George Gatewood and Inwoo Han

The similarities in their apparent magnitudes and placement in the sky led to the use of Procyon and Sirius as "fundamental stars", observed with meridian telescopes to determine observatory clock errors and the drift of the instrumental pole.  In these calculations, during the early 1800's Bessel noticed an increasing divergence in the expected time of transit of Sirius and the apparent declination of Procyon  (Bessel, F.W. 1844, MNRAS, 6, 136).   One hundred and sixty years later, their similarities still effect their observation.  While most of the Multichannel Astrometric Photometer (MAP) channels can be adjusted to accommodate a wide range in magnitudes, Procyon was observed with a specially filtered channel designed to allowed MAP observations of Sirius.  We report on the analysis of observations of Procyon obtained with the MAP during the years 1986 through 2004.  While the results significantly increase the precision of the estimated characteristics of the components of the system they are generally in good agreement with the most recent studies.   The F5 IV primary is found to have a mass of 1.43 ± 0.034 M8 while the white dwarf companion’s mass is 0.58 ± 0.014 M8.


This paper has been submitted to the Astronomical Journal.