The Nature of TT Hydrae

Abstract

Photometric solutions are made of previously published photoelectric light curves of TT Hydrae. The WINK model is employed to give radii of r_A = 0.0894 and r_B = 0.2431, and an orbital inclination of i = 84.4 deg. Spectrophotometry is presented and analyzed to give revised spectral types of B9.5 V and phase-variable G9 to K1 III-IV, and temperatures of T_A = 9800K and T_B = 4850 - 4670K. There is anomalous photometric behavior indicative of circumstellar material surrounding the primary component. The near-ultraviolet excess seen during totality is verified by spectrophotometry, and found to extend to ≡4200 Å. Photospheric features of Si II, Mg II, and He I are consistent with a B9.5 V classification for the hotter star, and give a v sin i of 168 km s^-1. The metallic-line spectrum (similar to an A2) and sharp hydrogen-line cores, both associated with the hotter star, arise almost totally from circumstellar material. The mass ratio is combined with a preliminary spectroscopic orbit for the cooler star to derive the component properties: M_A = 2.25 M_sun;, M_B = 0.41 M_sun;, R_A = 1.90 R_sun;, and R_B = 5.17 R_sun; The radiative properties imply that the system is 193 pc distant.