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Öğe Absolute Parameters of Detached Binaries in the Southern Sky - I: V349 Ara and V4403 Sgr(Cambridge Univ Press, 2015) Erdem, Ahmet; Sürgit, Derya; Engelbrecht, C. A.; Van Heerden, H. P.We present the first analysis of spectroscopic and photometric observations of the two southern eclipsing binary stars, V349 Ara and V4403 Sgr. Radial velocity curves of these two systems obtained at the South African Astronomical Observatory and their V light curves from the All Sky Automated Survey were solved simultaneously using the Wilson-Devinney code. Our photometric models describe these two systems as Algol-like binary stars with detached configurations. The masses and radii were found to be 2.59 +/- 0.07 M, 3.60 +/- 0.07 R and 2.51 +/- 0.06 M, 4.15 +/- 0.07 R for the primary and secondary components of V349 Ara, respectively. Those of V4403 Sgr were derived to be 1.33 +/- 0.02 M, 1.74 +/- 0.02 R and 1.59 +/- 0.03 M, 2.50 +/- 0.03 R for the primary and secondary components, respectively. The distances to V349 Ara and V4403 Sgr were computed to be 677 +/- 36 and 199 +/- 10 pc from the dynamic parallax, respectively, taking into account interstellar extinction. The evolution cases of these two systems are also examined. Both components of these two systems are evolved main-sequence stars, and the dynamic ages were estimated as approximately 0.67 and 2.29 Gyr for V349 Ara and V4403 Sgr, respectively, when compared to Geneva theoretical evolution models.Öğe Absolute parameters of three southern eclipsing binaries: DQ Car, BK Ind, and V4396 Sgr(Oxford Univ Press, 2020) Surgit, Derya; Erdem, Ahmet; Engelbrecht, Chris A.; Marang, FredWe present combined photometric and spectroscopic analyses of the three southern eclipsing binary stars: DQ Car, BK Ind, and V4396 Sgr. Radial velocity curves of these three systems were obtained at the South African Astronomical Observatory, and their light curves from the available data bases and surveys were used for the analysis. 75 new times of minima for these three eclipsing binaries were derived, and their ephemerides were updated. Only the O-C diagram of DQ Car indicates a cyclical variation, which was interpreted in terms of the light-time effect due to a third body in the system. Our final models describe these three systems as Algol-like binary stars with detached configurations. The masses and radii were found to be M-1 = 1.86(+/- 0.17) M-circle dot, R-1 = 1.63(+/- 0.06) R-circle dot and M-2 = 1.74(+/- 0.17) M-circle dot, R-2 = 1.52(+/- 0.07) R-circle dot for the primary and secondary components of DQ Car; M-1 = 1.16(+/- 0.05) M-circle dot, R-1 = 1.33(+/- 0.03) R-circle dot and M-1 = 0.98(+/- 0.04) M-circle dot, R-2 = 1.00(+/- 0.03) R-circle dot for BK Ind; and M-1 = 3.14(+/- 0.22) M-circle dot, R-1 = 3.00(+/- 0.09) R-circle dot and M-2 = 3.13(+/- 0.24) M-circle dot, R-2 = 2.40(+/- 0.08) R-circle dot for V4396 Sgr, respectively. The distances to DQ Car, BK Ind, and V4396 Sgr were derived to be 701(+/- 50), 285(+/- 20), and 414(+/- 30) pc from the distance modulus formula, taking into account interstellar extinction. The evolutionary status of these three systems was also studied. It has been found that the components of DQ Car arc very young stars at the age of similar to 25 Myr and those of BK Ind and V4396 Sgr are evolved main-sequence stars at the ages of similar to 2.69 Gyr and similar to 204 Myr, respectively.