arXiv subjects

K. Yakut

Publications and source records attributed to K. Yakut.

At least 19 recordsLinked to original sources

arXiv2026

The Binary-Binary Hierarchical System XY Leo: A Laboratory for Stellar Activity and Concealed Companions

The hierarchical multiple system XY Leo, despite nearly 90 yr of observations, remains enigmatic. It offers a unique testbed for close binary evolution, involving processes such as mass transfer, angular momentum loss, and the von Zeipel--Kozai--Lidov (ZKL) mechanism. Previously identified as a quadruple system, XY Leo shows long-term orbital period modulations. Our new ground-based and Transiting Exoplanet Survey Satellite data suggest that these may stem from either magnetic cycles or the influence of an unseen companion. While the latter remains speculative, both scenarios are discussed within a unified framework. Using all available photometric and spectroscopic data, we derived ultraprecise physical parameters for the contact binary XY Leo A as $M_{\rm A1}=0.629\pm0.009\,M_{\odot}$, $M_{\rm A2}=0.865\pm0.012\,M_{\odot}$, $R_{\rm A1}=0.739\pm0.007\,R_{\odot}$, $R_{\rm A2}=0.855\pm0.008\,R_{\odot}$, $L_{\rm A1}=0.271\pm0.026\,L_{\odot}$, $L_{\rm A2}=0.288\pm0.030\,L_{\odot}$, and orbital separation $a_{\rm A}=2.078\pm0.010\,R_{\odot}$, based on simultaneous solutions of light and radial velocity curves. The detached binary subsystem XY Leo B is confirmed to be on a wide $\sim 20$-year orbit around the contact system. A second $\sim 23$-year modulation is also detected, which may arise from either stellar magnetic activity or an additional unseen companion. After removing both trends, a coherent residual modulation with a characteristic timescale of $14.2 \pm 0.8$~yr remains in the $O$--$C$ diagram, consistent with a magnetic activity cycle of Applegate type. We modeled XY Leo A with the Cambridge STARS (EV/TWIN) code under non-conservative evolution, finding strong agreement between the tracks and observed parameters, highlighting the system's value for testing multiple-star evolution.

astro-ph.SR↗

arXiv2025

Uncovering the population of compact binary mergers and their formation pathways with gravitational waves through the Einstein Telescope

Ground-based gravitational-wave (GW) observatories have transformed our view of compact-object mergers, yet their reach still limits a comprehensive reconstruction of the processes that generate these systems. Only next-generation observatories, with order-of-magnitude improvements in sensitivity and access to lower frequencies, will be capable of radically extending this detection horizon. GW observations will make it possible to detect the complete population of binary black hole (BBH) mergers out to redshifts of $z \simeq 100$. This capability will deliver an unprecedented map of merger events across cosmic time and enable precise reconstruction of their mass and spin distributions, while for several thousand events the signal-to-noise ratio will surpass 100, enabling precision physics of BHs and neutron stars (NSs). The access to lower frequencies will also open the intermediate-mass window, detecting systems of order $\sim 10^3 M_\odot$, potentially in coordination with multi-band observations from LISA. At higher redshifts, where Population III stars have so far remained beyond reach - even for the James Webb Space Telescope - GW observations by next-generation detectors will routinely provide observations of BH mergers thought to originate from these primordial stellar populations. Such measurements are expected to play a central role in clarifying the early assembly of supermassive black holes. A single detection of a binary BH system at $z \gtrsim 30$, or of a compact object with sub-solar mass and no tidal deformability, would constitute strong evidence for the existence of primordial black holes. Such a discovery would have profound consequences for our understanding of dark matter and the early Universe. Ultimately, the GW observations will become revolutionary for identifying the physical channels responsible for compact binary formation.

astro-ph.HE↗

arXiv2025

A Deep Look into the Intermediate-Age Open Cluster NGC 2506: What Binary Systems Reveal About Cluster Distance and Age

