Yazar "Bilir, Selçuk" seçeneğine göre listele
Listeleniyor 1 - 13 / 13
Sayfa Başına Sonuç
Sıralama seçenekleri
Öğe Aktif Kromosferli Çift Yıldızların Kinematik Yaş ve Dinamik Davranışları(Türk Astronomi Derneği, 2020) Tüysüz, Mehmet; Soydugan, Faruk; Bilir, Selçuk; Demircan, Osman; Eker, ZekiGeri tayf türünden bileşen(ler)e sahip ve kromosferik aktivite belirteci gösteren ayrık ya da yarı-ayrık sistemler aktif kromosferli çift yıldızlar (CAB) olarak bilinir. Bu çalışmada kütle, yarıçap ve sıcaklık değerleri bilinen ve bileşenleri anakol yıldızlarından oluşan Güneş civarındaki CAB'lar kinematik özellikleri dikkate alınarak mercek altına alındı. Örnekteki sistemler, açısal momentumlarına göre alt gruplara ayrılarak ortalama kinematik yaşları hesaplandı. Grupların ortalama kinematik yaşlarıyla, ortalama açısal momentum, ortalama kütle ve ortalama dönem değişimleri incelendi. Ayrıca aktif ve aktif olmayan geri tayf türüne sahip (F veya daha geri) ayrık ve anakol bileşenli sistemlerin kinematik yaş ile dinamik davranışları birlikte ele alınarak, aktivitenin dinamik evrim üzerine etkileri tartışıldı.Öğe Çift Yıldızların Kinematik ve Dinamik Özellikleri: Açısal Momentum ve Yörünge Dönemi Evrimi(Türk Astronomi Derneği, 2020) Soydugan, Faruk; Bilir, Selçuk; Soydugan, Esin; Eker, Zeki; Demircan, Osman; Tüysüz, MehmetBu çalışmada, yaklaşık 1200 örten çift yıldızın temel parametrelerini içeren veri tabanları oluşturulmuş ve ek olarak 29 örten çift yıldızın analizleri yapılmış ve veri tabanları zenginleştirilmiştir. Verileri toplanan tüm örten çift yıldızların temel parametrelerinin dağılımları incelenmiş ve sistemlerin anakol bileşenleri için kütle-ışıtma bağıntıları üretilmiştir. Ayrık çift yıldızlar için farklı kütle aralıklarında dört ayrı kütle-ışıtma bağıntısı belirlenmiştir. Farklı tür çift yıldız grupları için kinematik analizler yapılarak alt-grup yaşları belirlenmiştir.Yapılan dinamik analizler sonucunda, türler arasındaki geçişlerin olabileceği görülmüştür. Oluşturulan büyük ölçekli veri tabanları yanında, çift yıldızların temel parametre dağılım ve ilişkileriyle özellikle toplam kütle, yörünge açısal momentumu ve yörünge döneminin yaş ile değişimi incelenerek tartışılmıştır.Öğe Delta scuti bileşenli örten çift sistemlerin zonklama özelliklerinin belirlenmesi(2011) Soydugan, Esin; Soydugan, Faruk; Bilir, Selçuk; Bakış, Volkan; Demircan, Osman[Abstract Not Available]Öğe Fundamentals of Stars: A Critical Look at Mass-Luminosity Relations and Beyond(Istanbul University, 2024) Eker, Zeki; Soydugan, Faruk; Bilir, SelçukDevelopments on various relations among stellar variables such as the main sequence empirical mass-luminosity (MLR), massradius (MRR) and mass-effective temperature (MTR) relations were reviewed. Conceptual changes in their understanding and usages were discussed. After its discovery, MLR was treated as one of the fundamental secrets of the cosmos. Differences between fundamental laws and statistical relations were used to understand long-term developments of MLR, MRR and MTR. Developments show a break point, initiated by Andersen (1991), in the line of progress. Before the break when reliable data were limited, MLR and MRR were calibrated using M, L, and R of binary components of all kinds visual, spectroscopic, and eclipsing for two purposes: i) to obtain mean mass, mean luminosity, and mean radius, ii) to estimate M and R of single stars. By the time of the break, the number of solutions from detached double-lined eclipsing binaries (DDEB) giving accurate M and R within a few percent levels are increased. Parameters