Abstract
We present the results of a 5 yr monitoring campaign of the close binary TWA 5Aab in the TW Hydrae association, using speckle and adaptive optics on the W. M. Keck 10 m telescopes. These measurements were taken as part of our ongoing monitoring of pre-main-sequence (PMS) binaries in an effort to increase the number of dynamically determined PMS masses and thereby calibrate the theoretical PMS evolutionary tracks. Our observations have allowed us to obtain the first determination of this system's astrometric orbit. We find an orbital period of 5.94 ± 0.09 yr and a semimajor axis of 0.066'' ± 0.005''. Combining these results with a kinematic distance, we calculate a total mass of 0.71 ± 0.14 M⊙(D/44 pc)3 for this system. This mass measurement, as well as the estimated age of this system, is consistent to within 2 σ of all theoretical models considered. In this analysis we properly account for correlated uncertainties, and we show that while these correlations are generally ignored, they increase the formal uncertainties by up to a factor of 5 and therefore are important to incorporate. With only a few more years of observation, this type of measurement will allow the theoretical models to be distinguished.
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