  The goal of this work is to study magnetic fields of the cool, eclipsing
binary star UV Piscium (UV Psc). This system contains two active late-type
stars, UV Psc A (G5V) and B (K3V). To obtain a complete picture, the properties
of both global and local magnetic field structures are studied for both
components. High-resolution intensity and circular polarisation spectra,
collected in 2016 with the ESPaDOnS spectropolarimeter at the CFHT, were used
to analyse the magnetic field of UV Psc. To increase the signal-to-noise ratio,
the multi-line technique of least-squares deconvolution (LSD) was used to
obtain average Stokes IV profiles. Then, a Zeeman-Doppler imaging (ZDI) code
was employed to obtain the large-scale magnetic field topology and brightness
distribution for both components of UV Psc. In addition, the small-scale
magnetic fields, not visible to ZDI, were studied using the Zeeman
intensification of Fe I lines. Maps of the surface magnetic field for both
components of UV Psc were obtained, the large-scale magnetic fields feature
strong toroidal and non-axisymetric components. UV Psc A and B have average
global field strengths of 137 G and 88 G, respectively. The small-scale fields
are notably stronger, with average strengths of 2.5 and 2.2 kG, respectively.
Our results are in agreement with previous studies of partly-convective stars.
Overall, UV Psc A has a stronger magnetic field compared to UV Psc B. Due to
the eclipsing binary geometry, certain magnetic field features are not
detectable using circular polarisation only. An investigation into theoretical
linear polarisation profiles shows that they could be used to reveal
antisymmetric components of the magnetic field. This result also has
implications for the study of exoplanetary transit hosts.
