The shape of M dwarf flares in Kepler light curves

AbstractUltra-precise light curves from Kepler provide the best opportunity to determine rates and statistical properties of stellar flares. From 11 months of data on the active M4 dwarf, GJ 1243, we have built the largest catalog of flares for a single star: over 6100 events. Combining 885 of our most pristine flares, we generated an empirical white-light flare template. This high-fidelity template shows a rapid initial rise, and two distinct exponential cooling phases. This template is useful in constraining flare energies and for improved flare detection in many surveys. Complex, multi-peaked events are more common for higher energy flares in this sample. Using our flare template we characterize the structure of complex events. In this contributed talk, I presented results from our boutique study of GJ 1243, and described an expanded investigation of the structure of complex flares and their connection to solar events.

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White-light continuum in stellar flares

Proceedings of the International Astronomical Union ◽

10.1017/s1743921316000028 ◽

2015 ◽

Vol 11 (S320) ◽

pp. 259-267 ◽

Cited By ~ 1

Author(s):

Adam F. Kowalski

Keyword(s):

White Light ◽

High Energy ◽

Continuum Emission ◽

Nonthermal Electrons ◽

White Light Continuum ◽

Optical Wavelength ◽

Near Ultraviolet ◽

Stellar Flares ◽

Optical Continuum ◽

M Dwarf

AbstractIn this talk, we discuss the formation of the near-ultraviolet and optical continuum emission in M dwarf flares through the formation of a dense, heated chromospheric condensation. Results are used from a recent radiative-hydrodynamic model of the response of an M dwarf atmosphere to a high energy flux of nonthermal electrons. These models are used to infer the charge density and optical depth in continuum emitting flare layers from spectra covering the Balmer jump and optical wavelength regimes. Future modeling and observational directions are discussed.

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Optical and X-ray observations of stellar flares on an active M dwarf AD Leonis with the Seimei Telescope, SCAT, NICER, and OISTER

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psaa051 ◽

2020 ◽

Vol 72 (4) ◽

Cited By ~ 2

Author(s):

Kosuke Namekata ◽

Hiroyuki Maehara ◽

Ryo Sasaki ◽

Hiroki Kawai ◽

Yuta Notsu ◽

...

Keyword(s):

Emission Line ◽

White Light ◽

High Energy ◽

Lower Atmosphere ◽

Line Profiles ◽

X Ray ◽

Energy Beam ◽

Stellar Flares ◽

Optical Continuum ◽

M Dwarf

Abstract We report on multi-wavelength monitoring observations of an M-dwarf flare star AD Leonis with the Seimei Telescope (6150–7930 Å), SCAT (Spectroscopic Chuo-university Astronomical Telescope; 3700–7500 Å), and NICER (Neutron Star Interior Composition Explorer; 0.2–12.0 keV), with the collaboration of the OISTER (Optical and Infrared Synergetic Telescopes for Education and Research) program. Twelve flares are detected in total, including ten Hα, four X-ray, and four optical-continuum flares; one of them is a superflare with a total energy of ∼2.0 × 1033 erg. We found that: (1) during the superflare, the Hα emission line full width at 1/8 maximum dramatically increases to 14 Å from 8 Å in the low-resolution spectra (R ∼ 2000) accompanied by large white-light flares, (2) some weak Hα/X-ray flares are not accompanied by white-light emissions, and (3) the non-flaring emissions show clear rotational modulations in X-ray and Hα intensity in the same phase. To understand these observational features, one-dimensional hydrodynamic flare simulations are performed using the RADYN code. We find the simulated Hα line profiles with hard and high-energy non-thermal electron beams to be consistent with the initial phase line profiles of the superflares, while those with a softer and/or weak-energy beam are consistent with those in decay phases, indicating the changes in the energy fluxes injected to the lower atmosphere. Also, we find that the relation between the optical continuum and Hα intensity is nonlinear, which can be one cause of the non-white-light flares. The flare energy budget exhibits diversity in the observations and models, and more observations of stellar flares are necessary for constraining the occurrence of various emission line phenomena in stellar flares.

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Stellar flares from blended and neighbouring stars in Kepler short cadence observations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab166 ◽

2021 ◽

Vol 502 (2) ◽

pp. 2033-2042

Author(s):

James A G Jackman ◽

Evgenya Shkolnik ◽

R O Parke Loyd

Keyword(s):

False Positive ◽

High Energy ◽

Light Curves ◽

Lower Mass ◽

Wide Binary ◽

Stellar Flares ◽

M Dwarf

ABSTRACT We present the results of a search for stellar flares from stars neighbouring the target sources in the Kepler short cadence data. These flares have been discarded as contaminants in previous surveys and therefore provide an unexplored resource of flare events, in particular high-energy events from faint stars. We have measured M dwarf flare energies up to 1.5 × 1035 erg, pushing the limit for flare energies measured using Kepler data. We have used our sample to study the flaring activity of wide binaries, finding that the lower mass counterpart in a wide binary flares more often at a given energy. Of the 4430 flares detected in our original search, 298 came from a neighbouring star, a rate of 6.7 ± 0.4 per cent for the Kepler short cadence light curves. We have used our sample to estimate a 5.8 ± 0.1 per cent rate of false positive flare events in studies using Transiting Exoplanet Survey Satellite short cadence data.

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Erratum: Optical and X-ray observations of stellar flares on an active M dwarf AD Leonis with Seimei Telescope, SCAT, NICER, and OISTER

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psab013 ◽

2021 ◽

Author(s):

Kosuke Namekata ◽

Hiroyuki Maehara ◽

Ryo Sasaki ◽

Hiroki Kawai ◽

Yuta Notsu ◽

...

