Multiplicity of Late-type B Stars with HgMn Peculiarity

According to theoretical predictions, late B-type stars exhibiting strong overabundances of the chemical elements Hg and Mn in their atmospheres, the so-called HgMn stars, are expected to display slow pulsations similar to those in Slowly Pulsating B stars. One of the major characteristics of this type of star is that they are frequently found in binary and multiple systems. We intend to study the multiplicity of HgMn stars, looking, for visual companions in the range of angular separation between 0 ''.05 and 8 ''. We carried out a survey of 56 stars using diffraction-limited near-infrared imaging with NAOS-CONICA at the Very Large Telescope (VLT). Thirty-three companion candidates in 24 binaries, three triples, and one quadruple system were detected. Nine companion candidates were found for the first time in this study. Five objects are likely to be chance projections. The detected companion candidates have K magnitudes between 5(m)T95 and 18(m)07 and angular separations ranging from <0 ''.05 to corresponding to linear projected separations of 13.5-1700 AU. Our study clearly confirms that HgMn stars are frequently members of binary and multiple systems. Taking into account companions found by other techniques, the multiplicity fraction in our sample may be as high as 91%. The membership in binary and multiple systems seems to he a key to understanding the abundance patterns in these stars.