Öğe Absolute parameters of young stars: PU Pup(IOP Publishing, 2021) Erdem, Ahmet; Sürgit, Derya; Banks, Timothy S.; Özkardeş, Burcu; Budding, EdwinWe present combined photometric and spectroscopic analyses of the southern binary star PU Pup. High-resolution spectra of this system were taken at the University of Canterbury Mt. John Observatory in the years 2008 and again in 2014-15. We find the light contribution of the secondary component to be only ∼2% of the total light of the system in optical wavelengths, resulting in a single-lined spectroscopic binary. Recent TESS data revealed grazing eclipses within the light minima, though the tidal distortion, examined also from HIPPARCOS data, remains the predominating light curve effect. Our model shows PU Pup to have the more massive primary relatively close to filling its Roche lobe. PU Pup is thus approaching the rare ‘fast phase’ of interactive (Case B) evolution. Our adopted absolute parameters are as follows: M1 = 4.10 (±0.20) M , M2 = 0.65 (±0.05) M , R1 = 6.60 (±0.30) R , R2 = 0.90 (±0.10) R ; T1 = 11500 (±500) K, T2 = 5000 (±350) K; photometric distance = 186 (±20) pc, age = 170 (±20) My. The less-massive secondary component is found to be significantly oversized and overluminous compared to standard Main Sequence models. We discuss this discrepancy referring to heating from the reflection effect.Öğe Apsidal motion and absolute parameters of GV Nor and V881 Sco based on mid-resolution spectroscopy and TESS photometry(Oxford University Press, 2023) Sürgit, Derya; Zasche, Petr; Hadrava, Petr; Erdem, Ahmet; Engelbrecht, Chris A.; Marang, Fred; Masek, MartinThe veracity of stellar evolution models and theoretical internal structure constants may be subjected to stringent tests by using physical parameters obtained from spectroscopic and photometric observations of eclipsing binary systems that exhibit apsidal motion. Two eclipsing binary stars from the southern hemisphere with no prior published spectroscopic analyses were selected for this study: GV Nor and V881 Sco. Spectroscopic observations of these two eccentric binary systems were made at the South African Astronomical Observatory (SAAO) in 2018 and 2019, and their mid-resolution spectra were obtained. The radial velocities were measured using the cross-correlation method as well as by disentangling the spectra. The rotational broadening of the disentangled spectra of the components was also determined. The absolute parameters of these two systems were obtained by analyzing the SAAO-based spectroscopic data in conjunction with photometric data from Transiting Exoplanet Survey Satellite. Apsidal motion parameters for these two eccentric binary systems were calculated by analysing eclipse timing variations. Granada and Padova evolution models indicated ages of 340 ± 35 Myr for GV Nor and 760 ± 15 Myr for V881 Sco, in agreement with the observational results. The theoretical internal structure constants estimated from the Granada models were compatible with the observational values within the error limits. However, for both systems, it was found that their circularization and synchronization timescales were shorter than their respective evolutionary ages. Therefore, the fact that the components rotate faster than their synchronized values and still have rather large eccentric orbits (e ∼ 0.11) challenges present theories of circularization and spin–orbit synchronization.Öğe Bazı eksantirik yörüngeli örten çift yıldızların fotometrik incelenmesi(2006) Çiçek, Caner; Erdem, Ahmet; Bakış, Volkan; Değirmenci, Ömer L.; Esenoğlu, Hasan; Demircan, Osman; Özdemir, Sacit[Abstract Not Available]Öğe Çanakkale Onsekiz Mart Üniversitesi Ar-Ge Strateji Belgesi (Astrofizik)(2017) Erdem, Ahmet; Erkan, Naci; Soydugan, Esin; Bulut, İbrahim; Bulut, Ahmet; Demircan, OsmanÇanakkale Onsekiz Mart Üniversitesi (ÇOMÜ)?de astronomi/astrofizik alanındaki tüm bilimsel çalışmalar 2000 yılından itibaren ÇOMÜ Astrofizik Araştırma Merkezi (ÇAAM) bünyesinde örgütlenmiştir (bkz: http://physics.comu.edu.tr/caam/). Üniversite içinde