Doppler imaging combined with high-cadence photometry. I. Revisiting the surface of a pre-main-sequence flare star

TL;DR

This study combines Doppler imaging and high-precision TESS photometry to improve the surface mapping of starspots on a young, rapidly rotating star, revealing more accurate latitude distributions and potential flare-spot associations.

Contribution

It demonstrates that integrating photometry with spectroscopy enhances starspot latitude recovery, especially at low latitudes and in poorly constrained regions, compared to Doppler imaging alone.

Findings

DI+LCI provides more accurate spot maps than DI-only.

Simulations show improved latitude and filling factor recovery with DI+LCI.

Potential correlation between flare locations and starspot longitudes.

Abstract

Latitude distribution of stellar magnetic activity is not well constrained by observations, despite its importance for a better understanding of stellar dynamos. We aim to obtain an accurate reconstruction of the surface spot distribution on the young, rapidly rotating K2 star PW And by combining spectroscopic and photometric diagnostics. In particular, we seek to 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 explore the spatial origins of the observed white-light flares. 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~65000) and high-precision TESS light curves. Surface reconstructions employ the SpotDIPy code to model both line profiles and continuum brightness variations. We compare DI+LCI maps with DI-only solutions, conduct artificial-spot simulations to evaluate the effects of latitude, phase coverage, and S/N on reconstruction reliability. We also investigate the spatial correlation between the DI+LCI reconstructed map and flares detected in the TESS data. The DI+LCI reconstruction reveals significant spot features at mid-to-low latitudes, equatorial regions, and even in the southern hemisphere. Simulations show that DI+LCI provides more accurate reconstructions than DI-only, especially under conditions of incomplete phase coverage and low S/N, by better recovering both spot latitudes and filling factors. A comparison between the DI+LCI map and the TESS flare timings also suggests potential association between flare occurrence and reconstructed spot longitudes.