THE PARTICLE-SIZE DISTRIBUTION IN THE DUST EJECTED FROM IRC PLUS 10216

We propose that in the outer envelope (more than 15'' from the star) around IRC + 10216 the grains are amorphous carbon spheres of radius a with a size distribution of the form n(a) approximately a-3.5 exp(- a/a0) and a0 almost-equal-to 0.10 mum. Small grains (a much-less-than a0) are required to explain the shielding of circumstellar molecules against destruction by interstellar ultraviolet radiation. Larger grains (a must-less-than a0) are required to explain the observed circumstellar polarization at the K band. In this model approximately 0.1% of the mass in the ejected dust is contained in particles that are larger than 1 mum in diameter. If the size distribution of the ejected SiC particles is similar to the size distribution that we derive for the amorphous carbon grains, then at least some of the micron-sized SiC inclusions in meteorites though to originate from mass-losing carbon stars may have been produced in the outflows from stars such as IRC + 10216.