New photometry and spectra OFAB 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_⊙ mass for the system. Once armed with an accurate spectrum and K_s flux, we find L = 0.0021 ±0.0005 L_⊙ and T_eff = 2925_-145⁺¹⁷⁰ K for AB Dor C. These values are consistent with a ∼75 Myr, 0.090 ±0.005 M_⊙ 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.