Keck Diffraction‐limited Imaging of the Young Quadruple Star System HD 98800

This paper presents diffraction-limited 1-18 micron images of the youngquadruple star system HD 98800 obtained with the W. M. Keck 10-m telescopesusing speckle and adaptive optics imaging at near-IR wavelengths and directimaging at mid-IR wavelengths. The two components of the visual binary, A andB, both themselves spectroscopic binaries, were separable at all wavelengths,allowing us to determine their stellar and circumstellar properties. Combiningthese observations with spectroscopic data from the literature, we derive anage of 10 Myr, masses of 0.93 and 0.64 M_sun and an inclination angle of 58 degfor the spectroscopic components of HD 98800 B, and an age of 10 Myr and a massof 1.1 M_sun for HD 98800 Aa. Our data confirm that the large mid-IR excess isentirely associated with HD 98800 B. This excess exhibits a black bodytemperature of 150 K and a strong 10 micron silicate emission feature. Thetheoretical equilibrium radius of large, perfectly absorbing, 150 K grainsaround HD 98800 B is 2.4 AU, suggesting a circum-spectroscopic binarydistribution. Our observations set important upper limits on the size of theinner dust radius of ~2 AU (mid-IR data) and on the quantity of scattered lightof <10% (H-band data). For an inner radius of 2 AU, the dust distribution musthave a height of at least 1 AU to account for the fractional dust luminosity of\~20% L_B. Based on the scattered light limit, the dust grains responsible forthe excess emission must have an albedo of <0.33. The presence of the prominentsilicate emission feature at 10 microns implies dust grain radii of >2 microns.The total mass of the dust, located in a circumbinary disk around the HD 98800B, is >0.002 M_earth. The orbital dynamics of the A-B pair are likelyresponsible for the disk geometry.Comment: 27 pages, 4 tables, 9 figures; small revisions to section 3.2.