2024MNRAS.535.2812S

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 $P_\mathrm{orb}=83\rm{.\!\!^{ {\rm{d}}}}219(3)$ and $e=0.8103(3)$. The primary component is a CP He-wk star with $T_{{\rm eff}A}$$\,\,=13000\pm 500$ K and $\upsilon _{\rm e}\sin i\,$$\,\,=75\pm 3$ km s$^{-1}\,$, while the secondary exhibits variability of Mg and Si lines, and has $T_{{\rm eff}B}$$\,\,=11500\pm 1000$ K and $\upsilon _{\rm e}\sin i\,$$\,\,=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 $P_{\mathrm{rot}A}=1\rm{.\!\!^{ {\rm{d}}}}279\, 988\, 5(11)$, which is lengthening at a rate of 1.26(6) s yr$^{-1}$. For the secondary, $P_{\mathrm{rot}B}=0\rm{.\!\!^{ {\rm{d}}}}522\, 693\, 8(5)$, reducing at a rate of $-0.14(3)$ s yr$^{-1}$. The longitudinal component $\langle B_{\rm z}\rangle$ 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.