Using high-precision observations from the space-based \textit{Gaia} and \textit{TESS} missions, complemented by ground-based spectroscopic data and multi-band photometric surveys, we perform a detailed investigation of the Galactic open cluster NGC~2506. We present a new analysis of the intermediate-age open cluster NGC~2506, using joint fits to the radial velocities (RVs) and spectral energy distributions (SEDs) of five double-lined binary systems, including two eclipsing binaries. The analysis yields self-consistent estimates of the cluster's age, distance, and extinction, based on 18 free parameters: 10 stellar masses, 5 orbital inclinations, and common values for age, distance, and $A_V$. The SED fitting incorporates stellar isochrones, and the resulting parameters are examined through HR diagrams (R--$T_{\rm eff}$, R--M, and M--$T_{\rm eff}$) to assess evolutionary consistency. The age we derive for the cluster is $1.94 \pm 0.03$ Gyr for an assumed [Fe/H] = -0.30, and a fitting formula is given for extrapolation to other metallicities. The distance we find from the SED fitting is $3189 \pm 53$ pc, and this is to be compared with our own inference from the Gaia data which is $3105 \pm 75$ pc, based on 919 stars identified as cluster members. Our results demonstrate the power of binary systems in tightly constraining cluster-wide age and distance at this evolutionary stage. This approach represents one of the most accurate characterizations of an intermediate-age open cluster using multiple binary systems.

astro-ph.SR↗

arXiv2025

A novel approach to determining the age of stellar clusters: application to NGC 188

We present a new independent determination for the age of one of the oldest open clusters, NGC 188: $6.41 \pm 0.33$ Gyr. We utilize a novel approach where we jointly fit the radial velocities (RVs) and spectral energy distributions (SED) of six binary star systems in the cluster. The joint fit has 21 free parameters: 12 stellar masses, 6 orbital inclination angles, as well as a common cluster age, distance, and extinction, $A_V$. The fit to the SEDs utilizes MIST stellar isochrones, and the fitted stellar parameters are presented in HR diagrams (R - $T_{\rm eff}$, R - M, and M - $T_{\rm eff}$) showing the stars' different states of evolution. These isochrones are compared with PARSEC and Y2 isochrones to obtain an estimate of the uncertainties introduced by different stellar models. Of the 3017 stars taken from the NGC 188 field, 333 possible member stars were selected using Gaia data and analyzed separately for their mean distances and proper motions. We find a distance to NGC 188 of $1850 \pm 12$ pc compared with the independent photometric distance found from the SED fitting of $1897 \pm 58$ pc.

astro-ph.SR↗

arXiv2025

Comprehensive analysis of CM Draconis: eclipse timing variations driven by either a third body or stellar magnetic activity

The CM Draconis system is a well-studied, double-lined spectroscopic binary that is totally eclipsing and exhibits strong magnetic activity. Nearly one million photometric measurements have been collected across multiple wavelengths over more than half a century. In addition to showing frequent flare activity and apsidal motion, CM Dra also hosts a distant white dwarf and has been proposed to harbor a Jupiter-sized circumbinary companion. At only 47 light-years from Earth, it remains one of the most observationally rich and dynamically intriguing low-mass binary systems. We present a comprehensive photometric and spectroscopic analysis of the system using new ground-based observations and data from 19 sectors of the \textit{TESS} mission. We derive precise fundamental parameters for both components: $M_1 = 0.2307 \pm 0.0008\,M_\odot$, $M_2 = 0.2136 \pm 0.0008\,M_\odot$, $R_1 = 0.2638 \pm 0.0011\,R_\odot$, $R_2 = 0.2458 \pm 0.0010\,R_\odot$, $L_1 = 0.0060 \pm 0.0005\,L_\odot$, and $L_2 = 0.0050 \pm 0.0004\,L_\odot$. The derived distance ($14.4 \pm 0.6$ pc) is consistent with \textit{Gaia} DR3 measurements. Eclipse timing variations (ETVs) spanning over five decades were analyzed in detail. A long-period ($\sim$56 yr) modulation was identified, which may be attributed either to the light-time effect of a possible circumbinary companion or to magnetic activity cycles. While the Bayesian Information Criterion statistically favors the model involving a light-time effect from a planetary companion, stellar activity remains a viable alternative that cannot yet be ruled out. Our results demonstrate that CM Dra is a valuable test case for studying both stellar activity and the potential presence of circumbinary companions in multiple-star systems. Continued long-term monitoring will be essential to distinguish between these competing scenarios.

