The MUSCLES Treasury Survey. V. FUV Flares on Active and Inactive M Dwarfs*

†

‡

Loyd, R. O. Parke; Youngblood, Allison; Schneider, Christian; Brown, Alexander; Hu, Renyu; Segura, Antígona; Linsky, Jeffrey L.; Redfield, Seth; Tian, Feng; Rugheimer, Sarah; Miguel, Yamila; Froning, Cynthia S.

doi:10.3847/1538-4357/aae2bd

Cited by 124 publications

(193 citation statements)

References 133 publications

(169 reference statements)

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“…Although these rates are high, they are constructed from active stars of each spectral type and do not hold for inactive stars. Loyd et al (2018) finds inactive stars to be 10× less active in the FUV-130 bandpass. Should similar relationships hold for white-light superflares, the impacts on planet atmospheres would be greatly reduced for inactive stars.…”

Section: Superflare Rate Vs Spectral Typementioning

confidence: 94%

EvryFlare. I. Long-term Evryscope Monitoring of Flares from the Cool Stars across Half the Southern Sky

Howard

Corbett

Law

et al. 2019

ApJ

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We search for superflares from 4,068 cool stars in 2+ years of Evryscope photometry, focusing on those with high-cadence data from both Evryscope and TESS. The Evryscope array of small telescopes observed 575 flares from 284 stars, with a median energy of 10 34.0 erg. Since 2016, Evryscope has enabled the detection of rare events from all stars observed by TESS through multi-year, high-cadence continuous observing. We report ∼2× the previous largest number of 10 34 erg high-cadence flares from nearby cool stars. We find 8 flares with amplitudes of 3+ g magnitudes, with the largest reaching 5.6 magnitudes and releasing 10 36.2 erg. We observe a 10 34 erg superflare from TOI-455 (LTT 1445), a mid-M with a rocky planet candidate a . We measure the superflare rate per flare-star and quantify the average flaring of active stars as a function of spectral type, including superflare rates, FFDs, and typical flare amplitudes in g . We confirm superflare morphology is broadly consistent with magnetic re-connection. We estimate starspot coverage necessary to produce superflares, and hypothesize maximum-allowed superflare energies and waiting-times between flares corresponding to 100% coverage of the stellar hemisphere. We observe decreased flaring at high galactic latitudes. We explore the effects of superflares on ozone loss to planetary atmospheres: we observe 1 superflare with sufficient energy to photo-dissociate all ozone in an Earth-like atmosphere in one event. We find 17 stars that may deplete an Earth-like atmosphere via repeated flaring. Of the 1822 stars around which TESS may discover temperate rocky planets, we observe 14.6±2% emit large flares.

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Section: Superflare Rate Vs Spectral Typementioning

confidence: 94%

EvryFlare. I. Long-term Evryscope Monitoring of Flares from the Cool Stars across Half the Southern Sky

Howard

Corbett

Law

et al. 2019

ApJ

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“…FUV-only flares have previously been observed in Gtype stars and M dwarfs (Mitra-Kraev et al 2005, Ayres 2015, Loyd et al 2018. Flares result from reconnections occurring in magnetic structures.…”

Section: Visit B -September 7/8 2011mentioning

confidence: 95%

MOVES III. Simultaneous X-ray and ultraviolet observations unveiling the variable environment of the hot Jupiter HD 189733b

