Zeeman Doppler Imaging of the eclipsing binary UV Piscium

University essay from Uppsala universitet/Observationell astrofysik

Abstract: Magnetic fields are important for multiple physical processes in and around stars, for these reasons improving the understanding of how they are generated and maintained is of great value. In this work the magnetic field structure of the eclipsing binary UV Piscium is investigated. This is done by utilising the Zeeman-Doppler Imaging technique that reconstructs stellar magnetic maps by combining the information of how the magnetic field affects spectral lines with the rotational modulation of spectral lines. In order to improve the signal-to-noise ratio the least squares deconvolution technique was used to combine multiple spectral lines into an average line profile. The high resolution circular polarisation observations analysed in this work were taken by the ESPaDOnS spectograph at the Canada-France-Hawaii Telescope during August and September of 2016. We reconstructed detailed magnetic field maps and obtained the average magnetic field strengths of 137G for the primary and 88G for the secondary, which is not unusual values for stars of this type. The methods used are however likely to underestimate the magnetic field strengths. This is because the lack of linear polarisation profiles likely results in systematic underestimation of magnetic field strengths, especially meridional components. Another issue that became apparent in this work is that in eclipsing binaries, without linear polarisation observations, there is a degeneracy between the different hemispheres, resulting in further uncertainties in the determination of surface magnetic field geometry. We also found that there is indication of surface evolution on the time scale of months as some observations taken around fifty days earlier were could not be phased with the main data set.

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