Multiplicity of late-type B stars with HgMn peculiarity ^⋆,⋆⋆

¹ European Southern Observatory , Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
e-mail: mschoell@eso.org
² Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
³ Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse 1, 85748 Garching, Germany

Received: 11 February 2010
Accepted: 17 June 2010

Abstract

Context. Observations at various wavelengths of late B-type stars exhibiting strong atmospheric overabundances of the chemical elements Hg and Mn indicate that these stars are frequently found in binary and multiple systems.

Aims. We intend to study the multiplicity of this type of chemically peculiar stars, looking for visual companions in the range of angular separation between 0″̣05 and 8″.

Methods. We carried out a survey of 56 stars using diffraction-limited near-infrared imaging with NAOS-CONICA at the VLT.

Results. 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 chance projections. The detected companion candidates have K magnitudes between 5ṃ95 and 18ṃ07 and angular separations ranging from  < 0″̣05 to 7″̣8, corresponding to linear projected separations of 13.5–1700 AU.

Conclusions. 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 be a key point to understanding the abundance patterns in these stars.