Bourrier

Wheatley

Étangs

et al. 2020

Monthly Notices of the Royal Astronomical Society

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In this third paper of the MOVES (Multiwavelength Observations of an eVaporating Exoplanet and its Star) programme, we combine Hubble Space Telescope far-ultraviolet observations with XMM-Newton/Swift X-ray observations to measure the emission of HD 189733 in various FUV lines, and its soft X-ray spectrum. Based on these measurements we characterise the interstellar medium toward HD 189733 and derive semi-synthetic XUV spectra of the star, which are used to study the evolution of its high-energy emission at five different epochs. Two flares from HD 189733 are observed, but we propose that the long-term variations in its spectral energy distribution have the most important consequences for the environment of HD 189733b. Reduced coronal and wind activity could favour the formation of a dense population of Si 2+ atoms in a bow-shock ahead of the planet, responsible for pre-and in-transit absorption measured in the first two epochs. In-transit absorption signatures are detected in the Lyman-α line in the second, third and fifth epochs, which could arise from the extended planetary thermosphere and a tail of stellar wind protons neutralised via charge-exchange with the planetary exosphere. We propose that increases in the X-ray irradiation of the planet, and decreases in its EUV irradiation causing lower photoionisation rates of neutral hydrogen, favour the detection of these signatures by sustaining larger densities of H 0 atoms in the upper atmosphere and boosting charge-exchanges with the stellar wind. Deeper and broader absorption signatures in the last epoch suggest that the planet entered a different evaporation regime, providing clues as to the link between stellar activity and the structure of the planetary environment.

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“…3 and Table 4; these spectra were derived by combining all of the out-of-transit, time-tag split subexposures in the quiescent and flare state. The flare spectrum seems to be blueshifted in relation to the quiescent spectrum for both spectral lines shown, which is unexpected given that other M dwarfs and the Sun exhibit a redshifted flare excess instead (Hawley et al 2003;Loyd et al 2018). We presume this blueshift is physical, since we applied wavelength shift corrections for systematic errors uniformly across visits before combining the flare and quiescent spectra; these correction factors are estimated using exposures from which the flare subexposure Linsky et al 2012;Bourrier et al 2018a).…”

Section: Discussionmentioning

confidence: 81%

The Hubble PanCET program: an extensive search for metallic ions in the exosphere of GJ 436 b

Santos

Ehrenreich

Bourrier

et al. 2019

A&A

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Context. The quiet M2.5 star GJ 436 hosts a warm Neptune that displays an extended atmosphere that dwarfs its own host star. Predictions of atmospheric escape in such planets state that H atoms escape from the upper atmosphere in a collisional regime and that the flow can drag heavier atoms to the upper atmosphere. It is unclear, however, what astrophysical mechanisms drive the process. Aims. Our objective is to leverage the extensive coverage of observations of the far-ultraviolet (FUV) spectrum of GJ 436 obtained with the Cosmic Origins Spectrograph (COS) to search for signals of metallic ions in the upper atmosphere of GJ 436 b, as well as study the activity-induced variability of the star. Methods. We analyzed flux time-series of species present in the FUV spectrum of GJ 436 and successfully performed geocoronal contamination removal in the COS Lyman-α profiles obtained near the Earth's night-side. Results. GJ 436 displays flaring events with a rate of ∼10 d −1 . There is evidence for a possibly long-lived active region or longitude that modulates the FUV metallic lines of the star with amplitudes up to 20%. Despite the strong geocoronal contamination in the COS spectra, we detected in-transit excess absorption signals of ∼50% and ∼30% in the blue and red wings, respectively, of the Lyman-α line. We rule out a wide range of excess absorption levels in the metallic lines of the star during transit. Conclusions. The large atmospheric loss of GJ 436 b observed in Lyman-α transmission spectra is stable over the timescale of a few years, and the red wing signal supports the presence of a variable hydrogen absorption source besides the stable exosphere. The previously claimed in-transit absorption in the Si iii line is likely an artifact resulting from the stellar magnetic cycle. The non-detection of metallic ions in absorption could indicate that the escape is not hydrodynamic or that the atmospheric mixing is not efficient in dragging metals high enough for sublimation to produce a detectable escape rate of ions to the exosphere.

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The MUSCLES Treasury Survey. V. FUV Flares on Active and Inactive M Dwarfs* † ‡

Cited by 124 publications

References 133 publications

EvryFlare. I. Long-term Evryscope Monitoring of Flares from the Cool Stars across Half the Southern Sky

EvryFlare. I. Long-term Evryscope Monitoring of Flares from the Cool Stars across Half the Southern Sky

MOVES III. Simultaneous X-ray and ultraviolet observations unveiling the variable environment of the hot Jupiter HD 189733b

The Hubble PanCET program: an extensive search for metallic ions in the exosphere of GJ 436 b

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