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Öğe A study of variability of the marginal Am star HD 176843 observed in the Kepler field(Elsevier Science Bv, 2019) Ulusoy, C.; Stateva, I.; Ulas, B.; Alicavus, F.; Iliev, I. Kh.; Napetova, M.; Kaygan, E.We present results of a study of variability of the marginal Am star HD 176843 observed in the Kepler field. Kepler photometry and ground-based spectroscopy are used to investigate the light variations of the star. HD 176843 is classified as a marginal Am star that shows delta Sct type pulsations. From an analysis of the Kepler time series, we find that the light curve of HD 176843 is dominated by three modes with frequencies f(1) = 0.1145, f(2) = 0.0162 and ,f(3) = 0.1078 d(-1). The amplitude of the radial velocity variations of about 10 km/s is much more than the radial velocity errors and allows us to conclude clear radial velocity variations. Using the radial velocity data and the adopted spectra, the orbital solution of HD 176843 is also obtained with an orbital period of 34.14 days. However, the available photometric data show no significant evidence for any possible motion in the binary system.Öğe Candidate Eclipsing Binary Systems with a ? Scuti Star in Northern TESS Field(Natl Astronomical Observatories, Chin Acad Sciences, 2022) Alicavus, F. Kahraman; Gumus, D.; Kirmizitas, O.; Ekinci, O.; Cavus, S.; Kaya, Y. T.; Alicavus, F.The existence of pulsating stars in eclipsing binaries has been known for decades. These types of objects are extremely valuable systems for astronomical studies as they exhibit both eclipse and pulsation variations. The eclipsing binaries are the only way to directly measure the mass and radius of stars with a good accuracy (<= 1%), while the pulsations are a unique way to probe the stellar interior via oscillation frequencies. There are different types of pulsating stars existing in eclipsing binaries. One of them is the delta Scuti variables. Currently, the known number of delta Scuti stars in eclipsing binaries is around 90 according to the latest catalog of these variables. An increasing number of these kinds of variables is important to understand the stellar structure, evolution and the effect of binarity on the pulsations. Therefore, in this study, we focus on discovering new eclipsing binaries with delta Scuti component(s). We searched within the northern Transiting Exoplanet Survey Satellite (TESS) field with a visual inspection by following some criteria such as light curve shape, the existence of pulsation like variations in the out-of-eclipse light curve and the T (eff) values of the targets. As a result of these criteria, we discovered some targets. The orbital variations were first removed from the TESS light curves and frequency analysis was performed on the residuals. The luminosity, and absolute and bolometric magnitudes of the targets were calculated as well. To find how much of these parameters represent the primary (more luminous) binary component, we also computed the flux density ratio of the systems by utilizing the area of the eclipses. In addition, the positions of the systems in the H-R diagram were examined considering the flux density ratios. As a consequence of the investigation, we defined 38 candidate delta Scuti stars and also one Maia variable in eclipsing binary systems.Öğe Detailed spectroscopic and photometric study of three detached eclipsing binaries(Oxford Univ Press, 2019) Alicavus, F. Kahraman; Alicavus, F.Detached eclipsing binaries are remarkable systems to provide accurate fundamental stellar parameters. Fundamental stellar parameters and the metallicity values of stellar systems are needed to deeply understand stellar evolution and formation. In this study, we focus on the detailed spectroscopic and photometric studies of three detached eclipsing binary systems, V372And, V2080Cyg, and CFLyn, to obtain their accurate stellar and atmospheric parameters, and chemical compositions. An analysis of light and radial velocity curves was carried out to derive the orbital and stellar parameters. The disentangled spectra of component stars were obtained for the spectroscopic analysis. Final T-eff, logg, xi, vsiniparameters and the element abundances of component stars were derived by using the spectrum synthesis method. The fundamental stellar parameters were determined with a high certainty for V372And, V2080Cyg (similar to 1-2percent) and with accuracy for CFLyn (similar to 2-6percent). The evolutionary status of the systems was examined and their ages were obtained. It was found that the component stars of V2080Cyg have similar iron abundances, slightly lower than the solar iron abundance. Additionally, we show that the primary component of CFLyn exhibits a non-spherical shape with an 80percent Roche lobe filling factor. It could be estimated that CFLyn will start its first Roche overflow in the next 0.02Gyr.