HD 34736: an intensely magnetised double-lined spectroscopic binary with rapidly rotating chemically peculiar B-type components

We report the results of a comprehensive study of the spectroscopic binary (SB2) system HD 34736 hosting two chemically peculiar (CP) late B-type stars. Using new and archival observational data, we characterize the system and its components, including their rotation and magnetic fields. Fitting of the radial velocities yields P-orb=83.(d)219(3) and e=0.8103(3). The primary component is a CP He-wk star with T-effA=13000 +/- 500 K and upsilon(e) sin i=75 +/- 3 km s(-1), while the secondary exhibits variability of Mg and Si lines, and has T-effB=11500 +/- 1000 K and upsilon(e)sin i=110-180 km s(-1). Transiting Exoplanet Survey Satellite and Kilodegree Extremely Little Telescope photometry reveal clear variability of the primary component with a rotational period P-rotA=1.d2799885(11), which is lengthening at a rate of 1.26(6) s yr(-1). For the secondary, P-rotB=0.d5226938(5), reducing at a rate of -0.14(3) s yr(-1). The longitudinal component < Bz > of the primary's strongly asymmetric global magnetic field varies from -6 to +5 kG. Weak spectropolarimetric evidence of a magnetic field is found for the secondary star. The observed X-ray and radio emission of HD 34736 may equally be linked to a suspected T Tau-like companion or magnetospheric emission from the principal components. Given the presence of a possible third magnetically active body, one can propose that the magnetic characteristics of the protostellar environment may be connected to the formation of such systems.