Scaling K2 VIII: Short-Period Sub-Neptune Occurrence Rates Peak Around Early-Type M Dwarfs

Abstract

We uniformly combined data from the NASA Kepler and K2 missions to compute planet occurrence rates across the entire FGK and M dwarf stellar range. The K2 mission, driven by targets selected by guest observers, monitored nine times more M dwarfs than the Kepler mission. Combined, Kepler and K2 observed 130 short-period ($P=1-40$ days) Earth to Neptune-sized candidate planets orbiting M dwarfs. K2 observed 3.5 times more of these planets than Kepler for host stars below 3700 K. Our planet occurrence rates show that short-period sub-Neptunes peak at $3750_{-97}^{+153}$ K and drop for cooler M dwarfs. A peak near this location was predicted by pebble accretion planet formation models and confirmed here by observations for the first time. Super-Earths continue to increase in occurrence toward cooler stars and show no clear evidence of a peak in the host star range considered here (3200 K$-$6900 K). Our observations provide critical input to further refine planet formation models. We strongly recommend further study of mid-to-late M dwarfs with TESS and soon the Nancy Grace Roman Space Telescope and PLATO to identify additional small planet trends.

15 pages, 5 figures, 7 tables. Accepted for publication in AJ. Uniform exoplanet and stellar parameters tables for Kepler and K2 are available to download at https://github.com/kevinkhu/KeplerK2

References in corpus (35)

• Array Programming with NumPy
• The Astropy Project: Sustaining and Growing a Community-oriented Open-source Project and the Latest Major Release (v5.0) of the Core Package
• Gaia Data Release 3: Summary of the content and survey properties
• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• The K2 Mission: Characterization and Early results
• How to Constrain Your M Dwarf: measuring effective temperature, bolometric luminosity, mass, and radius
• A stellar-mass-dependent drop in planet occurrence rates
• Asteroseismology and Gaia: Testing Scaling Relations Using 2200 Kepler Stars with TGAS Parallaxes
• The New Generation Planetary Population Synthesis (NGPPS). IV. Planetary systems around low-mass stars
• The Gaia-Kepler Stellar Properties Catalog. II. Planet Radius Demographics as a Function of Stellar Mass and Age
• The California-Kepler Survey. X. The Radius Gap as a Function of Stellar Mass, Metallicity, and Age
• Scaling K2. I. Revised Parameters for 222,088 K2 Stars and a K2 Planet Radius Valley at 1.9 $R_{\oplus }$
• Accounting for Incompleteness due to Transit Multiplicity in Kepler Planet Occurrence Rates
• The all-sky PLATO input catalogue
• How dust fragmentation may be beneficial to planetary growth by pebble accretion
• Why do M dwarfs have more transiting planets?
• A deep radius valley revealed by Kepler short cadence observations
• The Occurrence Rate of Terrestrial Planets Orbiting Nearby Mid-to-late M Dwarfs from TESS Sectors 1-42
• Bioverse: A Comprehensive Assessment of the Capabilities of Extremely Large Telescopes to Probe Earth-like O${}_2$ Levels in Nearby Transiting Habitable Zone Exoplanets
• Measuring the Galactic Distribution of Transiting Planets with WFIRST
• Measuring Transit Signal Recovery in the Kepler Pipeline IV: Completeness of the DR25 Planet Candidate catalog
• Scaling K2. VI. Reduced Small Planet Occurrence in High Galactic Amplitude Stars
• The MEarth project: searching for transiting habitable super-Earths around nearby M-dwarfs
• The Demographics of Kepler's Earths and super-Earths into the Habitable Zone
• Small Planets Around Cool Dwarfs: Enhanced Formation Efficiency of Super-Earths around M dwarfs
• EDEN: Sensitivity Analysis and Transiting Planet Detection Limits for Nearby Late Red Dwarfs
• Scaling K2. II. Assembly of a Fully Automated C5 Planet Candidate Catalog Using EDI-Vetter
• The PLATO field selection process. II. Characterization of LOPS2, the first long-pointing field
• Scaling K2 VII: Evidence for a high occurrence rate of hot sub-Neptunes at intermediate ages
• Assessing $TESS$'s Yield of Rocky Planets Around Nearby M Dwarfs
• The occurrence rate of exoplanets orbiting ultracool dwarfs as probed by K2
• Scaling K2. III. Comparable Planet Occurrence in the FGK Samples of Campaign 5 and Kepler
• Predicting the Yield of Small Transiting Exoplanets around Mid-M and Ultra-Cool Dwarfs in the Nancy Grace Roman Space Telescope Galactic Bulge Time Domain Survey
• Implicit biases in transit models using stellar pseudo-density
• EDEN Survey: Small Transiting Planet Detection Limits and Constraints on the Occurrence Rates for Late M Dwarfs within 15 pc