from very close, semi-detached, and contact binaries were excluded for refinement, however, MLR and MRR diagrams were found insufficient to derive MLR and MRR functions because the dispersions are not only due to random observational errors but also due to chemical composition and age differences. Then, a new trend was adopted by replacing classical MLR and MRR with empirical M and R predicting relations. Thus, the purpose one was suppressed also because the new trend found a fruitful application in determining M and R of exoplanet hosting single stars.Öğe Galaktik OB Oymaklarının Evrimi ve Kinematiği(Türk Astronomi Derneği, 2020) Bakış, Volkan; Bilir, Selçuk; Demircan, OsmanYıldız oluşum bölgeleri yıldız evriminin ilk basamaklarını ve bir çok astrofiziksel fenomeni daha iyi anlamamız açısından yegane yerlerdir. Ancak bu bölgelerdeki yoğun gaz ve toz küçük kütleli yıldızların gözlenmesini zorlaştırmaktadır. Sadece ön tayf türünden yıldızlar yüksek ışınım basınından dolayı etrafındaki gazı dağıtmışlar ve kendilerini açığa çıkarmışlardır. Bu çalışmada yıldız oluşum bölgelerinin kinematik ve evrimsel parametrelerinin içinde bulunan çift ve çoklu sistemlerin analizleri ile nasıl belirlendiği kullanılan yöntemler ile anlatılmıştır.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 Kataklismik Değişenlerin Kinematiği(Türk Astronomi Derneği, 2020) Özdönmez, Aykut; Bilir, Selçuk; Ak, Tansel; Soydugan, Faruk; Soydugan, Esin; Püsküllü, Çağlar; Ak, SerapKataklismik değişenlerin (KD) kinematik özellikleri; güncel paralaksları, öz hareketleri ve kütle merkezinin hızlarından ($\gamma$) hesaplanan uzay hızları kullanılarak popülasyon türlerine ve yörünge dönemine göre incelenmiş ve sonuçlar standart evrim kuramının öngörüleri ile karşılaştırılmıştır. Oluşturulan katalogdaki 216 KD’nin hız dispersiyonu 53.7 km/s ve ortalama kinematik yaşı 5.29 Gyıl’dır. Popülasyon türleri Galaktik yörüngelerinden belirlenen KD örneğinin %94’ü Galaksimizin ince disk bileşeninin üyesidir. Dönem boşluğunun altında ve üstündeki manyetik olmayan ince disk KD’lerinin ortalama yaşları sırasıyla 3.40 ve 3.90 Gyıl, dispersiyonları 24.95 ve 26.60 km/s dir. KD’ler yörünge dönemine göre incelendiğinde ise, ortalama kinematik yaşın kısa yörünge dönemlerine doğru arttığı bulunmuştur.Öğe Kinematics of Cataclysmic Variables in the Solar Neighborhood in the Gaia Era(Iop Publishing Ltd, 2025) Canbay, Remziye; Ak, Tansel; Bilir, Selçuk; Soydugan, Faruk; Eker, ZekiUsing high-precision astrometric data from Gaia DR3 and updated systemic velocities from the literature, the kinematical properties of cataclysmic variables (CVs) were investigated. By constraining the data according to the total space velocity error and Galactic population class, a reliable sample of data was obtained. Nonmagnetic CVs located in the thin disk have been found to have a total space velocity dispersion of sigma(nu) = 46.33 +/- 4.23 km s(-1), indicating that the thin disk CVs with a mean kinematical age of tau = 3.95 +/- 0.75 Gyr are much younger than the local thin disk of the Galaxy with tau similar to 6-9 Gyr. Total space velocity dispersions of nonmagnetic CVs belonging to the thin disk component of the Galaxy were found to be sigma(nu) = 47.67 +/- 3.94 and sigma(nu) = 44.43 +/- 4.33 km s(-1) for the systems below and above the orbital period gap, respectively, corresponding to kinematical ages of tau = 4.19 +/- 0.71 and tau = 3.61 +/- 0.74 Gyr. gamma velocity dispersions of the thin disk CVs below and above the gap were obtained sigma(gamma) = 27.52 +/- 2.28 and sigma(gamma) = 25.65 +/- 2.44 km s(-1), respectively. This study also shows that the orbital period is decreasing with increasing age, as expected from the standard theory. The age-orbital period relation for nonmagnetic thin disk CVs was obtained as dP/dt = -2.09(+/- 0.22) x 10(-5) s yr(-1). However, a significant difference could not be found between the gamma velocity dispersions of the systems below and above the gap, which were calculated to be sigma(gamma) = 27.52 +/- 2.28 and sigma(gamma) = 25.65 +/- 2.44 km s(-1), respectively.