– 32 – 5.2.3. Grain growth possibility. Target # 23 is a ∼ 0.19 ′′ (or 24 AU) separation binary with λ$_{turn}$$_{−}$$_{off}$ = 8.0 µ m. This object has a small 24 µ m excess, consistent with Wien side of the emission from a cold outer disk. Objects # 12 and 23 have a low disk masses ( < 1.7 M$_{JUP}$ ), negligible accretion, and L$_{D}$/L$_{∗}$ < 10 − $^{3}$. As discussed in the previous section, they are likely to be in the debris disk stage, regardless of the origin of the inner hole. After target #23, the next tighter binary is source #5, with a projected separation of 0.54 ′′ (or 68 AU). Since this object has λ$_{turn}$$_{−}$$_{off}$ = 5.8 µ m, suggesting the presence of dust at ≲ 1 AU distances, it is very unlikely that the presence of its inner hole is related to the observed companion. Since VLT-AO observations are clearly not sensitive to companions with separations ≲ 8 AU, a complementary radial velocity survey to find the tightest companions would be highly desirable to identify additional circumbinary disks within our sample. Once primordial sub-micron dust grains grow into somewhat larger bodies (r dust ≫ λ$_{stellar}$$_{−}$$_{photons}$ ), most of the solid mass ceases to interact with the stellar radiation, and the opacity function decreases dramatically. Grain growth is a strong function of radius; it is more efficient in the inner regions where the surface density is higher and the dynamical timescales are shorter, and hence can also produce opacity holes. Idealized dust coagulation models (i.e., ignoring fragmentation and radial drift) predict extremely efficient grain growth (Dullemond & Dominik, 2005) resulting in the depletion of all small grains in timescales of the order of 10 5 yrs, which is clearly inconsistent with the observational constraints on the lifetime of circusmtellar dust. In reality, however, the persistence of small opacity-bearing grains depends on a complex balance between dust coagulation and fragmentation (Dominik & Dullemond, 2008). Since grain growth affects only the dust and operates preferentially at smaller radii, a