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Öğe A comprehensive study of an oscillating eclipsing Algol: Y Camelopardalis(Oxford Univ Press, 2024) Çelik, Eda; Kahraman Aliçavuş, FilizY Camelopardalis (Y Cam) is classified as one of the oscillating eclipsing Algol (oEA) systems, which feature a (sic) Scuti-type pulsating component alongside mass transfer phenomena. oEA systems are invaluable for probing the evolutionary processes and internal structures of binary components, offering insights through their binary variations and oscillations. In this study, we conducted a comprehensive investigation of Y Cam utilizing high-quality photometric TESS data and high-resolution ELODIE spectra. Through our analysis, we examined the radial velocity variation, performed binary modeling, and calculated the effective temperature values of binary components. The fundamental stellar parameters, such as mass and radius, were determined with an accuracy of similar to 2%-6%. Furthermore, we examined the orbital period variation to assess the amount of mass transfer using the available minima times of the system and three new minima times obtained from TESS light curves. Analyzing the pulsation structure of the system with the TESS data revealed the dominant pulsation period and amplitude of the pulsating component to be 0.066 d and 4.65 mmag, respectively. Notably, we observed frequency modulations with the orbital period's frequency, along with variations in the amplitude of the highest amplitude frequency across different orbital phases. Remarkably, the amplitude reaches its peak at phases 0.5 and 1. These findings indicate a candidate for a tidally tilted pulsator. Consequently, we investigated the evolutionary status of the binary components using MESA binary evolution models, determining the age of the system to be 3.28 +/- 0.09 Gyr.Öğe A/F tayf türü zonklayan yıldızların fotometrik ve tayfsal çalışması(Çanakkale Onsekiz Mart Üniversitesi, Lisansüstü Eğitim Enstitüsü, 2017) Kahraman Aliçavuş, Filiz; Soydugan, EsinDelta Sct ve Gamma Dor yıldızları klasik kararsızlık kuşağının alt bölgesinde yer alan ve en çok bilinen zonklayan yıldızlardır. Bu değişenler, farklı katmanlarından bilgiler getiren farklı modlar ile zonklamaktadır. Her iki değişene ait teorik kararsızlık kuşakları birbirleri ile kısmı olarak örtüşmektedir ve kuşaklarının örtüştüğü bu bölgede hem Delta Sct hem de Gamma Dor modları ile zonklamalar gösterebilen A-F türü hibrit yıldızları keşfedilmiştir. A-F tayf türü zonklayanlar, yıldızların içyapılarının detaylı incelenebilmesi için oldukça önemlidirler. Aynı zamanda bu yıldızlarla ilgili hala cevaplanması beklenen birkaç sorun bulunmaktadır. Delta Sct ve Gamma Dor zonklayanlarının kararsızlık kuşaklarının sınırları, Delta Sct yıldızlarındaki düşük frekanslı zonklamalar ve Delta Sct ve Gamma Dor yıldızları arasındaki var olabilecek kimyasal farklılık ve/veya benzerlikler bu sorunlardan birkaçıdır. Bu soruların cevaplanabilmesi içinde tayfsal çalışmalar oldukça önemlidir. Bu tez çalışmasında, tek ve çift sistem üyesi Delta Scuti ve tek Gamma Dor yıldızlarının detaylı tayfsal çalışması sunuldu. Seçilen sistemlerin temel atmosfer parametreleri (Teff, log g, x), vsin i ve kimyasal element bollukları elde edildi. Parametrelerin kullanılması ile tek ve çift sistem üyesi Delta Scuti ve tek Delta Sct, Gamma Dor yıldızlarının özellikleri kıyaslandı. Çift Delta Sct yılızlarının bir katalogu hazırlanarak, ikinci bileşen ve dönme-dolanma gibi faktörlerin zonklama üzerine etkileri detaylı olarak incelendi.Öğe Discovery of delta Scuti variables in eclipsing binary systems II. Southern TESS field search(Oxford Univ Press, 2023) Kahraman Aliçavuş, Filiz; Çoban, C. G.; Çelik, E.; Doğan, D. S.; Ekinci, O.; Aliçavuş, FahriThe 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 δ Scuti variables. δ 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 δ Scuti stars in EBs. We produced an algorithm to search for detached and semidetached EBs considering three steps: the orbital period (Porb)’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 δ Scuti-type oscillations, the binary variation was removed from the light curve, and residuals were analysed. Consequently, we identified 42 δ Scuti candidates in EBs. The Porb, L, and MV 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 KIC 10486425: A Kepler eclipsing binary system with a pulsating component(Cambridge Univ Press, 2014) Kahraman Aliçavuş, Filiz; Soydugan, EsinWe 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).Öğe Maia Yıldızları Yeni Bir Zonklayan Yıldız Türü Mü?