Updated Parameters and a New Transmission Spectrum of HD 97658b

Abstract

Recent years have seen increasing interest in the characterization of sub-Neptune sized planets because of their prevalence in the Galaxy, contrasted with their absence in our solar system. HD 97658 is one of the brightest stars hosting a planet of this kind, and we present the transmission spectrum of this planet by combining four HST transits, twelve Spitzer/IRAC transits, and eight MOST transits of this system. Our transmission spectrum has higher signal to noise ratio than that from previous works, and the result suggests that the slight increase in transit depth from wavelength 1.1 to 1.7 microns reported in previous works on the transmission spectrum of this planet is likely systematic. Nonetheless, our atmospheric modeling results are not conclusive as no model provides an excellent match to our data. Nonetheless we find that atmospheres with high C/O ratios (C/O >~ 0.8) and metallicities of >~ 100x solar metallicity are favored. We combine the mid-transit times from all the new Spitzer and MOST observations and obtain an updated orbital period of P=9.489295 +/- 0.000005 d, with a best-fit transit time center at T_0 = 2456361.80690 +/- 0.00038 (BJD). No transit timing variations are found in this system. We also present new measurements of the stellar rotation period (34 +/- 2 d) and stellar activity cycle (9.6 yr) of the host star HD 97658. Finally, we calculate and rank the Transmission Spectroscopy Metric of all confirmed planets cooler than 1000 K and with sizes between 1 and 4 R_Earth. We find that at least a third of small planets cooler than 1000 K can be well characterized using JWST, and of those, HD 97658b is ranked fifth, meaning it remains a high-priority target for atmospheric characterization.

Accepted to AJ. 29 pages, 21 figures, 11 tables, 2 machine-readable tables (system RVs and TSM values). v2: updated typos

References in corpus (20)

• A Precise Water Abundance Measurement for the Hot Jupiter WASP-43b
• Spitzer Secondary Eclipses of the Dense, Modestly-irradiated, Giant Exoplanet HAT-P-20b Using Pixel-Level Decorrelation
• An ultrahot gas-giant exoplanet with a stratosphere
• Fingering convection and cloudless models for cool brown dwarf atmospheres
• A Sub-Neptune Exoplanet with a Low-Metallicity Methane-Depleted Atmosphere and Mie-Scattering Clouds
• Magnetic Cycles and Rotation Periods of Late Type Stars from photometric time series
• The Very Low Albedo of an Extrasolar Planet: MOST Spacebased Photometry of HD 209458
• Hubble Space Telescope Near-IR Transmission Spectroscopy of the Super-Earth HD 97658b
• The Transit Light Source Effect II: The Impact of Stellar Heterogeneity on Transmission Spectra of Planets Orbiting Broadly Sun-like Stars
• Spectral Fingerprints of Earth-like Planets Around FGK Stars
• Trends in Atmospheric Properties of Neptune-Size Exoplanets
• Exo-Transmit: An Open-Source Code for Calculating Transmission Spectra for Exoplanet Atmospheres of Varied Composition
• Statistical Analysis of Hubble/WFC3 Transit Spectroscopy of Extrasolar Planets
• Connecting planet formation and astrochemistry: A main sequence for C/O in hot-exoplanetary atmospheres
• The HARPS search for southern extra-solar planets. XXXI. Magnetic activity cycles in solar-type stars: statistics and impact on precise radial velocities
• The Very Low Albedo of WASP-12b From Spectral Eclipse Observations with $\text{Hubble}$
• An HST/STIS Optical Transmission Spectrum of Warm Neptune GJ 436b
• A Catalog of Stellar Unified Properties (CATSUP) for 951 FGK-Stars Within 30 pc
• Hubble Space Telescope search for the transit of the Earth-mass exoplanet Alpha Centauri Bb
• Zodiacal Exoplanets in Time (ZEIT) IX: a flat transmission spectrum and a highly eccentric orbit for the young Neptune K2-25b as revealed by Spitzer

Cited by in corpus (42)

