arXiv subjects

Selçuk Bilir

Publications and source records attributed to Selçuk Bilir.

12 recordsLinked to original sources

arXiv2026

Tracing Radial Migration in the Outer Disk: A Comprehensive Analysis of the Old Open Cluster Berkeley 36

We present a chemo-kinematical, structural, and photometric analysis of the old open cluster Berkeley 36 using Gaia DR3 astrometry and photometry together with high-resolution spectroscopy from the Gaia-ESO Survey DR5.1. Applying a Gaussian Mixture Model to Gaia astrometry, we identify 946 high-probability cluster members. We derive a core radius of 2.63 +/- 0.21 arcmin and a tidal radius of 14.84 +/- 0.47 arcmin, indicating a moderately concentrated and dynamically relaxed system. By fixing the cluster metallicity to the spectroscopic value of [Fe/H] = -0.19 +/- 0.02 dex and adopting an independently determined geometric distance of 4377 +/- 510 pc, we minimize the classical age-reddening-metallicity degeneracy and derive a robust isochrone age of 6.8 +/- 0.5 Gyr. Independent Ba-based chemical clocks yield a mean age of 7.75 +/- 1.94 Gyr, supporting the isochrone solution. The cluster exhibits a high main-sequence binary fraction of 48.0 +/- 1.7% and hosts 83 blue straggler star candidates with an extended spatial distribution, contrary to classical mass segregation. Orbit integration shows that Berkeley 36 follows a nearly circular orbit in the outer Galactic disc at R_GC = 11.42 +/- 0.44 kpc. Accounting for the Galactic warp and disc flare increases the cluster's maximum vertical excursion by 86% and the local disc scale height by 17%, respectively. Comparison with its chemically inferred birth radius at R_b = 6.71 +/- 0.66 kpc indicates an outward radial migration of approximately 5 kpc, predominantly driven by churning. These results establish Berkeley 36 as a benchmark for investigating radial migration, secular evolution, and the dynamical history of old Galactic open clusters.

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arXiv2026

Kings of the Milky Way: A Homogeneous Gaia DR3 Analysis of King Open Clusters and the Galactic Disc Metallicity Gradient

This study aims to establish an internally homogeneous set of structural, astrophysical, and kinematical parameters for King open clusters and to assess their role as tracers of the Galactic thin disc. We present a homogeneous structural, astrophysical, and kinematical analysis of 27 King open clusters using high-precision Gaia DR3 astrometry, photometry, and spectroscopy. Cluster reddenings, distances, metallicities, and ages are determined via a homogeneous Markov Chain Monte Carlo isochrone-fitting approach applied to Gaia colour-magnitude diagrams. The derived parameters span E(G_BP-G_RP) = 0.113-1.933 mag, metallicities of [Fe/H] = -0.40 to +0.28 dex, ages from 17 to 6166 Myr, and heliocentric distances between 739 and 6272 pc. A comparison between astrometric and isochrone-based distances yields a median parallax difference of $-13μ$as, indicating a good level of internal consistency between the photometric and astrometric distance scales within the adopted homogeneous framework. The radial metallicity behaviour of the King clusters is also examined using three complementary Galactic distance definitions and compared with the metallicity-radius relations obtained independently from 164 spectroscopically analysed open clusters from the literature. The King-cluster gradients are close to $-0.060$ dex kpc$^{-1}$ and are broadly consistent with those of the external reference sample, indicating that the homogeneously analysed King clusters follow the negative metallicity-radius trend traced by the broader thin-disc open-cluster population. Flatter gradients are found for young clusters, suggesting more homogeneous chemical enrichment at recent epochs. When dynamical constraints are applied to reduce the effects of radial migration and orbital blurring, the inferred gradient remains close to $-0.059$ dex kpc$^{-1}$.

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arXiv2026

Berkeley 32: A Metal-poor and Dynamically Evolved Open Cluster with Evidence of Radial Migration

We present a comprehensive chemo-dynamical analysis of the old, metal-poor open cluster Berkeley 32 based on Gaia DR3 astrometry and Gaia-ESO Survey DR5.1 spectroscopy. Cluster membership is determined using a Gaussian Mixture Model applied to proper-motion components and trigonometric parallaxes. Isochrone fitting yields an age of 4.9 +/- 0.5 Gyr, a heliocentric distance of 3325 pc, and an extinction of A_V = 0.38 +/- 0.12 mag. Spectroscopic member stars exhibit a mean metallicity of [Fe/H] = -0.39 +/- 0.02 dex, near-solar alpha-element abundances, and a weighted mean radial velocity of V_rad = 106.26 +/- 0.03 km s^-1. The [Y/Mg] chemical clock yields an age of 4.73 +/- 2.39 Gyr, consistent with the isochrone estimate. Orbital integration indicates a moderately eccentric orbit (e = 0.268 +/- 0.004) with a guiding radius of R_g = 8.82 kpc. The inferred chemical birth radius, R_b = 9.82 kpc, together with DeltaR ~ -1 kpc, suggests moderate inward radial migration, while the offsets among R_b, R_g, and R_GC are consistent with both churning and blurring processes. A photometric analysis identifies a binary fraction of f_b = 0.449 +/- 0.017 for systems with mass ratios q >= 0.5, implying a substantial unresolved binary population. Radial cumulative distribution functions further reveal significant mass segregation, with evolved stars more centrally concentrated than main-sequence stars. These results indicate that Berkeley 32 is a dynamically evolved old-disk cluster whose present-day structure and orbit preserve signatures of both internal dynamical evolution and radial migration within the Galactic disk.

