Bright Opportunities for Atmospheric Characterization of Small Planets: Masses and Radii of K2-3 b, c, d and GJ3470 b from Radial Velocity Measurements and Spitzer Transits

Abstract

We report improved masses, radii, and densities for four planets in two bright M-dwarf systems, K2-3 and GJ3470, derived from a combination of new radial velocity and transit observations. Supplementing K2 photometry with follow-up Spitzer transit observations refined the transit ephemerides of K2-3 b, c, and d by over a factor of 10. We analyze ground-based photometry from the Evryscope and Fairborn Observatory to determine the characteristic stellar activity timescales for our Gaussian Process fit, including the stellar rotation period and activity region decay timescale. The stellar rotation signals for both stars are evident in the radial velocity data and are included in our fit using a Gaussian process trained on the photometry. We find the masses of K2-3 b, K2-3 c and GJ3470 b to be 6.48${}_{-0.93}^{+0.99}$, 2.14${}_{-1.04}^{+1.08}$, and 12.58${}_{-1.28}^{+1.31}$ M${}_{\oplus }$ respectively. K2-3 d was not significantly detected and has a 3-$\sigma$ upper limit of 2.80 M${}_{\oplus }$. These two systems are training cases for future TESS systems; due to the low planet densities ($\rho$ $<$ 3.7 g cm${}^{-3}$) and bright host stars (K $<$ 9 mag), they are among the best candidates for transmission spectroscopy in order to characterize the atmospheric compositions of small planets.

arXiv comment21 pages, 11 figures, accepted to AJ

References in corpus (68)

