Yazar "Helminiak, K. G." seçeneğine göre listele

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    Comprehensive spectroscopic and photometric study of pulsating eclipsing binary star AI Hya
    (Oxford University Press, 2023) Kahraman Alicavuş, Filiz; Aliçavuş, Fahri; Pawar, T.; Helminiak, K. G.; Handler, G.; Moharana, A.
    The pulsating eclipsing binaries are remarkable systems that provide an opportunity to probe the stellar interior and to determine the fundamental stellar parameters precisely. Especially the detached eclipsing binary systems with (a) pulsating component(s) are significant objects to understand the nature of the oscillations since the binary effects in these systems are negligible. Recent studies based on space data have shown that the pulsation mechanisms of some oscillating stars are not completely understood. Hence, comprehensive studies of a number of pulsating stars within detached eclipsing binaries are important. In this study, we present a detailed analysis of the pulsating detached eclipsing binary system AI Hya which was studied by two independent groups with different methods. We carried out a spectroscopic survey to estimate the orbital parameters via radial velocity measurements and the atmospheric parameters of each binary component using the composite and/or disentangled spectra. We found that the more luminous component of the system is a massive, cool and chemically normal star while the hotter binary component is a slightly metal-rich object. The fundamental parameters of AI Hya were determined by the analysis of binary variations and subsequently used in the evolutionary modelling. Consequently, we obtained the age of the system as 850 ± 20 Myr and found that both binary components are situated in the δ Scuti instability strip. The frequency analysis revealed pulsation frequencies between 5.5 and 13.0 d−1 and we tried to estimate which binary component is the pulsating one. However, it turned out that those frequencies could originate from both binary components.
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    Öğe
    High-resolution spectroscopy and abundance analysis of ? Scuti stars near the ? Doradus instability strip
    (Oxford Univ Press, 2017) Kahraman Alicavus, F.; Niemczura, E.; Polinska, M.; Helminiak, K. G.; Lampens, P.; Molenda-Zakowicz, J.; Ukita, N.
    delta Scuti stars are remarkable objects for asteroseismology. In spite of decades of investigations, there are still important questions about these pulsating stars to be answered, such as their positions in log T-eff-log g diagram, or the dependence of the pulsation modes on atmospheric parameters and rotation. Therefore, we performed a detailed spectroscopic study of 41 delta Scuti stars. The selected objects are located near the gamma Doradus instability strip to make a reliable comparison between both types of variables. Spectral classification, stellar atmospheric parameters T-eff, log g, xi) and v sin i values were determined. The spectral types and luminosity classes of stars were found to be A1-F5 and III-V, respectively. The T-eff ranges from 6600 to 9400 K, whereas the obtained log g values are from 3.4 to 4.3. The v sin i values were found between 10 and 222 km s(-1). The derived chemical abundances of delta Scuti stars were compared to those of the non-pulsating stars and gamma Doradus variables. It turned out that both delta Scuti and gamma Doradus variables have similar abundance patterns, which are slightly different from the non-pulsating stars. These chemical differences can help us to understand why there are non-pulsating stars in classical instability strip. Effects of the obtained parameters on pulsation period and amplitude were examined. It appears that the pulsation period decreases with increasing T-eff. No significant correlations were found between pulsation period, amplitude and v sin i.