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Session 43 - Binary Stars.
Display session, Tuesday, January 16
North Banquet Hall, Convention Center
51 Tau was discovered as a single-lined spectroscopic binary by Deutsch (1971, PASP, 83, 298), with the peculiarity that only the sharp lines of the secondary are visible. It was subsequently resolved by speckle interferometry (McAlister 1977, ApJ, 212, 459), and after being followed over several of its 11-year cycles, it now has perhaps one of the best determined visual orbits for any binary in the Hyades cluster.
The primary has eluded spectroscopic detection until now, on account of its low radial velocity amplitude which causes its lines to be always blended with those of the secondary, and also the fact that it is a very fast rotator. We report here the first detection of the primary component using TODCOR, a two-dimensional cross-correlation technique. Thus we have converted the system into a double-lined spectroscopic binary.
Using our new radial velocities of both components spanning more than 14 years, in combination with all available astrometric data, we have determined the individual masses of 51 Tau A and B directly. In addition, we derive the orbital parallax of the system with an error of only 4%, corresponding to a distance of about 54 pc.
We use the orbital parallax to derive an estimate of the distance to the Hyades cluster independent of all other determinations. Our preliminary result (46 \pm 2 pc) is consistent with other recent estimates. The empirical mass-luminosity relation we derive for the Hyades with the new masses of 51 Tau and two other binaries is in very good agreement with recent evolutionary model calculations. Using the binary data we are also able to obtain a new estimate for the age of the cluster of 600 Myr.
