The magnetic activity of young suns: magnetic topologies and differential rotation of F- and G- dwarfs

摘要

Maps of magnetic field topologies for rapidly rotating, solar-type stars have been produced for the past decade, and offer a unique insight into the operation of the stellar dynamo. The creation of these maps uses the combined techniques of Least-Squares Deconvolution (LSD) to increase the signal-to-noise of the Stokes-V profiles, and Zeeman Doppler Imaging (ZDI) to create the magnetic maps from the Stokes-V profiles. However, for solar-type stars almost all of the targets imaged to date have been lower-mass (early-K) stars, limiting the range of operating parameters of the stellar dynamo. We present magnetic maps of two higher-mass, solar-type stars, the early G-dwarf HD171488 (v sin i = 38kms−1) and the late F-dwarf HR1817 (v sin i = 52kms−1). Both stars have been observed in left- and right-hand circularly polarized light using the SEMPOL spectro-polarimeter with the Anglo-Australian telescope. Both LSD and ZDI have then been used to infer topologies of the photospheric magnetic fields of the two stars, thus expanding the mass range of solar-type stars imaged using these techniques. In addition, the surface differential rotation of the two stars has been determined from the data, with both stars showing significantly higher differential rotation than that of lower-mass stars.