Multiwavelength Campaign Observations of a Young Solar-type Star, EK Draconis. III. Comparison between Starspot Mapping, Zeeman Doppler Imaging, and Multiwavelength Variability

TL;DR

This study compares starspot mapping, Zeeman Doppler Imaging, and multiwavelength variability observations of EK Draconis, revealing correlations between starspots, magnetic fields, and activity across different wavelengths, and providing insights into stellar activity and exoplanet atmospheric evolution.

Contribution

It integrates photometry, ZDI, and multiwavelength data to analyze starspot locations, magnetic fields, and activity, offering a comprehensive view of stellar surface and atmospheric phenomena.

Findings

Spot locations from TESS and ZDI are mostly consistent.

Hα variability correlates with TESS light curve due to chromospheric emission.

X-ray variability shows no clear association with starspots.

Abstract

Recent simultaneous multiwavelength observations of a nearby young solar-type star EK Dra in the optical, H$\alpha$ spectrum, and X-ray, have provided evidence for stellar prominence eruptions associated with superflares. The large prominence eruption is suggested to have been caused by a large mid-latitude spot on the polarity inversion lines near the stellar limb from the concurrent Zeeman Doppler Imaging (ZDI) and optical photometry by the TESS. In this study, we perform starspot mapping for the TESS data of EK Dra to investigate the relation of starspots and magnetic fields from the photometry and ZDI. We also explore the multiwavelength rotational variability ascribed to starspots and active regions for the TESS, B-band, H$\alpha$, and X-ray light curves. As a result, we find that (i) spot locations deduced from the TESS light curve are mostly consistent with the intensity map from the ZDI except for a polar spot, and (ii) the H$\alpha$ light curve exhibits clear periodicity with respect to the TESS light curve because the H$\alpha$ line is radiated around spots in the chromosphere. The X-ray light curve does not show such association probably because of multiple spots on high activity level and extended spatial structure of coronal active regions. The results provide clues to explore their association with stellar flares at different heights of active regions in chromospheric and coronal lines. Our study also enables us to quantify the stellar XUV radiation from the magnetic fields of active stars toward understanding atmospheric evolution of exoplanets.