A redetermination of the mass of Procyon

The parallax and astrometric orbit of Procyon have been redetermined from P DS measurements of over 250 photographic plates spanning 83 years, with rou ghly 600 exposures used in the solution. These data are combined with two m odern measurements of the primary-white dwarf separation, one utilizing a g round-based coronagraph, the other, the Planetary Camera (PC) of the Hubble Space Telescope. Together with the redetermined astrometric orbit and para llax, these yield new estimates of the component masses. The derived masses are 1.497 +/- 0.037 M. for the primary and 0.602 +/- 0.015M. for the white dwarf secondary. These mass values are heavily weighted by the PC separati on measurement, which, while being somewhat discordant with the ground-base d measures, we argue is more precise and more accurate and thus deserving o f its greater weight. This stated, the long-standing discrepancy between pr evious determinations of the observed mass of Procyon A (1.75 M.) and the v alue supported by stellar evolution models (1.50 M.) appears to be reconcil ed.