arXiv subjects

Volkan Bakış

Publications and source records attributed to Volkan Bakış.

16 recordsLinked to original sources

arXiv2026

CPD-82 291: Multi-sector TESS Photometry and SED Analysis of an Active Eclipsing Binary

We present a multi-sector $TESS$ photometric and spectral energy distribution analysis of the eclipsing binary CPD--82~291 (RX~J0853.1--8244). Eight $TESS$ sectors reveal well-defined eclipses and substantial, changing out-of-eclipse modulation. The asymmetries are reproduced by different surface-brightness configurations at different epochs, consistent with strong and evolving stellar activity, although the fitted circular regions are not unique maps of individual starspots. A detached-binary light-curve model yields an orbital inclination of $i\simeq82.1^\circ$ and a photometric mass ratio of $q_{\rm phot}\simeq0.464$. Without a spectroscopic radial-velocity orbit, the mass ratio and absolute parameters are model-dependent rather than dynamical measurements. Combining the light-curve geometry with the SED radius scale and \textit{Gaia} distance gives $R_1\simeq1.25\,R_\odot$ and $R_2\simeq3.70\,R_\odot$; the corresponding model-inferred masses remain substantially less secure than the dimensionless light-curve parameters. The stellar photospheres reproduce the observed SED from the optical region through WISE W4, with no statistically significant mid-infrared excess. The only positive long-wavelength deviation is a low-significance $60\,μ$m measurement, while the $90\,μ$m result is an upper limit. A cool circumbinary-dust model can reproduce this tentative signal, but such a component is not required by the photometry, and its inferred mass and radial extent are non-unique and strongly model dependent. Evolutionary tracks place the primary close to the zero-age main sequence and the secondary well above the main-sequence locus. However, the absence of radial velocities and spectroscopic youth indicators, together with $Gaia$ astrometry inconsistent with Chamaeleon~I membership, prevents a secure pre-main-sequence classification.

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arXiv2026

Herbig AeBe Star AS442A as a UXOR-type system

Detailed studies of the physical characteristics of young intermediate-mass Herbig Ae/Be (HAeBe) stars require extensive sets of homogeneous observational data collected over long periods. In this paper, we present the results of a multi-year study focusing on the faint Herbig Ae/Be star AS 442A. The goal of this study was to investigate the spectral and photometric variability of the star, utilizing long-term archival photometry alongside our own spectroscopic observations. The long-term photometric variability was statistically investigated using approximately 3,500 archival measurements spanning 1984 to 2025. Additionally, we examined the star's spectral variability using data obtained at the Shamakhy Astrophysical Observatory (ShAO) between 2020 and 2024. The three deepest brightness minima were detected in 1990, 2013, and 2023, with amplitudes of approximately ~2 mag in the U-band and up to ~1 mag in other bands. All three observed deep minima were accompanied by smaller brightness dips occurring both before and after the main event. The main light curve and color-magnitude diagrams show the "blueing" effect, which is characteristic of UXOR stars. A quasi-periodic occurrence of deep brightness minima with a period of P = 3759 +/- 35 days was detected for the first time. Our spectral observations were performed before the last deep light fading, which occurred in 2023. We show that the observed spectral variability, specifically the strengthening of emission lines and the reduction in depths and widths of absorption lines, is primarily related to the star's brightness variations. We have shown for the first time that the main reason for the UXOR-like brightness dip of the HAeBe star AS 442A can be explained by a periodic eclipse in a binary system. A close companion as a late-type secondary star with an orbit semimajor axis (a>7.5 au) likely drives the observed stellar variability.

