UV Ceti flare stars - Observational data

Moffett, T. J.

doi:10.1086/190330

Cited by 153 publications

(116 citation statements)

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“…Owing to its proximity and particularly high level of activity, GJ65 has been intensively studied for decades over a broad range of wavelengths, from X-rays (see, e.g., Ishikawa et al 2014) to the radio domain. Moffett (1974) established observationally that UV Ceti shows on average one flare every 36 minutes. The linear separation of the two stars varies between approximately 2 and 8 AU during their orbital cycle.…”

Section: Flaring and Interferometric Closure Phasesmentioning

confidence: 99%

The red dwarf pair GJ65 AB: inflated, spinning twins of Proxima

Kervella

Mérand

Ledoux

et al. 2016

A&A

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The nearby red dwarf binary GJ65 AB (UV+BL Ceti, M5.5Ve+M6Ve) is a cornerstone system to probe the physics of very low-mass stars. The radii of the two stars are currently known only from indirect photometric estimates, however, and this prevents us from using GJ65 AB as calibrators for the mass-radius (M-R) relation. We present new interferometric measurements of the angular diameters of the two components of GJ65 with the VLTI/PIONIER instrument in the near-infrared H band: θ UD (A) = 0.558 ± 0.008 ± 0.020 mas and θ UD (B) = 0.539 ± 0.009 ± 0.020 mas. They translate into limb-darkened angular diameters of θ LD (A) = 0.573 ± 0.021 mas and θ LD (B) = 0.554 ± 0.022 mas. Based on the known parallax, the linear radii are R(A) = 0.165 ± 0.006 R and R(B) = 0.159 ± 0.006 R (σ(R)/R = 4%). We searched for the signature of flares and faint companions in the interferometric visibilities and closure phases, but we did not identify any significant signal. We also observed GJ65 with the VLT/NACO adaptive optics and refined the orbital parameters and infrared magnitudes of the system. We derived masses for the two components of m(A) = 0.1225 ± 0.0043 M and m(B) = 0.1195 ± 0.0043 M (σ(m)/m = 4%). To derive the radial and rotational velocities of the two stars as well as their relative metallicity with respect to Proxima, we also present new individual UVES high-resolution spectra of the two components. Placing GJ65 A and B in the mass-radius diagram shows that their radii exceed expectations from recent models by 14 ± 4% and 12 ± 4% , respectively. Following previous theories, we propose that this discrepancy is caused by the inhibition of convective energy transport by a strong internal magnetic field generated by dynamo effect in these two fast-rotating stars. A comparison with the almost identical twin Proxima, which is rotating slowly, strengthens this hypothesis because the radius of Proxima does not appear to be inflated compared to models.

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Section: Flaring and Interferometric Closure Phasesmentioning

confidence: 99%

The red dwarf pair GJ65 AB: inflated, spinning twins of Proxima

Kervella

Mérand

Ledoux

et al. 2016

A&A

View full text Add to dashboard Cite

show abstract

“…In addition, the flares must be observed with the same optical systems. There are large data sets including U-band flares in the literature, such as those of Moffett (1974), and Ishida et al (1991). On the other hand, the methods used to determine the parameters of the detected flares are not the same in these studies and there are some differences between the optical systems.…”

Section: Analysesmentioning

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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“…These timescales are greater than the evolution timescales of whitelight emission, which are as fast as ≈10 s in the impulsive phase (Moffett 1974). Furthermore, these timescales are far longer than the timescales over which atmospheric properties change in radiative-hydrodynamic (RHD) flare models (Allred et al 2006, K15).…”

Section: Introductionmentioning

confidence: 99%

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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UV Ceti flare stars - Observational data

Cited by 153 publications

References 0 publications

The red dwarf pair GJ65 AB: inflated, spinning twins of Proxima

The red dwarf pair GJ65 AB: inflated, spinning twins of Proxima

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

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

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