Some results of the cooperative photometric observations of the UV Cet-type flare stars in the years 1967?71

Гершберг, Р. Е.

doi:10.1007/bf00643168

Cited by 140 publications

(124 citation statements)

References 9 publications

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“…The flare energy, which is expressed by Equation (2) given by Gershberg (1972), has generally been used to examine the level of flare activity in many studies (see, e.g., Mazeh et al 2001;Lacy et al 1976;Walker 1981;Gershberg & Shakhovskaya 1983;Pettersen et al 1984;Mavridis & Avgoloupis 1986). The luminosity parameter L occurs in the expression of the energy E, as in all these and other studies.…”

Section: Resultsmentioning

confidence: 99%

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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 We present the parameters of unpublished flares detected over two years of observations of V1005 Ori.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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Section: Resultsmentioning

confidence: 99%

“…The comparison and check stars were found to be constant in brightness during the period of observation. Equivalent durations and energies of all the flares were computed from photoelectric observations using Equations (1) and (2) taken from Gershberg (1972):…”

Section: Observationsmentioning

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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“…The expression P represents the length of time that the binary in its quiet state takes to emit the same energy that is produced by the flare (Gershberg 1972). Note that P can be interpreted as an equivalent width where the intensity of the flare is referred to with respect to the quiescent nonvariable level of the system.…”

Section: Parameters Of the Variabilitymentioning

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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“…According to the results of Herr and Brcich (1969) 1972-1973(Nicastro 1975. However, Contadakis et al (1982) detected no flares in 1975.…”

Section: Flare Activity and Flare Typesmentioning

confidence: 99%

“…In order to compare the flare powers of different stars, several studies have been done. In these studies, the flare energy spectra were derived for each star (Gershberg 1972;Lacy et al 1976;Wall 1981;Gershberg and Shakhovskaya 1983;Pettersen et al 1984;Mavridis and Avgoloupis 1986). According to the results of these studies, the energy levels of stars vary from one to the next.…”

Section: Introductionmentioning

confidence: 99%

Statistical Analysis and the OPEA Model of the White-Light Flares Occurring on Krüger 60B (DO Cep)

Dal¹

2011

Publ. – Astron. Soc. Aust

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Abstract:In this study, new observations and some results of statistical analyses are presented. The largest flare data set of DO Cep in the literature has been obtained with 89 flares detected in 67.61 hours of U-band flare patrol. First of all, the observations demonstrated that the star is one of the most active flare stars in respect to the computed flare frequency. Secondly, using the independent samples t-test, the detected flares were classified into two subtypes, and then they were modelled. Analysing the models demonstrated that the fast and slow flares occurring on the star can be separated with a critical value of the ratio of their decay time to rise time. The critical value was computed as 3.40. According to this value, the fast flare rate is 20.22%, while the slow flare rate is 79.78%. Besides, there is a 39.282 times difference between the energies of these two types of flares. However, the flare equivalent durations versus the flare rise times increase in similar ways for both groups. In addition, all the flares were modelled with the one-phase exponential association function. Analysing this model, the plateau value was found to be 2.810. Moreover, the half-life value was computed as 433.1 s from the model. The maximum flare rise time was found to be 1164 s, while the maximum flare total duration was found to be 3472 s. The results of the flare timescales indicate that the geometry of the flaring loop on the surface of the star might be similar to those seen on analogues of DO Cep. Consequently, considering both the half-life value and flare timescales, the flares detected on the surface of DO Cep get maximum energy in longer times, while the geometries of the flaring loops or areas get smaller.

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Some results of the cooperative photometric observations of the UV Cet-type flare stars in the years 1967?71

Cited by 140 publications

References 9 publications

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

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

Evidence for Optical Flares in Quiescent Soft X‐Ray Transients

Statistical Analysis and the OPEA Model of the White-Light Flares Occurring on Krüger 60B (DO Cep)

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