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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 Düşük kütle oranlı iki değen çift yıldızın yörünge dönemi değişimlerinin incelenmesi: V404 Peg ve V619 Peg(2020) Özkardeş, BurcuBu çalışmada düşük kütle oranına sahip iki aşırı değen çift yıldızın yörünge dönemi değişimleri, detaylı olarak ilk kez incelenmiştir. Hedef sistemlerin dönem analizleri, veri tabanlarından ve literatür yayınlarından alınan minimum ışık zamanları kullanılarak O-C yöntemine göre yapılmıştır. V404 Peg’in O-C diyagramının aşağı parabol şeklinde bir yapı gösterdiği ve döneminin 9.3(5)x10-2 s/yıl oranında azaldığı bulunmuştur. V619 Peg’in O-C diyagramının parabol+çevrimsel yapı gösterdiği ve döneminin 6.3(1)x10-2 s/yıl oranında arttığı bulunmuş; çevrimsel dönem değişimi, olası üçüncü cisme ve Applegate mekanizmasına göre tartışılmıştır.Öğe ... Lyrae türü örten çift yıldız LL Com: Işık eğrisi analizi ve yörünge dönemi değişimi(2017) Özalp, Gökçe Zeynep; Özkardeş, BurcuBu çalışmada, ilk kez, ? Lyrae türü (EB) olarak sınıflandırılmış örten çift yıldız LL Com (GSC 0253500670; V = 12m.39; P = 0.40692 gün)'un ıSistemin, SuperWASP arşivinde yer alan fotometrik gözlem verisi Wilson - Devinney (W-D) yöntemiyle analiz edilerek fotometrik kütle oranı belirlenmiş ve buradan bileşen yıldızların tahmini mutlak parametreleri hesaplanmıelde edilen tutulma zamanları kullanılarak O-C analizi yapılmıolan fiziksel mekanizmalar tartışılmıştırÖğe New spectroscopic observations of the semidetached binary V375 Cas(Slovak Academy Sciences Astronomical Inst, 2025) Özkardeş, Burcu; Bakış, H.We present the low resolution (R similar to 5099) spectroscopy of the eclipsing binary V375 Cas (TIC 326630342) in this study. The low resolution spectroscopic observations of the system were made at the TUBITAK National Observatory using a TFOSC spectrograph in 2020 and 2021. For measuring the radial velocities of both components of the eclipsing binary Gaussian fitting method was used. According to Keplerian orbital solution the spectroscopic mass ratio of the close binary was determined as 0.626 +/- 0.098. The best fitting orbital elements are a1sin i = 0.0243 +/- 0.0018 au, a2sin i= 0.0351 +/- 0.0018 au, M1sin3 i = 7.06 +/- 0.87 Mo and M2sin3 i = 4.42 +/- 0.75 Mo.Öğe Spectroscopic and photometric investigation of some potentially chemically peculiar δ Scuti stars(Oxford Univ Press, 2025) Kahraman Aliçavuş, Filiz; Aliçavuş, Fahri; Özkardeş, Burcu; Çelik, EdaInvestigating chemically peculiar pulsating stars is crucial for understanding the pulsation driving mechanism in detail. To reveal the true peculiarity properties of stars, detailed spectroscopic analysis is essential. Therefore, in this study, we focused on delta Scuti stars previously identified as chemically peculiar but which needed comprehensive updated spectroscopic analysis to uncover their chemical abundance structure. We selected 10 targets which have publicly available high-resolution spectroscopic and photometric data. Performing spectral analyses, we determined the spectral classification, atmospheric parameters, and detailed chemical abundance distributions of the selected stars. The pulsation properties were also analyzed using TESS data, and pulsation modes for the highest amplitude pulsation frequencies were derived. We estimated the masses and ages of the targets using the evolutionary tracks and isochrones. As a result of our study, we show that only three targets exhibit chemical peculiarity: AU Scl and FG Eri as metallic A (Am) stars, and HZ Vel as a lambda Bootis. However, others were found to be chemically normal stars. This study show us the importance of chemical abundance analysis in the classification of chemical peculiar stars.Öğe Spectroscopic Study of the Early-Type Binary HX Vel A(Cambridge Univ Press, 2012) Özkardeş, Burcu; Sürgit, Derya; Erdem, Ahmet; Budding, Edwin; Soydugan, Faruk; Demircan, OsmanThis paper presents high resolution spectroscopy of the HX Vel (IDS 08390-4744 AB) multiple system. New spectroscopic observations of the system were made at Mt. John University Observatory in 2007 and 2008. Radial velocities of both components of HX Vel A were measured using gaussian fitting. The spectroscopic mass ratio of the close binary was determined as 0.599 +/- 0.052, according to a Keplerian orbital solution. The resulting orbital elements are a(1)sini=0.0098 +/- 0.0003 AU, a(2)sini=0.0164 +/- 0.0003 AU, M(1)sin(3)i=1.19 +/- 0.07 M-circle dot and M(2)sin(3)i=0.71 +/- 0.04 M-circle dot.Öğe V355 And: a neglected detached binary in a multiple star system(Astronomical Institute, Slovak Academy of Sciences, 2021) Özkardeş, BurcuThe analysis of light curves (from TESS, ASAS-SN and KWS databases) of the eclipsing binary V355 And is presented for the first time. The O-C diagram was constructed using all available times of minimum light together with the ones determined in this study, and the revised ephemeris was obtained. The final photometric model describes V355 And as an Algollike type binary star with a detached configuration. Absolute parameters of the components of the system were found to be: masses, M1=1.56 ± 0.01 M⊙ and M2=1.38 ± 0.01 M⊙, radii, R1=1.70 ± 0.03 R⊙ and R2=1.38 ± 0.03 R⊙, and effective temperatures, T1=6650 ± 200 K and T2=6235 ± 201 K. Considering interstellar extinction the distance to V355 And was computed as 117 ± 7 pc. The evolutionary state of V355 And is also discussed using the Geneva stellar models.Öğe W UMa türü güneş benzeri örten çift yıldızların genel özellikleri(Çanakkale Onsekiz Mart Üniversitesi, 2004) Özkardeş, Burcu; Erdem, AhmetBu çalışmada, W UMa türü güneş benzeri örten çift yıldızların genel özellikleri hakkında, konu ile ilgili literatür taranarak, elde edinilen bilgiler verilmiştir. Uygulama kısmında, bir örnek olarak seçilen, W UMa türünden V829 Her yıldızı, 2002-2003 yıllarında ÇOMÜ Ulupınar Astrofizik Gözlemevi'nde gözlenerek ışık eğrileri elde edilmiş ve Wilson-Devinney yönteminin 1992 versiyonu kullanılarak ışık eğrileri çözülmüş ve sonuçlar tartışılmıştır. Anahtar kelimeler: Astrofizik - örten çift yıldızlar - W UMa türünden örten çift yıldızlar - V829 Her
