Southern wide very low-mass stars and brown dwarfs in resolved binary and multiple systems

Abstract

The results of the Koenigstuhl survey in the Southern Hemisphere are presented. I have searched for common-proper motion companions to 173 field very low-mass stars and brown dwarfs with spectral types > M5.0V and magnitudes J <= 14.5 mag. I have measured for the first time the common-proper motion of two new wide systems containing very low-mass components, Koenigstuhl 2 AB and 3 A-BC. Together with Koenigstuhl 1 AB and 2M0126-50AB, they are among the widest systems in their respective classes (r = 450-11900 AU). Koenigstuhl 3 A-BC contains a well-known F8V star and a M8.0+L3.0V tight binary. I have determined the minimum frequency of field wide multiples (r > 100 AU) with late-type components at 5.0+/-1.8 % and the frequency of field wide late-type binaries with mass ratios q > 0.5 at 1.2+/-0.9 %. These values represent a key diagnostic of evolution history and low-mass star and brown-dwarf formation scenarios. Additionally, the proper motions of 76 field very low-mass dwarfs are measured here for the first time.