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arXiv2026

Spectral Disentangling Reveals Deep CNO-cycle Exposure in ET Cru

Binary stars undergoing mass transfer provide unique laboratories for testing stellar evolution. Here, we present a comprehensive photometric and spectroscopic analysis of the semi-detached system ET Cru. Using spectral disentangling, we independently determined the effective temperatures and chemical abundances of both components with high precision, including nine elements (eleven species). We find masses of $13.41\,M_\odot$ and $6.00\,M_\odot$ for the primary and secondary, respectively, with uncertainties of only $\sim$1.3%. The radii are $5.58\,R_\odot$ and $5.68\,R_\odot$, measured to within 0.4% and 0.5%. Surface gravities are constrained to better than 1%, while effective temperatures are determined to within 3-5%. The secondary exhibits extreme chemical anomalies, with severe carbon depletion and nitrogen enrichment far exceeding those reported in classical Algol systems. Multi-wavelength spectral energy distribution modelling yields a distance of $\sim$2.5 kpc, inconsistent with the $Gaia$ DR3 parallax, suggesting systematic astrometric uncertainties in the parallax distance. Together, these results establish ET Cru as a benchmark Algol-type binary, revealing direct spectroscopic evidence of deep CNO-cycle exposure in the donor and confirming the primary star as a rejuvenated gainer. ET Cru thus provides a chemically and dynamically illustrative case for understanding advanced binary interactions and the late evolutionary stages of massive-star evolution.

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arXiv2026

Optical observations and atomic environment of supernova remnant G25.1-2.3

The supernova remnant (SNR) G25.1-2.3 was identified in the radio band during the Sino-German $λ$6 cm survey of the Galactic plane. We present a detailed investigation of the optical, HI, and CO emission towards the G25.1-2.3 to better understand its characteristics and environment. In this study, optical spectroscopic data of the remnant and its environment have been analysed for the first time, providing new insights into their emission properties. The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) and 1.5-m Russian-Turkish Telescope (RTT150) data show variations across the observed regions, with [SII]/H$α$ ranging from 0.16 to 0.83. We identified shock-heated gas in the northern and southern regions and several photoionized regions around the SNR based on their [SII]/H$α$ ratios derived from spectra. The [SII]$λ$6716/$λ$6731 ratio observed in the northern region suggests electron densities ($n_{\rm e}$) ranging from 120 to 1030 cm$^{-3}$, whereas the southern regions show higher values, between 490 and 4500 cm$^{-3}$. The variations in the observed H$α$/H$β$ ratios indicate significant differences in extinction across the regions. H$α$ images obtained using the 1-m Turkish Telescope (T100) reveal optical emission in the northern and southern, characterized by filamentary and diffuse structures. We newly found a hole-like distribution of HI, whose spatial extent is roughly consistent with the diameter of the SNR. Based on radio data, we examine the evolutionary stage of G25.1-2.3 using the surface brightness-diameter ($Σ-D$) relation and the equipartition method.

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arXiv2026

Parametric SED Modelling of Protoplanetary Discs: Validation and Application to an Unstudied YSO

We present a physically motivated spectral energy distribution (SED) modelling framework for deriving stellar and circumstellar disc parameters from broadband photometry. The model combines a parametrized disc structure, dust opacity, and interstellar extinction within a Bayesian Markov Chain Monte Carlo (MCMC) inference scheme, allowing correlated parameters to be constrained self-consistently. Initial parameter estimates are obtained via non-linear least-squares fitting and subsequently refined through MCMC sampling. The method is first validated using the well-studied debris disc system 49 Cet, for which the model successfully reproduces key literature properties. It is then applied to the previously uncharacterised young stellar object (YSO) candidate 2MASS J02512618+6012576, using photometric measurements compiled from multiple surveys. The resulting fit indicates a late-type pre-main-sequence star surrounded by a substantial circumstellar disc consistent with a moderately embedded Class II object. We further assess the sensitivity of the inferred parameters to the adopted extinction law and find that the high reddening required by the model is robust against variations in $R_V$. This work demonstrates that physically meaningful constraints on disc structure can be obtained from broadband SED modelling when extinction and distance are treated within a statistically consistent framework.