astronomi, astrofizik ve uzay bilimleriyle profesyonel olarak ilgilenen tüm elemanlar bu merkezin üyesidir. Bu gün ÇAAM kurmuş olduğu Gözlemevi ile Marmara Bölgesi?nin astronomi/astrofizik alanında en etkin çalışan merkez konumundadır. Merkezde ulusal ve uluslararası bağlantılı bilimsel araştırmalar yürütülmekte, eleman yetiştirilmekte ve bölge okulları ve halk için bilimtoplum etkinlikleri hizmeti verilmektedir. ÇAAM?da bilimsel araştırmalar, yıldız astrofiziği, güneş ve güneş sistemi, ötegezegenler, yüksek enerji astrofiziği ve kozmoloji alanlarında yoğunlaşmaktadır. ÇAAM üyeleri son on yılda hakemli dergilerde 200?ün üzerinde makale yayınlamış, bilimsel toplantılarda 300?e yakın bildiri sunmuş, 40 kadar bilimsel araştırma projesi yürütmüş, 10?a yakın bilimsel toplantı düzenlemiş veya düzenlenmesine katkı sunmuş, 8 kitapta yazarlık ve editörlük yapılmış, ve 50 kadar yüksek lisans ve doktora tez çalışması yürütmüştür. Gözlemevinde yapılan gözlemlere dayalı çok sayıda bulgu indekslere giren dergilerde yayınlandı. Gözlemevinde tek veya çift yıldız olarak bilinen 30 kadar yıldızın görünmeyen bileşenleri keşfedildi. Merkez üyeleri tarafından yazılan bir ders kitabı Cambridge Üniversitesi yayınları arasında basıldı. Güncel çift yıldız katalogları oluşturuldu. Çift yıldız yörüngelerinin, aşırı açısal momentum kaybı nedeniyle, gittikçe küçüldüğü ve zaman içinde çift yıldızların tek yıldıza dönüştüğü ilk kez ÇAAM üyeleri tarafından kanıtlandı. Yıldız sismolojisinin, yakınında başka bir yıldız olması halinde, o yıldızın kütle çekimine bağlı olduğu gözlemlerle gösterildi. Ülkemizde ilk kez asteroidlerin fotometrik gözlemlerinden şekillerinin modellenmesi çalışmalarına başlandı. Kuramsal kozmolojide quark gluon plazmasıyla ilgili çok önemli yayınlar yapıldı. Çift yıldızların etrafında görünmeyen başka yıldızların bulunabileceği ve bu istatistiğin oldukça yüksek olduğu kanıtlandı. Çift yıldızların etrafında gezegenler olabileceği bu gözlemevinin birçok yayınında not edildi. ÇOMÜ?nün astrofizik/astronomi alanında gelecek 5 yılda izleyeceği stratejisinde nihai hedefi, Astrofizik Araştırma Merkezi ve Ulupınar Gözlemevi?ni uluslararası kabul edilebilir nitelikte, bilimsel araştırmalar yapan, alanında uzman akademisyen yetiştiren, topluma popüler bilim hizmeti veren, teleskop, detektör, kubbe vb gözlem aletleri ve yazılımları konusunda ar-ge yapan bir mükemmeliyet merkezi haline getirmektir. Bu hedefe ulaşılması için izlenilecek adımlar (stratejik amaçlar): (i) Gözlemevi hizmet binasının yenilenmesi, (ii) 1.22 m ayna çaplı teleskop için modern bir tayfçekerin alınması, kurulması ve çalıştırılması, (iii) İstanbul Üniversitesi Fen Fakültesi Astronomi ve Uzay Bilimleri Bölümü ile ortaklaşa kullanılan 60 cm ayna çaplı teleskobun tam robotik hale getirilmesi, (iv) 40 cm ve 30 cm ayna çaplı teleskopların yarı-robotik hale (uzaktan gözlem yapılabilir hale) getirilmesi, (v) Yenilenmesi planlanan hizmet binasında, kütüphane, mutfak, dinlenme ve çalışma odalarının yanı sıra, ar-ge laboratuvarının kurulması, (vi) Astronomi alanında ar-ge için, örneğin ÇAAM üyelerinin ÇOMÜ TeknoPark bünyesinde kurduğu ASTROIA şirketi vb teknoloji şirketleriyle işbirliklerinin/çalışmaların artırılması, (vii) ÇOMÜ Gözlemevi sitesinde bir gezegenevinin (planetaryum) kurulması ve toplum-bilim hizmetlerinin verilmesi.