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

Abstract

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 ~2X 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. 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.

arXiv comment18 pages, 14 figures, 5 tables. Ancillary machine-readable files included. Accepted for publication in ApJ. Includes new sections on starspot coverage and superflare emission from starspots

References in corpus (84)

• Astropy: A Community Python Package for Astronomy
• Galactic Stellar and Substellar Initial Mass Function
• Gaia Data Release 2. Summary of the contents and survey properties
• The Gaia mission
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• The Man Behind the Curtain: X-rays Drive the UV through NIR Variability in the 2013 AGN Outburst in NGC 2617
• The K2 Mission: Characterization and Early results
• Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1
• A terrestrial planet candidate in a temperate orbit around Proxima Centauri
• The UKIRT Infrared Deep Sky Survey ZYJHK Photometric System: Passbands and Synthetic Colours
• How to Constrain Your M Dwarf: measuring effective temperature, bolometric luminosity, mass, and radius
• The Occurrence Rate of Small Planets around Small Stars
• Constraining the Age-Activity Relation for Cool Stars: The SDSS DR5 Low-Mass Star Spectroscopic Sample
• Correcting systematic effects in a large set of photometric lightcurves
• The Solar Neighborhood XVII: Parallax Results from the CTIOPI 0.9m Program -- Twenty New Members of the RECONS 10 Parsec Sample
• The Effect of a Strong Stellar Flare on the Atmospheric Chemistry of an Earth-like Planet Orbiting an M dwarf
• Design Considerations for a Ground-based Transit Search for Habitable Planets Orbiting M dwarfs
• Kepler Flares I. Active and Inactive M dwarfs
• Impulsive phase flare energy transport by large-scale Alfven waves and the electron acceleration problem
• The H$\alpha$ emission of nearby M dwarfs and its relation to stellar rotation
• A temperate rocky super-Earth transiting a nearby cool star
• The Kepler Catalog of Stellar Flares
• The Stellar Populations of Praesepe and Coma Berenices
• Trumpeting M Dwarfs with CONCH-SHELL: a Catalog of Nearby Cool Host-Stars for Habitable ExopLanets and Life
• Kepler Flares II: The Temporal Morphology of White-Light Flares on GJ 1243
• The Next Generation Transit Survey (NGTS)
• The stellar rotation--activity relationship in fully convective M dwarfs
• A revised estimate of the occurrence rate of terrestrial planets in the habitable zones around kepler m-dwarfs
• Time-Resolved Properties and Global Trends in dMe Flares from Simultaneous Photometry and Spectra
• A Unified Computational Model for Solar and Stellar Flares
• Can Superflares Occur on Our Sun?
• Modeling Repeated M-dwarf Flaring at an Earth-like Planet in the Habitable Zone: I. Atmospheric Effects for an Unmagnetized Planet
• A Stellar Census of the Tucana-Horologium Moving Group
• Modelling Quasi-Periodic Pulsations in Solar and Stellar Flares
• Magnetic activity in the HARPS M-dwarf sample. The rotation-activity relationship for very low-mass stars through R'HK
• Transit Detection in the MEarth Survey of Nearby M Dwarfs: Bridging the Clean-First, Search-Later Divide
• An Activity-Rotation Relationship and Kinematic Analysis of Nearby Mid-to-Late-type M Dwarfs
• Suppression of Coronal Mass Ejections in active stars by an overlying large-scale magnetic field: A numerical study
• Connecting Flares and Transient Mass Loss Events in Magnetically Active Stars
• Do Kepler superflare stars really include slowly-rotating Sun-like stars ? - Results using APO 3.5m telescope spectroscopic observations and Gaia-DR2 data -
• The MUSCLES Treasury Survey. V. FUV Flares on Active and Inactive M Dwarfs
• The Solar Neighborhood X: New Nearby Stars in the Southern Sky and Accurate Photometric Distance Estimates for Red Dwarfs
• UV Surface Environment of Earth-like Planets Orbiting FGKM Stars Through Geological Evolution
