K giants and the total amount of matter near the sun

The Poisson and Boltzmann equations are solved numerically for realistic Galaxy models which include multiple disk components (between 14 and 28), a Population II spheroid, and an unseen massive halo. As a guide in constructing the theoretical models, a population of normal-metallicity (disk) K giants is isolated using existing data and is shown to be well described by an isothermal distribution function with a velocity dispersion perpendicular to the plane of 20 km s⁻¹. The total amount of matter in the vicinity of the Sun is determined by comparing the observed distributions of K giants with the predictions of detailed Galaxy models. The volume density of unobserved material near the Sun is about 0.1 M_sun; pc⁻³; the corresponding column density is about 30 M_sun; pc⁻².