New photometry and spectra of AB Doradus C: An accurate mass determination of a young low-mass object with theoretical evolutionary tracks

We present new photometric and spectroscopic measurements for the unique, young, low-mass evolutionary track calibrator AB Dor C. While the new K-s photometry is similar to that we have previously published, the spectral type is found to be much earlier. Based on new H and K IFS spectra of AB Dor C from Thatte et al. (Paper I), we adopt a spectral type of M5.5 +/- 1.0 for AB Dor C. This is considerably earlier than the M8 +/- 1 previously estimated by Close et al. and Nielsen et al. yet is consistent with the M6 +/- 1 independently derived by Luhman& Potter. However, the spectrum presented in Paper I and analyzed here is a significant improvement over any previous spectrum of AB Dor C. We also present new astrometry for the system, which further supports a 0.090 +/- 0.005 M-circle dot mass for the system. Once armed with an accurate spectrum and K-s flux, we find L = 0.0021 +/- 0.0005 L-circle dot and T-eff= 2925(-145)(+170) 145 K for AB Dor C. These values are consistent with a similar to 75 Myr, 0.090 +/- 0.005 M-circle dot object like AB Dor C according to the DUSTY evolutionary tracks. Hence, masses can be estimated from the H-R diagram with the DUSTY tracks for young low-mass objects such as AB Dor C. However, we cautiously note that underestimates of the mass from the tracks can occur if one lacks a proper (continuum- preserved) spectrum or is relying on near-infrared fluxes alone.