Öğe Discovery of delta Scuti variables in eclipsing binary systems II. Southern TESS field search(Oxford Univ Press, 2023) Alicavus, F. Kahraman; Coban, C. G.; Celik, E.; Dogan, D. S.; Ekinci, O.; Alicavus, F.The 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 & delta; Scuti variables. & delta; 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 & delta; Scuti stars in EBs. We produced an algorithm to search for detached and semidetached EBs considering three steps: the orbital period (P-orb)'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 & delta; Scuti-type oscillations, the binary variation was removed from the light curve, and residuals were analysed. Consequently, we identified 42 & delta; Scuti candidates in EBs. The P-orb, L, and M-V 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 Empirical bolometric correction coefficients for nearby main-sequence stars in the Gaia era(Oxford Univ Press, 2020) Eker, Z.; Soydugan, Faruk; Bilir, S.; Bakis, V; Alicavus, F.; Ozer, S.; Aslan, G.Nearby detached double-lined eclipsing binaries with most accurate data were studied and 290 systems were found with at least one main-sequence component having a metallicity of 0.008 <= Z <= 0.040. Stellar parameters, light ratios, Gaia Data Release 2 trigonometric parallaxes, extinctions and/or reddening were investigated and only 206 systems were selected as eligible to calculate empirical bolometric corrections. NASA/IPAC Galactic dustmaps were the main source of extinctions. Unreliable extinctions at low Galactic latitudes vertical bar b vertical bar <= 5 degrees were replaced with individual determinations, if they exist in the literature, else associated systems were discarded. The main-sequence stars of te remaining systems were used to calculate the bolometric corrections (BCs) and to calibrate the BC-T-eff relation, which is valid in the range 3100-36 000 K. De-reddened (B - V)(0) colours, on the other hand, allowed us to calibrate two intrinsic colour-effective temperature relations; the linear one is valid for T-eff > 10 000 K, while the quadratic relation is valid for T-eff < 10 000 K; that is, both are valid in the same temperature range in which the BC-Teff relation is valid. New BCs computed from Teff and other astrophysical parameters are tabulated, 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.; Dogru, S.; Alicavus, F.This 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 Oscillating classical Algol-type binary XZ Aql(Elsevier Science Bv, 2016) Soydugan, Esin; Soydugan, Faruk; Alicavus, F.; Erdem, A.New CCD photometric observations of the neglected classical Algol-type binary XZ Aql were obtained over 53 nights during the observing season of 2011. Photometric elements were determined from analysis of multi-colour light curves. This first comprehensive investigation of the system revealed that the system is in semi-detached configuration with a mass ratio of 0.204 +/- 0.02 and a filling ratio of the primary of 50%. Absolute parameters of components and distance of the system were estimated. Based on all eclipse timings, the (O-C) variation indicating orbital period behaviour can be represented by a periodic term superimposed on an upward parabola. Secular increase with a rate of dP/dt = 7.82 x 10(-7) day yr(-1) is due to mass transfer from the less massive to more massive component. A possible third body around the eclipsing pair and also magnetic activity of the late-type component were used to interpret cyclic variation in the orbital period. Short-period light variations out-of-eclipse imply that XZ Aql is an oscillating eclipsing binary with a pulsating, mass gainer component. From Fourier analysis, two frequencies were detected as 30.6325 c/d and 34.5009 c/d. Pulsational properties and estimated absolute parameters indicate that the primary component may be classified as a delta Scuti type variable. (C) 2015 Elsevier B.V. All rights reserved.Öğe Period studies of classical Algol-type binaries II: UX Leo, RW Mon, EQ Ori, XZ UMa and AX Vul(Elsevier Science Bv, 2011) Soydugan, Faruk; Erdem, A.; Dogru, S. S.; Alicavus, F.; Soydugan, Esin; Cicek, C.; Demircan, O.This study presents an investigation of the orbital period variations of five Algol type binaries, UX Leo, RW Mon, EQ Ori, XZ UMa and AX Vul based on all available minima times. The O-C diagrams of all systems exhibit a periodic variation superimposed on a downward parabolic segment. The mass loss due to magnetic braking effect in the cooler components is assumed to account for the parabolic variation with a downward shape, while it is suggested that the light-time effect (LITE) due to an unseen component around the eclipsing binaries explains the tilted sinusoidal changes in their O-C diagrams. The orbital period decrease rates for the systems are estimated