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arXiv2026

First detailed optical spectroscopic observations of the supernova remnants G107.7-5.1 and G150.3+4.5

We present optical spectroscopic observations of the supernova remnants (SNRs) G107.7$-$5.1 and G150.3+4.5, each spanning nearly 3 degree. Both remnants were recently examined in the optical band through a deep H$α$ and [OIII] emission-line imaging survey, which led to the discovery of G107.7$-$5.1. Using long-slit spectra obtained with the 1.5-m Russian-Turkish Telescope (RTT150), we investigate the physical conditions of the pre-shock and post-shock gas in the optical filamentary regions of the SNRs. The SNR nature of G107.7$-$5.1 is confirmed by the measured [SII]/H$α$ and [NII]/H$α$ ratios, which range from 0.56 to 0.86 and from 0.7 to 1.4, respectively. A similar conclusion is reached for G150.3+4.5, where the observed [SII]/H$α$ (0.43-0.92) and [NII]/H$α$ (0.49-1.29) ratios likewise support a shock-excitation origin. Further confirmation of the shock-excited nature of both SNRs comes from their consistency with recent diagnostic diagrams based on multiple emission-line ratios. The [OIII]/H$β$ line ratios measured in both remnants indicate shocks with complete recombination zones and are consistent with shock velocities of $\gtrsim$100 km s$^{-1}$. The electron densities ($n_{\rm e}$), derived from the [SII] $λ$6716/$λ$6731 line ratios, exhibit substantial variation in the spectra of both SNRs. Additionally, extinction variations observed across the remnants suggest the presence of significant dust structures along the line of sight. We conclude that these two remnants display remarkable similarities across multiple diagnostic spectral properties, consistent with previous reports indicating comparable GeV gamma-ray characteristics.

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arXiv2025

V570 Per: Characterization of a Benchmark Eclipsing Binary

This study presents a comprehensive analysis of the detached binary system V570\,Per through combined photometric, spectroscopic, and astrometric observations. By disentangling the composite spectra, precise fundamental parameters and detailed chemical abundances were determined for both stars. The primary component has a mass of $1.4569_{-0.0100}^{+0.0094}$ $M_{\odot}$, a radius of $1.543_{-0.009}^{+0.012}$ $R_{\odot}$, an effective temperature of $6556_{-26}^{+64}$ K, and a metallicity of $+0.18_{-0.01}^{+0.03}$ dex, while the secondary has a mass of $1.3579_{-0.0089}^{+0.0094}$ $M_{\odot}$, a radius of $1.377_{-0.015}^{+0.013}$ $R_{\odot}$, an effective temperature of $6468_{-21}^{+32}$ K, and a metallicity of $+0.15_{-0.01}^{+0.02}$ dex. The system is estimated to be $577_{-60}^{+60}$ Myr old with a synchronized orbit. The available O-C data imply a minimum mass of 0.57 $M_{\odot}$ or 0.11 $M_{\odot}$ for the third body, corresponding to eccentric and circular orbits, respectively. \texttt{MESA} evolutionary models indicate that the primary will fill its Roche lobe and begin mass transfer to the secondary in about 2.8 Gyr, whereas the secondary will reach the terminal-age main sequence in approximately 3.2 Gyr. The chemical composition of both stars shows remarkable consistency, confirming their common origin, except for calcium, which is significantly enhanced in the primary. Line measurements support this difference and are therefore interpreted as an intrinsic abundance variation rather than an artifact of the analysis. The overall solar-rich metallicity, combined with a relatively low $α$-element content, links V570\,Per to the Galactic thin-disk population. In addition, Galactic orbit analyses of open clusters in the solar neighborhood have revealed that the V570\,Per system may have originated from the Melotte 25 open cluster.

