A LIKELY CLOSE-IN LOW-MASS STELLAR COMPANION TO THE TRANSITIONAL DISK STAR HD 142527

With the uniquely high contrast within 0 ''.1 (Delta mag(L') = 5-6.5 mag) available using Sparse Aperture Masking with NACO at Very Large Telescope, we detected asymmetry in the flux from the Herbig Fe star HD 142527 with a barycenter emission situated at a projected separation of 88 +/- 5 mas (12.8 +/- 1.5 AU at 145 pc) and flux ratios in H, K, and L' of 0.016 +/- 0.007, 0.012 +/- 0.008, and 0.0086 +/- 0.0011, respectively (3 sigma errors), relative to the primary star and disk. After extensive closure-phase modeling, we interpret this detection as a close-in, low-mass stellar companion with an estimated mass of similar to 0.1-0.4 M-circle dot. HD 142527 has a complex disk structure, with an inner gap imaged in both the near and mid-IR as well as a spiral feature in the outer disk in the near-IR. This newly detected low-mass stellar companion may provide a critical explanation of the observed disk structure.