In this study, a new method is presented to classify flares derived from the photoelectric photometry of UV Ceti type stars. Using Independent Samples t-Test, the method is based on statistical analysis. The data used in the analyses were obtained from four flare stars observed between the years 2004 and 2007.Total number of flares obtained in the observations of AD Leo, EV Lac, EQ Peg and V1054 Oph is 321 in the standard Johnson U band. As a result, flare can be separated into two types as slow and fast depending on the ratio of flare decay time to flare rise time. The ratio is below the value 3.5 for all slow flares, while it is above 3.5 for all fast flares. Also, according to the Independent Samples t-Test, there are about 157 seconds difference between equivalent durations of slow and fast flares. In addition, there are significant differences between amplitudes and rise times of slow and fast flares.

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 We present the parameters of unpublished flares detected over two years of observations of V1005 Ori.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

This study depends on KIC 9641031 eclipsing binary system with a chromospherically active component. There are three type variations, such as geometrical variations due to eclipses, sinusoidal variations due to the rotational modulations and also flares, in the light curves obtained with the data taken from the Kepler Mission Database. Taking into account results obtained from KIC 9641031's observations in the Kepler Mission Database, we present and discuss the details of chromospheric activity. The sinusoidal light variations due to rotational modulation and the flare events were modelled separately. 92 different data subsets separated using the analytic models described in the literature were modelled separately to obtain the cool spot configuration. It is seen that just one component of the system is chromospherically active star. On this component, there are two active regions separated by about 180 deg longitudinally between the latitudes of +50 deg and +100 deg, whose locations and forms are rapidly changing in short time intervals. 240 flares were detected and their parameters were computed. Using these parameters, the One Phase Exponential Association (hereafter OPEA) function model was derived, in which the Plateau value as a saturation level of the flare-equivalent duration was found to be 1.232 s for KIC 9641031, and half-life parameter was found to be 2291.7 s. The flare frequency N1 was found to be 0.41632 h-1, while the flare frequency N2 was found to be 0.00027. Considering these parameters together with the orbital period variations demonstrates that the period variations directly depend on chromospheric activity. Comparing the system with its analogue it is seen that the activity level of KIC 9641031 is remarkablely lower than the others.Comment: 26 pages, 7 figures, 4 tabel

RESUMENFavor de proporcionar un resumen en español. If you are unable to translate your abstract into Spanish, the editors will do it for you. ABSTRACTIn this study, we present the results obtained from KIC 9761199's the photometrical data acquired by the Kepler Mission. The light curve of the system, the sinusoidal variation out-of-eclipses and instant-short term flare events in the entire light curves were analyzed. The temperature of the secondary component was found to be 3891±1 K, while the mass ratio of the components (q) was found to be 0.69±0.01, and the orbital inclination (i) was computed as 77 • .4 ± 0 • .1. The sinusoidal variation is caused by the stellar spots of two active regions separated by about 180 • longitudinally located around the latitudes of +47 • and +30 • . In addition, 94 flares were detected and their parameters were computed. The OPEA model was derived for these flares and its parameters were computed. The P lateau value as saturation level for the active component was found to be 1.951±0.069 s, while the half − lif e value was found to be 1014 s. The flare frequency N 1 was found to be 0.01351 h −1 , while the flare frequency N 2 was found to be 0.00006. Maximum flare rise time (T r ) was found to be 1118.098 s, while maximum flare total time (T t ) was found to be 6767.72 s. Comparing its analogue it is seen that the chromospheric activity level of KIC 9761199, which is a low-mass close binary system according to the light curve analyses, is an expected level according to the (B − V ) color index of 1 m .303 for the active component.

In this study, we discuss stellar spots, stellar flares and also the relation between these two magnetic proccess that take place on UV Ceti stars. In addition, the hypothesis about slow flares described by Gurzadian (1986) will be discussed. All these discussions are based on the results of three years of observations of the UV Ceti type stars AD Leo, EV Lac, V1005 Ori, EQ Peg and V1054 Oph. First of all, the results show that the stellar spot activity occurs on the stellar surface of EV Lac, V1005 Ori and EQ Peg, while AD Leo does not show any short-term variability and V1054 Oph does not exhibits any variability. We report new ephemerides, for EV Lac, V1005 Ori and EQ Peg, obtained from the time series analyses. The phases, computed in intervals of 0.10 phase length, where the mean flare occurence rates get maximum amplitude, and the phases of rotational modulation were compared to investigate whether there is any longitudinal relation between stellar flares and spots. Although, the results show that flare events are related with spotted areas on the stellar surfaces in some of the observing seasons, we did not find any clear correlation among them. Finally, it is tested whether slow flares are the fast flares occurring on the opposite side of the stars according to the direction of the observers as mentioned in the hypothesis developed by Gurzadian (1986). The flare occurence rates reveal that both slow and fast flares can occur in any rotational phases. The flare occurence rates of both fast and slow flares are varying in the same way along the longitudes for all program stars. These results are not expected based on the case mentioned in the hypothesis.

