Koerner, D. W.; Jensen, E. L. N.; Cruz, K. L.; Guild, T. B.; Gultekin, K.
A Single Circumbinary Disk in the HD 98800 Quadruple System
The Astrophysical Journal, Volume 533, Issue 1, pp. L37-L40.
Abstract
We present subarcsecond thermal
infrared imaging of HD 98800, a young quadruple system composed of a
pair of low-mass spectroscopic binaries separated by 0.8" (38 AU),
each with a K-dwarf primary. Images at wavelengths ranging from 5 to
24.5 μm show unequivocally that the optically fainter binary, HD
98800B, is the sole source of a comparatively large infrared excess on
which a silicate emission feature is superposed. The excess is
detected only at wavelengths of 7.9 μm and longer, peaks at 25
μm, and has a best-fit blackbody temperature of 150 K, indicating
that most of the dust lies at distances greater than the orbital
separation of the spectroscopic binary. We estimate the radial extent
of the dust with a disk model that approximates radiation from the
spectroscopic binary as a single source of equivalent
luminosity. Given the data, the most likely values of disk properties
in the ranges considered are Rin=5.0+/-2.5 AU,
ΔR=13+/-8 AU, λ0=2+4-1.5
μm, γ=0+/-2.5, and σtotal=16+/-3
AU2, where Rin is the inner radius, ΔR is
the radial extent of the disk, λ0 is the effective
grain size, γ is the radial power-law exponent of the optical
depth τ, and σtotal is the total cross section of
the grains. The range of implied disk masses is 0.001-0.1 times that
of the Moon. These results show that, for a wide range of possible
disk properties, a circumbinary disk is far more likely than a narrow
ring.