Öğe Comparative study of the W UMa type binaries S Ant and ε CrA(Cambridge Univ Press, 2024) Bakış, Volkan; Budding, Edwin; Erdem, Ahmet; Love, Tom; Blackford, Mark G.; Wu, Zihao; Tang, AdamContact binaries challenge contemporary stellar astrophysics with respect to their incidence, structure, and evolution. We explore these issues through a detailed study of two bright examples: S Ant and ε CrA, that permit high-resolution spectroscopy at a relatively good S/N ratio. The availability of high-quality photometry, including data from the TESS satellite as well as Gaia parallaxes, allows us to apply the Russell paradigm to produce reliable up-to-date information on the physical properties of these binaries. As a result, models of their interactive evolution, such as the thermal relaxation oscillator scenario, can be examined. Mass transfer between the components is clearly evidenced, but the variability of the O’Connell effect over relatively short-time scales points to irregularities in the mass transfer or accretion processes. Our findings indicate that S Ant may evolve into an R CMa type Algol, while the low mass ratio of ε CrA suggests a likely merger of its components in the not-too-distant future.Öğe First detailed study of two eccentric eclipsing binaries: TYC 5378-1590-1 and TYC 8378-252-1(Edp Sciences S A, 2023) Zasche, P.; Sürgit, Derya; Erdem, Ahmet; Engelbrecht, C. A.; Marang, F.Aims. The analysis of combined photometry and spectroscopy of eccentric eclipsing binary systems facilitates the derivation of very precise values for a large ensemble of physical parameters of the component stars and their orbits, thereby providing stringent tests of theories of stellar structure and evolution. In this paper two eccentric eclipsing binary systems, TYC 5378-1590-1 and TYC 8378252-1, are studied in detail for the first time. Methods. Radial velocities were obtained using cross-correlation methods applied to mid-resolution spectra covering almost the entire orbital phase domains of these two systems. TESS photometry was used for the analysis of TYC 5378-1590-1, whereas ASAS-SN photometry was used for the analysis of TYC 8378-252-1. Results. We obtained the first precise derivation of the physical parameters of these systems. Both systems display moderately eccentric orbits (e similar to 0:3 and 0:2) with periods of 3.73235 and 2.87769 days, respectively. The apsidal motion is very slow, with a duration of several centuries for both systems. We present two models for the apsidal motion of TYC 5378-1590-1. The internal structure constant derived from observations for TYC 8378-252-1 is approximately 11% lower than theoretical predictions. We discuss possible reasons for this discrepancy. Our analysis indicates that the components of both systems are on the main sequence. The components of TYC 5378-1590-1 are relatively young stars (age similar to 600 Myr) close to the ZAMS, whereas the components of TYC 8378-252-1 are relatively old stars (age similar to 4 Gyr) close to the TAMS. Our finding that the circularization timescale for TYC 5378-1590-1 is similar to 200 times longer than its evolutionary age is compatible with circularization theory; however, our finding that the evolutionary age of TYC 8378-252-1 is approximately ten times longer than the circulation age, while its orbital eccentricity is quite high (e similar to 0:2), challenges the present theories of circularization.Öğe First photometric study of three eclipsing binary star systems: V495 Aur, V589 Aur and V478 Cam(Elsevier B.V., 2023) Öztürk, Oğuz; Erdem, AhmetThe light curve solutions and orbital period analysis of V495 Aur, V589 Aur and V478 Cam eclipsing binary star systems are presented for the first time in this study. Transiting Exoplanet Survey Satellite (TESS) observations were used as observational data. From the light curve solutions, it was concluded that all three systems are semi-detached binary star systems in which the secondary components fill their Roche lobes. The absolute parameters of the systems were also estimated. Accordingly, the photometric mass ratios of V495 Aur, V589 Aur and V478 Cam are found to be 0.251±0.035, 0.254±0.038 and 