Taking into account the results obtained from the models and analyses of the BVRI light curves, we discuss the nature of V1464 Aql. The analyses indicated that the mass ratio of the system is q = 0.71 ± 0.02, while the inclination of the system (i) is 38°.45 ± 0°.22. Taking the primary component's temperature as 7 420 ± 192 K, we found that the temperature of the secondary is 6 232 ± 161 K. The mass of the primary component was found to be 1.74 ± 0.05 M ࣻ , while it is 1.23 ± 0.01 M ࣻ for the secondary. The primary component's radius was found to be 2.10 ± 0.05 R ࣻ , while it was found as 1.80 ± 0.01 R ࣻ for the secondary. Revealing that the system should not exhibit any eclipses, we demonstrated that the main variation with large amplitude should be caused due to the ellipsoidal effect. Indeed, the Fourier analysis also supported the result. For the first time in the literature, we revealed that the primary component is a δ Scuti star. The period of pulsation was found to be 58.482 ± 0.002, 58.482 ± 0.001, 60.966 ± 0.002, and 60.964 ± 0.003 min in BVRI bands, respectively. We plotted V1464 Aql in the log(P orb )-log (P pulse ) plane. Using more than 160 binaries, whose one or both components are pulsating, we derived a new linear fit in the log (P orb )-log (P pulse ) plane for each type of binary. Using the linear fit of each group, we obtained new calibrations between log (P orb ) and log (P pulse ) for different types of pulsating stars. In addition, a calibration has been obtained for the first time for the pulsating stars with spectral types O and B. V1464 Aql seems to be located near the other ellipsoidal and close binaries. Thus, we listed V1464 Aql as a new candidate for the ellipsoidal variables with a δ Scuti component.

The results obtained from the photometrical models are presented for KIC 2557430, which is known as an eclipsing binary system in the literature. Its light curve was analysed for the first time. The secondary component temperature was found as 6271±1 K. The mass ratio was computed as 0.868±0.002, while the inclination (i) of the system was found as 69 • .75±0 • .01. There is a third light contribution of 0.339% in the total light. 50 frequencies were found in the period analysis. 48 frequencies of them are caused due to the primary component, a γ Doradus star, while two of them are caused by the rotational modulation due to the cool spots. 69 flares were detected in the analyses. Two OPEA models were derived for these flares detected from KIC 2557430. Obtained OPEA models indicate that the flares were come from two different sources. The Plateau value was found to be 1.4336±0.1104 s for Source 1, which is seen as possible the secondary component and 0.7550±0.0677 s for Source 2, which is seen as possible third body. The half-life value was computed as 2278.1 s for Group 1 and 1811.2 s for Group 2. The flare frequency N1 was found to be 0.02726 h −1 and the flare frequency N2 was computed as 0.00002 for Group 1, while N1 was found to be 0.01977 h −1 and N2 was computed as 0.00001 for Group 2. As a result of this study, KIC 2557430 is a possible triple system. Considering both components' temperatures and obtained two different OPEA models, the primary star is a γ Doradus-type star, and the secondary component is a chromospherically active star, which has both the cool spot and flare activities, and also the third body, whose the membership status is controversial for this system, is a flare star.

We present analysis of medium resolution optical spectra and long term V band photometry of four cool stars, BD+13 5000, BD+11 3024, TYC 3557-919-1 and TYC 5163-1764-1. Our spectroscopic analysis reveals that the stars are giant or sub-giant from K0 or K1 spectral type, and all of them exhibit emission features in their Ca ii H& K lines. These features appear to be modulated with the rotation of the stars. Except BD+11 3024, we observe that the radial velocities of the target stars are not stable, which suggests that each of them might be a member of a binary system. Global analysis of photometric data indicates clear cyclic variation for BD+13 5000 and TYC 5163-1764-1 with a period of 8.0±0.3 and 5.04±0.04 year, respectively. Besides that, we observe a dramatic increase (∼0. m 7) in the mean brightness of BD+11 3024, accompanied with a 2.87 ± 0.12 cyclic variation, embedded into the global brightening trend, which indicates possible multiple cycles on this star.