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On the Age, Spectral Type, Orbit, and Comparison to Evolutionary Models of AB Dor C
Close, L. M.; Nielsen, E. L.; Guirado, J. C.; Biller, B. A.; Lenzen, R.; Brandner, W.; Hartung, M.; Lidman, C.
Direct Imaging of Exoplanets: Science & Techniques. Proceedings of the IAU Colloquium #200, Edited by C. Aime and F. Vakili. Cambridge, UK: Cambridge University Press, 2006., pp.11-18
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We expand upon the results of Close et al. 2005 regarding the young, low-mass object AB Dor C and its role as a calibration point for theoretical tracks. We argue for a new 70±30 Myr age estimate and present two additional detections of C with the Simultaneous Differential Imaging (SDI) camera. Our improved analysis (Nielsen et al. 2005) confirms our spectral type of M8 (±1) and mass of 0.090 ±0.003 Msun for AB Dor C. However, Luhman & Potter (2006) argue for a hotter spectral type (M6±1). Here we adopt the consistent spectral range of M7±1 in this paper as a final spectral type. Plotting AB Dor C (and all other young ({ Myr), low-mass (0.3-0.05 Msun) objects with accurate dynamical masses) on the HR diagram suggests a trend where current evolutionary models tend to over-predict the temperature (or under-predict the mass) for young low-mass stars and high-mass brown dwarfs. With our uncertainties, there is a ˜90% chance that the mass of AB Dor C is underestimated by the DUSTY tracks in the HR diagram.

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