SOAR TESS Survey. I: Sculpting of TESS planetary systems by stellar companions

TESS is finding transiting planet candidates around bright, nearby stars across the entire sky. The large field-of-view, however, results in low spatial resolution, therefore multiple stars contribute to almost every TESS light curve. High-angular resolution imaging can detect the previously unknown companions to planetary candidate hosts that dilute the transit depths, lead to host star ambiguity, and in some cases are the source of false-positive transit signals. We use speckle imaging on SOAR to search for companions to 542 TESS planet candidate hosts in the Southern sky. We provide correction factors for the 117 systems with resolved companions due to photometric contamination. The contamination in TESS due to close binaries is similar to that found in surveys of Kepler planet candidates. For the solar-type population, we find a deep deficit of close binary systems with projected stellar separations less than 100 AU among planet candidate hosts (44 observed binaries compared to 124 expected based on field binary statistics). The close binary suppression among TESS planet candidate hosts is similar to that seen for the more distant Kepler population. We also find a large surplus of the TESS planet candidates in wide binary systems, detected in both SOAR and Gaia DR2 (119 observed binaries compared to 77 expected). These wide binaries host almost exclusively giant planets, however, suggesting orbital migration, caused by perturbations from the stellar companion, may lead to planet-planet scattering and suppress the population of small planets in wide binaries. Both trends are also apparent in the M-dwarf planet candidate hosts.