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Öğe Ayrık çift yıldız bileşenleri üzerine atmosfer ve evrim modelleri uygulamaları(Çanakkale Onsekiz Mart Üniversitesi, Lisansüstü Eğitim Enstitüsü, 2018) Aliçavuş, Fahri; Soydugan, FarukGörünür evrenin temel bileşeni olan yıldızların nasıl evrimleştiklerini ve içyapılarını anlamamız, bulundukları gökadaların oluşumunu ve evrimini anlamamızda oldukça önemlidir. Bu nedenle yıldızların temel fiziksel özelliklerinin belirlenmesi anahtar çalışma alanlarından birisidir. Bu çalışmada, seçilen dokuz adet ayrık örten çift sistemin detaylı analizleri yapılmış ve mutlak parametreleri elde edilmiştir. Seçilen sistemler için belirlenen kütleler, 1 Mʘ ile 4.8 Mʘ aralığında olup %0.5-3 duyarlılıkla belirlenmiştir. Seçilen yıldızlardan yeterli verisi bulunanların tayfsal analizleri yapılarak bileşenlerin ayrıştırılmış tayfları ayrı ayrı modellenmiştir. Ek olarak, ayrık çift yıldızlar kullanılarak fotometrik uzaklıklar ile Gaia ve Hipparcos ile elde edilen uzaklıklar karşılaştırılmış ve 300 pc üzeri uzaklıklarda Gaia ve fotometrik yolla belirlenen uzaklıkların daha güvenilir olduğu sonucuna varılmıştır. Bileşenler için belirlenen duyarlı atmosfer parametreleri kullanılarak oluşturulan tek ve çift yıldız evrim modelleri ele alınmıştır. Üretilen evrim modellerinde sistem yaşları 0.07 ile 4.5 milyar yıl aralığında değişmektedir. Ayrıca, tutulmalar dışındaki küçük genlikli etkiler incelenmiş ve ışık eğrisi üzerine etkileri tartışılmıştır. KIC 6525196 ve KIC 8043961 sistemlerinin leke modelleri ve zonklama yapıları ilk defa detaylı olarak araştırılmıştır ve KIC 8043961 üçlü sisteminde γ Doradus ve δ Scuti türü zonklamalar keşfedilmiştir. Eksen dönmesi gösteren sistemlerinin yörünge dönem değişimleri incelenmiştir. Çift yıldız evrim modelleri kullanılarak üretilen kuramsal modeller yardımıyla yörünge dönemi, basıklık, dönme hızı ve manyetik frenleme etkilerinin modeller üzerindeki ve çift yıldızın yörünge evrimine etkileri tartışılmıştır. Ayrıca, duyarlı mutlak parametreleri bilinen ayrık çift yıldızlar kullanılarak yörünge açısal momentumuyla yörünge dönemi, kütle ve yüzey çekim ivmesi arasındaki gözlemsel ilişkiler elde edilmiş ve kuramsal bağlılıklar ile karşılaştırılmıştır.Öğe Bazı zonklayan yıldızların tayfsal analizi(Çanakkale Onsekiz Mart Üniversitesi, 2011) Aliçavuş, Fahri; Demircan, OsmanBu tez çalışmasında, seçilen bazı zonklayan yıldızların tayflarında meydana gelen değişimler incelenerek yıldızların zonklama özellikleri belirlendi. Tez çalışması kapsamında FG Virgo, Epsilon Cephei yıldızları incelendi. Hedef yıldızların tayfları 1996?2004 yılları arasında ?ELODIE? tayfçekeri ile elde edilmiş ve uluslararası kullanıma serbest bırakılmış Elodie (Moultaka ve ark. 2004) arşivinden alındı. Arşivden elde edilen tayflar IRAF programı ve bu programın alt paketleri yardımı ile işlenerek analize hazır hale getirildi. Yıldızların mod analizlerinin ve zonklama yapılarının ortaya çıkarılması ise ?FAMIAS? (Zima, 2008) programı yardımı ile yapıldı.Tez kapsamında tayfları incelenen Epsilon Cephei' nin mod analizi FAMIAS programı kullanılarak ilk kez detaylı bir şekilde incelendi ve zonklama özellikleri ayrıntılı olarak belirlendi.Öğe BSN-I: the first in-depth photometric study of seven total-eclipse contact binary systems(Oxford Univ Press, 2025) Poro, A.; Li, K.; Paki, E.; Baudart, S.; Michel, R.; Wang, L.; Lajus, E. Fernandez; Aliçavuş, FahriThis is the first in-depth study of seven total-eclipse W Ursae Majoris-type contact binary systems using photometric light curves. The ground-based observations were conducted with four observatories in the Northern and Southern hemispheres. We also used the Transiting Exoplanet Survey Satellite for four target systems. We presented the analysis of orbital period variations of six systems and found that they display parabolic variations. The material transfer rates between the stars of the systems were calculated. Also, the results show that four systems have a long-term increase, while two have a long-term decrease in their orbital periods. We analysed light curves using the PHysics Of Eclipsing BinariEs python code and the Markov chain Monte Carlo algorithm to estimate different parameters of target systems and their uncertainties. Six of the target systems required the addition of a cold or hot star-spot. We estimated absolute parameters using the empirical relationship between the orbital period and the semimajor axis (P-a). According to each component's effective temperature and mass, it was recognized that the studied systems are W subtype. We examined the dynamic stability of two targets, which were low mass ratio contact binary systems. We also showed the evolution of stars in the M-R and M-L diagrams. Finally, we showed that the hotter stars in contact systems have a temperature difference of less than approximate to 400 K compared to the Gaia Data Release 3 temperature report.