J/AJ/169/302ivo://CDS.VizieR/J/AJ/169/302CDSCorbett H.Galliher N.Glazier A.Gonzalez Chavez R.Law N.M.,Howard W.S.Soto A.V.Ratzloff J.K.Quimby R.2026-04-02T06:28:33Z2026-03-04T14:26:02ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frstellar-flaresnarrow-band-photometryatomic-spectroscopyline-intensitiesvisible-astronomyspectroscopyphotometrytransient-sourcesWe present time-series optical spectroscopy of two stellar flares with complex multi-peaked light curves: a 2.1_-.3_^+.4^x10^34^erg flare from an M8 ultra-cool dwarf, and a 1.5_-.2_^+.2^x10^35^erg superflare from an M4 field star. Both flares were discovered by the Evryscope Fast Transient Engine and observed with the Southern Astrophysical Research 4.1m telescope ~10min after their initial peak. We model the blackbody temperature of the flares as a function of time, finding that the characteristic temperature reaches ~13,000K during the secondary peaks of both events and is likely higher during the initial, unobserved impulsive phase. Both nonthermal emission from the near-UV Balmer continuum and an evolving red continuum of uncertain origin are observed in both flares; we compare the relative contributions of the continua, line emission, and blackbody component as the flare evolves, and find that the secondary peak of the M4 superflare immediately follows inversion of the relative contributions of the Balmer and red continua. We additionally present a model that constrains the evolution of the electron density of the stellar chromosphere during the flare, based on the time evolution of the observed red continuum excess, which we interpret as components of the hydrogen recombination continuum. Our observations of a 10.5mag flare from an M8 dwarf, as well as a similar, unusually energetic event from an M4 dwarf, are comparable in intensity to the most energetic stellar flares reported in the literature to date.2025AJ....169..302Chttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/AJ/169/302CatalogResearchIsServedByTAP VizieR generic serviceIsServedByConesearch servicerelated-toII/179 : Southern Spectrophotometric Standards. I + II (Hamuy+ 1992,94)I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)I/349 : StarHorse, Gaia DR2 photo-astrometric distances (Anders+, 2019)II/371 : The Dark Energy Survey (DES): Data Release 2 (Abbott+, 2021)I/357 : Gaia DR3 Part 3. Non-single stars (Gaia Collaboration, 2022)VII/233 : 2MASS All-Sky Extended Source Catalog (XSC) (IPAC/UMass, 2003-2006)J/ApJ/743/154 : Multi-band phot. of GRB 110205A + 110213A (Cucchiara+, 2011)J/ApJ/767/95 : Improved stellar param. of smallest KIC stars (Dressing+, 2013)J/ApJS/207/15 : M dwarf flare spectra (Kowalski+, 2013)J/ApJ/788/48 : X-ray through NIR photometry of NGC 2617 (Shappee+, 2014)J/ApJ/807/45 : Potentially habit. planets orbiting M dwarfs (Dressing+, 2015)J/ApJS/230/16 : O5 to L3 empirical stellar spectra from SDSS (Kesseli+, 2017)J/AJ/156/241 : A first cat. of variab. stars measured by ATLAS (Heinze+, 2018)J/ApJ/858/55 : K2 ultracool dwarfs survey. III. M6-L0 flares (Paudel+, 2018)J/ApJ/867/105 : ATLAS all-sky stellar ref. cat., ATLAS-REFCAT2 (Tonry+, 2018)J/ApJ/881/9 : EvryFlare. I. Cool stars's flares in southern sky (Howard+, 2019)J/AJ/157/231 : MLSDSS-GaiaDR2 sample of M and L dwarfs (Kiman+, 2019)J/ApJ/876/115 : Optical follow-up of ASAS-SN M dwarf flares (Schmidt+, 2019)J/AJ/159/60 : 8695 flares from 1228 stars