The Pre–Main-Sequence Eclipsing Binary TY Coronae Australis: Precise Stellar Dimensions and Tests of Evolutionary Models

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 M 1 = 3.16 ± 0.02 M ☉ and M 2 = 1.64 ± 0.01 M ☉ , the radii are R 1 = 1.80 ± 0.10 R ☉ and R 2 = 2.08 ± 0.14 R ☉ , the luminosities are L 1 = 67 ± 12 L ☉ and L 2 = 2.4 ± 0.8 L ☉ , and the effective temperatures are T 1 = 12,000 ± 500 K and T 2 = 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.