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Öğe Analysis of TESS Field Eclipsing Binary Star V948 Her: A Pulsating or Non-pulsating Star?(Natl Astronomical Observatories, Chin Acad Sciences, 2022) Alicavus, F. Kahraman; Ekinci, O.Pulsating stars occupy a significant place in the H-R diagram and it was thought that all stars inside the classical instability strip should pulsate. However, recent studies showed that there are many non-pulsating stars located inside the classical instability strip. The existence of these non-pulsating stars is still a mystery. To deeply understand the properties of these non-pulsating and pulsating stars, one needs precise fundamental stellar parameters (e.g. mass). For this purpose, the eclipsing binaries are unique systems. Hence, in this study, we present the TESS data analysis of one candidate pulsating eclipsing binary system, V948 Her. TESS data were used for the binary modeling with the literature radial velocity measurements, and the precise fundamental parameters of the system were obtained. The system's age was derived as 1 +/- 0.24 Gyr. The positions of the binary components in the H-R diagram were examined and the primary component was found inside the delta Scuti instability strip. However, in the frequency analysis of TESS data, we found no significant pulsation frequencies. Only the harmonics of the orbital periods were obtained in the analysis. Therefore, the system was classified as a non-pulsator. V948 Her is an important object to understand the nature of non-pulsating stars inside the delta Scuti instability strip.Öğe Candidate Eclipsing Binary Systems with a ? Scuti Star in Northern TESS Field(Natl Astronomical Observatories, Chin Acad Sciences, 2022) Alicavus, F. Kahraman; Gumus, D.; Kirmizitas, O.; Ekinci, O.; Cavus, S.; Kaya, Y. T.; Alicavus, F.The existence of pulsating stars in eclipsing binaries has been known for decades. These types of objects are extremely valuable systems for astronomical studies as they exhibit both eclipse and pulsation variations. The eclipsing binaries are the only way to directly measure the mass and radius of stars with a good accuracy (<= 1%), while the pulsations are a unique way to probe the stellar interior via oscillation frequencies. There are different types of pulsating stars existing in eclipsing binaries. One of them is the delta Scuti variables. Currently, the known number of delta Scuti stars in eclipsing binaries is around 90 according to the latest catalog of these variables. An increasing number of these kinds of variables is important to understand the stellar structure, evolution and the effect of binarity on the pulsations. Therefore, in this study, we focus on discovering new eclipsing binaries with delta Scuti component(s). We searched within the northern Transiting Exoplanet Survey Satellite (TESS) field with a visual inspection by following some criteria such as light curve shape, the existence of pulsation like variations in the out-of-eclipse light curve and the T (eff) values of the targets. As a result of these criteria, we discovered some targets. The orbital variations were first removed from the TESS light curves and frequency analysis was performed on the residuals. The luminosity, and absolute and bolometric magnitudes of the targets were calculated as well. To find how much of these parameters represent the primary (more luminous) binary component, we also computed the flux density ratio of the systems by utilizing the area of the eclipses. In addition, the positions of the systems in the H-R diagram were examined considering the flux density ratios. As a consequence of the investigation, we defined 38 candidate delta Scuti stars and also one Maia variable in eclipsing binary systems.Öğe Discovery of delta Scuti variables in eclipsing binary systems II. Southern TESS field search(Oxford Univ Press, 2023) Alicavus, F. Kahraman; Coban, C. G.; Celik, E.; Dogan, D. S.; Ekinci, O.; Alicavus, F.The presence of pulsating stars in eclipsing binary systems (EBs) makes these objects significant since they allow us to investigate the stellar interior structure and evolution. Different types of pulsating stars could be found in EBs, such as & delta; Scuti variables. & delta; Scuti stars in EBs have been known for decades, and the increasing number of such systems is important for understanding pulsational structure. Hence, in this study, research was carried out on the southern TESS field to discover new & delta; Scuti stars in EBs. We produced an algorithm to search for detached and semidetached EBs considering three steps: the orbital period (P-orb)'s harmonics in the Fourier spectrum, skewness of the light curves, and classification of upsilon program. If two of these steps classify a system as an EB, the algorithm also identifies it as an EB. The TESS pixel files of targets were also analysed to see whether the fluxes were contaminated by other systems. No contamination was found. We researched the existence of pulsation through EBs with a visual inspection. To confirm & delta; Scuti-type oscillations, the binary variation was removed from the light curve, and residuals were analysed. Consequently, we identified 42 & delta; Scuti candidates in EBs. The P-orb, L, and M-V of systems were calculated. Their positions on the H-R diagram and the known orbital-pulsation period relationship were analysed. We also examined our targets to see if any of them showed frequency modulation with the orbital period and discovered one candidate of tidally tilted pulsators.Öğe Mass transfer and tidally tilted pulsation in the Algol-type system TZ Dra(Oxford University Press, 2022) Kahraman Aliçavuş, Filiz; Handler, G.; Aliçavuş, Fahri; De Cat, P.; Bedding, T.; Ekinci, O.Oscillating eclipsing Algols (oEAs) are remarkable systems that allow us to determine accurate fundamental stellar parameters (mass, radius) and probe the stellar interiors through pulsations. TZ Dra is an oEA system containing a δ Scuti component. To examine particular characteristics of such close systems including pulsations and mass transfer, we present a detailed photometric and spectroscopic study of TZ Dra. With the analysis of high-resolution spectra, the orbital parameters were determined by the radial velocity analysis and the atmospheric parameters were derived for the primary component. The binary modelling and the pulsational frequency analysis was carried out using the Transiting Exoplanet Survey Satellite data set. The H α line profiles show the signature of mass transfer from the cool to the hot binary component. The conclusion of mass transfer/mass-loss in the system was supported by the analysis of the orbital period changes. As a result, it was found that there is 3 . 52 × 10 −9 M yr −1 mass-loss from the system most probably through the hotspot and stellar winds. Additionally, most pulsation frequencies originating from the primary component were found to be spaced by harmonics of the orbital frequencies in particular, 12 doublets spaced by 2 f orb were detected from which we infer that this star is a tidally tilted pulsator. A mean p-mode frequency spacing of ≈7.2 d −1 was found as well.
