Multiplicity of late-type B stars with HgMn peculiarity

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 5. m 95 and 18. m 07 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.

The multiplicity ofφPhe revisited

“…Dolk et al (2003) reported T eff = 10 612 ± 200 K and log g = 3.79 ± 0.10 together with [Fe/H] = 0.15 from Smith & Dworetsky (1993). On the grid of stellar evolutionary tracks from Bertelli et al (2009), the three-solar-mass track with Y = 0.3 and Z = 0.017 gives the best match as far as log g and T eff are concerned (left panel of Fig.…”

“…The magnitudes of the two components differ by 5.7 in V and 3.9 in K. Such a large difference in V explains the absence of the signal in the Hipparcos data and in the spectra. The semi-major axis of the relative visual orbit is 36.3 mas only, making this system essentially inaccessible to VLT/NACO (Schöller et al 2010). The two components are nevertheless bright enough to be resolved with the VLTI.…”

Masses and age of the chemically peculiar double-lined binaryχLupi

“…Smith & Dworetsky (1993) measured the stellar parameters of the primary component and found T a = 10 750 K and log(g a ) = 4.0. Wahlgren et al (1994) iteratively determined the parameters of the two components by a detailed spectroscopic modeling and obtained T a = 10 650 K, T b = 9200 K, log(g a ) = 3.89 and log(g b ) = 4.2.…”

“…The CP stars of mercury-manganese (HgMn) type are exceptional cases where no clear magnetic field is detected but peculiarities (and sometimes spots) are still present on the stellar surface. Observations suggest a correlation between the presence of a weak magnetic field, abundance anomalies, and binary properties (Schöller et al 2010;Hubrig et al 2012). More studies of HgMn stars are especially important for understanding the role of the multiplicity and the magnetic field as well as the evolutionary aspects of the chemical peculiarity phenomenon.…”

A search for pulsations in the HgMn star HD 45975 with CoRoT photometry and ground-based spectroscopy

“…These late, main-sequence B stars have effective temperatures ranging from 10 500 to 15 000 K and masses roughly between 2.5 and 5 M (e.g., Adelman et al 2003). They are also often found in binary systems (e.g., Catanzaro & Leto 2004;Schöller et al 2010Schöller et al , 2012.…”