SOLAR CORONAL DUST SCATTERING IN THE INFRARED

Observations of the total and polarized brightness of the solar corona at wavelength 2.12 mu m during the total solar eclipse of 1991 July 1 1 are employed to separate the contribution of the electron-scattered component and the remaining, nonpolarized component, the latter domina ting in the outer corona. After corrections are applied to account for a two-component sky or instrument background, the brightness of the e cliptic and polar corona are fitted by r(-1.9) and r(-2.3), respective ly, over the radial distance range 3-8 Ro from Sun center. The eclipti c outer-coronal brightness is compared with a Mie-scattering model of interplanetary dust particles based upon three particle-size distribut ions deduced from, respectively, lunar microcrater counts (Lamy and Pe rrin 1986), interplanetary dust flux measurements (Grun et al. 1985), and for an arbitrary population of large particles (radii > 3 x 10(-5) cm). Particle physical characteristics and spatial distributions are those assumed in past studies of the zodiacal cloud. For reasonable as sumed space number densities of particles, the models agree with the m agnitude of observed ecliptic coronal brightness. But in all cases, th e models predict a steeper brightness fall off with radial distance th an that observed, with those models for which the power-law exponent f or the space distribution is v = 1.3 being the most discrepant with th e observed radial gradient.