KOI-126: A Triply Eclipsing Hierarchical Triple with Two Low-Mass Stars

The Kepler spacecraft has been monitoring the light from 150,000 stars in its primary quest to detect transiting exoplanets. Here, we report on the detection of an eclipsing stellar hierarchical triple, identified in the Kepler photometry. KOI-126 [A, (B, C)], is composed of a low-mass binary [masses M_B = 0.2413 ± 0.0030 solar mass (M_⊙), M_C = 0.2127 ± 0.0026 M_⊙; radii R_B = 0.2543 ± 0.0014 solar radius (R_⊙), R_C = 0.2318 ± 0.0013 R_⊙; orbital period P₁ = 1.76713 ± 0.00019 days] on an eccentric orbit about a third star (mass M_A = 1.347 ± 0.032 M_⊙; radius R_A = 2.0254 ± 0.0098 R_⊙; period of orbit around the low-mass binary P₂ = 33.9214 ± 0.0013 days; eccentricity of that orbit e₂ = 0.3043 ± 0.0024). The low-mass pair probe the poorly sampled fully convective stellar domain offering a crucial benchmark for theoretical stellar models.