Spitzer transit follow-up of planet candidates from the K2 mission

Abstract

We present precision 4.5 $\mu$m Spitzer transit photometry of eight planet candidates discovered by the K2 mission: K2-52 b, K2-53 b, EPIC 205084841.01, K2-289 b, K2-174 b, K2-87 b, K2-90 b, and K2-124 b. The sample includes four sub-Neptunes and two sub-Saturns, with radii between 2.6 and 18 $R_{\oplus }$, and equilibrium temperatures between 440 and 2000 K. In this paper we identify several targets of potential interest for future characterization studies, demonstrate the utility of transit follow-up observations for planet validation and ephemeris refinement, and present new imaging and spectroscopy data. Our simultaneous analysis of the K2 and Spitzer light curves yields improved estimates of the planet radii, and multi-wavelength information which help validate their planetary nature, including the previously un-validated candidate EPIC 205686202.01 (K2-289 b). Our Spitzer observations yield an order of magnitude increase in ephemeris precision, thus paving the way for efficient future study of these interesting systems by reducing the typical transit timing uncertainty in mid-2021 from several hours to a dozen or so minutes. K2-53 b, K2-289 b, K2-174 b, K2-87 b, and K2-90 b are promising radial velocity (RV) targets given the performance of spectrographs available today or in development, and the M3V star K2-124 hosts a temperate sub-Neptune that is potentially a good target for both RV and atmospheric characterization studies.

21 pages, 8 figures, 9 tables, accepted for publication in AJ

References in corpus (22)

• The Gaia mission
• The Transiting Exoplanet Survey Satellite
• The James Webb Space Telescope
• The K2 Mission: Characterization and Early results
• The effect of red noise on planetary transit detection
• The Transit Light Curve Project. IX. Evidence for a Smaller Radius of the Exoplanet XO-3b
• Precision Stellar Characterization of FGKM Stars using an Empirical Spectral Library
• Spitzer Secondary Eclipses of the Dense, Modestly-irradiated, Giant Exoplanet HAT-P-20b Using Pixel-Level Decorrelation
• Modeling Kepler transit light curves as false positives: Rejection of blend scenarios for Kepler-9, and validation of Kepler-9d, a super-Earth-size planet in a multiple system
• The Atmospheric Signatures of Super-Earths: How to Distinguish Between Hydrogen-Rich and Hydrogen-Poor Atmospheres
• 197 Candidates and 104 Validated Planets in K2's First Five Fields
• PASTIS: Bayesian extrasolar planet validation. I. General framework, models, and performance
• Zodiacal Exoplanets in Time (ZEIT) IV: seven transiting planets in the Praesepe cluster
• The effect of stellar limb darkening values on the accuracy of the planet radii derived from photometric transit observations
• A global analysis of Spitzer and new HARPS data confirms the loneliness and metal-richness of GJ 436 b
• SPIRou: the near-infrared spectropolarimeter/high-precision velocimeter for the Canada-France-Hawaii telescope
• Spitzer Observations Confirm and Rescue the Habitable-Zone Super-Earth K2-18b for Future Characterization
• Zodiacal Exoplanets in Time (ZEIT) VI: a three-planet system in the Hyades cluster including an Earth-sized planet
• Four Sub-Saturns with Dissimilar Densities: Windows into Planetary Cores and Envelopes
• K2 Discovers a Busy Bee: An Unusual Transiting Neptune Found in the Beehive Cluster
• Planet Candidates from K2 Campaigns 5-8 and Follow-Up Optical Spectroscopy
• Three statistically validated K2 transiting warm Jupiter exoplanets confirmed as low-mass stars

Cited by in corpus (15)

• TESS Hunt for Young and Maturing Exoplanets (THYME) IV: Three small planets orbiting a 120 Myr-old star in the Pisces--Eridanus stream
• ExoClock Project: An open platform for monitoring the ephemerides of Ariel targets with contributions from the public
• K2-19b and c are in a 3:2 Commensurability but out of Resonance: A Challenge to Planet Assembly by Convergent Migration
• The K2 and TESS Synergy. I. Updated Ephemerides and Parameters for K2-114, K2-167, K2-237, and K2-261
• Revisiting the Kepler field with TESS: Improved ephemerides using TESS 2min data
• Obliquity measurement and atmospheric characterization of the WASP-74 planetary system
• Critical Analysis of TESS Transit Photometric Data: Improved Physical Properties for Five Exoplanets
• Terminus: A Versatile Simulator for Space-based Telescopes
• K2-138 g: Spitzer Spots a Sixth Planet for the Citizen Science System
• Transit Light-curves for Exomoons: Analytical Formalism
• A young progenitor for the most common planetary systems in the Galaxy
• Gaussian Processes and Nested Sampling Applied to Kepler's Small Long-period Exoplanet Candidates
• Searching for substellar companion candidates with Gaia. II. A catalog of 9,698 planet candidate solar-type hosts
• K2, Spitzer, and TESS Transits of Four Sub-Neptune Exoplanets
• A sub-Neptune transiting the young field star HD 18599 at 40 pc