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

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.

SOAR TESS Survey. II: The impact of stellar companions on planetary populations

“…Applying the best-fit step suppression model to the expected binary distribution results in 11±1 and 32±2 binaries expected within projected separations of 50 and 100 AU, in agreement with observations. This model also predicts a peak binary separation for planet hosts at approximately 100 AU, in agreement with the findings of Howell et al (2021) for TESS targets.…”

“…Paper I found similar suppression in close binaries around TESS planet candidate hosts. Recently, Howell et al (2021) observed 186 TESS planet candidate hosts in high-resolution using speckle imaging. They also found fewer close binaries than would be expected from field star multiplicity rates, which they interpret as the binary distribution peaking at wider separations.…”

Dynamical orbital evolution scenarios of the wide-orbit eccentric planet HR 5183b

“…Indeed, observationally, the binary companions of exoplanet systems seem to have a wider semimajor axis distribution than the companions of field stars chosen without reference to their exoplanet systems. This is seen in studies of transiting planetary systems (Kraus et al 2016;Ziegler et al 2020;Howell et al 2021), as well as of giant planets within a few au of their host star (Fontanive et al 2019;Hirsch et al 2020). Meanwhile, the masses and semimajor axes of planets in binaries wider than 1 000 au are the same as those of planets orbiting single stars (Fontanive & Bardalez Gagluiffi 2021).…”

Revising Properties of Planet-host Binary Systems I.: Methods and Pilot Study

“…The physical effects of multiplicity on planets are most important for close binary stars, but binaries affect observed planetary properties across a wide range of separations. Binaries on solar-system scales (projected separation ρ 50 au) suppress planet occurrence by at least two-thirds (Wang et al 2014a,b;Kraus et al 2016;Howell et al 2021;Ziegler et al 2021)), but some close binaries still successfully form and retain circumstellar planets (planets on S-type orbits; e.g., Kraus et al 2016). Accurate stellar properties for binaries in this separation regime are vital for understanding both the suppression of planets at solar-system scales and the properties of the planets that survive in the hostile birth environment of a close binary.…”