The Ultraviolet Radiation Environment Around M Dwarf Exoplanet Host Stars

France, Kevin; Froning, Cynthia S.; Linsky, Jeffrey L.; Roberge, Aki; Stocke, John T.; Tian, Feng; Bushinsky, Rachel; Désert, Jean-Michel; Mauas, P. J. D.; Vieytes, M.; Walkowicz, Lucianne M.

doi:10.1088/0004-637x/763/2/149

Cited by 271 publications

(348 citation statements)

References 102 publications

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“…The uncertainties on these values were obtained by varying the peak flux of the Lyman-α line constrained by Bourrier et al (2015a) within its 1σ error bars. We note that France et al (2013) performed a similar estimation using the intrinsic Lyman-α line of GJ 436 observed in 2010 . With a maximum uncertainty of 30%, the total flux they obtained ranges from 1.1 to 2.0 erg s −1 cm −2 at 1 au from the star.…”

Section: Stellar Xeuv Emission and Photoionization Ratementioning

confidence: 89%

An evaporating planet in the wind: stellar wind interactions with the radiatively braked exosphere of GJ 436 b

Bourrier

Étangs

Ehrenreich

et al. 2016

A&A

155

205

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Observations of the warm Neptune GJ 436 b were performed with HST/STIS at three different epochs (2012, 2013, 2014) in the stellar Lyman-α line. They showed deep, repeated transits that were attributed to a giant exosphere of neutral hydrogen. The low radiation pressure from the M-dwarf host star was shown to play a major role in the dynamics of the escaping gas and its dispersion within a large volume around the planet. Yet by itself it cannot explain the specific time-variable spectral features detected in each transit. Here we investigate the combined role of radiative braking and stellar wind interactions using numerical simulations with the EVaporating Exoplanet code (EVE) and we derive atmospheric and stellar properties through the direct comparison of simulated and observed spectra. The first epoch of observations is difficult to interpret because of the lack of out-of-transit data. In contrast, the results of our simulations match the observations obtained in 2013 and 2014 well. The sharp early ingresses observed in these epochs come from the abrasion of the planetary coma by the stellar wind. Spectra observed at later times during the transit can be produced by a dual exosphere of planetary neutrals (escaped from the upper atmosphere of the planet) and neutralized protons (created by charge-exchange with the stellar wind). We find similar properties at both epochs for the planetary escape rate (∼2.5 × 10 8 g s −1 ), the stellar photoionization rate (∼2 × 10 −5 s −1 ), the stellar wind bulk velocity (∼85 km s −1 ), and its kinetic dispersion velocity (∼10 km s −1 , corresponding to a kinetic temperature of 12 000 K). We also find high velocities for the escaping gas (∼50−60 km s −1 ) that may indicate magnetohydrodynamic (MHD) waves that dissipate in the upper atmosphere and drive the planetary outflow. In 2014 the high density of the stellar wind (∼3 × 10 3 cm −3 ) led to the formation of an exospheric tail that was mainly composed of neutralized protons and produced a stable absorption signature during and after the transit. The observations of GJ 436 b allow for the first time to clearly separate the contributions of radiation pressure and stellar wind and to probe the regions of the exosphere shaped by each mechanism. The overall shape of the cloud, which is constant over time, is caused by the stability of the stellar emission and the planetary mass loss, while the local changes in the cloud structure can be interpreted as variations in the density of the stellar wind.