• emcee: The MCMC Hammer
• The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets
• Planet Occurrence within 0.25 AU of Solar-type Stars from Kepler
• The false positive rate of Kepler and the occurrence of planets
• batman: BAsic Transit Model cAlculatioN in Python
• A continuum from clear to cloudy hot-Jupiter exoplanets without primordial water depletion
• Efficient, uninformative sampling of limb darkening coefficients for two-parameter laws
• Prevalence of Earth-size planets orbiting Sun-like stars
• Most 1.6 Earth-Radius Planets are not Rocky
• Understanding the Mass-Radius Relation for Sub-Neptunes: Radius as a Proxy for Composition
• The Occurrence Rate of Small Planets around Small Stars
• The Mass-Radius Relation for 65 Exoplanets Smaller than 4 Earth Radii
• The Transiting Exoplanet Survey Satellite: Simulations of planet detections and astrophysical false positives
• RadVel: The Radial Velocity Modeling Toolkit
• Planets and Stellar Activity: Hide and Seek in the CoRoT-7 system
• An asteroseismic view of the radius valley: stripped cores, not born rocky
• Chromospheric Activity and Jitter Measurements for 2630 Stars on the California Planet Search
• Measuring the rotation period distribution of field M-dwarfs with Kepler
• Mass-Radius Relation for Rocky Planets based on PREM
• The California Planet Survey I. Four New Giant Exoplanets
• Characterizing transiting exoplanet atmospheres with JWST
• The H$\alpha$ emission of nearby M dwarfs and its relation to stellar rotation
• 3.6 and 4.5 Micron Phase Curves and Evidence for Non-Equilibrium Chemistry in the Atmosphere of Extrasolar Planet HD 189733b
• A population study of gaseous exoplanets
• PandExo: A Community Tool for Transiting Exoplanet Science with JWST & HST
• A stellar-mass-dependent drop in planet occurrence rates
• The K2 Ecliptic Plane Input Catalog (EPIC) and Stellar Classifications of 138,600 Targets in Campaigns 1-8
• Breeding Super-Earths and Birthing Super-Puffs in Transitional Disks
• Spitzer Secondary Eclipses of the Dense, Modestly-irradiated, Giant Exoplanet HAT-P-20b Using Pixel-Level Decorrelation
• Make Super-Earths, Not Jupiters: Accreting Nebular Gas onto Solid Cores at 0.1 AU and Beyond
• Planetary Candidates from the First Year of the K2 Mission
• 197 Candidates and 104 Validated Planets in K2's First Five Fields
• Hubble PanCET: An extended upper atmosphere of neutral hydrogen around the warm Neptune GJ 3470 b
• Spitzer Transit and Secondary Eclipse Photometry of GJ 436b
• Stellar and Planetary Properties of K2 Campaign 1 Candidates and Validation of 17 Planets, Including a Planet Receiving Earth-like Insolation
• Fluxes in Hαand Ca II H and K for a sample of Southern stars
• Formation of TRAPPIST-1 and other compact systems
• 275 Candidates and 149 Validated Planets Orbiting Bright Stars in K2 Campaigns 0-10
• A nearby M star with three transiting super-Earths discovered by K2
• The HARPS search for southern extra-solar planets XLI. A dozen planets around the M dwarfs GJ 3138, GJ 3323, GJ 273, GJ 628, and GJ 3293
• Constraining Exoplanet Mass from Transmission Spectroscopy
• A hot Uranus transiting the nearby M dwarf GJ3470. Detected with HARPS velocimetry. Captured in transit with TRAPPIST photometry
• Characterizing the Cool KOIs IV: Kepler-32 as a prototype for the formation of compact planetary systems throughout the Galaxy
• H-alpha Activity of Old M Dwarfs: Stellar Cycles and Mean Activity Levels For 93 Low-Mass Stars in the Solar Neighborhood
• Long-term magnetic activity of a sample of M-dwarf stars from the HARPS program II. Activity and radial velocity
• Spitzer Observations Confirm and Rescue the Habitable-Zone Super-Earth K2-18b for Future Characterization
• Exo-Transmit: An Open-Source Code for Calculating Transmission Spectra for Exoplanet Atmospheres of Varied Composition
• Kepler-21b: A rocky planet around a V = 8.25 magnitude star
• Evryscope science: exploring the potential of all-sky gigapixel-scale telescopes
• Characterizing K2 Candidate Planetary Systems Orbiting Low-Mass Stars II: Planetary Systems Observed During Campaigns 1-7
• The HARPS search for southern extra-solar planets XXXV. Planetary systems and stellar activity of the M dwarfs GJ 3293, GJ 3341, and GJ 3543
• Repeatability and Accuracy of Exoplanet Eclipse Depths Measured with Post-Cryogenic Spitzer
• Accretion and Evolution of ~2.5 Earth-mass Planets with Voluminous H/He Envelopes
• Warm Ice Giant GJ 3470b. II Revised Planetary and Stellar Parameters from Optical to Near-infrared Transit Photometry
• Warm Ice Giant GJ 3470b. I. A Flat Transmission Spectrum Indicates a Hazy, Low-methane, and/or Metal-rich Atmosphere
• The Impact of Stellar Rotation on the Detectability of Habitable Planets Around M Dwarfs
• Optical-to-Near-Infrared Simultaneous Observations for the Hot Uranus GJ3470b: A Hint for Cloud-free Atmosphere
• Spitzer Observations of GJ3470b: a Very Low-density Neptune-size Planet Orbiting a Metal-rich M dwarf
• The blue sky of GJ3470b: the atmosphere of a low-mass planet unveiled by ground-based photometry
• Doppler Monitoring of five K2 Transiting Planetary Systems
• Stellar Activity and its Implications for Exoplanet Detection on GJ 176
• The GTC exoplanet transit spectroscopy survey. VI. A spectrally-resolved Rayleigh scattering slope in GJ 3470b
• Eyes on K2-3: A system of three likely sub-Neptunes characterized with HARPS-N and HARPS
• Challenges to Constraining Exoplanet Masses via Transmission Spectroscopy
• A HARPS view on K2-3
• Spitzer Observations of Exoplanets Discovered with The Kepler K2 Mission
• Long-term chromospheric activity in southern M dwarfs: Gl 229 A and Gl 752 A
• Ground-based Transit Observation of the Habitable-zone Super-Earth K2-3d

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• Exoplanet atmosphere evolution: emulation with neural networks
• A sub-Neptune planet around TOI-1695 discovered and characterized with SPIRou and TESS
• A Population Analysis of 20 Exoplanets Observed from the Optical to the Near-infrared Wavelengths with HST: Evidence for Widespread Stellar Contamination
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• HST Transmission Spectra of the Hot-Neptune HD 219666 b: Detection of Water and the Challenge of Constraining Both Water and Methane
• K2, Spitzer, and TESS Transits of Four Sub-Neptune Exoplanets
• Homogeneous search for spot transits in Kepler and TESS photometry of K $-$ M-type main-sequence stars
• ExoEcho: Exoplanet Ephemerides Change Observations. III. A JWST Survey for Transit Timing Variations of 37 Exoplanets