2009A&A...507..251C

I look for and characterise very wide binaries and multiple systems with projected physical separations larger than s=0.1pc, which is generally believed to be a sharp upper limit to the distribution of wide binary semimajor axes. I investigated in detail 30 Washington double stars with angular separations of ρ>1000arcsec. I discarded 23 of them as probably unbound systems based on discordant astrometry, photometry, spectral types, and radial velocities. The remaining seven systems were subject to a comprehensive data compilation and derivation (multi-wavelength photometry, heliocentric distance, multiplicity, age, mass, metallicity, membership in a young kinematic group). Of the seven very wide systems, six have projected physical separations greater than the hypothetical cutoff at s=0.1 pc and four have separations s>0.2pc. Although there are two systems in young kinematic groups (namely HD 136654 and BD+32 2572 in the Hyades Supercluster, and AU Mic and AT Mic AB in the β Pictoris moving group), there is no clear prevalence of young systems (τ<1Ga) among these very wide binaries. Finally, I compare the binding energies of the seven systems with those of other weakly bound systems in the field.