Fast colorimetry of the flare star EV Lacertae from<i><b>UBVRI</b></i>observations in 2004

Zhilyaev, B. E.; Romanyuk, Ya. O.; Svyatogorov, O. A.; Verlyuk, I. A.; Kaminsky, B.; Андреев, М. В.; Сергеев, А. В.; Гершберг, Р. Е.; Lovkaya, M. N.; Avgoloupis, S.; Seiradakis, J. H.; Contadakis, M. E.; Antov, A.; Konstantinova-Antova, R.; Bogdanovski, R.

doi:10.1051/0004-6361:20065632

Cited by 37 publications

(36 citation statements)

References 19 publications

(24 reference statements)

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“…High timeresolution (0.1 s) broadband colorimetry (U − B versus B − V) variations of moderateamplitude dMe flares as a function of time evolve over "spaces" corresponding to optically thin Balmer continuum emission, optically thick Balmer continuum emission, or pure blackbody emission (Zhilyaev et al 2007;Lovkaya 2013). These colorimetry analyses are often consistent with pure blackbody emission with T=14,000-22,000 K at flare peak.…”

Section: Flare Color-color Diagramsmentioning

confidence: 82%

M Dwarf Flare Continuum Variations on One-Second Timescales: Calibrating and Modeling of Ultracam Flare Color Indices*

Kowalski

Mathioudakis

Hawley

et al. 2016

ApJ

132

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We present a large dataset of high-cadence dMe flare light curves obtained with custom continuum filters on the triple-beam, high-speed camera system ULTRACAM. The measurements provide constraints for models of the near-ultraviolet (NUV) and optical continuum spectral evolution on timescales of ≈1 s. We provide a robust interpretation of the flare emission in the ULTRACAM filters using simultaneously obtained low-resolution spectra during two moderate-sized flares in the dM4.5e star YZ CMi. By avoiding the spectral complexity within the broadband Johnson filters, the ULTRACAM filters are shown to characterize bonafide continuum emission in the NUV, blue, and red wavelength regimes. The NUV/blue flux ratio in flares is equivalent to a Balmer jump ratio, and the blue/red flux ratio provides an estimate for the color temperature of the optical continuum emission. We present a new "color-color" relationship for these continuum flux ratios at the peaks of the flares. Using the RADYN and RH codes, we interpret the ULTRACAM filter emission using the dominant emission processes from a radiative-hydrodynamic flare model with a high nonthermal electron beam flux, which explains a hot, T≈10 4 K, color temperature at blue-to-red optical wavelengths and a small Balmer jump ratio asobserved in moderate-sized and large flares alike. We also discuss the high time resolution, high signal-to-noise continuum color variations observed in YZ CMi during a giant flare, which increased the NUV flux from this star by over a factor of 100.

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Section: Flare Color-color Diagramsmentioning

confidence: 82%

M Dwarf Flare Continuum Variations on One-Second Timescales: Calibrating and Modeling of Ultracam Flare Color Indices*

Kowalski

Mathioudakis

Hawley

et al. 2016

ApJ

132

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“…On the Sun, such flares are selected with spectroscopic observations when there is a strong continuum. On stars, multicolor observations allow the definition of a phase when blackbody radiation that is a continuum, dominates (Zhilyaev et al 2007).…”

Section: Resultsmentioning

confidence: 99%

Saturation Levels for White-Light Flares of Flare Stars: Variation of Minimum Flare Duration for Saturation

Dal¹,

Evren²

2010

The Astronomical Journal

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Taking into account results obtained from models and from statistical analyses of obtained parameters, we discuss flare activity levels and flare characteristics of five UV Ceti stars. We present the parameters of unpublished flares detected over two years of observations of V1005 Ori. We compare parameters of the U-band flares detected over several seasons of observations of AD Leo, EV Lac, EQ Peg, V1054 Oph, and V1005 Ori. Flare frequencies calculated for all program stars and maximum energy levels of the flares are compared, and we consider which is the most correct parameter as an indicator of flare activity levels. Using the One Phase Exponential Association function, the distributions of flare equivalent duration versus flare total duration are modeled for each program star. We use the Independent Samples t-Test in the statistical analyses of the parameters obtained from the models. The results reveal some properties of flare processes occurring on the surfaces of UV Ceti type stars. (1) Flare energies cannot be higher than a specific value regardless of the length of the flare total duration. This must be a saturation level for white-light flares occurring in flare processes observed in the U band. Thus, for the first time it is shown that white-light flares have a saturation in a specific energy range. (2) The span values, which are the difference between the equivalent durations of flares with the shortest and longest total durations, are almost equal for each star. (3) The half-life values, minimum flare durations for saturation, increase toward the later spectral types. (4) Both maximum total durations and maximum rise times computed from the observed flares decrease toward the later spectral types among the UV Ceti stars. According to the maximum energy levels obtained from the models, both EV Lac and EQ Peg are more active than the other three program stars, while AD Leo is the most active flare star according to the flare frequencies.

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“…The initial burst, or impulsive phase, is also characterized in the optical spectrum by increases in chromospheric line emission, particularly in the hydrogen Balmer lines (Hawley & Pettersen 1991;Martín & Ardila 2001;Fuhrmeister & Schmitt 2004). The impulsive phase is followed by a gradual decay phase which can last from tens of minutes to hours for the largest flares (Moffett 1974;Zhilyaev et al 2007).…”

Section: Introductionmentioning

confidence: 99%

M Dwarf Flares from Time-Resolved SDSS Spectra

Hilton¹,

Hawley²,

West³

et al. 2009

AIP Conference Proceedings

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We have identified 63 flares on M dwarfs from the individual component spectra in the Sloan Digital Sky Survey using a novel measurement of emission line strength called the Flare Line Index. Each of the ∼38,000 M dwarfs in the SDSS low mass star spectroscopic sample of West et al. was observed several times (usually 3-5) in exposures that were typically 9-25 minutes in duration. Our criteria allowed us to identify flares that exhibit very strong Hα and Hβ emission line strength and/or significant variability in those lines throughout the course of the exposures. The flares we identified have characteristics consistent with flares observed by classical spectroscopic monitoring. The flare duty cycle for the objects in our sample is found to increase from 0.02% for early M dwarfs to 3% for late M dwarfs. We find that the flare duty cycle is larger in the population near the Galactic plane and that the flare stars are more spatially restricted than the magnetically active but non-flaring stars. This suggests that flare frequency may be related to stellar age (younger stars are more likely to flare) and that the flare stars are younger than the mean active population.

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Fast colorimetry of the flare star EV Lacertae fromUBVRIobservations in 2004

Cited by 37 publications

References 19 publications

M Dwarf Flare Continuum Variations on One-Second Timescales: Calibrating and Modeling of Ultracam Flare Color Indices*

M Dwarf Flare Continuum Variations on One-Second Timescales: Calibrating and Modeling of Ultracam Flare Color Indices*

Saturation Levels for White-Light Flares of Flare Stars: Variation of Minimum Flare Duration for Saturation

M Dwarf Flares from Time-Resolved SDSS Spectra

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