Binary Masses as a Test for Pre–Main-Sequence Tracks

Observations of binaries have traditionally provided the means for ascertaining stellar masses. Here, we use the published data on 8 pre–main-sequence pairs to gauge the accuracy of our own, recently calculated, evolutionary tracks (Palla & Stahler 1999). We consider both eclipsing, double-lined spectroscopic binaries, which provide the mass of each star separately, and non-eclipsing, double-lined systems, which yield only the ratio. We also analyze the visual, quadruple system GG Tau, for which the sum of the two component masses follows from observations of the circumbinary disk. In almost all cases, our theoretically derived masses or mass ratios are in good agreement with the empirical values. For two binaries (NTTS 162814−2427 and P1540), the observational results are still too uncertain for a proper comparison. We also find that the derived contraction ages within each pre–main-sequence pair are nearly equal. This result extends earlier findings regarding visual pairs, and indicates that the components of all binaries form in proximity, perhaps within the same dense cloud core. Finally, our study reveals that the Trapezium star BM Ori is very young, since both the star itself and its companion have contraction ages less than 10 years. Subject headings: stars: formation stars: evolution stars: binaries stars: pre–main-sequence individual: BM Ori, EK Cep, GG Tau, NTTS 162814−2427, P1540, Rs Cha, TY CrA, V773 Tau stars: main-sequence individual: CM Dra, EW Ori, HS Aur, YY Gem