astro-ph.SR↗

arXiv2021

The nature of the eccentric doubled-lined eclipsing binary system KIC 2306740 with Kepler space photometry

We present a detailed study of KIC 2306740, an eccentric double-lined eclipsing binary system. Kepler satellite data were combined with spectroscopic data obtained with the 4.2 m William Herschel Telescope (WHT). This allowed us to determine precise orbital and physical parameters of this relatively long period (P=10.3 d) and slightly eccentric, ($e=0.3$) binary system. The physical parameters have been determined as $M_1 = 1.194\pm0.008$ M$_{\odot}$, $M_2 = 1.078\pm0.007$ M$_{\odot}$, $R_1 = 1.682\pm0.004$ R$_{\odot}$, $R_2 = 1.226\pm0.005$ R$_{\odot}$, $L_1 = 2.8\pm0.4$ L$_{\odot}$, $L_2 = 1.8\pm0.2$ L$_{\odot}$ and orbital seperation $a = 26.20\pm0.04$ R$_{\odot}$ through simultaneous solutions of Kepler light curves and of the WHT radial velocity data. Binarity effects were extracted from the light curve in order to study intrinsic variations in the residuals. Five significant and more than 100~combination frequencies were detected. We modeled the binary system assuming non-conservative evolution models with the Cambridge STARS (TWIN) code and we show evolutionary tracks of the components in the $\log L - \log T$ plane, the $\log R - \log M$ plane and the $\log P - \rm age$ plane for both spin and orbital periods together with eccentricity $e$ and $\log R_1$. The model of the non-conservative processes in the code led the system to evolve to the observed system parameters in roughly $5.1 $ Gyr.

astro-ph.SR↗

arXiv2016

Evolution of Cataclysmic Variables and Related Binaries Containing a White-Dwarf

We present a binary evolution study of cataclysmic variables (CVs) and related systems with white dwarf accretors, including for example, AM CVn systems, classical novae, supersoft X-ray sources, and systems with giant donor stars. Our approach intentionally avoids the complications associated with population synthesis algorithms thereby allowing us to present the first truly comprehensive exploration of all of the subsequent binary evolution pathways that ZACVs might follow (assuming fully non-conservative, Roche-lobe overflow onto an accreting WD) using the sophisticated binary stellar evolution code MESA. The grid consists of 56,000 initial models, including 14 white dwarf accretor masses, 43 donor-star masses ($0.1-4.7$ $M_{\odot}$), and 100 orbital periods. We explore evolution tracks in the orbital period and donor-mass ($P_{\rm orb}-M_{\rm don}$) plane in terms of evolution dwell times, masses of the white dwarf accretor, accretion rate, and chemical composition of the center and surface of the donor star. We report on the differences among the standard CV tracks, those with giant donor stars, and ultrashort period systems. We show where in parameter space one can expect to find supersoft X-ray sources, present a diagnostic to distinguish among different evolutionary paths to forming AM CVn binaries, quantify how the minimum orbital period in CVs depends on the chemical composition of the donor star, and update the $P_{\rm orb}(M_{\rm wd})$ relation for binaries containing white dwarfs whose progenitors lost their envelopes via stable Roche-lobe overflow. Finally, we indicate where in the $P_{\rm orb}-M_{\rm don}$ the accretion disks will tend to be stable against the thermal-viscous instability, and where gravitational radiation signatures may be found with LISA.