0.078±0.010, respectively. Upward parabolic change was observed in the O-C diagrams of all the systems considered. As a result of parabolic changes, we concluded that the orbital periods of the V495 Aur, V589 Aur and V478 Cam systems increased secularly with a rate of 0.050±0.010 s/year, 0.018±0.004 s/year and 0.070±0.015 s/year, respectively. The increases in orbital periods are explained by the dominant mass transfer mechanism from the secondary components to the primary components. In addition, the mass transfer rates between components and the rates of mass lost from the systems were estimated.Öğe First photometric study of two eclipsing binary star systems: V523 And and V543 And(Elsevier B.V., 2022) Öztürk, Oğuz; Erdem, AhmetDetailed photometric analysis of V523 And and V543 And from the Wide Angle Search for Planets survey is presented for the first time. It was found that while V523 And is a detached binary, V543 And is a semi-detached binary star system. The adopted masses and radii for the primary and secondary components are M1=0.77±0.08 M⊙, R1=0.87±0.08 R⊙ and M2=0.50±0.12 M⊙, R2=0.77±0.17 R⊙ for V523 And; and M1=1.59±0.16 M⊙, R1=1.46±0.09 R⊙ and M2=0.58±0.17 M⊙, R2=1.66±0.22 R⊙ for V543 And. Orbital period variations of the systems were analyzed using the O-C method. The O-C change of V523 And is discussed in terms of the magnetic activity cycle of one or both components and light travel time effect (LTTE) due to a third body in the system. Among these mechanisms, LTTE seems to be the most appropriate mechanism to explain the O-C variation of the system since the quadrupole moments of the primary and secondary components (ΔQ) were found to be in the order of 1049 g cm2. The O-C diagram of V543 And shows a downward parabolic trend, which suggests a secular period decrease with a rate of 0.080±0.012 s/year. The parabolic O-C variation of V543 And was interpreted in terms of the non-conservative mass transfer mechanism. According to this scenario, the range of possible values of the mass gain rate (Ṁ1) of the primary component of V543 And as well as the mass-loss rate (Ṁ) of the system were found to be 10−5–10−11 M⊙/year and 10−6–10−8 M⊙/year, respectively.Öğe Galaktik Düzlemdeki Yakın Yıldızların Yerel Kütle Yoğunluk Profillerinin İncelenmesi(Türk Astronomi Derneği, 2020) Öztürk, Oğuz; Erdem, Ahmet; Hobbs, DavidBu çalışmada Hipparcos Kataloğundan seçilen güneş komşuluğuna yakın yıldızların yerel kütle yoğunluğu tahmin edilmiştir. Katalogda yer alan yakın yıldızlar, seçim kriterlerine göre, 9 gruba ayrılmıştır. Kütle yoğunluğu, yıldızların ortalama uzay hızı dağılımının ($\sigma_w$) ve yıldızların sayı yoğunluğunun ($n(z)$) bir fonksiyonudur. Kütle yoğunluğunu tahmin etmek için ilk önce $\sigma_w^2$ değerleri hesaplanmıştır. Yıldızların sayı yoğunluğu, galaktik düzlemden olan uzaklıklarına ($z$) göre değişmektedir: $\ln n = \ln n(z)$. Her bir yıldız grubundan elde edilecek ``$\ln n$ - $z$'' diyagramı ile $\ln n(z)$ fonksiyonunun biçimi tahmin edilebilir ve yerel kütle yoğunluğunu tahmin etmek için kullanılabilir. Bu yöntemle; yerel kütle yoğunluk değer aralığı $0.0839-0.2157 M_\odot$ pc$^{-3}$ olarak bulunmuştur.Öğe Güney Yarımküre Gökyüzünden Seçilen Ayrık Çift Yıldızların Mutlak Parametreleri(2016) Sürgit, Derya; Erdem, Ahmet[Abstract Not Available]Öğe Güney Yarımküre'den V4396 Sgr ve BK Ind Ayrık Çift Yıldızlarının Tayfsal Gözlemleri(Türk Astronomi Derneği, 2020) Apak, Burcu; Sürgit, Derya; Erdem, Ahmet; Engelbrecht, Chris A.Bu çalışmada Güney Yarımküre gökyüzünden seçilen V4396 Sgr ve BK Ind ayrık çift yıldızlarının, Güney Afrika Astronomi Gözlemevi'nde elde edilen, ilk tayfsal gözlem verileri sunulmuştur. V4396 Sgr ve BK Ind ayrık çift yıldızlarının bileşenlerinin dikine hız eğrileri çapraz-eşleme (cross-correlation function) ve KOREL yöntemleri kullanılarak elde edilmiştir. Seçilen ayrık çift yıldızların tayfsal kütle oranları sırasıyla 0.88$\pm$0.03 ve 0.86$\pm$0.05 olarak belirlenmiş ve yörünge parametreleri hesaplanmıştır.