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Absolute parameters of young stars: NO Puppis
(Cambridge Univ Press, 2025) Erdem, Ahmet; Bakış, Volkan; Southworth, John; Rhodes, Michael; Kahraman Alicavus, Filiz; Budding, Edwin; Blackford, Mark G.; Kahraman Aliçavuş, Filiz
The southern early-type, young, eccentric-orbit eclipsing binary NO Puppis forms the A component of the multiple star Gaia DR3 5528147999779517568. The B component is an astrometric binary now at a separation of about 8.1 arcsec. There may be other fainter stars in this interesting but complex stellar system. We have combined several lines of evidence, including TESS data from four sectors, new ground-based BVR photometry, HARPS (ESO) and HERCULES (UCMJO) high-resolution spectra and astrometry of NO Pup. We derive a revised set of absolute parameters with increased precision. Alternative optimal curve-fitting programs were used in the analysis, allowing a wider view of modelling and parameter uncertainties. The main parameters are as follows: 𝑀𝐴⁢𝑎 =3.58 ±0.11, 𝑀𝐴⁢𝑏 =1.68 ±0.09 (M⊙); 𝑅𝐴⁢𝑎 =2.17 ±0.03, 𝑅𝐴⁢𝑏 =1.51 ±0.06 (R⊙), and 𝑇e⁢Aa =13 300 ±500, 𝑇e⁢Ab =7 400 ±500 (K). We estimate approximate masses of the wide companions, Ba and Bb, as 𝑀𝐵⁢𝑎 =2.0 and 𝑀𝐵⁢𝑏 =1.8 (M⊙). The close binary’s orbital separation is 𝑎 =8.51 ±0.05 (R⊙); its age is approximately 20 Myr and distance 172 ±1 pc. The close binary’s secondary (Ab) appears to be the source of low amplitude 𝛿 Scuti-type oscillations, although the form of these oscillations is irregular and unrepetitive. Analysis of the 𝜆 6678 He I profile of the primary show synchronism of the mean bodily and orbital rotations. The retention of significant orbital eccentricity, in view of the closeness of the A-system components, is unexpected and poses challenges for the explanation that we discuss.
Spectroscopic and photometric investigation of some potentially chemically peculiar δ Scuti stars
(Oxford Univ Press, 2025) Kahraman Aliçavuş, Filiz; Aliçavuş, Fahri; Özkardeş, Burcu; Çelik, Eda
Investigating 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.
Pulsating and Nonpulsating Components of Detached Eclipsing Binaries in the δ Scuti Instability Strip
(Iop Publishing Ltd, 2025) Kahraman Aliçavuç, Filiz; Aliçavuş, Fahri; Çelik Orhan, Zeynep; Çelik, Eda; Catanzaro, Giovanni; Giarrusso, Marina
Pulsating detached eclipsing binary systems are crucial for studying the internal structure of oscillating stars. These systems are advantageous because binary effects on pulsations are minimal, allowing for more accurate determinations of fundamental stellar parameters such as mass and radius. They serve as unique laboratories for detailed investigations of pulsating stars. In this study, we focused on four detached eclipsing binaries exhibiting δ Scuti−type oscillations: HD 117476, 205 Dra, HY Vir, and V1031 Ori. Our preliminary investigation showed that all binary components of these targets lie within the δ Scuti instability strip. Therefore, we aimed to determine which components are pulsating and which are not and to explore the differences between them. To achieve this, we analyzed TESS photometric data and high-resolution spectra of the targets. Radial velocity (RV) variations were measured, and atmospheric parameters for each component were derived using spectral disentangling or synthetic composite spectra. We also modeled the binary light and RV curves to determine the fundamental physical parameters of the components. Furthermore, we examined pulsation properties using three different approaches to identify the pulsating components. The evolutionary status of the targets was also assessed. Our analysis revealed that, in each system, only one component exhibits δ Scuti−type pulsations, while the others are nonpulsating. Interestingly, we found that the key difference between pulsating and nonpulsating components within the same binary is metallicity: the metal-rich components were found to be nonpulsators, supporting theoretical studies on the effect of metallicity on δ Scuti−type pulsations.
δ Scuti-type pulsation in the hot component of the Algol-type binary system BG Peg
(Cambridge Univ Press, 2014) Şenyüz, Tunç; Soydugan, Esin
In this study, 23 Algol-type binary systems, which were selected as candidate binaries with pulsating components, were observed at the canakkale Onsekiz Mart University Observatory. One of these systems was BG Peg. Its hotter component shows delta Scuti-type light variations. Physical parameters of BG Peg were derived from modelling the V light curve using the Wilson-Devinney code. The frequency analysis shows that the pulsational component of the BG Peg system pulsates in two modes with periods of 0.039 and 0.047 d. Mode identification indicates that both modes are most likely non-radial l = 2 modes.
