No hydrogen exosphere detected around the super-Earth HD97658 b

Abstract

The exoplanet HD97658b provides a rare opportunity to probe the atmospheric composition and evolution of moderately irradiated super-Earths. It transits a bright K star at a moderate orbital distance of 0.08 au. Its low density is compatible with a massive steam envelope that could photodissociate at high altitudes and become observable as escaping hydrogen. Our analysis of 3 transits with HST/STIS at Ly-alpha reveals no such signature, suggesting that the thermosphere is not hydrodynamically expanding and is subjected to a low escape of neutral hydrogen (<10^8 g/s at 3 sigma). Using HST Ly-alpha and Chandra & XMM-Newton observations at different epochs, we find that HD97658 is a weak and soft X-ray source with signs of chromospheric variability in the Ly-alpha line core. We determine an average reference for the intrinsic Ly-alpha line and XUV spectrum of the star, and show that HD97658 b is in mild conditions of irradiation compared to other known evaporating exoplanets with an XUV irradiation about 3 times lower than the evaporating warm Neptune GJ436 b. This could be why the thermosphere of HD97658b is not expanding: the low XUV irradiation prevents an efficient photodissociation of any putative steam envelope. Alternatively, it could be linked to a low hydrogen content or inefficient conversion of the stellar energy input. The HD97658 system provides clues for understanding the stability of low-mass planet atmospheres. Our study of HD97658 b can be seen as a control experiment of our methodology, confirming that it does not bias detections of atmospheric escape and underlining its strength and reliability. Our results show that stellar activity can be efficiently discriminated from absorption signatures by a transiting exospheric cloud. They also highlight the potential of observing the upper atmosphere of small transiting planets to probe their physical and chemical properties

arXiv comment15 pages, 8 figures

References in corpus (58)

• Collisional Plasma Models with APEC/APED: Emission Line Diagnostics of Hydrogen-like and Helium-like Ions
• Atomic Data for Astrophysics. II. New Analytic Fits for Photoionization Cross Sections of Atoms and Ions
• Detection of oxygen and carbon in the hydrodynamically escaping atmosphere of the extrasolar planet HD209458b
• HST Time-Series Photometry of the Transiting Planet of HD 209458
• A giant comet-like cloud of hydrogen escaping the warm Neptune-mass exoplanet GJ 436b
• Roche lobe effects on the atmospheric loss of "Hot Jupiters"
• Planetary evaporation by UV & X-ray radiation: basic hydrodynamics
• The MUSCLES Treasury Survey I: Motivation and Overview
• Evaporation of the planet HD189733b observed in HI Lyman-alpha
• The Structure of the Local Interstellar Medium V: Electron Densities
• Metals in the Exosphere of the Highly Irradiated Planet WASP-12b
• Observations of Mass Loss from the Transiting Exoplanet HD 209458b
• What is the Total Deuterium Abundance in the Local Galactic Disk?
• A map of the large day-night temperature gradient of a super-Earth exoplanet
• Stellar Lyman-alpha Emission Lines in the Hubble Space Telescope Archive: Intrinsic Line Fluxes and Absorption from the Heliosphere and Astrospheres
• Atmospheric Escape from Hot Jupiters
• The MUSCLES Treasury Survey II: Intrinsic Lyman Alpha and Extreme Ultraviolet Spectra of K and M Dwarfs with Exoplanets
• Lyman-$\alpha$ Transit Spectroscopy and the Neutral Hydrogen Tail of the Hot Neptune GJ436b
• Temporal variations in the evaporating atmosphere of the exoplanet HD 189733b
• The escape of heavy atoms from the ionosphere of HD209458b. I. A photochemical-dynamical model of the thermosphere
• Near-UV Absorption, Chromospheric Activity, and Star-Planet Interactions in the WASP-12 system
• Hubble Space Telescope Near-IR Transmission Spectroscopy of the Super-Earth HD 97658b
• The Intrinsic Extreme Ultraviolet Fluxes of F5 V to M5 V Stars
• Thermal Phase Variations of WASP-12b: Defying Predictions
• 3D model of hydrogen atmospheric escape from HD209458b and HD189733b: radiative blow-out and stellar wind interactions
• Temperature-Pressure Profile of the hot Jupiter HD 189733b from HST Sodium Observations: Detection of Upper Atmospheric Heating
• HST/STIS Optical Transit Transmission Spectra of the hot-Jupiter HD209458b
• Simulating the escaping atmospheres of hot gas planets in the solar neighborhood
• An evaporating planet in the wind: stellar wind interactions with the radiatively braked exosphere of GJ436 b
• Hint of a transiting extended atmosphere on 55 Cancri b
• Exoplanet HD 209458b : Evaporation strengthened
• The Evolution of Stellar Rotation and the hydrogen atmospheres of habitable-zone Terrestrial Planets
• Atmospheric escape from HD 189733b observed in HI Lyman-alpha: detailed analysis of HST/STIS September 2011 observations
• Towards consistent mapping of distant worlds: secondary-eclipse scanning of the exoplanet HD189733b
• Exoplanet HD209458b: inflated hydrogen atmosphere but no sign of evaporation
• Energy-limited escape revised
• On the existence of energetic atoms in the upper atmosphere of exoplanet HD209458b
• New observations of the extended hydrogen exosphere of the extrasolar planet HD209458b
• XUV-driven mass loss from extrasolar giant planets orbiting active stars
• Age consistency between exoplanet hosts and field stars
• Magnesium in the atmosphere of the planet HD209458b: Observations of the thermosphere-exosphere transition region
• Heating efficiency in hydrogen-dominated upper atmospheres
• Mass-loss rates for transiting exoplanets
• UV driven evaporation of close-in planets: energy-limited; recombination-limited and photon-limited flows
• Hubble Space Telescope detection of oxygen in the atmosphere of exoplanet HD189733b
• Probing the Blow-Off Criteria of Hydrogen-Rich "Super-Earths"
• The NASA-UC Eta-Earth Program: III. A Super-Earth orbiting HD 97658 and a Neptune-mass planet orbiting Gl 785
• The escape of heavy atoms from the ionosphere of HD209458b. II. Interpretation of the observations
• MOST detects transits of HD 97658b, a warm, likely volatile-rich super-Earth
• Spitzer/MIPS 24 micron Observations of HD 209458b: 3 eclipses, 2.5 transits, and a Phase Curve Corrupted by Instrumental Sensitivity Variations
• Solar parameters for modeling interplanetary background
• The deuterium-to-oxygen ratio in the interstellar medium
• Radiative braking in the extended exosphere of GJ436b
• Spectral, Spatial, and Time properties of the hydrogen nebula around exoplanet HD209458b
• Transit confirmation and improved stellar and planet parameters for the super-Earth HD 97658 b and its host star
• HST/STIS Lyman-alpha observations of the quiet M dwarf GJ436: Predictions for the exospheric transit signature of the hot neptune GJ436b
• An observational signature of evolved oceans on extra-solar terrestrial planets
• The MgI line: a new probe of the atmospheres of evaporating exoplanets

