The Pre-Main-Sequence Eclipsing Binary TY Coronae Australis: Precise Stellar Dimensions and Tests of Evolutionary Models
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We analyze new photometric data for the Herbig Be eclipsing binary TY CrA, which securely reveal the secondary eclipse, 0.03 mag deep in y. From the light-curve solution and our previous spectroscopic data, absolute dimensions of the primary and secondary stars are derived. The masses are found to be M1 = 3.16 0.02 M and M2 = 1.64 0.01 M, the radii are R1 = 1.80 0.10 R and R2 = 2.08 0.14 R, the luminosities are L1 = 67 12 L and L2 = 2.4 0.8 L, and the effective temperatures are T1 = 12,000 500 K and T2 = 4900 400 K. Here the uncertainties represent high-confidence limits, not standard deviations. The secondary star is a pre-main-sequence star located at the base of the Hayashi tracks. As such, it is the least evolved star with a dynamically measured mass. Given higher effective temperatures for the primary (e.g., 12,500 K), the solar-composition 1.64 M evolutionary tracks of Swenson et al., Claret, and D'Antona & Mazzitelli are all consistent with the properties of the TY CrA secondary and suggest an age of order 3 Myr. The radius and projected rotational velocity of the secondary star are consistent with synchronous rotation. The primary star is located near the zero-age main sequence, which, for solar compositions, is consistent with an age of 3 Myr. However, the primary star is not well represented by any of the 3.16 M evolutionary models, which predict somewhat higher effective temperatures than observed.