Hasan Ali Dal

High-Level Magnetic Activity on a Low-Mass Close Binary: GSC 02038-0293

Taking into account results obtained from light-curve analysis and out-of-eclipse analyses, we discuss the nature of GSC 02038-00293 and also its magnetic activity behaviour. We obtained light curves of the system during observing seasons 2007, 2008 and 2011. We obtained its secondary minimum clearly in I-band observations in 2008 for the first time. Analysing this light curve, we found the physical parameters of the components. The light-curve analysis indicates that the possible mass ratio of the system is 0.35. We obtained the remaining V-band light curves, extracting the eclipses. We modelled these remaining curves using the spotmodel program and found possible spot configurations of the magnetically active component for each observing season. The models demonstrated that there are two active longitudes for the active component. The models reveal that both active longitudes migrate in the direction of decreasing longitude. We also examined the light curves in out-of-eclipse phases with respect to minimum and maximum brightness, amplitude, etc. The amplitude of the curves during out-of-eclipse phases varies in a sinusoidal way with a period of ~8.9 yr; the mean brightness of the system is dramatically decreasing. The phases of the deeper minimum during out-of-eclipse periods exhibit a migration toward decreasing phase.

Brightness variations in totally eclipsing binary GSC 4589-2999

Abstract We present multi-colour CCD photometry of GSC 4589-2999 obtained in 2008 and 2009. The observations indicate that the system is an active Algol binary. Based on the new data, the mean brightness of the system decreased through the years 2007–2009. The light curves obtained in 2008–2009 are modelled using the Wilson–Devinney code. We also discuss the light and colour variations of the system at different orbital phases. Evidence suggests that these brightness and colour variations are due to the rotation of unevenly distributed starspots on two components of the system.

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

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.

KOI-256’s Magnetic Activity Under the Influence of the White Dwarf

We present the findings about chromospheric activity nature of KOI-256 obtained from the Kepler Mission data. Firstly, it was found that there are some sinusoidal variations out-of-eclipses due to cool spot activity. The sinusoidal variations modelled by the SPOTMODEL program indicate that the active component has two different active regions. Their longitudinal variation revealed that one of them has a migration period of 3.95 years, while the other has a migration period of 8.37 years. Secondly, 225 flares were detected from the short cadence data in total. The parameters, such as increase (Tr) and decay (Td) times, total flare time (Tt), equivalent durations (P), were calculated for each flare. The distribution of equivalent durations versus total flare times in logarithmic scale is modelled to find flare activity level. The Plateau value known as the saturation level of the active component was calculated to be 2.3121+-0.0964 s, and the Half-life value, which is required flare total time to reach the saturation, was computed to be 2233.6 s. In addition, the frequency of N1, which is the number of flares per an hour in the system, was found to be 0.05087 1/h, while the flare frequency N2 that the flare-equivalent duration emitting per an hour was found to be 0.00051. Contrary to the spot activity, it has been found that the flares are in tends to appear at specific phases due to the white dwarf component.

KIC 2557430: A Triple System Containing One γ Dor and Two Flaring Components?

The results are presented for eclipsing binary KIC 2557430. The mass ratio was computed as 0.868+-10.002, while the inclination (i) was found as 69.75+-0.01 deg with T2=6271+-1 K. 50 frequencies were found in the period analysis. 48 frequencies of them are caused due to the primary component, a Gamma Doradus star, while two of them are caused by the cool spots. 69 flares were detected in the analyses. Two OPEA models were derived for flares, which indicates 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 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. In a results, KIC 2557430 is a possible triple system consisting of a Gamma Doradus-type star, a chromospherically active star, and also a flaring third body.

Detailed Chromospheric Activity Nature of KIC 9641031

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 9641031s 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.

The Nature of the Light Variation of the Unique Binary DK CVn

We present BVR observations of DK CVn from 2007 and 2008. We analysed the BVR light curves of the system and obtained the system’s parameters. Using the ‘q-search’ method, we measured the mass ratio of the system (q) as 0.55. Taking the temperature of the primary component as 4040 K, the temperature of the secondary was found to be 3123 K. Several flares were detected, and the distributions of flare equivalent duration versus flare total duration were modelled using the One-Phase Exponential Association Function for these flares. The parameters of the model demonstrated that the flares are the same as those detected from UV Ceti stars. We also demonstrate that the variation at out-of-eclipse must be caused by some cool spot(s) on one of the components. The star is found to show two active longitudes in which the spots are mainly formed. Consequently, this study reveals that DK CVn should be a chromospherically active binary star.

High-level magnetic activity nature of the eclipsing binary KIC 12418816

We present comprehensive spectroscopic and photometric analysis of the detached eclipsing binary KIC 12418816, which is composed of two very similar and young main sequence stars of spectral type K0 on a circular orbit. Combining spectroscopic and photometric modelling, we find masses and radii of the components as 0.88+-0.06 Msun and 0.84+-0.05 Msun, and 0.85+-0.02 Rsun, and 0.84+-0.02 Rsun for the primary and the secondary, respectively. Both components exhibit narrow emission features superposed on the cores of the Ca II H&K lines, while H alpha and H beta photospheric absoprtion is more completely infilled by broader emission. Very high precision Kepler photometry reveals remarkable sinusoidal light variation at out-of-eclipse phases, indicating strong spot activity, presumably on the surface of the secondary component. Spots on the secondary component appear to migrate towards decreasing orbital phases with a migration period of 0.72+-0.05 year. Besides the sinusoidal variation, we detect 81 flares, and find that both components possess flare activity. Our analysis shows that 25 flares among 81 come exhibit very high energies with lower frequency, while the rest of them are very frequent with lower energies.

Spectroscopic and photometric confirmation of chromospheric activity in four stars

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

KIC 7385478: An Eclipsing Binary with a γ Doradus Component

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