Magnetic fields and differential rotation on the pre-main sequence - II. The early-G star HD 141943 - coronal magnetic field, Hα emission and differential rotation

Abstract

Spectropolarimetric observations of the pre-main sequence early-G star HD 141943 were obtained at three observing epochs (2007, 2009 and 2010). The observations were obtained using the 3.9-m Anglo-Australian telescope with the UCLES echelle spectrograph and the SEMPOL spectropolarimeter visitor instrument. The brightness and surface magnetic field topologies (given in Paper I) were used to determine the star's surface differential rotation and reconstruct the coronal magnetic field of the star. The coronal magnetic field at the 3 epochs shows on the largest scales that the field structure is dominated by the dipole component with possible evidence for the tilt of the dipole axis shifting between observations. We find very high levels of differential rotation on HD 141943 (~8 times the solar value for the magnetic features and ~5 times solar for the brightness features) similar to that evidenced by another young early-G star, HD 171488. These results indicate that a significant increase in the level of differential rotation occurs for young stars around a spectral type of early-G. Also we find for the 2010 observations that there is a large difference in the differential rotation measured from the brightness and magnetic features, similar to that seen on early-K stars, but with the difference being much larger. We find only tentative evidence for temporal evolution in the differential rotation of HD 141943.