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arXiv2025

Empirical Bolometric Correction and Zero-Point Constants of Visual Magnitudes from High-Resolution Spectra

A method of obtaining bolometric corrections ($BC_{\rm V}$) from observed high-resolution, high-$S/N$ spectra is described. The method is applied to spectra of 128 stars collected from the literature with well-determined effective temperatures ($T_{\rm eff}$) with $S_λ(V)$ transparency profiles of Bessell and Landolt. Computed $BC_{\rm V}$ are found accurate within several milimagnitudes and the effect of different $S_λ(V)$ is found to be no more than 0.015 mag. Measured visual to bolometric ratio ($L_{\rm V}/L$) from the sample spectra and classically determined $BC_{\rm V}$ from bolometric ($M_{\rm Bol}$) and visual ($M_{\rm V}$) absolute magnitudes helped us to determine the zero-point constant ($C_{\rm 2}$) of the $BC_{\rm V}$ scale. Determined $C_{\rm 2}$ for each star for each $S_λ(V)$ profile revealed $C_{\rm 2} = 2.3653\pm0.0067$ mag if $S_λ(V)$ profile of Bessell is used, and $C_{\rm 2} = 2.3826\pm0.0076$ mag if $S_λ(V)$ profile of Landolt is used. Expanding $C_{\rm Bol} = 71.197425 ...$ mag and $c_{\rm Bol} = -18.997351 ...$ mag announced by IAU2015GARB2, and using definition of $C_{\rm 2} = C_{\rm Bol}-C_{\rm V} = c_{\rm Bol}-c_{\rm V}$, where capital $C$ is for the absolute and small $c$ is for the apparent, subscripts indicating bolometric and visual, the zero-point constants: $C_{\rm V} = 68.8321\pm0.0067$ mag and $c_{\rm V} = -21.3627\pm0.0067$ mag, if $L_{\rm V}$ and are in SI units, were determined corresponding to $S_λ(V)$ of Bessell. The zero-point constants corresponding to $S_λ(V)$ of Landolt are smaller, but the difference is not more than 0.02 mag. Typical and limiting accuracies for predicting a stellar luminosity from an apparent magnitude and a distance are analyzed.

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arXiv2025

Absolute Parameters of the Southern Detached Eclipsing Binary DG Mic

As part of an ongoing programme of observing detached eclipsing binary stars in the southern sky, we present the first analysis of spectroscopic observations of the Algol-type binary system DG Mic. A spectroscopic analysis of mid-resolution spectra allowed us to constrain the effective temperature of the primary component and to test the consistency of the system parameters with its spectral energy distribution (SED). Combined solutions of mid-resolution spectra and TESS, ASAS and WASP light curves imply a system of two almost identical components ($q$ = 0.99) in circular orbits. Our final model shows that the system is a detached binary star. The masses and radii of the primary and secondary components of DG Mic were derived to be 1.65($\pm$0.12) M$_\odot$, 1.64($\pm$0.18) M$_\odot$ and 1.63($\pm$0.10) R$_\odot$, 1.91($\pm$0.13) R$_\odot$, respectively. According to Geneva evolution models, both components of the system are main-sequence stars and their age is approximately 713 Myr.

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arXiv2025

Absolute Parameters of Young Stars: NO Puppis

The southern early-type, young, eccentric-orbit eclipsing binary NO Puppis forms the A component of the multiple star Gaia DR3 552\-8147999779517568. 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 4 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: $M_{Aa} = 3.58 \pm 0.11$, $M_{Ab} = 1.68 \pm 0.09$ (M$_\odot$); $R_{Aa} = 2.17 \pm 0.03$, $R_{Ab} = 1.51 \pm 0.06$ (R$_\odot$), and $T_{\rm e Aa} = 13300 \pm 500$, $T_{\rm e Ab} = 7400 \pm 500$ (K). We estimate approximate masses of the wide companions, Ba and Bb, as $M_{Ba} = 2.0$ and $M_{Bb} = 1.8$ (M$_\odot$). The close binary's orbital separation is $a= 8.51 \pm 0.05$ (R$_\odot$); its age is approximately $20$ Myr and distance $172 \pm 1$ 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.

