Context :

Aims : We present the first high-angular resolution survey for multiple systems among very low-mass stars and brown dwarfs in the Hyades open cluster .

Methods : Using the Keck II adaptive optics system , we observed a complete sample of 16 objects with estimated masses \lesssim 0.1 M _ { \odot } .

Results : We have identified three close binaries with projected separation \lesssim 0 \aas@@fstack { \prime \prime } 11 , or \lesssim 5 AU .
A number of wide , mostly faint candidate companions are also detected in our images , most of which are revealed as unrelated background sources based on astrometric and/or photometric considerations .
The derived multiplicity frequency , 19 ^ { +13 } _ { -6 } % over the 2–350 AU range , and the rarity of systems wider than 10 AU are both consistent with observations of field very low-mass objects .
In the limited 3–50 AU separation range , the companion frequency is essentially constant from brown dwarfs to solar-type stars in the Hyades cluster , which is also in line with our current knowledge for field stars .
Combining the binaries discovered in this surveys with those already known in the Pleiades cluster reveals that very low-mass binaries in open clusters , as well as in star-forming regions , are skewed toward lower mass ratios ( 0.6 \lesssim q \lesssim 0.8 ) than are their field counterparts , a result that can not be accounted for by selection effects .
Although the possibility of severe systematic errors in model-based mass estimates for very low-mass stars can not be completely excluded , it is unlikely to explain this difference .

Conclusions : We speculate that this trend indicates that surveys among very low-mass field stars may have missed a substantial population of intermediate mass ratio systems , implying that these systems are more common and more diverse than previously thought .