• Habitability and Biosignatures of Hycean Worlds
• The nature and origins of sub-Neptune size planets
• TESS Transit Timing of Hundreds of Hot Jupiters
• Analysis of Early Science observations with the CHaracterising ExOPlanets Satellite (CHEOPS) using pycheops
• ExoClock Project III: 450 new exoplanet ephemerides from ground and space observations
• How to identify exoplanet surfaces using atmospheric trace species in hydrogen-dominated atmospheres
• ARES V: No Evidence For Molecular Absorption in the HST WFC3 Spectrum of GJ 1132 b
• TESS Hunt for Young and Maturing Exoplanets (THYME) IV: Three small planets orbiting a 120 Myr-old star in the Pisces--Eridanus stream
• Clouds and Clarity: Revisiting Atmospheric Feature Trends in Neptune-size Exoplanets
• On The Compatibility of Ground-based and Space-based Data: WASP-96 b, An Example
• A Heavy Molecular Weight Atmosphere for the Super-Earth π Men c
• Haze Evolution in Temperate Exoplanet Atmospheres Through Surface Energy Measurements
• Evidence for disequilibrium chemistry from vertical mixing in hot Jupiter atmospheres. A comprehensive survey of transiting close-in gas giant exoplanets with warm-Spitzer/IRAC
• The TESS-Keck Survey II: An Ultra-Short Period Rocky Planet and its Siblings Transiting the Galactic Thick-Disk Star TOI-561
• Implementation of disequilibrium chemistry to spectral retrieval code ARCiS and application to sixteen exoplanet transmission spectra: Indication of disequilibrium chemistry for HD 209458b and WASP-39b
• TOI-431/HIP 26013: a super-Earth and a sub-Neptune transiting a bright, early K dwarf, with a third RV planet
• Transmission spectroscopy for the warm sub-Neptune HD3167c: evidence for molecular absorption and a possible high metallicity atmosphere
• Cleaning our Hazy Lens: Exploring Trends in Transmission Spectra of Warm Exoplanets
• TOI-1231 b: A Temperate, Neptune-Sized Planet Transiting the Nearby M3 Dwarf NLTT 24399
• Examining the orbital decay targets KELT-9 b, KELT-16 b and WASP-4 b, and the transit-timing variations of HD 97658 b
• Exoplanet Volatile Carbon Content as a Natural Pathway for Haze Formation
• A transiting, temperate mini-Neptune orbiting the M dwarf TOI-1759 unveiled by TESS
• Investigating the detectability of hydrocarbons in exoplanet atmospheres with JWST
• Directly Determined Properties of HD 97658 from Interferometric Observations
• Where are the Water Worlds?: Self-Consistent Models of Water-Rich Exoplanet Atmospheres
• Importance of Sample Selection in Exoplanet Atmosphere Population Studies
• Understanding the Effects of Systematics in Exoplanetary Atmospheric Retrievals
• Measuring Tracers of Planet Formation in the Atmosphere of WASP-77A b: Sub-stellar O/H and C/H ratios, with a stellar C/O ratio and a potentially Super-stellar Ti/H ratio
• GJ 3090 b: one of the most favourable mini-Neptune for atmospheric characterisation
• Coronal X-Ray Emission from Nearby, Low-Mass, Exoplanet Host Stars Observed by the MUSCLES and Mega-MUSCLES HST Treasury Survey Projects
• The transmission spectrum of WASP-17 b from the optical to the near-infrared wavelengths: combining STIS, WFC3 and IRAC datasets
• Non-detection of Helium in the Hot Jupiter WASP-48b
• Wolf 503 b: Characterization of a Sub-Neptune Orbiting a Metal-Poor K Dwarf
• Is the hot, dense sub-Neptune TOI-824b an exposed Neptune mantle? Spitzer detection of the hot day side and reanalysis of the interior composition
• HST Transmission Spectra of the Hot-Neptune HD 219666 b: Detection of Water and the Challenge of Constraining Both Water and Methane
• The SPACE Program. I. The featureless spectrum of HD 86226 c challenges sub-Neptune atmosphere trends
• The Featureless HST/WFC3 Transmission Spectrum of the Rocky Exoplanet GJ 1132b: No Evidence For A Cloud-Free Primordial Atmosphere and Constraints on Starspot Contamination
• A re-analysis of equilibrium chemistry in five hot Jupiters
• K2, Spitzer, and TESS Transits of Four Sub-Neptune Exoplanets
• Using Stellar Spectral Energy Distributions to Measure Exoplanet Parameters
• Sub-Neptunes as Soot Factories: Deep Atmosphere Hydrocarbon Formation and Quenching as the Origin of Sub-Neptune Aerosol Trends
• Grain Growth in Escaping Atmospheres: Implications for the Radius Inflation of Super-Puffs