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, similar to 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-circle dot and M-2 = 1.64 +/- 0.01 M-circle dot, the radii are R-1 = 1.80 +/- 0.10 R-circle dot and R-2 = 2.08 +/- 0.14 R-circle dot, the luminosities are L-1 = 67 +/- 12 L-circle dot and L-2 = 2.4 +/- 0.8 L-circle dot, 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-circle dot evolutionary models, which predict somewhat higher effective temperatures than observed.