astro-ph.SR↗

arXiv2016

Angular Momentum Loss and Gravitational wave amplitudes for X-ray Binaries with a Neutron Star Component

Binary systems with neutron stars and double degenerate systems are crucial objects to test current stellar evolution models and Einstein's general relativity. In this study, we present angular momentum loss mechanism via gravitational radiation and magnetized stellar winds for some selected systems with a neutron star. We calculated and plotted their time scales for angular momentum loss. Gravitational wave amplitudes of binary systems with a neutron star components are also estimated and their detectability with a gravitational wave detector (LISA) has been plotted.

astro-ph.SR↗

arXiv2016

Binary Systems with a Black Hole Component as Sources of Gravitational Waves

Discovery of gravitational waves by LIGO team (Abbott et al. 2016) bring a new era for observation of black hole systems. These new observations will improve our knowledge on black holes and gravitational physics. In this study, we present angular momentum loss mechanism through gravitational radiation for selected X-ray binary systems. The angular momentum loss in X-ray binary systems with a black hole companion due to gravitational radiation and mass loss time-scales are estimated for each selected system. In addition, their gravitational wave amplitudes are also estimated and their detectability with gravitational wave detectors has been discussed.

astro-ph.SR↗

arXiv2016

Comments on the Effect of Frame Dragging

The effect of the frame dragging on the equation of motions, depends on the approaches that have been considered. Accordingly, additional force terms may appear or disappear. To understand the effect of radial and non-radial perturbations that may exist in the case of mass distribution of spherical shell form, modifications should be predicted to the approaches of the components of elastic tensor $E^{μν}$ given in Bass and Pirani (1955). Different relations between $ω$ and $ω'$ have been discussed.

gr-qc↗

arXiv2015

A Turnoff Detached Binary Star V568 Lyr in the Kepler Field of the Oldest Open Cluster (NGC 6791) in the Galaxy

We present the Kepler photometric light-variation analysis of the late-type double-lined binary system V568 Lyr that is in the field of the high metallicity old open cluster NGC 6791. The radial velocity and the high-quality short-cadence light curve of the system are analysed simultaneously. The masses, radii and luminosities of the component stars are $M_1 = 1.0886\pm0.0031\, M{\odot}$, $M_2 = 0.8292 \pm 0.0026\, M{\odot}$, $R_1 = 1.4203\pm 0.0058\, R{\odot}$, $R_2 = 0.7997 \pm 0.0015\, R{\odot}$, $L_1 = 1.85\pm 0.15\, L{\odot}$, $L_2 = 0.292 \pm 0.018\, L{\odot}$ and their separation is $a = 31.060 \pm 0.002\, R{\odot}$. The distance to NGC 6791 is determined to be $4.260\pm 0.290\,$kpc by analysis of this binary system. We fit the components of this well-detached binary system with evolution models made with the Cambridge STARS and TWIN codes to test low-mass binary star evolution. We find a good fit with a metallicity of $Z = 0.04$ and an age of $7.704\,$Gyr. The standard tidal dissipation, included in TWIN is insufficient to arrive at the observed circular orbit unless it formed rather circular to begin with.

astro-ph.SR↗

arXiv2014

An Interacting O+O Supergiant Close Binary System: Cygnus OB2-5 (V729 Cyg)

The massive interacting close binary system V729 Cyg (OIa+O/WN9), plausibly progenitor of a Wolf-Rayet system, is studied using new observations gathered over 65 nights and earlier published data. Radial velocity and five colour light curves are analysed simultaneously. Estimated physical parameters of the components are $M_1 = 36\pm 3 M_{\odot}$, $M_2 = 10 \pm 1 M_{\odot}$, $R_1 = 27\pm 1 R_{\odot}$, $R_2 = 15 \pm 0.6 R_{\odot}$, $\log{(L_1/L_{\odot})} = 5.59\pm 0.06$, and $\log{(L_2/L_{\odot})} = 4.65\pm 0.07$. We give only the formal 1$σ$ scatter, but we believe systematic errors in the luminosities, of uncertain origin as discussed in the text, are likely to be much bigger. The distance of the Cygnus OB2 association is estimated as $967\pm 48$ pc by using our newly obtained parameters.

