et al 2021;Xu, Gu, & Ioannidis 2021), the planet does not experience an atmospheric mass loss strong enough to alter its atmospheric mass substantially throughout the lifetime. Overall, it loses less than 1% of its atmosphere, and its evolution (in particular, pl ( ), green line in the top panel of Figure 2 ) is mainly controlled by thermal evolution.…”

The Properties and Evolutions of Starspots on Three Detached Eclipsing Binaries in the LAMOST-Kepler survey

“…The lifetime, active longitude, and surface differential rotation can be deduced by comparing Doppler images at different epochs (Hussain 2002;Xiang et al 2020b). This technique is limited to bright stars or rapid rotating stars and hardly can be observed continuously in a long term (Korhonen et al 2007;Xu et al ★ E-mail:jnfu@bnu.edu.cn 2021). However, photometry provides complementary to that and can continuously monitor relative faint stars over a long duration, such as the 𝐾𝑒 𝑝𝑙𝑒𝑟 mission (Borucki 2016).…”