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HD 21190 is a known $\delta$ Scuti star showing Ap star characteristics and avariability period of 3.6 h discovered by the Hipparcos mission. Using Gaia DR1data for an astrometric analysis, it was recently suggested that HD 21190 formsa physical binary system with the companion CPD -83$^{\circ}$ 64B. Anatmospheric chemical analysis based on HARPS observations revealed the presenceof overabundances of heavy and rare-earth elements, which are typicallyobserved in chemically peculiar stars with large-scale organized magneticfields. Previous observations of HD 21190 indicated a magnetic field strengthof a few hundred Gauss. The presence of a magnetic field in CPD -83$^{\circ}$64B remained unexplored. In this work, we reanalyse this system using Gaia DR2data and present our search for the magnetic field in both stars based onmulti-epoch HARPSpol high-resolution and FORS 2 low-resolutionspectropolarimetric observations. The Gaia DR2 results clearly indicate thatthe two star are not physically associated. A magnetic field detection at asignificance level of more than 6$\sigma$ ($\left< B_{\rm z}\right>_{\rmall}=230\pm38$ G) was achieved for the $\delta$ Scuti variable HD 21190 in FORS2 observations using the entire spectrum for the measurements. The magneticfield appears to be stronger in CPD -83$^{\circ}$ 64B. The highest value forthe longitudinal magnetic field in CPD -83$^{\circ}$ 64B, $\left< B_{\rmz}\right>_{\rm all}=509\pm104$ G, is measured at a significance level of4.9$\sigma$. Furthermore, the high-resolution HARPS\-pol observations of thiscomponent indicate the presence of pulsational variability on a time scale oftens of minutes.

A magnetic study of the $\delta$ Scuti variable HD 21190 and the close solar-type background star CPD -83$^{\circ}$ 64B