astro-ph.SR↗

arXiv2014

KIC 3858884: a hybrid δ Sct pulsator in a highly eccentric eclipsing binary

The analysis of eclipsing binaries containing non-radial pulsators allows: i) to combine two different and independent sources of information on the internal structure and evolutionary status of the components, and ii) to study the effects of tidal forces on pulsations. KIC 3858884 is a bright Kepler target whose light curve shows deep eclipses, complex pulsation patterns with pulsation frequencies typical of δ Sct, and a highly eccentric orbit. We present the result of the analysis of Kepler photometry and of high resolution phaseresolved spectroscopy. Spectroscopy yielded both the radial velocity curves and, after spectral disentangling, the primary component effective temperature and metallicity, and line-of-sight projected rotational velocities. The Kepler light curve was analyzed with an iterative procedure devised to disentangle eclipses from pulsations which takes into account the visibility of the pulsating star during eclipses. The search for the best set of binary parameters was performed combining the synthetic light curve models with a genetic minimization algorithm, which yielded a robust and accurate determination of the system parameters. The binary components have very similar masses (1.88 and 1.86 Msun) and effective temperatures (6800 and 6600 K), but different radii (3.45 and 3.05 Rsun). The comparison with the theoretical models evidenced a somewhat different evolutionary status of the components and the need of introducing overshooting in the models. The pulsation analysis indicates a hybrid nature of the pulsating (secondary) component, the corresponding high order g-modes might be excited by an intrinsic mechanism or by tidal forces.

astro-ph.SR↗

arXiv2011

The short-period low-mass binary system CC Com revisited

In this study we determined precise orbital and physical parameters of the very short period low-mass contact binary system CC Com. The parameters are obtained by analysis of the new CCD data with the archival spectroscopic data. The physical parameters of the components derived as $M_\textrm{c}$ = 0.717(14) $M_{\odot}$, $M_\textrm{h}$ = 0.378(8) $M_{\odot}$, $R_\textrm{c}$ = 0.708(12) $R_{\odot}$, $R_\textrm{h}$ = 0.530(10) $R_{\odot}$, $L_\textrm{c}$ = 0.138(12) $L_{\odot}$, $L_\textrm{h}$ = 0.085(7) $L_{\odot}$, and the distance of the system is estimated as 64(4) pc. The times of minima obtained in this study and with those published before enable us to calculate the mass transfer rate between the components which is $1.6\times10^{-8}$ M$_{\odot}$yr$^{-1}$. Finally, we discuss the possible evolutionary scenario of CC Com.

astro-ph.SR↗

arXiv2011

Close Binary System GO Cyg

In this study, we present long term photometric variations of the close binary system \astrobj{GO Cyg}. Modelling of the system shows that the primary is filling Roche lobe and the secondary of the system is almost filling its Roche lobe. The physical parameters of the system are $M_1 = 3.0\pm0.2 M_{\odot}$, $M_2 = 1.3 \pm 0.1 M_{\odot}$, $R_1 = 2.50\pm 0.12 R_{\odot}$, $R_2 = 1.75 \pm 0.09 R_{\odot}$, $L_1 = 64\pm 9 L_{\odot}$, $L_2 = 4.9 \pm 0.7 L_{\odot}$, and $a = 5.5 \pm 0.3 R_{\odot}$. Our results show that \astrobj{GO Cyg} is the most massive system near contact binary (NCB). Analysis of times of the minima shows a sinusoidal variation with a period of $92.3\pm0.5$ years due to a third body whose mass is less than 2.3$M_{\odot}$. Finally a period variation rate of $-1.4\times10^{-9}$ d/yr has been determined using all available light curves.

