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Coverage at high spectral resolution in soft X-rays is essential for understanding the EUV emission: The 30-60 Å range exhibits transitions of the same ions that dominate the shorter EUV wavelengths. Stars, but the high-resolution spectra of superflares and also of more modestįlares needed to infer their EUV emission require a high resolution large effective area soft X-ray spectrometerįigure 1: Left: The key X-ray to EUV spectral region computed for ProximaĪnd responsible for upper planetary atmospheric ionization, heating and loss. Chandra has observed superflares on M dwarf and young Superflares have been observed with energies as large asĮ = 10 35 ergs. Occur as often as 1 per 10 days ( Shibayama et al., 2013). Solar-like stars but are far more common on young G-type stars, and Likely on a time scale of ∼ 500 days for slowly rotating That high-energy superflares (total energy E > 10 32 ergs) are Monitoring of the optical radiation of G-type stars by Kepler shows Have high X-ray and EUV emission and emit energetic flares. The X-ray emission of stars is variable on many time scalesĮspecially for M dwarfs, which many astronomers think are the best host star candidates for locating nearby habitable exoplanets. Observing these enables prediction of the EUV spectrum.ĭetecting the relevant lines in exoplanet hosts requiresĪ high-resolution ( R ≥ 5, 000) spectrum that is not feasible with any existing or slated future missions, including Chandra, XMM-Newton or ATHENA. The 30–60 Å range contains many of the same ionization stages that are important in the EUV range. Spectral energy distribution of a star’s EUV emission instead arises from the transition region and corona. The chromospheric UV and FUV are inadequate EUV proxies. The thermospheric heating is by EUV photons but this radiationĬannot be observed directly because of interstellar H absorption. Producing lighter atoms (e.g., H) that are more easily lost to space. Stellar UV and EUV radiation increases the mass-loss rate by Photodissociation and ionization of molecules, including Thermosphere and levitate gas against the exoplanet’s gravitational Thermal process is hydrodynamical outflow energized by extreme ultraviolet Atmospheric mass loss canīe driven by both thermal and non-thermal processes, whichĭepend upon the radiation and winds of their host stars. The rate at which gas is lost from an exoplanet’s atmosphere isĬritical for the survivability of surface water. This is the only capability that can: (1) characterize by proxy the crucial, difficult to observe, EUV stellar flux, its history and its variations for planet hosting stars (2) observe the stellar wind (3) detect the subtle Doppler signatures of coronal mass ejections. High-resolution X-ray imaging and spectroscopic observatory.

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In line with the Committee on an Exoplanet Science Strategy recognition that holistic observational approaches are needed, we point out here thatĪ full understanding of exoplanet atmospheres, their evolution and determination of habitability requires a powerful Observation of stellar coronal mass ejections and winds are also beyond current instrumentation. Key exoplanet host stars will be too faint at X-ray wavelengths for accurate characterization using existing generation and future slated X-ray telescopes. It is now recognized that energetic stellar photon and particle radiation evaporates and erodes planetary atmospheres and controls upper atmospheric chemistry. Panayiotis Tzanavaris (NASA/GSFC & CRESST/UMBC), Salvatore Sciortino (INAF-Oss. Astron. Palermo), Giusi Micela (INAF-Oss. Astron. Palermo), Jeffrey Linsky (JILA, Univ. Colorado), Mercedes López-Morales (CfA), Joel Kastner (RIT), Jinyoung Serena Kim (University of Arizona),

Gelino (NASA Exoplanet Science Institute), Christian (Cal. State Northridge),Ĭhuanfei Dong (Princeton), William Forman (CfA),ĭawn M.