Yazar "Alicavus, Filiz Kahraman" seçeneğine göre listele

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    KIC 10486425: A Kepler eclipsing binary system with a pulsating component
    (Cambridge Univ Press, 2014) Alicavus, Filiz Kahraman; Soydugan, Esin
    We present frequency analysis of the Kepler light curve of KIC 10486425, an eclipsing binary system with a pulsating component. The parameters of the binary were obtained by modelling the light curve with the Wilson-Devinney program. The residuals from this modelling were subject to Fourier analysis which allowed us to detect 120 periodic terms characteristic for gamma Dor-type pulsations. The dominant frequency of these changes amounts to 1.3189 d(-1).
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    On the existence of 'Maia variables'
    (Cambridge Univ Press, 2024) Alicavus, Filiz Kahraman; Handler, Gerald; Chowdhury, Sowgata; Niemczura, Ewa; Jayaraman, Rahul; De Cat, Peter; Ozuyar, Dogus
    There are different classes of pulsating stars in the H-R diagram. While many of those classes are undisputed, some remain a mystery such as the objects historically called 'Maia variables'. Whereas the presence of such a class was suggested seven decades ago, no pulsational driving mechanism is known that could excite short-period oscillations in these late B to early A-type stars. Alternative hypotheses that would render the reports of variability of those stars erroneous have been proposed such as incorrect effective temperatures, binarity or rapid rotation, but no certain conclusions have been reached yet. Therefore, the existence of these variables as a homogeneous class of pulsating star is still under discussion. Meanwhile, many new candidates of these variables have been claimed especially by using photometric observations of space telescopes. In this study, we examined 31 objects that are alleged members of this hypothetical group and carried out detailed spectroscopic and photometric analyses to test the proposed hypotheses for their cause of variability. The T-eff, log g , v sin i , and chemical abundances of the targets were determined and the TESS photometric data were examined. As a result, we found that most of these targets are located inside the delta Scuti, beta Cephei, or SPB star instability strips, a few show evidence for binarity and others for rapid rotation. We give arguments that none of the apparently rapid pulsations in our targets is caused by a star outside any known instability strip. By extrapolation, we argue that most stars proposed as pulsators outside well-established instability domains are misclassified. Hence there is no sufficient evidence justifying the existence of a class of pulsating stars formerly known as the 'Maia variables'.
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    Spectroscopic and photometric studies of a candidate pulsating star in an eclipsing binary: V948 Her
    (Natl Astronomical Observatories, Chin Acad Sciences, 2018) Alicavus, Filiz Kahraman
    Eclipsing binary stars with a pulsating component are powerful tools that allow us to probe the stellar interior structure and the evolutionary statuses with a good accuracy. Therefore, in this study, spectroscopic and photometric examinations of an eclipsing binary system V948 Her are presented. The primary component of the system is classified to be a candidate delta Scuti variable in the literature. The fundamental stellar, atmospheric and orbital parameters, and the surface abundance of the star were determined and the pulsation behaviour was investigated in this study. The orbital parameters were derived by the analysis of radial velocity and SuperWASP light curves. The spectral classification was found to be F2V. The initial atmospheric parameters of the primary component were derived by analysis of the spectral energy distribution and hydrogen lines. The final atmospheric parameters and chemical abundances of the primary component were obtained by using the method of spectrum synthesis. As a result, the final atmospheric parameters were determined as T-eff = 7100 +/- 200 K, log g= 4.3 +/- 0.1 cgs and xi = 2.2 +/- 0.2 km s(-1) . The surface abundance was found to be similar to solar. The fundamental stellar parameters of both components were also obtained to be M = 1.722 +/- 0.123, 0.762 +/- 0.020 M-circle dot , R = 1.655 +/- 0.034, 0.689 +/- 0.016 R-circle dot for primary and secondary components, respectively. The pulsation characteristic of the primary component was examined using SuperWASP data and the pulsation period was found to be similar to 0.038 d. The position of the primary pulsating component was also obtained inside the instability strip of delta Sct stars. The primary component of V948 Her was defined to be a delta Sct variable.