Hubble Space Telescope High Resolution Imaging of Kepler Small and Cool Exoplanet Host Stars

TL;DR

This study uses HST high-resolution imaging to analyze 23 Kepler exoplanet host stars, identifying companions and background objects to refine planetary parameters and assess false positive risks.

Contribution

It provides new high-resolution imaging data for small, cool Kepler planet hosts, revealing a higher-than-expected rate of binary companions across spectral types.

Findings

Physically-associated binaries are more common than expected, especially at M spectral types.

Detection of background stars helps exclude false positives in planet detection.

Ambiguity in host star identification affects planetary parameter estimates.

Abstract

High resolution imaging is an important tool for follow-up study of exoplanet candidates found via transit detection with the Kepler Mission. We discuss here HST imaging with the WFC3 of 23 stars that host particularly interesting Kepler planet candidates based on their small size and cool equilibrium temperature estimates. Results include detections, exclusion of background stars that could be a source of false positives for the transits, and detection of physically-associated companions in a number of cases providing dilution measures necessary for planet parameter refinement. For six KOIs, we find that there is ambiguity in which star hosts the transiting planet(s), with potentially strong implications for planetary characteristics. Our sample is evenly distributed in G, K, and M spectral types. Albeit with a small sample size, we find that physically-associated binaries are more common than expected at each spectral type, reaching a factor of 10 frequency excess at M. We document the program detection sensitivities, detections, and deliverables to the Kepler follow-up program archive.