(2023) Kahraman Aliçavuş, Filiz; Özuyar, Doğuş; Aliçavuş, Fahri; Çoban, Gani Çağlar; Doğan, Duygu SenaUzay tabanlı gözlemlerin artmasıyla birlikte zonklayan yıldızlar üzerine yer tabanlı gözlemlerden elde edilmiş olan birçok bilginin güncellenmesi gerekliliği ortaya çıkmıştır. Daha önceden varlıkları tam olarak kanıtlanmaya hatta değişen yıldız grupları içerisinde sayılmayan yıldız gruplarının da birçok yeni adayı uzay gözlemeleriyle keşfedilmiştir ve bu yıldızların varlıkları tekrar ortaya koymuştur. Maia değişen yıldızları da bu yıldız gruplarından biridir. Maia yıldızlarının varlığı ile ilgili birçok hipotez ortaya atılmıştır ve gerçekten böyle bir yıldız grubu olup olmadığı tartışılagelmektedir. Projemiz kapsamında HERMES ve FIES tayfçekerleri gözlem projeleri ile elde edilen tayfsal verilerden ve Mikulski Archive for Space Telescopes (MAST) arşivinden alınan TESS uydu gözlemlerinden yararlanarak detaylı tayfsal ve fotometrik çalışmalar yürütülmüştür. Bu çalışmalar neticesinde Maia yıldızlarının varlığı üzerine ortaya konan yanlış etkin sıcaklık, çift sistem olma durumu ve hızlı dönme hipotezlerinin doğru olmadığı gösterilmiştir. Ayrıca incelenen sistemler içerisinde varlığı açıklanamayan ve Maia yıldızı olduğu kuvvetli olan sistemler tespit edilmiştir. Bu yıldızların varlığının açıklanması için önerilebilecek tek yol yeni bir zonklama mekanizması ya da mevcut zonklama mekanizmaları arasındaki bilinmeyen bir ilişki olabileceği ortaya konmuştur. Bu çalışmayla birlikte Maia yıldızları varlığı üzerine literatürde ilk kez bu denli detaylı bir çalışmayla yaklaşımda bulunulmuştur.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.Öğe On the existence of 'Maia variables'(Cambridge Univ Press, 2024) Kahraman Aliçavuş, Filiz; Handler, Gerald; Chowdhury, Sowgata; Niemczura, Ewa; Jayaraman, Rahul; De Cat, Peter; Özuyar, Doğuş; Aliçavuş, FahriThere 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'.Öğe Single-lined eclipsing binaries with ? Scuti components: GQ Dra, RR Lep, and TYC 683-640-1(Oxford University Press, 2024) Kahraman Aliçavuş, Filiz; Aliçavuş, Fahri; Çoban, Çağlar Gani; Handler, G.; De Cat, P.Eclipsing binaries with (a) pulsating component(s) are remarkable objects to investigate the evolution and structure of stellar systems. Detailed studies of such systems are also important to reveal their pulsation properties. The largest sample of pulsating eclipsing binaries is the one containing δ Scuti variables. In this study, we present a comprehensive spectroscopic and photometric study of three such systems, GQ Dra, RR Lep, and TYC 683-640-1. Their orbital parameters were derived from their large-amplitude radial velocity variations. All systems were found to be single-lined eclipsing binaries. We determined the atmospheric parameters of the primary components, which are the more luminous ones. By using the results of the spectroscopic analysis, the binarity of the systems was modelled and the fundamental stellar parameters (mass, radius) of each system were obtained. In addition, the pulsations of the systems were analysed. Both GQ Dra and RR Lep exhibit frequencies that are modulated with the orbital period. Therefore, the pulsating components of these systems are identified as candidate tidally tilted pulsators.Öğe The First Light Curve Solutions and Period Study of BQ Ari(Springer, 2021) Poro, A.; Davoudi, F.; Kahraman Aliçavuş, Filiz; Khakpash, S.; Esmer, E. M.; Baştürk, O.The first analysis of the photometric observation in BVR filters of a W UMa type binary system BQ Ari was performed. Light curve analysis was performed using Wilson-Devinney (W-D) code combined with a Monte Carlo (MC) simulation to determine its photometric and geometric elements and their uncertainties. These results show that BQ Ari is a contact binary system with a photometric mass ratio q = 0.548 +/- 0.019, a fillout factor f = 24 +/- 0.8%, and an orbital inclination of i = 85.09 +/- 0.45. We used the parallax from Gaia EDR3 for calculating the absolute parameters of the binary system. This study suggested a new linear ephemeris for BQ Ari, combining our new mid-eclipse times and the previous observations, which we analyzed using the Monte Carlo Markov Chain (MCMC) method. We present the first analysis of the system's orbital period behavior by analyzing the O - C diagram using the Genetic Algorithm (GA) and the MCMC approaches in OCFit code. We attempted to explain the analysis of the residuals of linear fit in the O - C diagram with two approaches; "LiTE + Quadratic" and "Magnetic activity + Quadratic." Although we consider the magnetic activity to be probable, the system should be studied further in order to reveal the nature of orbital period variations.