Öğe Half-Sandwich Ru(II) Complexes Bearing 2-(2'-quinoly)benzimidazoles with Anticancer Activity(AMG Transcend Association, 2024) Erdem, Ahmet; Mutlu, Doğukan; Kılınçarslan, Rafet; Dayan, Osman; Arslan, ŞevkiIn this article, cytotoxic and apoptotic properties of previously synthesized and characterized four different half?sandwich ruthenium (II) complexes (C1-C4) with 2-(2¢-quinoly) benzimidazole frameworks (L1-L5) were described. These Ru (II) complexes (C1-C4) had strong cytotoxic activity towards the human glioblastoma (U373) cancer cell line with low toxicity to the non-cancerous human embryonic kidney (HEK293) cell line. Mechanistic studies revealed that all complexes caused apoptosis induction by activating caspases with upregulation of Bax and downregulation of Bcl-2. Our results indicate that ruthenium (II) complexes with 2-(2¢-quinoly) benzimidazole frameworks, especially C1 and C4, had a higher cytotoxic and apoptotic activity in human glioblastoma cells, and they should be further evaluated in detail for its anticancer properties as a new therapeutical strategy for glioblastoma. © 2024 by the authors.Öğe Klasik algollerde yörünge dönemi değişimlerinin çok yönlü incelenmesi(2012) Erdem, Ahmet; Çiçek, Caner; Demircan, Osman; Soydugan, Esin; Soydugan, Faruk[Abstract Not Available]Öğe Modelling of eclipsing binary systems with pulsating components and tertiary companions: BF Vel and RR Lep(Edp Sciences S A, 2024) Liakos, A.; Moriarty, D. J. W.; Erdem, Ahmet; West, J. F.; Evans, P.This research paper presents a comprehensive analysis of RR Lep and BF Vel, two southern short-period, semi-detached, oscillating Algols (oEA stars) that have been shown to be triple systems. We determined the spectral types of the primary components and calculated the radial velocities from spectra observed with the Australian National University's 2.3 m telescope and Wide Field Spectrograph. The spectra of the Na I D doublet confirmed the presence of tertiary components that were apparent in the broadening function analyses. During primary eclipses chromospherical activity in their secondary components was apparent in their H-alpha spectra; it was also apparent in the Na I D spectra of BF Vel with its almost complete annular eclipse. Ground-based telescopes were used for observations in several pass bands for photometric analyses. These observations were complemented by data from the Transiting Exoplanet Survey Satellite (TESS) mission, allowing us to model the light curves, followed by a detailed analysis of pulsations. Eclipse-timing variation (ETV) analyses of both systems were used to determine the most likely mechanisms modulating the orbital period. We found mass values of M-1 = 2.9 M-circle dot and M-2 = 0.75 M-circle dot for the components of RR Lep, along with M-1 = 1.93 M-circle dot and M-2 = 0.97 M-circle dot for those of BF Vel. By integrating information from photometry, spectroscopy, and ETV analysis, we found that tertiary components revolve around both systems. The primary star of RR Lep pulsates in 36 frequencies; of these, five were identified as independent modes, with the dominant one being 32.28 d(-1). The pulsating component of BF Vel oscillates in 37 frequencies, with the frequency 46.73 d(-1) revealed as the only independent mode. For both systems, a number of frequencies were found to be related to the orbital frequency. Their physical properties were compared with other oEA stars in mass-radius and Hertzsprung-Russell diagrams, while the pulsational properties of their delta Sct components were compared with currently known systems of this type within the orbital-pulsation period and logg-pulsation period diagrams.