Öğe BSN: The First Photometric Study of 10 Contact Binary Systems from the Northern and Southern Hemispheres(Iop Publishing Ltd, 2024) Poro, Atila; Li, Kai; Michel, Raul; Castro, Angel; Lajus, Eduardo Fernandez; Wang, Li-Heng; Coliac, Jean-Francois; Aliçavuş, FahriPhotometric observations were made with standard filters in four observatories for 10 contact binary systems. We analyzed the orbital period variations of the systems and found that six of them show long-term changes. The increase in the orbital period of the J07, N65, and PU Vir systems is caused by mass transfer, and the reduction in the orbital period of the J05, LO Psc, and N49 systems is caused by the combination of angular momentum loss and mass transfer. The first light-curve analysis was performed with the PHysics Of Eclipsing BinariEs Python code and Markov Chain Monte Carlo. We discussed the accuracy of photometric mass ratio estimates for contact binary systems with total and partial eclipses compared to spectroscopic results. We also compared our mass ratio findings to a recent method that estimates mass ratios from the light curve's third derivative. Then, we also discussed this new mass ratio estimate method for photometric data. The systems' positions were displayed in 18 empirical parameter relationships. According to the light-curve analysis and estimation of absolute parameters, systems BE Mus, J07, J08, N49, and N65 are A subtypes, and the others are W subtypes.Öğe BVRI Photometric Observations, Light Curve Solutions and Orbital Period Analysis of BF Pav(IOP Publishing, 2021) Poro, Atila; Aliçavuş, Fahri; Fernandez-Lajus, Eduardo; Davoudi, Fatemeh; MirshafieKhozani, PegahSadat; Blackford, Mark G.; Budding, Edwin; Jalalabadi, Behjat Zarei; Rahimi, Jabar; Farahani, Farzaneh AhangaraniA new ephemeris, period change analysis and light curve modeling of the W UMa-type eclipsing binary BF Pav are presented in this study. Light curves of the system taken in BVRI filters from two observatories, in Australia and Argentina, were modeled using the Wilson-Devinney code. The results of this analysis demonstrate that BF Pav is a contact binary system with a photometric mass ratio q = 1.460 +/- 0.014, a fillout factor f = 12.5%, an inclination of 87.97 +/- 0.45 deg and a cold spot on the secondary component. By applying the distance modulus formula, the distance of BF Pav was calculated to be d = 268 +/- 18 pc which is in good agreement with the Gaia EDR3 distance. We obtain an orbital period increase at a rate of 0.142 s century(-1) due to a quadratic trend in the O - C diagram. Also, an alternative sudden period jump probably occurred which could be interpreted as a rapid mass transfer from the lower mass star to its companion of about Delta M = 2.45 x 10(-6) M (circle dot). Furthermore, there is an oscillatory behavior with a period of 18.3 +/- 0.3 yr. Since BF Pav does not seem to have significant magnetic activity, this behavior could be interpreted as the light-time effect caused by an undetected third body in this system. In this case, the probability for the third body to be a low mass star with M >= 0.075 M (circle dot) or a brown dwarf is 5.4% and 94.6% respectively. If we assume i ' = 90 degrees, a (3) = 8.04 +/- 0.33 AU. The mass of the secondary component was also determined following two different methods which result close to each other.Öğe 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.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 First photometric investigation of V517 Cam combined with ground-based and TESS data(Elsevier, 2025) Alan, Neslihan; Aliçavuş, Fahri; Alpsoy, MehmetThe observations of eclipsing binary systems are of great importance in astrophysics, as they allow direct measurements of fundamental stellar parameters. By analysing high-quality space-based observations with ground-based photometric data, it becomes possible to detect these fundamental parameters with greater precision using multicolour photometry. Here, we report the first photometric analysis results of the V517 Cam eclipsing binary system by combining the Transiting Exoplanet Survey Satellite ( TESS ) light curve and new CCD observations in BVRI filters, obtained with a 60 cm robotic telescope (T60) at the T & Uuml;B & Idot;TAK National Observatory. By means of photometric analyses, the masses and radii of the primary and secondary stars were carefully determined to be M1 = 1.47 +/- 0.06 M ae, M2 = 0.79 +/- 0.05 M ae, and R1 = 1.43 +/- 0.03 R ae, R2 = 0.75 +/- 0.04 R ae, respectively. Furthermore, the distance to V517 Cam was calculated to be 284 +/- 20 pc. The overall age of the system is estimated to be around 63 +/- 15 Myr. At this age, the primary component stands near the onset of its main-sequence evolution, near the ZAMS, whereas the secondary component remains in the pre-main- sequence evolutionary phase. To better understand the evolutionary status and nature of V517 Cam, the mass ratio and temperature values, obtained with relatively low sensitivity by photometric measurements, need to be confirmed by spectral analysis.