Doppler images and chromospheric variability of TWA 6

Abstract

[Abstract]: We present Doppler imaging and Balmer line analysis of the weak-line T Tauri star TWA 6. Using these data we have made one of the first attempts to measure differential rotation in a T Tauri star, and the first detection of a slingshot prominence in such a star. We also show the most direct evidence to date of the existence of solar-type plages in a star other than the Sun. Observations were made over six nights: 2006 February 11–13 and 2006 February 18–20, when spectra were taken with the UCL Echelle Spectrograph on the 3.9-m Anglo-Australian Telescope. Using least-squares deconvolution to improve the effective signal-to-noise ratio we produced two Doppler maps. These show similar features to maps of other rapidly rotating T Tauri stars, i.e. a polar spot with more spots extending out of it down to equator. Comparison of the two maps was carried out to measure the differential rotation. Cross-correlation and parameter fitting indicates that TWA 6 does not have detectable differential rotation. The Balmer emission of the star was studied. The mean Hα profile has a narrow component consistent with rotational broadening and a broad component extending out to ±250 km s−1. The variability in Hα suggests that the chromosphere has active regions that are cospatial with the spots in the photosphere, similar to the ‘plages’ observed on the Sun. In addition the star has at least one slingshot prominence 3R∗ above the surface – the first such detection in a T Tauri star.