in TESS Sect. 1 & 2 (Gunther+, 2020)J/ApJ/902/115 : EvryFlare. III. Superflares: Evryscope & TESS (Howard+, 2020)J/ApJ/909/106 : R-band LC and spectrum of a superstellar flare (Xin+, 2021)J/MNRAS/512/L60 : Flare detections of TOI host stars (Howard+, 2022)J/ApJ/926/204 : TESS monitor. campaign of low-mass flare stars (Howard+, 2022)J/ApJ/960/62 : Red dwarfs, Xray, UV, and CaII (Engle, 2024)http://asas-sn.ifa.hawaii.edu/skypatrol/ : ASAS-SN Sky Patrol v2.0 databasehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/AJ/169/302https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/AJ/169/302http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/AJ/169/302https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/AJ/169/302https://vizier.iucaa.in/viz-bin/votable?-source=J/AJ/169/302http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/AJ/169/302GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapCone search capability for table J/AJ/169/302/table1 (EFTE Flare discovery coordinates, number of significant detections in Evryscope, peak magnitudes, and time stamps for detection and alert generation)https://vizier.cds.unistra.fr/viz-bin/conesearch/J/AJ/169/302/table1?https://vizier.iucaa.in/viz-bin/conesearch/J/AJ/169/302/table1?http://vizieridia.saao.ac.za/viz-bin/conesearch/J/AJ/169/302/table1?GETtext/xml+votable180.050000true21.825125-60.9618750.0055555555555555566/33507 40176https://cdsarc.cds.unistra.fr/viz-bin/moc/J/AJ/169/302?format=asciiOpticaldefaultJ/AJ/169/302/table1EFTE Flare discovery coordinates, number of significant detections in Evryscope, peak magnitudes, and time stamps for detection and alert generationrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintFlareFlare identifiermeta.id;meta.maincharRAJ2000Hour of right ascension (J2000)pos.eq.ra;meta.mainLCAssociated light curve with link to the interactive plot (data behind Figure 1.a & Figure 2.a)meta.ref.urlcharFileLCLink to the light curve file in MRT formatmeta.filecharEWAssociated equivalent width changes with link to the interactive plot (data behind Figure 1.bc & 2.bc)meta.ref.urlcharFileEW-HLink to the Balmer lines fit parameters file in MRT formatmeta.filecharFileEW-CaLink to the Ca lines fit parameters file in MRT formatmeta.filecharTabEWLink to the line fit parameters data (Tables fig1EW and fig2EW)meta.ref.urlcharTempAssociated best-fit temperature evolution with link to the interactive plot (data behind Figure 8)meta.ref.urlcharXtAssociated filling factor evolution (flaring region size as a fraction of the stellar disk) with link to interactive plot (data behind Figure 8)meta.ref.urlcharFileFig8Link to the temperature and filling factor evolution file in MRT formatmeta.filecharnSpNumber of spectra taken during the decay phasemeta.numberintSimbadNameSimbad column added by the CDSmeta.idcharnullableDateDate of detection (UT)time.epochnullableDEJ2000Degree of declination (J2000)pos.eq.dec;meta.main1stDetTime stamp of first detection (UT)time.epochcharTrigTimeTrigger time (UT)time.epochcharNdet[3/7] Number of significant detections in Evryscopemeta.numberintgmag[10.3/12.7] g-band peak magnitudemagphot.mag;em.opt;stat.maxfloatJ/AJ/169/302/fig1EWFit parameters for the Balmer and Ca lines of EVRT-2509887 (Tables fig1b & fig1c)Heta-SNRHeta signal-to-noise ratio (3)stat.snr;spect.linefloatrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintEpochUTC mid-point of