Identifying Bound Stellar Companions to Kepler Exoplanet Host Stars Using Speckle Imaging

Abstract

The Kepler mission and subsequent ground-based follow-up observations have revealed a number of exoplanet host stars with nearby stellar companions. This study presents speckle observations of 57 Kepler objects of interest (KOIs) that are also double stars, each observed over a 3–8 yr period, which has allowed us to track their relative motions with high precision. Measuring the position angle and separation of the companion with respect to the primary can help determine if the pair exhibits common proper motion, indicating it is likely to be a bound binary system. We report on the motions of 34 KOIs that have close stellar companions, three of which are triple stars, for a total of 37 companions studied. Eighteen of the 34 systems are confirmed exoplanet hosts, including one triple star, while four other systems have been subsequently judged to be false positives and twelve are yet to be confirmed as planet hosts. We find that 21 are most likely to be common proper motion pairs, 4 are line-of-sight companions, and 12 are of an uncertain disposition at present. The fraction of the confirmed exoplanet host systems that are common proper motion pairs is approximately 86% in this sample. In this subsample, the planets are exclusively found with periods of less than 110 days, so that in all cases the stellar companion is found at a much larger separation from the planet host star than the planet itself. A preliminary period–radius relation for the confirmed planets in our sample suggests no obvious differences at this stage with the full sample of known exoplanets.

TOI-2076 and TOI-1807: Two Young, Comoving Planetary Systems within 50 pc Identified by TESS that are Ideal Candidates for Further Follow Up

“…The detection of transiting planets in both TOI-2076 and TOI-1807 reveals that the planetary orbital planes are co-aligned, which hints at a common formation process whereby the both components maintain a nearly edge-on inclination to our line of sight. There is some initial evidence of such alignment between planetary orbits and the orbits of their binary hosts (Colton et al 2021) with more evidence to come from high-resolution imaging studies such as Howell et al (2021).…”

Speckle Observations of TESS Exoplanet Host Stars. II. Stellar Companions at 1–1000 au and Implications for Small Planet Detection

“…We are currently monitoring exoplanet host binaries with shorter periods to resolve the visual and spectroscopic orbits and determine each system's orbital parameters (e.g., Colton et al 2021). We plan to test each system's dynamical stability and potential for habitable planets in order to investigate how these other binary properties affect planet formation and survival.…”

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

“…of ±0.5 mag (Howell et al 2011). Stars with companions within ∼30 au will have binary orbital periods of decades and be systems that will reveal orbital motions within only a few years (see Colton et al 2020). Two TOIs, 1163 and 1228, are shown to be triple systems having a close companion with a wider tertiary.…”