UV Ceti stars - Statistical analysis of observational data

Lacy, Claud H.; Moffett, T. J.; Evans, David S.

doi:10.1086/190358

Cited by 239 publications

(299 citation statements)

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“…Lacy et al (1976) and Gershberg & Shakhovskaia (1983) found high optical flare rates, however, at the lowest flare energies in their samples of UV Ceti stars. Robinson et al (1995) analyzed UV flare events on CN Leo down to the microflare scale observed with the High Speed Photometer onboard HST.…”

Section: The Active M Dwarf Cn Leomentioning

confidence: 87%

Multiwavelength observations of a giant flare on CN Leonis

Liefke¹,

Fuhrmeister²,

Schmitt³

2010

A&A

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Context. Stellar flares affect all atmospheric layers from the photosphere over chromosphere and transition region up into the corona. Simultaneous observations in different spectral bands allow to obtain a comprehensive picture of the environmental conditions and the physical processes going on during different phases of the flare. Aims. We investigate the properties of the coronal plasma during a giant flare on the active M dwarf CN Leo observed simultaneously with the UVES spectrograph at the VLT and XMM-Newton. Methods. From the X-ray data, we analyze the temporal evolution of the coronal temperature and emission measure, and investigate variations in electron density and coronal abundances during the flare. Optical Fe xiii line emission traces the cooler quiescent corona.Results. Although of rather short duration (exponential decay time τ LC < 5 min), the X-ray flux at flare peak exceeds the quiescent level by a factor of ≈100. The electron density averaged over the whole flare is greater than 5 × 10 11 cm −3 . The flare plasma shows an enhancement of iron by a factor of ≈2 during the rise and peak phase of the flare. We derive a size of <9000 km for the flaring structure from the evolution of the the emitting plasma during flare rise, peak, and decay. Conclusions. The characteristics of the flare plasma suggest that the flare originates from a compact arcade instead of a single loop. The combined results from X-ray and optical data further confine the plasma properties and the geometry of the flaring structure in different atmospheric layers.

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Section: The Active M Dwarf Cn Leomentioning

confidence: 87%

Multiwavelength observations of a giant flare on CN Leonis

Liefke¹,

Fuhrmeister²,

Schmitt³

2010

A&A

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“…The reported time-averaged flare luminosity is $1:9 Â 10 30 ergs s À1 in the U band. Assuming that these flares have the same color as in dMe stars near the peak intensity, using L U ¼ 1:79L V (Lacy, Moffett, & Evans 1976), the expected time-averaged flare luminosity in the V band would be $1:1 Â 10 30 ergs s À1 . On the other hand, the time-averaged R 0 -band luminosity in V404 Cyg is L R 0 h i $ 10 33 ergs s À1 , i.e., 3 orders of magnitude larger than the time-averaged luminosity in II Peg.…”

Section: Chromospheric Emissionmentioning

confidence: 99%

Evidence for Optical Flares in Quiescent Soft X‐Ray Transients

Zurita

Casares

Shahbaz

2003

ApJ

120

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We present the results of high time resolution optical photometry of five quiescent soft X-ray transients (SXTs): V404 Cyg, A0620À00, J0422+32, GS 2000+25, and Cen X-4. We detect fast optical variations superposed on the secondary star's double-humped ellipsoidal modulation. The variability resembles typical flare activity and has amplitudes ranging from 0.06 to 0.6 mag. Flares occur on timescales of minutes to a few hours, with no dependency on orbital phase, and contribute $19%-46% to the total veiling observed in the R band. We find that the observed level of flaring activity is veiled by the light of the companion star, and therefore, systems with cool companions (e.g., J0422+32) exhibit stronger variability. After correcting for this dilution, we do not find any correlation between the flaring activity and fundamental system parameters. We find no underlying coherent periods in the data, only quasi-periodic variations ranging between 30 and 90 minutes for the short-period SXTs and longer than 1 hr for V404 Cyg. The power-law index of the power spectra is consistent with what is observed at X-rays wavelengths, i.e., a 1/f distribution, which is compatible with the cellular automaton model. Our observed R 0 -band luminosities, which are in the range 10 31 -10 33 ergs s À1 , are too large to be due to chromospheric activity in the rapidly rotating companions. Since the typical timescale of the flares increases with orbital period, they are most likely produced in the accretion disk. The associated dynamical (Keplerian) timescales suggest that flares are produced at $0.3R d -0.7R d . Possible formation mechanisms are magnetic loop reconnection events in the disk or, less likely, optical reprocessing of X-ray flares. In the former scenario, the maximum duration of the flares suggests that the outer disk is responsible for the flare events and so allows us to constrain the sharing timescale to $ 5 6 ð Þ À1 K .

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“…The strongest flare we observed on V410 Tau has been excluded from this figure because we did not observe it in the UBV bands. The empirical relation derived by Lacy et al (1976) based on flare data for UV Cet stars is also plotted. Gahm (1990) claimed that flares on T Tauri stars are found in the upper right part of this diagram with energies exceeding those of the bulk of UV Cet stars by ∼4−5 orders of magnitude.…”

Section: Comparison With Flares On Other Starsmentioning

confidence: 99%

“…On the other hand, the quasi-periodic X-ray flares detected by Tsuboi et al (2000) on the protostar YLW 15 seem to orginate in a star-disk interaction. Lacy et al (1976) based on flare data for UV Cet stars is plotted with a solid line. The T Tauri stars' locus, according to Gahm (1990), is shown by the dashed line.…”

Section: Comparison With Flares On Other Starsmentioning

confidence: 99%

The weak-line T Tauri star V410 Tau

Fernández¹,

Stelzer

Henden

et al. 2004

A&A

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Abstract. We show that V410 Tau, a weak-line T Tauri star, is a flaring star. This result comes from an intensive, coordinated monitoring campaign carried out in November 2001 at visible and X-ray wavelength ranges. It is confirmed by previous, isolated observations found in the literature. Flares tend to occur mainly around the star's minimum brightness, when the most active regions face us. We report on the strongest flare detected up to now on this star, for which we have obtained simultaneous visible Strömgren photometry and intermediate resolution spectroscopy. We derive decay times from 3 to 0.7 h at several wavelengths for the continuum in the 3600−5600 Å range. We estimate the energy involved in this and the other flares for which we have good time sampling, and conclude that the strongest event, at least, could have important consequences for the matter in the surroundings of the star. If similar events took place on the young Sun and lasted for several Myr, they could explain the anomalous abundances of elemental isotopes found in some meteorites. They could have also contributed to eliminate part of the primary atmospheres of the planet embryos and would have provided enough energy for the melting of solid iron-magnesium silicates, a process that may explain the presence of chondrules in chondritic meteorites. High resolution spectroscopy of the H α emission line in the quiescent states of V410 Tau enables us to study the variability of the broad component. We suggest that this component is related to microflaring activity, such as the one observed on more evolved, magnetically-active stars. The large velocities and the energy associated with this component support this hypothesis.

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UV Ceti stars - Statistical analysis of observational data

Cited by 239 publications

References 0 publications

Multiwavelength observations of a giant flare on CN Leonis

Multiwavelength observations of a giant flare on CN Leonis

Evidence for Optical Flares in Quiescent Soft X‐Ray Transients

The weak-line T Tauri star V410 Tau

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