exposure, ISO 8601 formattime.epochcharHa-X0Halpha peak position (1)1e-10mem.wl.centralfloatHa-AmpHalpha Lorentzian amplitude; 1e+16 erg/s/cm/Angstrom (1)1e+14W.m**-2.nm**-1src.var.amplitudefloatHa-FWHM-LHalpha Lorentzian full width at half maximum (2)1e-10mspect.line.widthfloatHa-FWHM-GHalpha Gaussian full width at half maximum (2)1e-10mspect.line.widthfloatHa-EWHalpha equivalent width1e-10mspect.line.eqWidthfloate_Ha-EWUncertainty in Ha-EW1e-10mstat.error;spect.line.eqWidthfloatHa-SNRHalpha signal-to-noise ratio (3)stat.snr;spect.linefloatHb-X0Hbeta peak position (1)1e-10mem.wl.centralfloatHb-AmpHbeta Lorentzian amplitude; 1e-16 erg/s/cm/Angstrom (1)1e+14W.m**-2.nm**-1src.var.amplitudefloatHb-FWHM-LHbeta Lorentzian full width at half maximum (2)1e-10mspect.line.widthfloatHb-FWHM-GHbeta Gaussian full width at half maximum (2)1e-10mspect.line.widthfloatHb-EWHbeta equivalent width1e-10mspect.line.eqWidthfloate_Hb-EWUncertainty in Hb-EW1e-10mstat.error;spect.line.eqWidthfloatHb-SNRHbeta signal-to-noise ratio (3)stat.snr;spect.linefloatHg-X0Hgamma peak position (1)1e-10mem.wl.centralfloatHg-AmpHgamma Lorentzian amplitude; 1e-16 erg/s/cm/Angstrom (1)1e+14W.m**-2.nm**-1src.var.amplitudefloatHg-FWHM-LHgamma Lorentzian full width at half maximum (2)1e-10mspect.line.widthfloatHg-FWHM-GHgamma Gaussian full width at half maximum (2)1e-10mspect.line.widthfloatHg-EWHgamma equivalent width1e-10mspect.line.eqWidthfloate_Hg-EWUncertainty in Hg-EW1e-10mstat.error;spect.line.eqWidthfloatHg-SNRHgamma signal-to-noise ratio (3)stat.snr;spect.linefloatHd-X0Hdelta peak position (1)1e-10mem.wl.centralfloatHd-AmpHdelta Lorentzian amplitude; 1e-16 erg/s/cm/Angstrom (2)1e+14W.m**-2.nm**-1src.var.amplitudefloatHd-FWHM-LHdelta Lorentzian full width at half maximum (2)1e-10mspect.line.widthfloatHd-FWHM-GHdelta Gaussian full width at half maximum (2)1e-10mspect.line.widthfloatHd-EWHalpha equivalent width1e-10mspect.line.eqWidthfloate_Hd-EWUncertainty in Hd-EW1e-10mstat.error;spect.line.eqWidthfloatHd-SNRHdelta signal-to-noise ratio (3)stat.snr;spect.linefloatHeps-X0Hepsilon peak position (1)1e-10mem.wl.centralfloatHeps-AmpHepsilon Lorentzian amplitude; 1e-16 erg/s/cm/Angstrom (1)1e+14W.m**-2.nm**-1src.var.amplitudefloatHeps-FWHM-LHepsilon Lorentzian full width at half maximum (2)1e-10mspect.line.widthfloatHeps-FWHM-GHepsilon Gaussian full width at half maximum (2)1e-10mspect.line.widthfloatHeps-EWHepsilon equivalent width1e-10mspect.line.eqWidthdoublee_Heps-EWUncertainty in He-EW1e-10mstat.error;spect.line.eqWidthfloatHeps-SNRHepsilon signal-to-noise ratio (3)stat.snr;spect.linefloatHz-X0Hzeta peak position (1)1e-10mem.wl.centralfloatHz-AmpHzeta Lorentzian amplitude; 1e-16 erg/s/cm/Angstrom (1)1e+14W.m**-2.nm**-1src.var.amplitudefloatHz-FWHM-LHzeta Lorentzian full width at half maximum (2)1e-10mspect.line.widthfloatHz-FWHM-GHzeta Gaussian full width at half maximum (2)1e-10mspect.line.widthfloatHz-EWHzeta equivalent width1e-10mspect.line.eqWidthdoublee_Hz-EWUncertainty in Hz-EW1e-10mstat.error;spect.line.eqWidthfloatHz-SNRHzeta signal-to-noise ratio (3)stat.snr;spect.linefloatHeta-X0Heta peak position (1)1e-10mem.wl.centralfloatHeta-AmpHeta Lorentzian amplitude; 1e-16 erg/s/cm/Angstrom (1)1e+14W.m**-2.nm**-1src.var.amplitudefloatHeta-FWHM-LHeta Lorentzian full width at half maximum (2)1e-10mspect.line.widthfloatHeta-FWHM-GHeta Gaussian full width at half maximum (2)1e-10mspect.line.widthfloatHeta-EWHeta