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The data were obtained using two spectropolarimeters - Narval at the BernardLyot Telescope, Pic du Midi, France, and ESPaDOnS at CFHT, Hawaii. Thirty-eightcircularly-polarized spectra have been collected in the period June 2010 -January 2012. The Least Square Deconvolution method was applied for extractinghigh signal-to-noise ratio line profiles, from which we measure thesurface-averaged longitudinal magnetic field Bl. Chromospheric activityindicators CaII K, H_alpha, CaII IR (854.2 nm) and radial velocity weresimultaneously measured and their variability was analysed together with thebehavior of Bl. The Zeeman Doppler Imaging (ZDI) inversion technique wasemployed for reconstruction of the large-scale magnetic field and two magneticmaps of Beta Ceti are presented for two periods (June 2010 - December 2010 andJune 2011 - January 2012). Bl remains of positive polarity for the wholeobservational period. The behavior of the line activity indicators is in goodagreement with the Bl variations. The two ZDI maps show a mainly axisymmetricand poloidal magnetic topology and a simple surface magnetic fieldconfiguration dominated by a dipole. Little evolution is observed between thetwo maps, in spite of a 1 yr interval between both subsets. We also usestate-of-the-art stellar evolution models to constrain the evolutionary statusof Beta Ceti. We derive a mass of 3.5 M_sun and propose that this star isalready in the central-helium burning phase. Taking into account all ourresults and the evolutionary status of the star, we suggest that dynamo actionalone may not be eficient enough to account for the high magnetic activity ofBeta Ceti. As an alternate option, we propose that it may be an Ap stardescendant presently undergoing central helium-burning and still exhibiting aremnant of the Ap star magnetic field.

Magnetic field structure in single late-type giants: Beta Ceti in 2010 - 2012