Öğe On the zero point constant of the bolometric correction scale(Oxford University Press, 2021) Eker, Zeki; Bakiş, Volkan; Soydugan, Faruk; Bilir, SelçukArbitrariness attributed to the zero-point constant of the V-band bolometric corrections (BCV) and its relation to ‘bolometric magnitude of a star ought to be brighter than its visual magnitude’ and ‘bolometric corrections must always be negative’ was investigated. The falsehood of the second assertion became noticeable to us after IAU 2015 General Assembly Resolution B2, where the zero-point constant of bolometric magnitude scale was decided to have a definite value CBol(W) = 71.197 425 ... . Since the zero-point constant of the BCV scale could be written as C2 = CBol − CV, where CV is the zero-point constant of the visual magnitudes in the basic definition BCV = MBol − MV = mbol − mV, and CBol > CV, the zero-point constant (C2) of the BCV scale cannot be arbitrary anymore; rather, it must be a definite positive number obtained from the two definite positive numbers. The two conditions C2 > 0 and 0 < BCV < C2 are also sufficient for LV < L, a similar case to negative BCV numbers, which means that ‘bolometric corrections are not always negative’. In sum it becomes apparent that the first assertion is misleading causing one to understand bolometric corrections must always be negative, which is not necessarily true.Öğe Outputs and Effects of Astronomy and Astrophysics Research in Turkey - I: 2020 Publications(Türk Astronomi Derneği, 2022) Bilir, Selçuk; Göğüş, Ersin; Soydugan, Faruk; Dursun, Deniz Cennet; Öztürk, Burçin Tanık; Özel, CemIn this first study, which is aimed to regularly examine the annual publication performances of the Turkish institutions conducting research in the fields of astronomy and astrophysics. The time frame of 2020 was selected for this investigation and 135 scientific articles published by researchers from Turkey in journals included in Science Citation Index Expanded were examined in detail. Results of our investigations reveal the 2020 scientific performance of Turkish institutions, as well as their national and international cooperation trends. Moreover, the role of research support in publication performances could also be evaluated. Similar investigations in the future could address annual comparative variations in performance indications and cooperation trendsÖğe Photometric and Kinematic Studies of Open Clusters Ruprecht 1 and Ruprecht 171(Wiley-V C H Verlag Gmbh, 2024) Çakmak, Hikmet; Yontan, Talar; Bilir, Selçuk; Banks, Timothy S.; Michel, Raul; Soydugan, Esin; Koç, SelizThis study outlines a detailed investigation using CCD UBV and Gaia DR3 data sets of the two open clusters Ruprecht 1 (Rup-1) and Ruprecht 171 (Rup-171). Fundamental astrophysical parameters such as color excesses, photometric metallicities, ages, and isochrone distances were based on UBV-data analyses, whereas membership probability calculations, structural and astrophysical parameters, as well as the kinematic analyses were based on Gaia DR3-data. We identified 74 and 