equivalent width1e-10mspect.line.eqWidthdoublee_Heta-EWUncertainty in He-EW1e-10mstat.error;spect.line.eqWidthfloatH-X0Ca II H line peak position (1)1e-10mem.wl.centralfloatH-AmpCa II H line Lorentzian amplitude; 1e-16 erg/s/cm/Angstrom (1)1e+14W.m**-2.nm**-1src.var.amplitudefloatH-FWHM-LCa II H line Lorentzian full width at half maximum (2)1e-10mspect.line.widthfloatH-FWHM-GCa II H line Gaussian full width at half maximum (2)1e-10mspect.line.widthfloatH-EWCa II H line equivalent width1e-10mspect.line.eqWidthdoublee_H-EWUncertainty in H-EW1e-10mstat.error;spect.line.eqWidthfloatH-SNRCa II H line signal-to-noise ratio (3)stat.snr;spect.linefloatK-X0Ca II K line peak position (1)1e-10mem.wl.centralfloatK-AmpCa II K line Lorentzian amplitude; 1e-16 erg/s/cm/Angstrom (1)1e+14W.m**-2.nm**-1src.var.amplitudedoubleK-FWHM-LCa II K line Lorentzian full width at half maximum (2)1e-10mspect.line.widthfloatK-FWHM-GCa II K line Gaussian full width at half maximum (2)1e-10mspect.line.widthfloatK-EWCa II K line equivalent width1e-10mspect.line.eqWidthdoublee_K-EWUncertainty in K-EW1e-10mstat.error;spect.line.eqWidthfloatK-SNRCa II K line signal-to-noise ratio (3)stat.snr;spect.linefloatJ/AJ/169/302/fig2EWFit parameters for the Balmer and Ca lines of EVRT-3586872 (Tables fig2b & fig2c)Ha-EWHalpha equivalent width1e-10mspect.line.eqWidthfloatK-X0Ca II K line peak position (1)1e-10mem.wl.centralfloatrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintHa-X0Halpha peak position (1)1e-10mem.wl.centralfloatHa-AmpHalpha Lorentzian amplitude; 1e-16 erg/s/cm/Angstrom (1)1e+14W.m**-2.nm**-1src.var.amplitudefloatHa-FWHM-LHalpha Lorentzian full width at half maximum (2)1e-10mspect.line.widthfloatHa-FWHM-GHalpha Gaussian full width at half maximum (2)1e-10mspect.line.widthfloate_Ha-EWUncertainty in Ha-EW1e-10mstat.error;spect.line.eqWidthfloatHa-SNRHalpha signal-to-noise ratio (3)stat.snr;spect.linefloatHb-X0Hbeta peak position (1)1e-10mem.wl.centralfloatHb-AmpHbeta Lorentzian amplitude; 1e-16 erg/s/cm/Angstrom (1)1e+14W.m**-2.nm**-1src.var.amplitudefloatHb-FWHM-LHbeta Lorentzian full width at half maximum (2)1e-10mspect.line.widthfloatHb-FWHM-GHbeta Gaussian full width at half maximum (2)1e-10mspect.line.widthfloatHb-EWHbeta equivalent width1e-10mspect.line.eqWidthfloate_Hb-EWUncertainty in Hb-EW1e-10mstat.error;spect.line.eqWidthfloatHb-SNRHbeta signal-to-noise ratio (3)stat.snr;spect.linefloatHg-X0Hgamma peak position (1)1e-10mem.wl.centralfloatHg-AmpHgamma Lorentzian amplitude; 1e-16 erg/s/cm/Angstrom (1)1e+14W.m**-2.nm**-1src.var.amplitudefloatHg-FWHM-LHgamma Lorentzian full width at half maximum (2)1e-10mspect.line.widthfloatHg-FWHM-GHgamma Gaussian full width at half maximum (2)1e-10mspect.line.widthfloatHg-EWHgamma equivalent width1e-10mspect.line.eqWidthfloate_Hg-EWUncertainty in Hg-EW1e-10mstat.error;spect.line.eqWidthfloatHg-SNRHgamma signal-to-noise ratio (3)stat.snr;spect.linefloatHd-X0Hdelta peak position (1)1e-10mem.wl.centralfloatHd-AmpHdelta Lorentzian amplitude; 1e-16 erg/s/cm/Angstrom (2)1e+14W.m**-2.nm**-1src.var.amplitudefloatHd-FWHM-LHdelta Lorentzian full width at half maximum (2)1e-10mspect.line.widthfloatHd-FWHM-GHdelta Gaussian full width at half maximum (3)1e-10mspect.line.widthfloatHd-EWHalpha equivalent width1e-10mspect.line.eqWidthfloate_Hd-EWUncertainty in Hd-EW1e-10mstat.error;spect.line.eqWidthfloatHd-SNRHdelta signal-to-noise