Magnetic fields and differential rotation on the pre-main sequence - III. The early-G star HD 106506

Abstract

We present the photometry and spectropolarimetry of the pre-main-sequence star HD 106506. A photometric rotational period of ∾1.416 ± 0.133 d has been derived using observations at Mount Kent Observatory (MKO). Spectropolarimetric data obtained with the 3.9-m Anglo-Australian Telescope (AAT) were used to derive spot occupancy and magnetic maps of the star through the technique of Zeeman Doppler imaging (ZDI). The resulting brightness maps indicate that HD 106506 displays photospheric spots at all latitudes including a predominant polar spot. Azimuthal and radial magnetic images of this star have been derived, and a significant azimuthal magnetic field is indicated, in line with other active young stars. A solar-like differential rotation law was incorporated into the imaging process. Using Stokes I information the equatorial rotation rate, Ωeq, was found to be 4.54 ± 0.01 rad d-1, with a photospheric shear δΩ of 0.21+0.02-0.03 rad d-1. This equates to an equatorial rotation period of ˜1.39 ± 0.01 d, with the equatorial region lapping the poles every ˜ 30+5-3 d. Using the magnetic features, the equatorial rotation rate, Ωeq, was found to be 4.51 ± 0.01 rad d-1, with a photospheric shear δΩ of 0.24 ± 0.03 rad d-1. This differential rotation is approximately four times that observed on the Sun.