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arXiv2025

RS Sagittarii: Revealing the component spectra and the mass transfer

We present an analysis of high-resolution (R ~ 48000) spectroscopic and photometric data of RS Sgr, a short-period Algol-type binary system. For the first time, precise spectroscopic and absolute parameters of the system have been determined. The primary component is identified as a B3 main-sequence star with an effective temperature of 19000K, while the secondary is classified as an A0-type star with a temperature of 9700 K. The secondary appears to have recently evolved off the main sequence and currently fills its Roche lobe, transferring material through the inner Lagrangian point (L1) to the hotter primary component. The Hα emission and absorption features observed in the spectra are attributed to a combination of a low-density circumprimary disk, a gas stream originating from the secondary, and a hot spot formed at the impact site on the primary. The combined analysis of spectroscopic and photometric data yields a system distance of approximately 418 pc, which is consistent with the value derived from GAIA DR3 within the uncertainty limits.

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arXiv2024

The Fundamental Parameters and Evolutionary Status of V454 Aurigae

Eclipsing binary systems have a unique feature, which enables scientists to obtain precise fundamental star parameters, which opens to greater area of astrophysics studies. In this study, we have derived the fundamental parameters, the evolutionary status, and the birthplace of V454 Aur in the Galaxy by combining radial velocity, photometric, and spectral energy distribution data. We have updated ephemerides and period of V454 Aur as $2458850.80136_{-0.00001}^{\,+0.00001}$ and $27.0198177_{-0.0000003}^{\,+0.0000003}$, respectively. We obtain $1.173^{\,+0.016}_{-0.016}$ $M_\odot$ and $1.203^{\,+0.022}_{-0.026}$ $R_\odot$ for the primary component and $1.045^{\,+0.015}_{-0.014}$ $M_\odot$ and $0.993^{\,+0.034}_{-0.027}$ $R_\odot$ for the secondary component. The effective temperatures for the components are accurately determined via SED data as $6250^{\,+150}_{-150}$ K and $5966^{\,+109}_{-89}$ K for the primary component and the secondary component, respectively. The metallicity of the components is derived from evolutionary tracks, which implies slightly higher than Solar metallicity. According to analysis, the components of V454 Aur are on the main sequence. Our distance calculation for the system is, which is $65.07^{\,+2}_{-3}$ pc, in excellent agreement with \textit{Gaia} astrometric data, which is $65.07^{\,+0.09}_{-0.09}$ pc. The current age of the system is $1.19_{-0.09}^{\,+0.08}$ Gyr, and it will start to mass transfer between components in 5 Gyr from now on. Dynamical orbital analysis shows that V454 Aur follows a boxy pattern around the Galactic centre and is a member of the thin-disc component of the Galaxy. Considering the age and metallicity of this system, it was found to have formed just outside the Solar circle.

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arXiv2022

Detailed Evolutionary Models for Twins in Sight of New Spectral Data: AN Cam, RS Ari, and V455 Aur

We present the evolutionary scenarios for three eclipsing twin ($q(M_2/M_1)\sim$1) binary systems using their combined spectroscopic and photometric data. Using accurate \textit{TESS} photometric data, RV measurements, and spectroscopic data enabled us to calculate fundamental parameters, such as mass and radius, better than 2 percent. The temperature of each component and metallicity of the systems have been obtained via high-resolution spectra. According to our spectral analysis, the metallicity values of AN Cam, RS Ari, and V455 Aur are \text{[M/H]}=\,0.00$\pm$0.12, 0.05$\pm$0.08, and -0.07$\pm$0.07, respectively. Using the derived metallicity for each system, initial orbital parameters and detailed evolutionary status of these three systems are calculated with high precision by using \textsc{mesa}. According to our analysis, both components of AN Cam have passed the terminal age main-sequence, the primary component of RS Ari is in the giant phase while the secondary component has passed the terminal age main-sequence, finally, both components of V455 Aur are still on the main-sequence. The current ages of the three systems AN Cam, RS Ari, and V455 Aur are 3.0, 3.3, and 1.4 Gyrs, respectively, and they will approximately start to transfer mass between components in 400, 250, and 2700 Myrs, respectively.

