Keck diffraction-limited imaging of the young quadruple star system HD 98800

This paper presents diffraction-limited 1-18 mum images of the young quadru ple star system HD 98800 obtained with the W. M. Keck 10 m telescopes using speckle and adaptive optics imaging at near-infrared wavelengths and direc t imaging at mid-infrared wavelengths. The two components of the visual bin ary, A and B, both themselves spectroscopic binaries, were separable at all wavelengths, allowing us to determine their stellar and circumstellar prop erties. Combining these observations with spectroscopic data from the liter ature, we derive an age of similar to 10(7) yr, masses of 0.93 and 0.64 M., and an inclination angle of 58 degrees for the spectroscopic components of HD 98800 B and an age of similar to 10(7) yr and a mass of 1.1 M. for HD 9 8800 Aa. Our data confirm that the large mid-infrared excess is entirely as sociated with HD 98800 B. This excess exhibits a blackbody temperature of 1 50 K and a strong 10 mum silicate emission feature. The theoretical equilib rium radius of large, perfectly absorbing, 150 K grains around HD 98800 B i s 2.4 AU, suggesting a circumspectroscopic binary distribution. Our observa tions set important upper limits on the size of the inner dust radius of si milar to2 AU (from the mid-infrared data) and on the quantity of scattered light of less than 10% (from the H-band data). For an inner radius of 2 AU, the dust distribution must have a height of at least 1 AU to account for t he fractional dust luminosity of similar to 20% L-B. Based on the scattered -light limit, the dust grains responsible for the excess emission must have an albedo of less than 0.33. The presence of the prominent silicate emissi on feature at 10 mum implies dust grain radii of greater than or similar to 2 mum. The total mass of the dust is greater than 0.002 M+. We conclude tha t the dust is located in a circumbinary disk around the HD 98800 B spectros copic binary with an inner gap of similar to2 AU and a height of greater th an or similar to1 AU, and we speculate that the A-Bc orbital dynamics are r esponsible for the characteristics of the observed dust in the system.