KIC 10486425: A Kepler eclipsing binary system with a pulsating component
(Cambridge Univ Press, 2014) Kahraman Aliçavuş, Filiz; Soydugan, Esin
We present frequency analysis of the Kepler light curve of KIC 10486425, an eclipsing binary system with a pulsating component. The parameters of the binary were obtained by modelling the light curve with the Wilson-Devinney program. The residuals from this modelling were subject to Fourier analysis which allowed us to detect 120 periodic terms characteristic for gamma Dor-type pulsations. The dominant frequency of these changes amounts to 1.3189 d(-1).
Kinematic Properties of Chromospheric Active Binary Stars
(Cambridge Univ Press, 2012) Tüysüz, Mehmet; Soydugan, Faruk; Bilir, S.; Demircan, Oya
The kinematic behaviour of 362 chromospherically active binary stars (CABs) in the solar neighbourhood were investigated. The Third CABs Catalog by Eker et al. (2008) was used as the main source. The spatial distribution and the components of the Galactic space velocities of the programme stars were determined. The effects of differential rotation and Local Standard of Rest (LSR) were corrected for all systems. Forty probable moving group (MG) members were determined by Eggen's criteria. The kinematic age of the young systems, which are probable members of MGs, was calculated as 0.79 (0.21) Gyr and the rest of 322 field stars were found to have a kinematic age of 4.38 (1.1) Gyr. Field CABs were separated into two sub-groups: dwarf systems, which were formed by main sequence (dwarf) stars, and evolved systems included at least one evolved (giant or sub-giant) component. The kinematic age of 134 dwarf systems was calculated as 4.69 (0.75) Gyr and 4.15 (1.29) Gyr for 188 evolved CABs.
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, Osman
This 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.
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, Ahmet
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).
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, Seliz
This 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.
New photometric solutions of contact binaries HX UMa and FP Boo
(Elsevier, 2023) Yıldırım, Muhammed Faruk
By using different databases (TESS, SuperWASP, KWS and ASAS-SN), light curve analyzes of HX UMa and FP Boo systems were performed, and the changes in the orbital period of the systems were also examined. The light curve analyzes of the systems were conducted simultaneously with the radial velocities using the Wilson and Devinney (WD) code. As a result of the analyzes, the masses and radii of the components were determined as M1 = 1.29 +/- 0.02 M AE, M2 = 0.38 +/- 0.02 M AE, R1 = 1.21 +/- 0.02 R AE, R2 = 0.78 +/- 0.02 R AE for HX UMa and M1 = 1.68 +/- 0.05 M AE, M2 = 0.16 +/- 0.01 M AE, R1 = 2.28 +/- 0.02 R AE, R2 = 0.82 +/- 0.02 R AE for FP Boo, respectively. The distances of HX UMa and FP Boo were calculated as 123 +/- 11 pc and 350 +/- 23 pc, respectively, and were almost the same as Gaia DR3 values. When the orbital period changes were examined, it was determined that the orbital period of the HX UMa system increased, while the FP Boo decreased. The orbital period increase rate of HX UMa was calculated as dP/dt = 9 x 10-8 d yr-1 and the period decrease rate of FP Boo was calculated as dP/dt = 1.7 x 10-6 d yr-1. Mass transfer between components has been suggested as the reason for the period changes. Along with the orbital period changes, a cyclical change was observed in both systems. Magnetic activity or a possible third component can cause cyclical variation. The periods of these cyclical changes are determined as 24 +/- 4 yr and 20 +/- 1 yr, respectively.
Northern Binaries in the Evrena Project
(Cambridge Univ Press, 2012) Bakış, V.; Hensberge, H.; Zejda, M.; de Cat, P.; Yılmaz, F.; Bloemen, S.; Svoboda, P.; Demircan, Osman
In the framework of the EVRENA project, high-resolution spectra. of northern eclipsing close binaries in stellar groups are obtained with the HERMES Echelle spectrograph at the Mercator telescope (Roque de los Muchachos Observatory). This contribution gives the first results on DV Camelopardalis.
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, Fahri
There 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'.
