AAS 207th Meeting, 8-12 January 2006
Session 11 Binary Models and Parameters
Poster, Monday, 9:20am-7:00pm, January 9, 2006, Exhibit Hall

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[11.08] Measuring the Mass of a Pre-Main Sequence Binary Star Through the Orbit of TWA 5A

Q.M. Konopacky, A.M. Ghez (UCLA), C. McCabe (JPL), G. Duchene (Observatoire de Grenoble), B.A. Macintosh (LLNL)

We present the results of a five year 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 5.55 ± 0.07 years and a semi-major axis of 0\farcs063 ± 0\farcs004. Combining these results with a kinematic distance, we calculate a total mass of 0.70 ± 0.24 M\odot for this system. This mass measurement, as well as the estimated age of this system, are in best agreement with the model predictions of Baraffe et al. (1998), but are also consistent to within 1.6\sigma of all other models considered. Our formal significance is low due to our proper accounting of correlated uncertainties; these correlations are important and generally not accounted for in comparisons of this kind. Nonetheless, with only a few more years of observation, these models will be easily distinguished. Support for this work was provided by the NASA Astrobiology Institute, the NSF Science & Technology Center for AO, managed by UCSC (AST-9876783), and the Packard Foundation.

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