本田 敏志

Context . Latitude distribution of stellar magnetic activity is not well constrained by observations, despite its importance for a better understanding of stellar dynamos and their effects on planetary environments. Aims . Our aim is to obtain an accurate reconstruction of the surface spot distribution on the young rapidly rotating K2 star PW Andromedae by combining spectroscopic and photometric diagnostics. In particular, we assess how the inclusion of continuous high-precision TESS photometry in parallel with high-resolution spectroscopy improves latitude recovery of starspots, especially at low latitudes and in the southern hemisphere, which are poorly constrained by Doppler imaging (DI) alone. We thereby explore the spatial origins of the observed white-light flares. Methods . We performed simultaneous Doppler imaging and light curve inversion (DI+LCI) using contemporaneous high-resolution GAOES-RV spectra from the 3.8 m Seimei telescope ( R ∼ 65 000) and high-precision TESS light curves. Surface reconstructions employed the SpotDIPy code to model both line profiles and continuum brightness variations. We compared DI+LCI maps with DI-only solutions, conducted artificial-spot simulations to evaluate the effects of latitude, phase coverage, and signal-to-noise ratio on reconstruction reliability. We also investigated the spatial correlation between the DI+LCI reconstructed map and flares detected in the TESS data. Results . The DI+LCI reconstruction reveals significant spot features at mid to low latitudes, equatorial regions, and even in the southern hemisphere. These are the regions where DI-only fails to provide reliable information. Meanwhile, the high-latitude spot features, which are already recovered by DI-only, remain present, though with a restructured distribution. The estimated spot coverage is approximately 9.9% of the area of the stellar surface visible to the observer. Simulations show that DI+LCI provides more accurate reconstructions than DI-only, especially under conditions of incomplete phase coverage and low signal-to-noise, by better recovering both spot latitudes and filling factors. A comparison between the DI+LCI map and the TESS flare timings also suggests a potential association between flare occurrence and reconstructed spot longitudes. Conclusions . Simultaneous DI and continuous photometry improves the inversion accuracy of starspot distributions, also improving flare localization.

Abstract Coronal mass ejections (CMEs) on the early Sun may have profoundly influenced the planetary atmospheres of early Solar System planets. Flaring young solar analogues serve as excellent proxies for probing the plasma environment of the young Sun, yet their CMEs remain poorly understood. Here we report the detection of multi-wavelength Doppler shifts of the far-ultraviolet and optical lines during a flare on the young solar analogue EK Draconis. During and before a Carrington-class (~10 ³²  erg) flare, warm far-ultraviolet lines (~10 ⁵  K) exhibited blueshifted emission at 300–550 km s ⁻¹ , indicative of a warm eruption. Then, 10 min later, the Hα line showed slow (70 km s ⁻¹ ), long-lasting (≳2 h) blueshifted absorptions, indicating a cool (~10 ⁴  K) filament eruption. This provides evidence of the multi-temperature and multi-component nature of a stellar CME. If Carrington-class flares or CMEs occurred frequently on the young Sun, they may have cumulatively impacted the early Earth’s magnetosphere and atmosphere.