EDP Sciences
Free Access
Volume 507, Number 1, November III 2009
Page(s) 251 - 259
Section Galactic structure, stellar clusters, and populations
DOI https://doi.org/10.1051/0004-6361/200912596
Published online 08 September 2009
A&A 507, 251-259 (2009)
DOI: 10.1051/0004-6361/200912596

Reaching the boundary between stellar kinematic groups and very wide binaries

The Washington double stars with the widest angular separations
J. A. Caballero

Departamento de Astrofísica y Ciencias de la Atmósfera, Facultad de Física, Universidad Complutense de Madrid, 28040 Madrid, Spain
    e-mail: caballero@astrax.fis.ucm.es

Received 29 May 2009 / Accepted 12 August 2009

Aims. I look for and characterise very wide binaries and multiple systems with projected physical separations larger than s = 0.1 pc, which is generally believed to be a sharp upper limit to the distribution of wide binary semimajor axes.
Methods. I investigated in detail 30 Washington double stars with angular separations of $\rho$ > 1000 arcsec. 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).
Results. 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 > 0.2 pc. 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 $\beta$ Pictoris moving group), there is no clear prevalence of young systems ($\tau$ < 1 Ga) 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.

Key words: astronomical data bases: miscellaneous -- binaries: general -- binaries: visual -- stars: kinematics

© ESO 2009