Speckle Observations of TESS Exoplanet Host Stars: Understanding the Binary Exoplanet Host Star Orbital Period Distribution

TL;DR

This study uses high-resolution speckle imaging to analyze the binary star properties of TESS exoplanet hosts, revealing wider binary separations compared to field stars, which impacts planet formation theories.

Contribution

It provides new observational data on the binary star distribution among TESS exoplanet hosts, especially regarding orbital periods and separations, challenging existing models.

Findings

Approximately 24% of observed TESS stars have likely bound companions.

Binary systems with exoplanets tend to have wider separations than field binaries.

The orbital period distribution peaks near 100 au, higher than typical field binaries.

Abstract

We present high-resolution speckle interferometric imaging observations of TESS exoplanet host stars using the NN-EXPLORE NESSI instrument the at the 3.5-m WIYN telescope. Eight TOIs, that were originally discovered by Kepler, were previously observed using the Differential Speckle Survey Instrument (DSSI). Speckle observations of 186 TESS stars were carried out and 45 (24%) likely bound companions were detected. This is approximately the number of companions we would expect to observe given the established 46% binarity rate in exoplanet host stars. For the detected binaries, the distribution of stellar mass ratio is consistent with that of the standard Raghavan distribution and may show a decrease in high-q systems as the binary separation increases. The distribution of binary orbital periods, however, is not consistent with the standard Ragahavan model and our observations support the premise that exoplanet-hosting stars with binary companions have, in general, wider orbital separations than field binaries. We find that exoplanet-hosting binary star systems show a distribution peaking near 100 au, higher than the 40-50 au peak that is observed for field binaries. This fact led to earlier suggestions that planet formation is suppressed in close binaries.