Long-term stability of spotted regions and the activity-induced Rossiter-McLaughlin effect on V889 Herculis. A synergy of photometry, radial velocity measurements, and Doppler imaging

TL;DR

This study investigates the stability and evolution of active regions on V889 Herculis over more than a decade, using photometry, spectroscopy, and Doppler imaging to understand their impact on radial velocity measurements and stellar activity.

Contribution

It demonstrates the long-term stability of large starspots and their influence on RV variations, integrating multiple observational methods for comprehensive analysis.

Findings

Large spotted regions persist for over a year with similar structures.

Long-lasting starspots influence RV measurements and are confirmed by Doppler imaging.

Rotation period of V889 Her is precisely measured as 1.3371 days.

Abstract

The young active G-dwarf star V889 Herculis (HD 171488) shows pronounced spots in Doppler images as well as large variations in photometry and radial velocity (RV) measurements. However, the lifetime and evolution of its active regions are not well known. We study the existence and stability of active regions on the star's surface using complementary data and methods. Furthermore, we analyze the correlation of spot-induced RV variations and Doppler images. Photometry and high-resolution spectroscopy are used to examine stellar activity. A CLEAN-like Doppler Imaging (DI) algorithm is used to derive surface reconstructions. We study high-precision RV curves to determine their modulation due to stellar activity in analogy to the Rossiter-McLaughlin effect. To this end we develop a measure for the shift of a line's center and compare it to RV measurements. We show that large spotted regions exist on V889 Her for more than one year remaining similar in their large scale structure and position. This applies to several time periods of our observations, which cover more than a decade. Furthermore we use DI line profile reconstructions to identify influences of long-lasting starspots on RV measurements. In this way we verify the RV curve's agreement with our Doppler images. Based on long-term RV data we confirm V889 Her's rotation period of $1.3371 \pm 0.0002$ days.