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arXiv2022

A Method of Improving Standard Stellar Luminosities with Multiband Standard Bolometric Corrections

Standard luminosity ($L$) of 406 main-sequence stars with the most accurate astrophysical parameters are predicted from their absolute magnitudes and bolometric corrections at Johnson $B,V$, and Gaia EDR3 $G$, $G_{BP}$, $G_{RP}$ filters. Required multiband $BC$ and $BC-T_{eff}$ relations are obtained first from the parameters of 209 DDEB (Double-lined Detached Eclipsing Binaries) with main-sequence components and Gaia EDR3 parallaxes. A simplified SED is formulated to give filter dependent component light contributions and interstellar dimming, which are essential in computing $BC$ of a component virtually at any filter. The mean standard $L$ of a star is calculated from the mean $M_{Bol}$ which is a mathematical average of independent $M_{Bol}$ values predicted at different filters, while the uncertainty of $L$ is the uncertainty propagated from the uncertainty of the mean $M_{Bol}$. The mean standard $L$ of the sample stars are compared to the corresponding $L$ values according to the Stefan-Boltzmann law. A very high correlation ($R^2>0.999$) is found. Comparing histogram distributions of errors shows that uncertainties associated with the mean standard $L$ (peak at $\sim2.5$ per cent) are much smaller than the uncertainties of $L$ (peak at $\sim8$ per cent) by the Stefan-Boltzmann law. Increasing the number of filters used in predicting the mean $M_{Bol}$ increases the accuracy of the standard stellar luminosity. Extinction law, color-color relations and color excess - color excess relations for Gaia passbands are demonstrated for main-sequence stars for the first time.

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arXiv2022

A List of 49 New Stellar Twins from the Kepler Catalog of Eclipsing Binary Stars

49 new eclipsing twin binary candidates are identified and analyzed based on Kepler eclipsing binary light curves. Their colours and spectral types are calculated according to our classification. A comparison of the spectral type distribution of eclipsing twin binary systems showed that F-type twins dominate among others, which agrees well with recent studies. The distance of eclipsing twin binaries from the galactic plane shows that F and G-type twins can be seen at any distance from the galactic plane and most of the known eclipsing binary twins are located within 200 pc of the galactic plane, which could be interpreted as these systems are members of thin disk population. As a case study, a twin binary system selected from our updated list of twins, V396~Gem, has been analyzed with spectroscopic and Kepler data. As a result, we have derived the physical parameters of the components of V396~Gem as $M_{1,2}(M_\odot)= 1.814\pm0.114$, $1.797\pm0.114$; $R_{1,2}(R_\odot)= 2.655\pm0.078$, $2.659\pm0.090$; $T_{\mathrm{eff}_{1,2}}(K)=7000\pm100$, $6978\pm100$; $[M/H]=0.11\pm0.03$. We have calculated the evolutionary status of the components by using MESA. Accurately derived physical parameters of the components of V396~Gem have allowed us to determine the age of the system as 1.168$\pm$0.149 Byrs.

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arXiv2020

ASAS Census of Twins

Twin binaries were identified among the eclipsing binaries with $δ$>--30$^\circ$ listed in the ASAS catalog. In addition to the known twin binaries in the literature, 68 new systems have been identified, photometric and spectroscopic observations were done. Color, spectral type, temperature, ratio of radii and masses of the components have been derived and presented. Including 12 twin binary systems that exist in both ASAS and the catalogue of absolute parameters of detached eclipsing binary stars, a total of 80 twin detached binary systems have been statistically studied. A comparison of the spectral type distribution of the twins with those of detached eclipsing binary stars in the ASAS database showed that the spectral type distribution of twins is similar to that of detached systems. This result has been interpreted as there is no special formation mechanism for twins than for normal detached binaries. As a result of our case study for HD~154010, a twin binary, we presented the precise physical parameters of the system.

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