Abstract
Abstract We validate the planetary nature of an ultra-short-period planet orbiting the M dwarf KOI-4777. We use a combination of space-based photometry from Kepler, high-precision, near-infrared Doppler spectroscopy from the Habitable-zone Planet Finder, and adaptive optics imaging to characterize this system. KOI-4777.01 is a Mars-sized exoplanet (R p = 0.51 ± 0.03R ⊕) orbiting the host star every 0.412 days (∼9.9 hr). This is the smallest validated ultra-short period planet known and we see no evidence for additional massive companions using our HPF RVs. We constrain the upper 3σ mass to M p < 0.34 M ⊕ by assuming the planet is less dense than iron. Obtaining a mass measurement for KOI-4777.01 is beyond current instrumental capabilities.
Highlights
Ultra-short period planets (USPs) have orbital periods < 1 day and represent a rare class of exoplanet
We investigate the M dwarf system, Kepler objects of interest (KOIs)-4777 (V = 16.4, J = 13.2), hosting a USP that was initially classified as a false positive by the Kepler DR25 automatic vetting
We have validated the planetary nature of the smallest known USP, a Mars-sized exoplanet transiting KOI-4777, an early M dwarf that was recovered from false positive status via manual vetting by the Kepler False Positive Working Group (FPWG) and independently identified by the autoregressive planet search procedure (ARPS) analysis
Summary
Ultra-short period planets (USPs) have orbital periods < 1 day and represent a rare class of exoplanet. A majority of USPs are found in multi-planet systems (e.g., Sanchis-Ojeda et al 2014; Adams et al 2017; Winn et al 2018) and, when observed in multi-planet systems, USPs have larger period ratios with their nearest neighbor when compared to the period ratios between neighboring planets of the same system (Steffen & Farr 2013; Winn et al 2018), and larger mutual inclinations than when compared to planets on wider orbits (Dai et al 2018) These observations suggest USPs have experienced inclination excitation and orbital shrinkage, which may indicate the existence of additional, non-transiting companions.
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