The fate of the solid matter orbiting HR 4796A

We have obtained optical spectra, 2 μm speckle images, and an upper limit to the 800 μm flux for HR 4796A, and optical spectra for its physical companion separated by 7″.7, HR 4796B. We detect Hβ, Hγ, and the calcium H and K lines in emission from HR 4796B; these data are consistent with the hypothesis that it is later than spectral type M2 and lies substantially above the main-sequence. From the location of HR 4796B on the H-R diagram, the estimated age of this star is 3 × 10⁶ yr, and assuming this age for the entire system, we find from our 2 μm speckle data that there is no close stellar companion to HR 4796A (M > 0.125 M_⊙) between 11 and 120 AU from the star. From the IRAS and ground-based photometry, it seems that there is a hole in the dust distribution around HR 4796A with an inner radius of between ∼40 and ∼200 AU. The observed circumstellar dust grains, which lie at D > 40 AU from the star, are likely to be at least 3 μm in radius in order to be gravitationally bound to HR 4796A, if the circumstellar dust cloud is optically thin. Since they are larger than almost all interstellar grains, the circumstellar dust grains probably grew by coalescence. Because the existing grains at D > 40 AU have undergone measurable coalescence, it is possible that particles that presumably once existed at D < 40 AU, where the collision times were shorter than at D > 40 AU, grew into macroscopic objects. A likely explanation for the dust hole is that there is a companion located at about half the inner radius of the dust hole, or between 20 and 100 AU from the star. If such a companion exists, it must have a mass less than 0.125 M_⊙. Since grain coalescence has occurred, this putative companion possibly could be a planet.