Öğe Genç Ayrık Çift Yıldız HD 350731'in Doğası(Türk Astronomi Derneği, 2020) Aliçavuş, Fahri; Soydugan, Faruk; Bilir, Selçuk; Soydugan, Esin; Püsküllü, Çağlar; Şenyüz, TunçBu çalışmada, ayrık çift yıldız olan HD 350731'in tayfsal ve fotometrik analizleri yapılarak, eksen dönmesi, bileşenlerinin kütle, yarıçap gibi mutlak parametreleri belirlenmiş ve teorik yıldız evrim modelleri ile karşılaştırılmıştır. Tayfsal ayırma yöntemiyle elde edilen bileşen tayflarından sıcaklık, dönme hızı, yüzey çekim ivmesi bulunarak kimyasal bolluk tahmini yapılmıştır. Sistemin yaşı izokronlar yardımıyla yaklaşık 60 Myıl olarak tahmin edilmiştir. HD 350731'in kinematik analizi yapılarak gökadanın ince-disk popülasyonuna ait olduğu belirlenmiştir.Öğe Kepler Light Curve Modeling of KIC 9788457(2023) Aliçavuş, FahriEclipsing binary systems are significant objects for astrophysical studies since they offer more accurate fundamental stellar parameters (mass, radius). In particular, the determination of the astrophysical parameters of semi-detached binary stars is important in terms of examining the physical processes that occur as a result of interactions between components such as mass transfers and mass losses, since one of their components fills the Rochelobe. Therefore, in this study, the first binary modeling of KIC 9788457 is presented to estimated the fundamental stellar parameters of the system. The photometric data of the system were taken from Kepler that provides highquality data. When the light curve was checked it was found that the more luminous massive component has a significant light contribution into total. Therefore, using the spectral energy distribution and also color index (B-V) values effective temperature (Teff ) value was estimated for the primary component. Utilizing this Teff value, the binary modeling of the system was carried out. As a result, fundamental physical parameters of KIC9788457 were obtained. The radius (R) and mass (M) values of the components are M1=1.89 ± 0.05 Msun and R1= 2.03 ± 0.02 Rsun for the massive component and M2=0.81 ± 0.02 Msun and R2= 1.74 ± 0.03 Rsun for the less massive component, respectively. Additionally, the distance of the system was determined to be 1407 ± 85 pc.Öğe Maia Yıldızları Yeni Bir Zonklayan Yıldız Türü Mü?(2023) Aliçavuş, Filiz Kahraman; 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 O-C Analysis of Selected 3-Body Systems(Cambridge Univ Press, 2012) Ogloza, W.; Kreiner, J. M.; Stachowski, G.; Winiarski, M.; Zakrzewski, B.; Doğru, Serkan; Aliçavuş, Fahri; Demircan, Oya; Erdem, AhmetThis paper presents the results of the analysis of (O-C) diagrams of four eclipsing variables. The diagrams are based on times of minima collected in the Cracow database, which contains times of minima found in the literature, from observations at Mt. Suhora and Ulupinar Observatories, or determined using publicly-available photometric surveys (NSVS, ASAS etc).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 V1095 her ve V1101 her sistemlerinin dönem değişimleri(Çanakkale Onsekiz Mart Üniversitesi, 2016) Öztürk, Oğuz; Erdem, Ahmet; Aliçavuş, FahriŞu ana kadar literatürde, her iki sistem üzerine yapılan ne fotometrik ne de tayfsal çalışma bulunmamaktadır. Bu çalışmada, V1095 Her ve V1101 Her sistemlerinin SuperWASP ışık eğrileri ile birlikte dönem değişimleri ilk kez analiz edilmiştir. Sistemlerin parabolik dönem değişimleri, her bir sistem için elde edilen O-C verilerine, Zasche ve ark. (2009) tarafından yazılan MATLAB kodu kullanılarak ağırlıklı en küçük kareler yöntemi ile incelenmiştir. O-C diyagramlarında çevrimsel bir değişim görüldüğünden, aynı MATLAB kodu kullanarak, ışık zaman etkisi (LTE) analizi de yapılmıştır. SuperWASP ışık eğrileri çözümü için Wilson & Devinney (1971) kodu kullanılmıştır. V1095 Her ve V1101 Her sistemlerinin O-C diyagramları, sırasıyla, aşağı ve yukarı yönlü parabol üzerine binmiş sinüzoidal bir değişim göstermektedir. V1095 Her’de düzenli olarak görülen dönem azalma hızı ve V1101 Her’de düzenli olarak görülen dönem artış hızı hesaplanmıştır. Dönem değişimine sebep olabilecek fiziksel mekanizmalar tartışılmıştır. O-C diyagramlarında görülen çevirimsel değişimler LTE ile yorumlanmıştır. Her iki sistemin fotometrik kütle oranları elde edilmiş ve mutlak parametreleri yaklaşık olarak tahmin edilmiştir.
