Spectropolarimetry of Magnetic Stars

University essay from Uppsala universitet/Observationell astrofysik

Author: Lisa Rosén; [2011]

Keywords: ;


A star´s magnetic field is important although stellar magnetic field generation is not completely understood. It´s necessary to investigate different types of stars and stars of different ages to learn how the magnetic fields are generated and how they affect the star and its surroundings. In this thesis I investigated six stars, HD 171488, GQ Lup, Tau Boo, HR 1099, HD 216489 and AU Mic with the help of high resolution circular polarization observations. They are all cool stars with relatively weak magnetic fields spanning in age from a young T-Tauri star, (GQ Lup), to an evolved subgiant, (HR 1099). Some of them have never before been investigated in terms of polarization. To obtain polarization profiles the Least Squares Deconvolution, LSD, technique was applied. A magnetic field was detected for all stars except Tau Boo, probably because the S/N ratio was too low. The values of the mean longitudinal magnetic field varied from a few G for Tau Boo up to -300 G for GQ Lup. GQ Lup also had two emission lines of HeI with even higher negative values up to -2000 G. The shape of the LSD polarization profiles indicates that AU Mic might have a dipole like field not aligned with the rotation axis, while GQ Lup showed the same polarity in all observations, possibly indicating a stable magnetic structure being observed pole-on. The two binaries, (HR 1099 and HD 216489), seemed to have complex fields, while HD 171488 seemed to have an azimuthal field.

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