596 stars as the most probable cluster members with membership probabilities over 50% for Rup-1 and Rup-171, respectively. The color excesses E(B-V) were obtained as 0.166 +/- 0.022 and 0.301 +/- 0.027 mag for Rup-1 and Rup-171, respectively. Photometric metallicity analyses were performed by considering F-G type main-sequence member stars and found to be [Fe/H]=-0.09 +/- 0.16 and [Fe/H]=-0.20 +/- 0.20 dex for Rup-1 and Rup-171, respectively. Ages and distances were based on both UBV and Gaia-data analyses; according to isochrone-fitting these values were estimated to be t=580 +/- 60 Myr, d=1469 +/- 57 pc for Rup-1 and t=2700 +/- 200 Myr, d=1509 +/- 69 pc for Rup-171. The present-day mass function slope of Rup-1 was estimated as 1.26 +/- 0.32 and Rup-171 as 1.53 +/- 1.49. Galactic orbit integration analyses showed that both of the clusters might be formed outside the solar circle.Öğe Standard stellar luminosities: what are typical and limiting accuracies in the era after Gaia?(Oxford University Press, 2021) Eker, Zeki; Soydugan, Faruk; Bilir, Selçuk; Bakiş, VolkanMethods of obtaining stellar luminosities (L) have been revised and a new concept, standard stellar luminosity, has been defined. In this paper, we study three methods: (i) a direct method from radii and effective temperatures; (ii) a method using a mass–luminosity relation (MLR); and (iii) a method requiring a bolometric correction. If the unique bolometric correction (BC) of a star extracted from a flux ratio (fV/fBol) obtained from the observed spectrum with sufficient spectral coverage and resolution are used, the third method is estimated to provide an uncertainty (ΔL/L) typically at a low percentage, which could be as accurate as 1 per cent, perhaps more. The typical and limiting uncertainties of the predicted L of the three methods were compared. The secondary methods, which require either a pre-determined non-unique BC or MLR, were found to provide less accurate luminosities than the direct method, which could provide stellar luminosities with a typical accuracy of 8.2–12.2 per cent while its estimated limiting accuracy is 2.5 per cent.Öğe Updated absolute parameters and kinematics of IS CMa(Wiley-V C H Verlag Gmbh, 2024) Evcil, Serkan; Adalalı, Simge; Alan, Neslihan; Canbay, Remziye; Bilir, SelçukEclipsing binary systems are significant objects for astrophysics in that direct observations can determine the fundamental parameters of stars. In this study, we precisely determined the fundamental parameters of the binary component stars obtained by simultaneous analysis of radial velocities and the TESS light curve using the Wilson and Devinney code. Following the analysis, the masses and radii of the primary and secondary components were determined as M1 = 1.58 +/- 0.01M(circle dot), M-2 = 0.48 +/- 0.02M(circle dot), and R-1 = 1.93 +/- 0.01R(circle dot), R-2 = 1.14 +/- 0.01R(circle dot), respectively. Furthermore, the distance of IS CMa is calculated as 92.7 +/- 6.5$$ 92.7\pm 6.5 $$ pc. On the basis of the analysis of the mid-eclipse times, it was found that the variation in the orbital period is represented by an upward parabola. It has an increasing rate of dP/dt = 1.09 x 10(-7). Using PARSEC stellar evolutionary tracks and isochrones with solar metallicity estimated the age of IS CMa as 1.3 +/- 0.1 Gyr. Kinematic and Galactic orbital parameters of IS CMa were obtained from the astrometric and spectroscopic data of the system. The Galactic orbit analysis reveals that IS CMa formed inside the solar circle and it is a member of the young thin-disc population.
