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

¹ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany e-mail: khuber@hs.uni-hamburg.de
² Thüringer Landessternwarte Tautenburg, Sternwarte 5, 07778 Tautenburg, Germany
³ Astrophysikalisches Institut Postdam, An der Sternwarte 16, 14482 Potsdam, Germany

Received: 18 July 2008
Accepted: 6 April 2009

Abstract

Context. 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.

Aims. 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.

Methods. 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.

Results. We show that large spotted regions are present 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. We use DI line profile reconstructions to identify the influence 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   ±   0.0002 days.