as approximately between about 0.7 and 2.5 s per century. It is clearly seen that mass loss effect is more dominant than the expected mass transfer for classical Algols in this study. The minimum mass of the probable third bodies around the eclipsing pairs was calculated to be <= 0.5 M-circle dot, except for UX Leo, in which it was estimated to be approximately 0.9 M-circle dot. In order to search for third lights in the light curves of five systems, the V-light curves of the systems were analyzed and their physical and photometric parameters were determined. For UX Leo, a significant third light contribution was determined. We found a very small third light that can be tested using multi-color light curves, for RW Mon, EQ On and XZ UMa, while a third light for AX Vul could not be exposed. (C) 2010 Elsevier B.V. All rights reserved.Öğe The detached eclipsing binary TX Her revisited(Elsevier, 2011) Erdem, A.; Alicavus, F.; Soydugan, Faruk; Dogru, S. S.; Soydugan, Esin; Cicek, C.; Demircan, O.This paper presents new CCD Bessell BVRI light curves and photometric analysis of the Algol-type binary star TX Her. The CCD observations were carried out at Canakkale Onsekiz Mart University Observatory in 2010. New BVRI light curves from this study and radial velocity curves from Popper (1970) were solved simultaneously using modern light and radial velocity curves synthesis methods. The general results show that TX Her is a well-detached eclipsing binary, however, both component stars fill at least half of their Roche lobes. A significant third light contribution to the total light of the system could not be determined. Using O-C residuals formed by the updated minima times, an orbital period study of the system was performed. It was confirmed that the tilted sinusoidal O-C variation corresponds to an apparent period variation caused by the light travel time effect due to an unseen third body. The following absolute parameters of the components were derived: M-1 = 1.62 +/- 0.04 M-circle dot, M-2 = 1.45 +/- 0.03 M-circle dot, R-1 = 1.69 +/- 0.03 R-circle dot, R-2 = 1.43 +/- 0.03 R-circle dot, L-1 = 8.21 +/- 0.90 L-circle dot, and L-2 = 3.64 +/- 0.60 L-circle dot. The distance to TX Her was calculated as 155 +/- 10 pc, taking into account interstellar extinction. The position of the components of TX Her in the HR diagram are also discussed. The components are young stars with an age of similar to 500 Myr. (C) 2011 Elsevier B.V. All rights reserved.Öğe The first light curve solutions and period changes of EW Psc and HN Psc(Elsevier, 2020) Davoudi, F.; Poro, A.; Alicavus, F.; Rahimi, J.; Lashgari, E.; Ghanbarzadehchaleshtori, M.; Boudesh, A.The first light curve solutions of the stars EW and HN in the Pisces constellation are presented. Photometry, and its' periodic changes are calculated and discussed. The analysis of the O-C diagram is done by the MCMC approach in the OCFit code and a new ephemeris is provided for the two binary systems. The results show that EW Psc is a near contact eclipsing binary system with a photometric mass ratio q = 0.587, and the fillout factor is -0.034 and -0.018 for the primary and secondary components, respectively. The solution results also show that the system HN Psc is a weak-contact W UMa eclipsing binary with a photometric mass ratio q = 0.853, and with a fillout factor of 5.6%. The light curves solutions required a cold spot to account for the O'Connell effect.Öğe TOWARD UNDERSTANDING THE NATURE OF THE YOUNG DETACHED BINARY SYSTEM HD 350731(Iop Publishing Ltd, 2015) Soydugan, Faruk; Alicavus, F.; Bilir, S.; Soydugan, Esin; Puskullu, C.; Senyuz, T.The young binary system HD 350731 is a noteworthy laboratory for studying early-type binaries with similar components. We present here an analysis of differential multi-color photometric and spectroscopic observations of the double-lined detached system. Accurate absolute parameters were determined for the first time from a simultaneous solution of the light and radial velocity curves. HD 350731 consists of two B8V-type components with masses and radii, respectively, of M-1= 2.91 +/- 0.13 M-circle dot, M-2= 2.80 +/- 0.14 M-circle dot, R-1= 2.11 +/- 0.05 R-circle dot, and R-2= 2.07 +/- 0.05 R-circle dot. The effective temperatures were determined based on analysis of disentangled spectra of the components and were derived to be 12,000 +/- 250 and 11,830 +/- 300 K for the primary and secondary components, respectively. The measured projected rotational velocities, 69.2 +/- 1.5 km s(-1) for the primary and 70.1 +/- 1.7 km s-1 for the secondary, were found to be closer to the pseudo-synchronous velocities of the components. Comparison with evolutionary models suggests an age of 120 +/- 35 Myr. Kinematic analysis of the unevolved binary system HD 350731 revealed that it belongs to the young thin-disk population of the Galaxy.
