THE CONNECTION BETWEEN SUBMILLIMETER CONTINUUM FLUX AND BINARY SEPARATION IN YOUNG BINARIES - EVIDENCE OF INTERACTION BETWEEN STARS AND DISKS

We present 800 mu m continuum photometry of pre-main-sequence binary s tars with projected separations a(p) < 150 AU in the Scorpius-Ophiuchu s star-forming region. Combining our observations with published 1300 mu m continuum photometry from Andre & Montmerle (1994), we find that binaries in Sco-Oph with 1 < a(p) < 50-100 AU have lower submillimeter continuum fluxes than wider binaries or single stars, as previously f ound for Taurus-Auriga binaries. The wide binaries and single stars ha ve indistinguishable submillimeter flux distributions. When the Sco-Op h and Tau-Aur samples are combined, this dependence of submillimeter f lux on binary separation is detected with a confidence level of greate r than 99%. Thus, binary companions with separations less than 50-100 AU significantly influence the nature of associated disks. We have exp lored the hypothesis that the reduction in submillimeter flux is the r esult of gaps cleared in 100 AU disks by companions. Gap clearing prod uces the qualitative dependence of submillimeter flux on binary separa tion, and a simple model suggests that large gaps in disks with surfac e densities typical of wide-binary or single-star disks can reduce sub millimeter fluxes to levels consistent with the observed limits. This model shows that the present submillimeter flux upper limits do not ne cessarily imply a large reduction in disk surface densities. Two-third s of the pre-main-sequence binaries were detected by IRAS at 60 mu m, showing that most binaries have at least one circumstellar disk. We ha ve used these fluxes to place lower limits of 10(-5) M. on circumstell ar disk masses. Similarly, the 60 mu m fluxes indicate that the circum stellar disk surface densities are no more than 2 orders of magnitude smaller than those of typical disks around single stars. Our upper lim its on submillimeter fluxes place upper limits of 0.005 M. on circumbi nary disk masses. Thus massive circumbinary disks (such as that found around GG Tau) are rare among binaries with projected separations betw een a few AU and 100 AU. Circumbinary disks are found around some bina ries with separations less than a few AU.