Cited by in corpus (36)

• Hubble PanCET: An extended upper atmosphere of neutral hydrogen around the warm Neptune GJ 3470 b
• The nature and origins of sub-Neptune size planets
• The long egress of GJ~436b's giant exosphere
• Outgassing on stagnant-lid super-Earths
• Reconnaissance of the TRAPPIST-1 exoplanet system in the Lyman-$\alpha$ line
• Temporal evolution of the high-energy irradiation and water content of TRAPPIST-1 exoplanets
• Atmospheric Regimes and Trends on Exoplanets and Brown Dwarfs
• EUV irradiation of exoplanet atmospheres occurs on Gyr timescales
• Detection of Ongoing Mass Loss from HD 63433c, a Young Mini Neptune
• Non-detection of Helium in the Upper Atmospheres of Three Sub-Neptune Exoplanets
• Constraints on Metastable Helium in the Atmospheres of WASP-69b and WASP-52b with Ultra-Narrowband Photometry
• The impact of coronal mass ejections and flares on the atmosphere of the hot Jupiter HD189733b
• Hot, rocky and warm, puffy super-Earths orbiting TOI-402 (HD 15337)
• Is pi Men c's atmosphere hydrogen-dominated? Insights from a non-detecton of Hy Ly-alpha absorption
• The high-energy environment and atmospheric escape of the mini-Neptune K2-18 b
• The fundamentals of Lyman-alpha exoplanet transits
• Caught in the Act: Core-powered Mass-loss Predictions for Observing Atmospheric Escape
• MOVES III. Simultaneous X-ray and ultraviolet observations unveiling the variable environment of the hot Jupiter HD 189733b
• Super-Earths and Earth-like Exoplanets
• MOVES IV. Modelling the influence of stellar XUV-flux, cosmic rays, and stellar energetic particles on the atmospheric composition of the hot Jupiter HD 189733b
• Strong HI Lyman-$\alpha$ variations from the 11 Gyr-old host star Kepler-444: a planetary origin ?
• The effect of ISM absorption on stellar activity measurements and its relevance for exoplanet studies
• A multi-wavelength look at the GJ 9827 system -- No evidence of extended atmospheres in GJ 9827 b and d from HST and CARMENES data
• Lyman-alpha in the GJ 1132 System: Stellar Emission and Planetary Atmospheric Evolution
• Secondary atmospheres on HD 219134 b and c
• Transit Ly-$\alpha$ signatures of terrestrial planets in the habitable zones of M dwarfs
• Planetary parameters, XUV environments and mass-loss rates for nearby gaseous planets with X-ray detected host-stars
• The XUV irradiation and likely atmospheric escape of the super-Earth $\pi$ Men c
• Observability of hydrogen-rich exospheres in Earth-like exoplanets
• Using Lyman-$\alpha$ transits to constrain models of atmospheric escape
• HST PanCET program: Non-detection of atmospheric escape in the warm Saturn-sized planet WASP-29 b
• The Hubble PanCET program: Long-term chromospheric evolution and flaring activity of the M dwarf host GJ 3470
• On the feasibility of studying the exospheres of Earth-like exoplanets by Lyman-alpha monitoring. Detectability constraints for nearby M stars
• TOI-5108 b and TOI 5786 b: Two transiting sub-Saturns detected and characterized with TESS, MaHPS and SOPHIE
• Potential Interior Structures and Habitability of Super-Earth Exoplanets LHS 1140 b, K2-18 b, TOI-1452 b and TOI-1468 c
• A Novel Solution for Resonant Scattering Using Self-Consistent Boundary Conditions