A Lyman-alpha transit left undetected: the environment and atmospheric behavior of K2-25b

Abstract

K2-25b is a Neptune-sized exoplanet (3.45 Earth radii) that orbits its M4.5 host with a period of 3.48 days. Due to its membership in the Hyades Cluster, the system has a known age (727 +/- 75 Myr). K2-25b's youth and its similarities with Gl 436b suggested that K2-25b could be undergoing strong atmospheric escape. We observed two transits of K2-25b at Lyman-alpha using HST/STIS in order to search for escaping neutral hydrogen. We were unable to detect an exospheric signature, but placed an upper limit of (R_p/R_s) < 0.56 at 95% confidence by fitting the light curve of the Lyman-alpha red-wing, or < 1.20 in the blue-wing. We reconstructed the intrinsic Lyman-alpha profile of K2-25 to determine its Lyman-alpha flux, and analyzed XMM-Newton observations to determined its X-ray flux. Based on the total X-ray and extreme ultraviolet irradiation of the planet (8763 +/- 1049 erg/s/cm^2), we estimated the maximum energy-limited mass loss rate of K2-25b to be 10.6 x 10^10 g/s (0.56 Earth masses per 1 Gyr), five times larger than the similarly estimated mass loss rate of Gl 436b (2.2 x 10^10 g/s). The photoionization time is about 3 hours, significantly shorter than Gl 436b's 14 hours. A non-detection of a Lyman-alpha transit could suggest K2-25b is not significantly losing its atmosphere, or factors of the system are resulting in the mass loss being unobservable (e.g., atmosphere composition or the system's large high energy flux). Further observations could provide more stringent constraints.

References in corpus (77)

• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Array Programming with NumPy
• emcee: The MCMC Hammer
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• Atomic Data for Astrophysics. II. New Analytic Fits for Photoionization Cross Sections of Atoms and Ions
• The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets
• batman: BAsic Transit Model cAlculatioN in Python
• The Revised TESS Input Catalog and Candidate Target List
• Kepler planets: a tale of evaporation
• The evaporation valley in the Kepler planets
• Atmospheric Escape from Hot Jupiters
• 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
• The California Kepler Survey VII. Precise Planet Radii Leveraging Gaia DR2 Reveal the Stellar Mass Dependence of the Planet Radius Gap
• The Role of Core Mass in Controlling Evaporation: the Kepler Radius Distribution and the Kepler-36 Density Dichotomy
• Core-powered mass loss and the radius distribution of small exoplanets
• Roche lobe effects on the atmospheric loss of "Hot Jupiters"
• New Mass Loss Measurements from Astrospheric Lyman-alpha Absorption
• Planetary evaporation by UV & X-ray radiation: basic hydrodynamics
• The Structure of the Local Interstellar Medium V: Electron Densities
• Planetary population synthesis coupled with atmospheric escape: a statistical view of evaporation
• Dearth of short-period Neptunian exoplanets - a desert in period-mass and period-radius planes
• What is the Total Deuterium Abundance in the Local Galactic Disk?
• Atmospheric Escape and the Evolution of Close-in Exoplanets
• The stellar rotation--activity relationship in fully convective M dwarfs
• Hot super-Earths stripped by their host stars
• A diagram for the evaporation status of extrasolar planets
• The Ultraviolet Radiation Environment Around M dwarf Exoplanet Host Stars
• 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
• Photoevaporation and High-Eccentricity Migration Created the Sub-Jovian Desert
• A short-period censor of sub-Jupiter mass exoplanets with low density
• Hubble PanCET: An extended upper atmosphere of neutral hydrogen around the warm Neptune GJ 3470 b
• The Intrinsic Extreme Ultraviolet Fluxes of F5 V to M5 V Stars
• 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
• Emerging Trends in a Period-Radius Distribution of Close-in Planets
• Energetic neutral atoms as the explanation for the high velocity hydrogen around HD 209458b
• An evaporating planet in the wind: stellar wind interactions with the radiatively braked exosphere of GJ436 b
• Zodiacal Exoplanets In Time (ZEIT) I: A Neptune-sized planet orbiting an M4.5 dwarf in the Hyades Star Cluster
• K2 rotation periods for low-mass Hyads and a quantitative comparison of the distribution of slow rotators in the Hyades and Praesepe
• The MUSCLES Treasury Survey. V. FUV Flares on Active and Inactive M Dwarfs
• Orbital misalignment of the Neptune-mass exoplanet GJ 436b with the spin of its cool star
• Age Determinations of the Hyades, Praesepe, and Pleiades via MESA Models with Rotation
• Atmospheric escape from HD 189733b observed in HI Lyman-alpha: detailed analysis of HST/STIS September 2011 observations
• On the existence of energetic atoms in the upper atmosphere of exoplanet HD209458b
• The long egress of GJ~436b's giant exosphere
• Colliding Planetary and Stellar Winds: Charge Exchange and Transit Spectroscopy in Neutral Hydrogen
• Atmosphere expansion and mass loss of close-orbit giant exoplanets heated by stellar XUV: I. Modeling of hydrodynamic escape of upper atmospheric material
• Two New Low Galactic D/H Measurements from FUSE
• Mass-Loss Evolution of Close-In Exoplanets: Evaporation of Hot Jupiters and the Effect on Population
• Solar parameters for modeling interplanetary background
• Primordial Radius Gap and Potentially Broad Core Mass Distributions of Super-Earths and Sub-Neptunes
• The deuterium-to-oxygen ratio in the interstellar medium
• Evidence for a lost population of close-in exoplanets
• Morphology of Hydrodynamic Winds: A Study of Planetary Winds in Stellar Environments
• EUV irradiation of exoplanet atmospheres occurs on Gyr timescales
• The Interaction of Venus-like, M-dwarf Planets with the Stellar Wind of Their Host Star
• The Habitable-zone Planet Finder Reveals A High Mass and a Low Obliquity for the Young Neptune K2-25b
• Stellar wind interaction and pick-up ion escape of the Kepler-11 "super-Earths"
• Stellar wind effects on the atmospheres of close-in giants: a possible reduction in escape instead of increased erosion
• Radiative braking in the extended exosphere of GJ436b
• 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
• Predicting Exoplanets Mass and Radius: A Nonparametric Approach
• Magnetised winds and their influence in the escaping upper atmosphere of HD 209458b
• HAZMAT VI: The Evolution of Extreme Ultraviolet Radiation Emitted from Early M Star
• Predicting the Extreme Ultraviolet Radiation Environment of Exoplanets Around Low-Mass Stars: GJ 832, GJ 176, GJ 436
• Is pi Men c's atmosphere hydrogen-dominated? Insights from a non-detecton of Hy Ly-alpha absorption
• Effects of the stellar wind on the Ly-alpha transit of close-in planets
• The Hubble PanCET program: An extensive search for metallic ions in the exosphere of GJ 436 b
• The dichotomy of atmospheric escape in AU Mic b
• Effects of Radiation Pressure on the Evaporative Wind of HD 209458b
• Zodiacal Exoplanets in Time. XI. The Orbit and Radiation Environment of the Young M Dwarf-Hosted Planet K2-25b
• 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
• Chemo-kinematic ages of eccentric-planet-hosting M dwarf stars
• The young planetary system K2-25: constraints on companions and starspots

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• TESS Hunt for Young and Maturing Exoplanets (THYME) IX: a 27 Myr extended population of Lower-Centaurus Crux with a transiting two-planet system
• TESS Hunt for Young and Maturing Exoplanets (THYME) VII : Membership, rotation, and lithium in the young cluster Group-X and a new young exoplanet
• A Mini-Neptune from TESS and CHEOPS Around the 120 Myr Old AB Dor member HIP 94235
• Probing atmospheric escape through metastable He I triplet lines in 15 exoplanets observed with SPIRou
• Heating and ionization by non-thermal electrons in the upper atmospheres of water-rich exoplanets
• Planetary parameters, XUV environments and mass-loss rates for nearby gaseous planets with X-ray detected host-stars
• The Variable Detection of Atmospheric Escape around the young, Hot Neptune AU Mic b
• Using Lyman-$\alpha$ transits to constrain models of atmospheric escape
• Far-ultraviolet flares and variability of the young M dwarf AU Mic: a non-detection of planet c in transit at Lyman-alpha
• Analytical modeling of helium absorption signals of isothermal atmospheric escape