astro-ph.SR↗

arXiv2011

Marginally low mass ratio close binary system V1191 Cyg

In this study, we present photometric and spectroscopic variations of the extremely small mass ratio ($q\simeq 0.1$) late-type contact binary system \astrobj{V1191 Cyg}. The parameters for the hot and cooler companions have been determined as $M_\textrm{h}$ = 0.13 (1) $M_{\odot}$, $M_\textrm{c}$ = 1.29 (8) $M_{\odot}$, $R_\textrm{h}$ = 0.52 (15) $R_{\odot}$, $R_\textrm{c}$ = 1.31 (18) $R_{\odot}$, $L_\textrm{h}$ = 0.46 (25) $L_{\odot}$, $L_\textrm{c}$ = 2.71 (80) $L_{\odot}$, the separation of the components is $a$= 2.20(8) $R_{\odot}$ and the distance of the system is estimated as 278(31) pc. Analyses of the times of minima indicates a period increase of $\frac{dP}{dt}=1.3(1)\times 10^{-6}$ days/yr that reveals a very high mass transfer rate of $\frac{dM}{dt}=2.0(4)\times 10^{-7}$$M_{\odot}$/yr from the less massive component to the more massive one. New observations show that the depths of the minima of the light curve have been interchanged.

astro-ph.SR↗

arXiv2010

Towards ensemble asteroseismology of the young open clusters Chi Persei and NGC 6910

As a result of the variability survey in Chi Persei and NGC6910, the number of Beta Cep stars that are members of these two open clusters is increased to twenty stars, nine in NGC6910 and eleven in Chi Persei. We compare pulsational properties, in particular the frequency spectra, of Beta Cep stars in both clusters and explain the differences in terms of the global parameters of the clusters. We also indicate that the more complicated pattern of the variability among B type stars in Chi Persei is very likely caused by higher rotational velocities of stars in this cluster. We conclude that the sample of pulsating stars in the two open clusters constitutes a very good starting point for the ensemble asteroseismology of Beta Cep-type stars and maybe also for other B-type pulsators.

astro-ph.SR↗

arXiv2010

Photometric multi-site campaign on the open cluster NGC 884 I. Detection of the variable stars

CONTEXT: Recent progress in the seismic interpretation of field beta Cep stars has resulted in improvements of the physics in the stellar structure and evolution models of massive stars. Further asteroseismic constraints can be obtained from studying ensembles of stars in a young open cluster, which all have similar age, distance and chemical composition. AIMS: To improve our comprehension of the beta Cep stars, we studied the young open cluster NGC 884 to discover new B-type pulsators, besides the two known beta Cep stars, and other variable stars. METHODS: An extensive multi-site campaign was set up to gather accurate CCD photometry time series in four filters (U, B, V, I) of a field of NGC884. Fifteen different instruments collected almost 77500 CCD images in 1286 hours. The images were calibrated and reduced to transform the CCD frames into interpretable differential light curves. Various variability indicators and frequency analyses were applied to detect variable stars in the field. Absolute photometry was taken to deduce some general cluster and stellar properties. RESULTS: We achieved an accuracy for the brightest stars of 5.7 mmag in V, 6.9 mmag in B, 5.0 mmag in I and 5.3 mmag in U. The noise level in the amplitude spectra is 50 micromag in the V band. Our campaign confirms the previously known pulsators, and we report more than one hundred new multi- and mono-periodic B-, A- and F-type stars. Their interpretation in terms of classical instability domains is not straightforward, pointing to imperfections in theoretical instability computations. In addition, we have discovered six new eclipsing binaries and four candidates as well as other irregular variable stars in the observed field.

astro-ph.SR↗