Keyword(s):

X Ray ◽

Stellar Flares ◽

M Dwarf

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Hydrodynamic Models of Solar and Stellar Flares

International Astronomical Union Colloquium ◽

10.1017/s0252921100031948 ◽

1989 ◽

Vol 104 (1) ◽

pp. 289-298

Author(s):

Giovanni Peres

Keyword(s):

High Resolution ◽

Light Curve ◽

Solar Flares ◽

Impulsive Phase ◽

Light Curves ◽

Physical Parameters ◽

The Sun ◽

Hydrodynamic Models ◽

X Ray ◽

Stellar Flares

AbstractThis paper discusses the hydrodynamic modeling of flaring plasma confined in magnetic loops and its objectives within the broader scope of flare physics. In particular, the Palermo-Harvard model is discussed along with its applications to the detailed fitting of X-ray light curves of solar flares and to the simulation of high-resolution Caxix spectra in the impulsive phase. These two approaches provide complementary constraints on the relevant features of solar flares. The extension to the stellar case, with the fitting of the light curve of an X-ray flare which occurred on Proxima Centauri, demonstrates the feasibility of using this kind of model for stars too. Although the stellar observations do not provide the wealth of details available for the Sun, and, therefore, constrain the model more loosely, there are strong motivations to pursue this line of research: the wider range of physical parameters in stellar flares and the possibility of studying further the solar-stellar connection.

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X-Ray Emission from Stellar Flares: Exosat Results

International Astronomical Union Colloquium ◽

10.1017/s0252921100153710 ◽

1989 ◽

Vol 104 (2) ◽

pp. 17-20 ◽

Cited By ~ 1

Author(s):

R. Pallavicini ◽

G. Tagliaferri

Keyword(s):

Main Sequence ◽

Late Type ◽

X Ray ◽

Visual Binary ◽

Stellar Flares ◽

Flare Stars ◽

M Dwarf

AbstractWe present an overview of recent observations of stellar X-ray flares obtained with the EXOSAT Observatory. We discuss a few examples of flares from M dwarf flare stars, from RS CVn and Algol-type binaries, from single late-type stars (including a G0 dwarf and an A-type visual binary), and from pre-main-sequence objects. We also draw some general conclusions from the pieliminary analysis of the EXOSAT data sample.

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Activity and rotation of the X-ray emitting Kepler stars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731674 ◽

2019 ◽

Vol 628 ◽

pp. A41 ◽

Cited By ~ 2

Author(s):

D. Pizzocaro ◽

B. Stelzer ◽

E. Poretti ◽

S. Raetz ◽

G. Micela ◽

...

Keyword(s):

White Light ◽

Main Sequence ◽

Magnetic Activity ◽

Light Curves ◽

Late Type ◽

Main Sequence Stars ◽

Photometric Variability ◽

X Ray ◽

Rotation Periods ◽

Flare Frequency

The relation between magnetic activity and rotation in late-type stars provides fundamental information on stellar dynamos and angular momentum evolution. Rotation-activity studies found in the literature suffer from inhomogeneity in the measurement of activity indexes and rotation periods. We overcome this limitation with a study of the X-ray emitting, late-type main-sequence stars observed by XMM-Newton and Kepler. We measured rotation periods from photometric variability in Kepler light curves. As activity indicators, we adopted the X-ray luminosity, the number frequency of white-light flares, the amplitude of the rotational photometric modulation, and the standard deviation in the Kepler light curves. The search for X-ray flares in the light curves provided by the EXTraS (Exploring the X-ray Transient and variable Sky) FP-7 project allows us to identify simultaneous X-ray and white-light flares. A careful selection of the X-ray sources in the Kepler field yields 102 main-sequence stars with spectral types from A to M. We find rotation periods for 74 X-ray emitting main-sequence stars, 20 of which do not have period reported in the previous literature. In the X-ray activity-rotation relation, we see evidence for the traditional distinction of a saturated and a correlated part, the latter presenting a continuous decrease in activity towards slower rotators. For the optical activity indicators the transition is abrupt and located at a period of ~10 d but it can be probed only marginally with this sample, which is biased towards fast rotators due to the X-ray selection. We observe seven bona-fide X-ray flares with evidence for a white-light counterpart in simultaneous Kepler data. We derive an X-ray flare frequency of ~0.15 d−1, consistent with the optical flare frequency obtained from the much longer Kepler time-series.

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The Timescales of Variations in Continuum and Hydrogen Lines During Stellar Flares

International Astronomical Union Colloquium ◽

10.1017/s0252921100096159 ◽

1983 ◽

Vol 71 ◽

pp. 239-243

Author(s):

B.R. Pettersen

Keyword(s):

Emission Line ◽

Narrow Band ◽

Light Curves ◽

Emission Lines ◽

Continuum Radiation ◽

Stellar Flares ◽

Hydrogen Lines ◽

The Continuum

AbstractLight curves of major stellar flares have been used to study the behavior of U-B, B-V, and V-R. The majority of the flux transmitted through these filters is continuum radiation, but U and B are affected by emission lines. The variability of Ha and H$ emission lines were monitored through narrow band filters. The timescales of emission line variability are considerably longer than those for the continuum, and the emission line flare peak occurs a few minutes after the continuum flare maximum. No variability in lines at a timescale of seconds is detected in our data.

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