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Section: Stellar Xeuv Emission and Photoionization Ratementioning

confidence: 89%

An evaporating planet in the wind: stellar wind interactions with the radiatively braked exosphere of GJ 436 b

Bourrier

Étangs

Ehrenreich

et al. 2016

A&A

155

205

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“…A very important contribution in the FUV band is given by the Lyα line emission, which can carry up to 70-90% of the total FUV flux (Schindhelm et al 2012). However, due to resonant scattering of neutral hydrogen and deuterium in the interstellar medium (ISM), the calculation of the Lyα fluxes must rely on line profile reconstruction (France et al 2013), which is beyond the scope of this work. Moreover, Bethell & Bergin (2011) show that Lyα is efficiently scattered through the atomic layers of protoplanetary disks by neutral hydrogen and dominates the energy budget over FUV continuum deeper in the disk, where the chemical environment is rich in molecules.…”

Section: Fuv Luminositiesmentioning

confidence: 99%

[O I] disk emission in the Taurus star-forming region

Aresu

Kamp²,

Meijerink

et al. 2014

A&A

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Context. The structure of protoplanetary disks is thought to be linked to the temperature and chemistry of their dust and gas. Whether the disk is flat or flaring depends on the amount of radiation that it absorbs at a given radius and on the efficiency with which this is converted into thermal energy. The understanding of these heating and cooling processes is crucial for providing a reliable disk structure for interpreting dust continuum emission and gas line fluxes. Especially in the upper layers of the disk, where gas and dust are thermally decoupled, the infrared line emission is strictly related to the gas heating/cooling processes. Aims. We aim to study the thermal properties of the disk in the oxygen line emission region and to investigate the relative importance of X-ray (1-120 Å) and far-UV radiation (FUV, 912-2070 Å) for the heating balance there. This contrasts with what is predicted from our models. Possible explanations are that the disks in Taurus are less flaring than the hydrostatic models predict and/or that other disk structure aspects that were left unchanged in our models are important. Disk models should include flat geometries, varying parameters such as outer radius, dust settling, and the dust-to-gas mass ratio, which might play an equally important role for the [O ] emission. To improve statistics and draw more robust conclusions on the thermal processes that dominate the atmosphere of protoplanetary disks surrounding T Tauri stars, more L FUV and L X measurements are needed. High spatial and spectra resolution data is required to disentangle the fraction of [O ] flux emitted by the disk in outflow sources.

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“…We describe the process of matching the GALEX data to the M dwarf samples Figure 1. The spectrum of Gl 876 from France et al (2013), a moderately UVactive M4 dwarf imaged with the Hubble Space Telescopeʼs Space Telescope Imaging Spectrograph (STIS) and Cosmic Origins Spectrograph (COS). We have over-plotted the GALEX NUV (red) and FUV (blue) throughput curves (with an arbitrary scale factor).…”

Section: Introductionmentioning

confidence: 99%

A Catalog of Galex Ultraviolet Emission From Spectroscopically Confirmed M Dwarfs*

Jones¹,

West²

2016

ApJ

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We present a catalog of Galaxy Evolution Explorer Near-UV (NUV) and Far-UV (FUV) photometry for the Palomar/MSU and SDSS DR7 spectroscopic M dwarf catalogs. The catalog contains NUV measurements matched to 577 spectroscopically confirmed M dwarfs and FUV measurements matched to 150 spectroscopically confirmed M dwarfs. Using these data, we find that NUV and FUV luminosities strongly correlate with Hα emission, a typical indicator of magnetic activity in M dwarfs. We also examine the fraction of M dwarfs with varying degrees of strong line emission at NUV wavelengths. Our results indicate that the frequency of M dwarf NUV emission peaks at intermediate spectral types, with at least ∼30% of young M4-M5 dwarfs having some level of activity. For mid-type M dwarfs, we show that NUV emission decreases with distance from the Galactic plane, a proxy for stellar age. Our complete matched source catalog is available online.

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The Ultraviolet Radiation Environment Around M Dwarf Exoplanet Host Stars

Cited by 271 publications

References 102 publications

An evaporating planet in the wind: stellar wind interactions with the radiatively braked exosphere of GJ 436 b

An evaporating planet in the wind: stellar wind interactions with the radiatively braked exosphere of GJ 436 b

[O I] disk emission in the Taurus star-forming region

A Catalog of Galex Ultraviolet Emission From Spectroscopically Confirmed M Dwarfs*

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