• The Stellar CME-flare relation: What do historic observations reveal?
• Strong dipole magnetic fields in fast rotating fully convective stars
• The First Naked-Eye Superflare Detected from Proxima Centauri
• Habitability of Terrestrial-Mass Planets in the HZ of M Dwarfs. I. H/He-Dominated Atmospheres
• A path towards understanding the rotation-activity relation of M dwarfs with K2 mission, X-ray and UV data
• A Catalog of Cool Dwarf Targets for the Transiting Exoplanet Survey Satellite
• Superflare occurrence and energies on G-, K- and M-type dwarfs
• Evryscope science: exploring the potential of all-sky gigapixel-scale telescopes
• Measuring the Recoverability of Close Binaries in Gaia DR2 with the Robo-AO Kepler Survey
• MOST Observations of our Nearest Neighbor: Flares on Proxima Centauri
• The Evolution of Flare Activity with Stellar Age
• A temperate exo-Earth around a quiet M dwarf at 3.4 parsecs
• Statistical Properties of Quasi-Periodic Pulsations in White-Light Flares Observed With Kepler
• Multi-wavelength characterization of stellar flares on low-mass stars using SDSS and 2MASS time domain surveys
• HAZMAT. IV. Flares and Superflares on Young M Stars in the Far Ultraviolet
• Atmospheric effects of stellar cosmic rays on Earth-like exoplanets orbiting M-dwarfs
• Constraining Stellar Coronal Mass Ejections Through Multi-Wavelength Analysis of the Active M Dwarf EQ Peg
• Stellar flares observed in long cadence data from the Kepler mission
• M Dwarf Flare Continuum Variations on One-Second Timescales: Calibrating and Modeling of ULTRACAM Flare Color Indices
• Spectra of Earth-like Planets Through Geological Evolution Around FGKM Stars
• The Properties of Long-Period Variables in the Large Magellanic Cloud from MACHO
• About Exobiology: The Case for Dwarf K Stars
• Predicted Number, Multiplicity, and Orbital Dynamics of TESS M Dwarf Exoplanets
• Flares in Open Clusters with K2. I. M45 (Pleiades), M44 (Praesepe) and M67
• The largest M dwarfs flares from ASAS-SN
• Detection of a giant flare displaying quasi-periodic pulsations from a pre-main sequence M star with NGTS
• Modeling Stellar Proton Event-induced particle radiation dose on close-in exoplanets
• Can flare loops contribute to the white-light emission of stellar superflares ?
• Galactic cosmic rays on extrasolar Earth-like planets: II. Atmospheric implications
• High-Density Off-Limb Flare Loops Observed by SDO
• Building the Evryscope: Hardware Design and Performance
• Lessons from early Earth: UV surface radiation should not limit the habitability of active M star systems
• K2 Ultracool Dwarfs Survey. V. High superflare rates on rapidly rotating late-M dwarfs
• HAZMAT II: Ultraviolet Variability of Low-Mass Stars in the GALEX Archive
• Ground-based detection of G star superflares with NGTS
• iPTF Archival Search for Fast Optical Transients
• An increased rate of large flares at intermediate rotation periods for mid-to-late M dwarfs
• TESS Habitable Zone Star Catalog
• The Palomar Transient Factory Sky2Night programme
• Stellar Flares in the CSTAR Field: Results from the 2008 Data Set
• Observation of a possible superflare on Proxima Centauri

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• The Flaring TESS Objects of Interest: Flare Rates for all Two Minute Cadence TESS Planet Candidates
• Rotation periods of TESS Objects of Interest from the Magellan-TESS Survey with multiband photometry from Evryscope and TESS
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• Minute-cadence Observations of the LAMOST Fields with the TMTS: III. Statistic Study of the Flare Stars from the First Two Years
• COCOPLOT: COlor COllapsed PLOTting software : Using color to view 3D data as a 2D image
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• Theoretical and Observational Evidence for Coriolis Effects in Coronal Magnetic Fields Via Direct Current Driven Flaring Events
• New Clues to the Evolution of Dwarf Carbon Stars From Their Variability and X-ray Emission
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