A comprehensive photometric analysis of the shallow contact binary IR Vir
(Elsevier, 2024) Yıldırım, Muhammed Faruk
The light curves (LC(s)) of the shallow contact binary (SCB(s)) IR Vir were retrieved from the TESS, Kepler (K2), ASAS, ASAS-SN, and KWS databases and comprehensively analyzed in this paper. For IR Vir, a q search was conducted to determine the mass ratio, which was found to be 0.371 +/- 0.008. The analysis indicates that IR Vir was a typical A-type W UMa. Since the determination of absolute parameters is crucial for analyzing the evolution of such systems, the masses of the bodies of IR Vir were estimated as M-1 = 1.03 +/- 0.10 M-circle dot, M-2 = 0.38 +/- 0.05 M-circle dot, and the radii as R-1 = 1.16 +/- 0.06 R-circle dot, R-2 = 0.73 +/- 0.04 R-circle dot. In the analysis of the orbital period (OP(s)) for IR Vir, it was found that the OP of IR Vir was increasing, and this value was calculated to be 0.0376 s per year. The OP increase can be explained by the conserved mass exchange between the bodies, and it can be proposed to be from the low mass body to the more one. This value was calculated as 2.4 x 10(-7) M-circle dot per year. Furthermore, a sinusoidal change in the OP was also identified, and it was proposed that this could be attributed to the presence of a third body or magnetic activity. Finally, to gain a better understanding of the nature of IR Vir, it was positioned in the logM(tot) - logJ and HR (Hertzsprung-Russell) diagrams.
Investigation of the stability of the extreme low mass ratio contact binaries SX Crv and XX Sex, which are analysed photometrically
(Elsevier Sci Ltd, 2024) Yıldırım, Muhammed Faruk
The photometric analyses of the extreme low mass ratio contact binaries SX Crv and XX Sex were conducted in detail. Light curves of SX Crv and XX Sex were retrieved from TESS, and light curve analyses were performed simultaneously with radial velocities. The mass ratios for SX Crv and XX Sex were calculated as 0.077(1) and 0.099(2). The masses of the primary components account for about 90% of the total masses of the systems and were determined to be 1.256(48) M (R) (R) and 1.337(37) M (R) (R) for SX Crv and XX Sex, respectively. It has been observed that the orbital periods of both systems have increased. The orbital period change rate of SX Crv has been calculated to be 0.39 s per century, while that of XX Sex has been calculated to be 2.68 s per century. The orbital angular momentum (Jo) o ) determined for both systems is more than 3 times the spin angular momentum (Js), s ), and it can be said that the SX Crv and XX Sex systems are stable. The calculated instability separation ( a ins. ) and instability mass ratio (q ins. ) values for both systems are smaller than those obtained in the analyses, which supports the stability. The estimated ages of the systems are 7.4 Gyr for SX Crv and 3.9 Gyr for XX Sex. logMtot tot - logJ and logTeff- eff - logL diagrams were also interpreted to better understand the evolution of the extreme low mass ratio contact binaries.
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, Fahri
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 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.
On the nature of the eccentric eclipsing binary star SY Phe with a pulsating ? Dor component
(Oxford Univ Press, 2024) Erdem, Ahmet; Sürgit, Derya; Engelbrecht, Chris A.; Zasche, Petr; Bakış, Volkan; Marang, Fred
Spectroscopic observations of the eccentric binary system SY Phe were made at the South African Astronomical Observatory in 2019, 2020, and 2021, and its mid-resolution spectra were obtained. The radial velocities of the component stars were measured using the cross-correlation method and Fourier disentangling of the spectra. The spectral type (hence the effective temperature) of the primary star was determined from a model-atmosphere analysis. The radial velocity and Transiting Exoplanet Survey Satellite ( TESS ) light curves of the system were analysed, and its absolute parameters were derived. A strong (5.2 mmag) periodic signal with a frequency typical of gamma Dor stars (1.169 cycles per day) dominates the Fourier spectrum of the light curve between the eclipses. Apsidal motion parameters of SY Phe were calculated by studying eclipse timing variations. The Geneva evolution models indicate an evolutionary age of 2 Gyr and solar metallicity for the primary component; however, although the position of the secondary component in the H-R diagram matches the isochrone of 2Gyr, it appears to have a larger radius and higher effective temperature than expected for its determined mass. Here, the secondary component has too large a radius, which is in accordance with the radius discrepancy problem that has been encountered in other studies, especially in late-type dwarfs, and has not been solved for half a century.
