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

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5951458b (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 13 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 Jup 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.

Giant Outer Transiting Exoplanet Mass (GOT ‘EM) Survey. II. Discovery of a Failed Hot Jupiter on a 2.7 Yr, Highly Eccentric Orbit*

“…We did not acquire a high signal-to-noise ratio (S/N) template spectrum, as is typical for HIRES RV observations (e.g., Howard et al 2010). Instead, we identified a preexisting "best-match" template spectrum in the HIRES spectral library following Dalba et al (2020a). The best-match star was HD 203473, a brighter G6V star with similar spectroscopic properties to Kepler-1704 according to a SpecMatch-Emp 16 analysis (Yee et al 2017).…”

“…The use of a best-match template incurs extra uncertainty in addition to internal RV errors. Following conservative estimations by Dalba et al (2020a, their Table 2), we added 6.2 m s −1 to our internal RV errors in quadrature to account for this method. After swapping in the template of HD 203473, the RV extraction proceeded following the standard forwarding techniques employed by the California Planet Search (e.g., Howard et al 2010;Howard & Fulton 2016).…”

“…We provide the full RV data set for Kepler-1704 in Table 1. The uncertainties listed include the additional uncertainty incurred by the matched-template method of RV extraction (Dalba et al 2020a). We also include corresponding S HK activity indicators derived from the Ca II H and K spectral lines (Wright et al 2004;Isaacson & Fischer 2010).…”

“…A photometric dimming event with a depth corresponding to a giant planet transit can be created by substellar or stellar objects or various systematic signals (e.g., Brown 2003;Torres et al 2005;Cameron 2012;Foreman-Mackey et al 2016;Dalba et al 2020a). False-positive signals can be harder to identify for longer (compared to shorter) orbital periods owing to the difficulty in quantifying the reliability of genuine transit events from similarly long-period exoplanets (e.g., Thompson et al 2018).…”

Asteroseismology of iota Draconis and Discovery of an Additional Long-period Companion

“…We approximated this envelope as the interface between the white and red/green regions in Figure 6 and used it to divide the posteriors from The Joker. This kind of analysis has been employed previously to interpret results from The Joker in combination with additional limiting information (Dalba et al 2020a). The resulting posteriors are overplotted on those for all surviving draws in Figure 7.…”