HD 161701, a chemically peculiar binary with a HgMn primary and an Ap secondary

Context. In recent years, HgMn stars have attracted attention after in several of them surface chemical spots of different elements were discovered, whose origin and possible connection with binarity and magnetic fields is not clear yet. Aims. We perform a complete study of the HgMn binary HD 161701, including the determination of physical parameters and photospheric chemical abundances. Methods. We analyzed time series of high-resolution spectroscopic observations obtained with ESO's spectrograph FEROS and the spectro-polarimeter HARPS, in addition to a near-IR spectrum obtained with CRIRES. Radial velocity curves for both stars were combined with additional spectroscopic information to estimate absolute stellar parameters. A spectral separation technique was applied, which enabled us to conduct a detailed spectral analysis of both the HgMn primary and the low-luminosity secondary component, which turned out to be a peculiar star as well. Chemical abundances were determined by spectral synthesis. Using HARPS and FEROS spectra obtained at 11 rotational phases, we detected line profile variations in both stellar companions, indicating a nonuniform surface distribution of chemical composition. Results. HD 161701 is a binary system formed by two chemically peculiar stars in an almost circular orbit with a period of 12.451 d. The primary is a 4.0 M-circle dot star with a chemical pattern typical of HgMn stars with notable overabundances of P, Mn, Ga, Y, Xe, and Hg. The secondary is a 2.4 M-circle dot star showing moderate (1-2 dex) overabundance in metals of the iron group, and strong (2-5 dex) overabundaces in Sr, Y, and particularly rare-earth elements. This star presents a remarkable surface chemical spot pattern with Ti and rare-earths concentrated on the surface region that is pemanently facing the binary companion, and Fe concentrated on the far side. The primary star shows weak profile variations in Mn and Cr spectral lines. Conclusions. The coincidence of chemical spots with the position of the binary companion, a fact that has recently been reported also in a few other chemically peculiar stars, suggests a possible connection between the presence of the companion and the origin of chemical anomalies.