Multiple Explanations for the Single Transit of KIC 5951458 based on Radial Velocity Measurements Extracted with a Novel Matched-template Technique

TL;DR

This paper introduces a novel matched-template technique for precise radial velocity measurements, revealing complex system dynamics in KIC 5951458 that challenge the initial single-transit interpretation.

Contribution

A new matched-template method for RV extraction is validated, enabling detailed analysis of complex exoplanetary systems from single-transit events.

Findings

Detection of a long-term RV trend indicating a stellar companion

Identification of an additional RV signal possibly from a planet or brown dwarf

Inability to determine the cause of the single transit with current data

Abstract

Planetary systems that show single-transit events are a critical pathway to increasing the yield of long-period exoplanets from transit surveys. From the primary Kepler mission, KIC 5951458b (Kepler-456b) was thought to be a single-transit giant planet with an orbital period of 1310 days. However, radial velocity (RV) observations of KIC 5951458 from the HIRES instrument on the Keck telescope suggest that the system is far more complicated. To extract precise RVs for this $V\approx13$ star, we develop a novel matched-template technique that takes advantage of a broad library of template spectra acquired with HIRES. We validate this technique and measure its noise floor to be 4 - 8 m s$^{-1}$ (in addition to internal RV error) for most stars that would be targeted for precision RVs. For KIC 5951458, we detect a long-term RV trend that suggests the existence of a stellar companion with an orbital period greater than a few thousand days. We also detect an additional signal in the RVs that is possibly caused by a planetary or brown dwarf companion with mass in the range of 0.6 - 82 $M_{\rm J}$ and orbital period below a few thousand days. Curiously, from just the data on hand, it is not possible to determine which object caused the single "transit" event. We demonstrate how a modest set of RVs allows us to update the properties of this unusual system and predict the optimal timing for future observations.