LOCAL DARK MATTER FROM A CAREFULLY SELECTED SAMPLE

We present the first analysis of the amount of local dark matter in which the systematic effects can be modeled easily and evaluated accurately. We have made use of the precise data obtained by Flynn & Freeman on K giants at the south Galactic pole. We defined, prior to beginning the theoretical analysis, a well-mixed homogeneous sample formed with the aid of the Flynn-Freeman apparent magnitudes, abundances, absolute magnitudes, and radial velocities. The uncertainties in the data for individual stars are well determined and relatively small, but the process of producing a homogeneous sample reduces the number of stars in the final sample to 125 out of a total of 560 giants. We use the method of Bahcall to solve the self-consistent equations for the distribution of disk matter. We find that the K-giant survey provides significant, but not overwhelming, evidence for disk dark matter. Taking into account all recognized sources of error using a statistical test devised by Gould, a model with no dark matter is inconsistent with the data at the 86% confidence level. Because of the conservative construction of the statistical test, and because of the close attention we have paid to possible systematic effects, we believe that the resulting 6-to-1 odds against the no-dark-matter model should be taken at face value. The best-fit P-model (in which dark matter is distributed proportionally to known matter) has 53% more dark matter than visible matter.