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Session 60 - Multiple Stars.
Display session, Wednesday, June 12
Great Hall,

[60.02] A Redetermination of the Mass of Procyon

T. M. Girard, H. Wu, J. T. Lee, S. E. Dyson, E. P. Horch, W. F. van Altena (Yale Obs.), C. Ftaclas (Michigan Tech. Univ.)

The Procyon binary system consists of an F5 IV-V primary and a white dwarf secondary in an approximately 40-year orbit. The mass of the F5 primary as determined from stellar evolution theory does not agree with the value derived astrometrically by K. Aa. Strand in 1951, nor with a more recent determination by A. W. Irwin et al. in 1992 who combined Strand's photographic measures with radial velocity data.

We have used the Yale PDS microdensitometer to remeasure the plates used in Strand's analysis as well as a substantial number of additional plates, doubling the total time baseline to over 80 years. These new measures yield improved orbital elements for the astrometric orbit, (i.e. that of the primary relative to the barycenter). In turn, the new elements and PDS measurement of the USNO parallax series for Procyon allow us to derive the trigonometric parallax for the system to within a formal uncertainty of 1.5 milliarcseconds.

The final datum needed to calculate the individual component masses is the angular scale of the visual orbit, (i.e. that of the secondary relative to the primary). An accurate measurement of the primary/white dwarf separation was recently made by R. Brown et al. using the CoCo coronograph and the NASA IRTF 3-meter telescope. With this final ingredient, we are able to derive mass estimates for the two components which are free of any possible systematic error associated with the visual measures of the separation made early in this century, an extremely difficult task considering the \approx 10-magnitude difference and 5-arcsecond separation. Our new determination of the mass of Procyon A falls midway between the theoretical value and the previous astrometric estimates.

This research was supported by funds from the National Science Foundation, including a grant from the AAS/REU program.

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