ratio (3)stat.snr;spect.linefloatHeps-X0Hepsilon peak position (1)1e-10mem.wl.centralfloatHeps-AmpHepsilon Lorentzian amplitude; 1e-16 erg/s/cm/Angstrom (1)1e+14W.m**-2.nm**-1src.var.amplitudefloatHeps-FWHM-LHepsilon Lorentzian full width at half maximum (2)1e-10mspect.line.widthfloatHeps-FWHM-GHepsilon Gaussian full width at half maximum (2)1e-10mspect.line.widthfloatHeps-EWHepsilon equivalent width1e-10mspect.line.eqWidthfloate_Heps-EWUncertainty in He-EW1e-10mstat.error;spect.line.eqWidthfloatHeps-SNRHepsilon signal-to-noise ratio (3)stat.snr;spect.linefloatHz-X0Hzeta peak position (1)1e-10mem.wl.centralfloatHz-AmpHzeta Lorentzian amplitude; 1e-16 erg/s/cm/Angstrom (1)1e+14W.m**-2.nm**-1src.var.amplitudefloatHz-FWHM-LHzeta Lorentzian full width at half maximum (2)1e-10mspect.line.widthfloatHz-FWHM-GHzeta Gaussian full width at half maximum (2)1e-10mspect.line.widthfloatHz-EWHzeta equivalent width1e-10mspect.line.eqWidthfloate_Hz-EWUncertainty in Hz-EW1e-10mstat.error;spect.line.eqWidthfloatHz-SNRHzeta signal-to-noise ratio (3)stat.snr;spect.linefloatHeta-X0Heta peak position (1)1e-10mem.wl.centralfloatHeta-AmpHeta Lorentzian amplitude; 1e-16 erg/s/cm/Angstrom (1)1e+14W.m**-2.nm**-1src.var.amplitudefloatHeta-FWHM-LHeta Lorentzian full width at half maximum (2)1e-10mspect.line.widthfloatHeta-FWHM-GHeta Gaussian full width at half maximum (2)1e-10mspect.line.widthfloatHeta-EWHeta equivalent width1e-10mspect.line.eqWidthfloate_Heta-EWUncertainty in He-EW1e-10mstat.error;spect.line.eqWidthfloatHeta-SNRHeta signal-to-noise ratio (3)stat.snr;spect.linefloatH-X0Ca II H line peak position (1)1e-10mem.wl.centralfloatH-AmpCa II H line Lorentzian amplitude; 1e-16 erg/s/cm/Angstrom (1)1e+14W.m**-2.nm**-1src.var.amplitudedoubleH-FWHM-LCa II H line Lorentzian full width at half maximum (2)1e-10mspect.line.widthfloatH-FWHM-GCa II H line Gaussian full width at half maximum (2)1e-10mspect.line.widthfloatH-EWCa II H line equivalent width1e-10mspect.line.eqWidthfloate_H-EWUncertainty in H-EW1e-10mstat.error;spect.line.eqWidthfloatH-SNRCa II H line signal-to-noise ratio (3)stat.snr;spect.linefloatK-AmpCa II K line Lorentzian amplitude; 1e-16 erg/s/cm/Angstrom (1)1e+14W.m**-2.nm**-1src.var.amplitudedoubleK-FWHM-LCa II K line Lorentzian full width at half maximum (2)1e-10mspect.line.widthfloatK-FWHM-GCa II K line Gaussian full width at half maximum (2)1e-10mspect.line.widthfloatK-EWCa II K line equivalent width1e-10mspect.line.eqWidthfloate_K-EWUncertainty in K-EW1e-10mstat.error;spect.line.eqWidthfloatK-SNRCa II K line signal-to-noise ratio (3)stat.snr;spect.linefloatEpochUTC mid-point of exposure, ISO 8601 formattime.epochcharJ/AJ/169/302/fig3List of spectra from the decay phase of EVRT-3586872 (added by CDS)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintEpochTime of observationtime.epochcharFlagFlag marking the quiescent flux spectrummeta.code.errorcharSpAssociated spectrum with link to the interactive plotmeta.id.assoccharFileLink to the spectrum file in MRT formatmeta.ref;pos.framecharJ/AJ/169/302/fig4List of spectra from the decay phase of EVRT-2509887 (added by CDS)recnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintEpochTime of observationtime.epochcharFlagFlag marking the quiescent flux spectrummeta.code.errorcharSpAssociated spectrum with link to the interactive plotmeta.id.assoccharFileLink to the spectrum file in MRT formatmeta.ref;pos.framechar