The Catalogue of Stellar Parameters from the Detached Double-Lined Eclipsing Binaries in the Milky Way
(Cambridge Univ Press, 2014) Eker, Z.; Bilir, Selçuk; Soydugan, Faruk; Yaz Gökçe, Esma; Soydugan, Esin; Tüysüz, Mehmet; Şenyüz, Tunç; Demircan, Oya
The most accurate stellar astrophysical parameters were collected from the solutions of the light and the radial velocity curves of 257 detached double-lined eclipsing binaries in the Milky Way. The catalogue contains masses, radii, surface gravities, effective temperatures, luminosities, projected rotational velocities of the component stars, and the orbital parameters. The number of stars with accurate parameters increased 67% in comparison to the most recent similar collection by Torres, Andersen, & Gimenez (2010). Distributions of some basic parameters were investigated. The ranges of effective temperatures, masses, and radii are 2 750 < T-eff (K)< 43 000, 0.18 < M/M-circle dot < 33, and 0.2 < R/R-circle dot < 21.2, respectively. Being mostly located in one kpc in the Solar neighborhood, the present sample covers distances up to 4.6 kpc within the two local Galactic arms, Carina-Sagittarius and Orion Spur. The number of stars with both mass and radius measurements better than 1% uncertainty is 93, better than 3% uncertainty is 311, and better than 5% uncertainty is 388. It is estimated from the Roche lobe filling factors that 455 stars (88.5% of the sample) are spherical within 1% of uncertainty.
A large topographic feature on the surface of the trans-Neptunian object (307261) 2002 MS4 measured from stellar occultations
(Edp Sciences S A, 2023) Rommel, F. L.; Braga-Ribas, F.; Ortiz, J. L.; Sicardy, B.; Santos-Sanz, P.; Desmars, J.; Camargo, J. I. B.; Özer, Simge
Context. The physical characterization of trans-Neptunian objects is essential for improving our understanding of the formation and evolution of our Solar System. Stellar occultation is a ground-based technique that can be successfully used to determine some of the TNOs' fundamental physical properties with high precision, such as size and shape. Aims. This work is aimed at constraining the size, shape, and geometric albedo of the dwarf planet candidate (307261) 2002 MS4 through the analysis of nine stellar occultation events. Using multichord detection, we also study the object's topography by analyzing the obtained limb and residuals between the observed chords and the best-fit ellipse. Metods. We predicted and organized the observational campaigns of nine stellar occultations by 2002 MS4 between 2019 and 2022, resulting in two single-chord events, four double-chord detections, and three events with between 3 and 61 positive chords. We derived the occultation light curves using differential aperture photometry, from which the star ingress and egress instants were calculated. Using 13 selected chords from the 8 August 2020 event, we determined the global elliptical limb of 2002 MS4. The best-fit ellipse, combined with the object's rotational information from the literature, sets constraints on the object's size, shape, and albedo. Additionally, we developed a new method to characterize the topography features on the object's limb. Results. The global limb has a semi-major axis of a' = 412 +/- 10 km, a semi-minor axis of b'= 385 +/- 17 km, and the position angle of the minor axis is 121 degrees +/- 16 degrees. From this instantaneous limb, we obtained 2002 MS4's geometric albedo of p(V) = 0.1 +/- 0.025, using HV = 3.63 +/- 0.05 mag and a projected area-equivalent diameter of 796 +/- 24 km. Significant deviations from the fitted ellipse in the northernmost limb were detected from multiple sites, highlighting three distinct topographic features: one 11 km depth depression, followed by a 25(-5)(+4) km height elevation next to a crater-like depression, with an extension of 322 +/- 39 km and 45.1 +/- 1.5 km deep. Conclusions. Our results indicate the presence of an object that is approximate to 138 km smaller in diameter than that derived from thermal data, possibly indicating the presence of a thus-far unknown satellite. However, within the error bars, the geometric albedo in the V-band is in agreement with the results published in the literature, even with the radiometric-derived albedo. This stellar occultation has allowed for the first multichord measurement of a large topography in a TNO.
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, Martin
The 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.
Behaviors of dark energy and mesonic scalar field for anisotropic universe in f (R) gravity
(Elsevier, 2012) Aktaş, Can; Aygün, Sezgin; Yılmaz, İhsan
In this Letter, we study behaviors of dark energy in the form of perfect fluid and mesonic scalar field for Marder space-time which is anisotropic and homogeneous in f (R) gravity. Exact solutions of the modified Einstein field equations in f (R) gravity are obtained by using anisotropic features, of Marder space-time. We do not make any assumptions about f (R) function while we are solving f (R I equations. We have investigated dark energy behaviors in f (R) gravity. We have concluded that dark energy in our model behaves like phantom type. Also we have concluded that mesonic scalar field transforms to another matters into time. In our solutions, obtained f (R) functions existed by dark energy and mesonic scalar field are same like general one accepted in the literature. Furthermore, physical and kinematical quantities are examined for two matters, separately. Finally obtained solutions are discussed. (C) 2011 Elsevier B.V. All rights reserved.

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