The Circumbinary Disk of Hd 98800b: Evidence for Disk Warping

The quadruple young stellar systemHD 98800 consists of two spectroscopic binary pairs with a circumbinary disk around the B component. Recent work by Boden and collaborators using infrared interferometry and radial velocity data resulted in a determination of the physical orbit for HD 98800B. We use the resulting inclination of the binary and the measured extinction toward the B component stars to constrain the distribution of circumbinary material. Although a standard optically and geometrically thick disk model can reproduce the spectral energy distribution, it cannot account for the observed extinction if the binary and the disk are coplanar. We next constructed a dynamical model to investigate the influence of the A component, which is not in the Ba-Bb orbital plane, on the B disk.We find that these interactions have a substantial impact on the inclination of the B circumbinary disk with respect to the Ba-Bb orbital plane. The resulting warp would be sufficient to place material into the line of sight and the noncoplanar disk orientation may also cause the upper layers of the disk to intersect the line of sight if the disk is geometrically thick. These simulations also support that the dynamics of the Ba-Bb orbit clear the inner region to a radius of 3 AU. We then discuss whether the somewhat unusual properties of the HD 98800B disk are consistent with material remnant from the star formation process or with more recent creation by collisions from larger bodies. Subject headinggs: binaries: spectroscopic — circumstellar matter — stars: formation — stars: individual (HD 98800B)