Öğe New photometric analysis of five exoplanets: CoRoT-2b, HAT-P-12b, TrES-2b, WASP-12b, and WASP-52b(Oxford Univ Press, 2019) Ozturk, Oguz; Erdem, AhmetWe report 12, 11, 9, 10, and 8 new transit light curves of CoRoT-2b, HAT-P-12b, TrES-2b, WASP-12b, and WASP-52b, respectively, obtained at Canakkale Onsekiz Mart University Observatory and TUBITAK National Observatory in 2016 and 2017. These transit light curves were analysed using JKTEBOP code. Planetary radii of CoRoT-2b, HAT-P-12b, TrES-2b, WASP-12b, and WASP-52b were found to be 1.41 +/- 0.06 R-J, 0.95 +/- 0.04 R-J, 1.23 +/- 0.07 R-J, 1.82 +/- 0.14 R-J, and 1.22 +/- 0.06 R-J, respectively. The transit ephemerides of these five exoplanets were updated and transit-timing variation analyses were also performed, using the maximum likelihood method (MLM). Most of the Lomb-Scargle (LS) periodograms of the timing residuals do not give any peak above false alarm probability levels. However, LS periodograms of CoRoT-2b show several significant peaks, and they are probably due to the magnetic activity of the host star and additional bodies in the system. On the other hand, the O-C diagram of WASP-12b displays a downward parabolic variation and indicates that the orbital period of the exoplanet is secularly decreasing. The mechanism responsible for this period decrease is discussed in terms of the orbital decay model. The tidal quality parameter Q(star)' of the host star WASP-12 was found to be (1.75 +/- 0.16) x10(5), which is close to theoretical predictions for sun-like stars. Classification of the five exoplanets based on their equilibrium temperatures and Safronov numbers was re-examined, comparing the sensitive data of 211 well-known exoplanets from the Exoplanet Data Explorer data base with ours.Öğe New photometric analysis of hot Jupiter: WASP-135b(Elsevier B.V., 2021) Öztürk, Oğuz; Erdem, AhmetWe report photometric follow-up observations of WASP-135b obtained using the 1.23-m telescope at Calar Alto Observatory and 1.00-m telescope at TÜBİTAK National Observatory during the 2017 and 2018 observational seasons. Eight new transit light curves of WASP-135b were analyzed with JKTEBOP code. The ratio of the planet radius to radius of host star, fractional radius of host star, and orbital inclination of WASP-135b were found to be 0.138 ± 0.002, 0.181 ± 0.008 and 82.44 ± 0.64 degrees, respectively. Planetary radius of WASP-135b was derived from transit parameters to be 1.075 ± 0.150 RJ. The transit ephemeris of WASP-135b was also updated using the maximum likelihood method (MLM). 165 well-known hot Jupiters (HJs) were selected from the Exoplanet Data Explorer database and the classification of these HJs together with WASP-135b, based on their equilibrium temperatures and Safronov numbers, is discussed.Öğe New Spectroscopic Solution of the Eclipsing Binary HX Vel A(Astronomical Soc Pacific, 2015) Surgit, Derya; Erdem, Ahmet; Ozkardes, Burcu; Butland, Roger; Budding, EdwinWe present a preliminary analysis of new spectroscopic observations of the southern binary HX Vel A. High-resolution spectroscopic observations were made at the Mt. John University Observatory in 2014. Radial velocities for HX Vel A were determined from the Gaussian profile-fitting method. The Keplerian radial velocity model gives the close binary mass ratio as 0.57 +/- 0.06. The resulting orbital elements are ai sin i = 0.0086 +/- 0.0003 au, a(2) sin i = 0.0151 +/- 0.0003 au, M-1 sin(3) i = 0.887 +/- 0.046 M-circle dot, and M-2 sin(3) i = 0.504 +/- 0.032 M-circle dot.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).
