The Aladin sky atlas of the Virtual Observatory has shown to be a powerful and easy-handling tool for the discovery, confirmation, and characterisation of high proper-motion, multiple stellar systems of large separation in the solar vicinity. Some of these systems have very low mass components (at the star/brown dwarf boundary) and are amongst the least bound systems found to date. With projected physical separations of up to tens of thousands astronomical units, these systems represent a challenge for theoretical scenarios of formation of very low-mass stars and brown dwarfs. Here we show preliminary results of a novel "virtual" search of binary systems and companions to Luyten stars with proper motions between 0.5 and 1.0 arcsec a −1 .

In spite of its importance for the study of star formation at all mass domains, the nearby young Orionis cluster still lacks a comprehensive survey for multiplicity. We try to fill that observational gap by looking for wide resolved binaries with angular separations between 0.4 and 4.0 arcsec. We search for companions to 331 cataloged cluster stellar members and candidates in public K-band UKIDSS images outside the innermost 1 arcmin, which is affected by the glare of the bright, eponymous Ori multiple system, and investigate their cluster membership with color-magnitude diagrams and previous knowledge of youth features. Of the 18 identified pairs, 10 have very low individual probabilities of chance alignment (< 1%) and are considered here as physical pairs. Four of them are new, while the other six had been discovered previously but never investigated homogeneously and in detail. Projected physical separations and magnitude differences of the 10 probably bound pairs range from 180 to 1220 au, and from 0.0 to 3.4 mag in K, respectively. Besides, we identify two cluster stars with elongated point spread functions. We determine the minimum frequency of wide multiplicity in the interval of projected physical separations s = 160-1600 au in Orionis at 3.0 +1.2 −1.1 %. We discover a new Lindroos system, find that massive and X-ray stars tend to be in pairs or trios, conclude that multiplicity truncates circumstellar disks and enhances X-ray emission, and ascribe a reported lithium depletion in a young star to unresolved binarity in spectra of moderate resolution. When accounting for all known multiples, including spectroscopic binaries, the minimum frequency of multiplicity increases to about 10%, which implies that of the order of 80-100 unknown multiple systems still await discovery in Orionis.

Aims. We investigated in detail the system WDS 19312+3607, whose primary is an active M4.5Ve star previously inferred to be young (τ ∼ 300-500 Ma) based on its high X-ray luminosity. Methods. We collected intermediate-and low-resolution optical spectra taken with 2 m-class telescopes, photometric data from the B to 8 μm bands, and data for eleven astrometric epochs with a time baseline of over 56 years for the two components in the system, G 125-15 and G 125-14. Results. We derived the M4.5V spectral types of both stars, confirmed their common proper motion, estimated their heliocentric distance and projected physical separation, determined their Galactocentric space velocities, and deduced a most-probable age of older than 600 Ma. We discovered that the primary, G 125-15, is an inflated, double-lined, spectroscopic binary with a short period of photometric variability of P ∼ 1.6 d, which we associated with orbital synchronisation. The observed X-ray and Hα emissions, photometric variability, and abnormal radius and effective temperature of G 125-15 AB are indicative of strong magnetic activity, possibly because of the rapid rotation. In addition, the estimated projected physical separation between G 125-15 AB and G 125-14 of about 1200 AU ensures that WDS 19312+3607 is one of the widest systems with intermediate M-type primaries. Conclusions. G 125-15 AB is a nearby (d ≈ 26 pc), bright (J ≈ 9.6 mag), active spectroscopic binary with a single proper-motion companion of the same spectral type at a wide separation. They are thus ideal targets for specific follow-ups to investigate wide and close multiplicity or stellar expansion and surface cooling because of the lower convective efficiency.