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arXiv2026

Chemo-dynamical Analysis of Eight UBC Open Clusters

We present a comprehensive chemo-dynamical analysis of eight open clusters selected from the UBC catalog using Gaia DR3 data. These clusters are located at heliocentric distances of ~2-5 kpc, probing regions of the Galactic disk beyond the solar neighborhood. Cluster membership is determined using the UPMASK algorithm, while structural parameters are derived from radial density profiles through King model fitting combined with MCMC sampling. Their structural parameters reveal diverse internal configurations, from diffuse to moderately concentrated systems. Fundamental astrophysical parameters (extinction, distance, metallicity, and age) are obtained via Bayesian isochrone fitting based on PARSEC models. The clusters span a wide age range (~20 Myr to ~5 Gyr) and show a broad metallicity distribution (-0.34 <= [Fe/H] (dex) <= +0.25). Orbital analysis based on backward integrations shows that all clusters follow nearly circular orbits (e ~ 0.03-0.09) with low vertical distances from the Galactic plane (Zmax < 0.4 kpc), confirming their membership in the Galactic thin disk and dynamically cold kinematics. Comparison between inferred traceback orbital radii and present-day guiding radii indicates modest radial displacements, with Delta R < 0.5 kpc for the UBC sample. These offsets are consistent with mild radial redistribution expected for young, dynamically cold open clusters rather than strong radial migration. The results suggest that radial migration should be considered when interpreting the present-day spatial and chemical distribution of these clusters, although the inferred migration amplitudes remain moderate. Our results demonstrate that relatively distant open clusters can be characterized with high precision using Gaia DR3 data and that mild radial redistribution should be considered when interpreting the present-day distribution of stellar populations in the Galactic disk.

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arXiv2026

Hot Degenerate Components in Blue Stragglers: A Multi-Wavelength SED Analysis of Nine Open Clusters with Swift/UVOT

We present a homogeneous multi-wavelength analysis of 35 blue straggler star (BSS) candidates in nine open clusters, combining Swift/UVOT near-ultraviolet data with Gaia DR3 astrometry and optical-to-infrared photometry. We construct spectral energy distributions (SEDs) to search for signatures of hot companions associated with past mass transfer. Among the sample, 15 BSSs (~43%) show ultraviolet excesses that are better described by two-component SED fits. The inferred companions are consistent with hot white dwarfs and pre-extremely low-mass (pre-ELM) white dwarf candidates, suggesting systems observed at different stages following mass transfer. We examine the radial distribution of the BSSs and find evidence for mass segregation in dynamically evolved clusters, a result that is broadly consistent with the estimated half-mass relaxation timescales of the host systems. To place the clusters in a Galactic context, we compute their orbits using galpy, obtaining low eccentricities (e <= 0.1) and disk-like trajectories. We also find a positive relation between the half-number radius of the BSS population (r50) and the total number of BSSs. Overall, our results are consistent with a scenario in which the BSS population in these clusters is dominated by binary evolution. The systems identified here provide observational constraints on post-mass-transfer evolutionary phases. While the number of robust detections is limited and intrinsic degeneracies remain in SED-based decomposition, these results provide a useful foundation for future spectroscopic confirmation.

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arXiv2026

Gaia DR3 Analysis of Four Open Clusters Toward the Galactic Anticenter

This study provides a detailed examination of the structural, astrophysical, kinematic, and dynamical properties of the open clusters COIN-Gaia 24, Czernik 24, FSR 0893, and UBC 74, which are located in the direction opposite to the Galactic center. Astrometric, photometric, and spectroscopic data from the Gaia Data Release 3 catalog were used to ensure a precise characterization of cluster members and their physical properties. Membership determination was performed using the UPMASK algorithm applied to a five-dimensional parameter space, yielding 116, 179, 238, and 387 likely members for each cluster, respectively. Structural parameters were derived by fitting King profiles to the radial density distributions of high-probability members. Astrophysical parameters were estimated through Bayesian Markov Chain Monte Carlo isochrone fitting based on PARSEC evolutionary models, complemented by spectral energy distribution analysis using ARIADNE. The resulting extinctions, distances, metallicities, and ages indicate that these are moderately reddened, intermediate-age clusters located between 1 and 3.5 kpc from the Sun. Mean radial velocities combined with Galactic orbital integrations computed with galpy show that all four clusters follow nearly circular, low-eccentricity orbits typical of thin-disc populations. All four OCs have dynamical relaxation times of 22-98 Myr. However, their ages exceed these times by several factors, particularly in Czernik 24, indicating that they are dynamically evolved systems, even though the calculated T_E values represent lower limits. The results confirm that these OCs serve as reliable tracers of the chemical and dynamical evolution of the Galactic thin disc.

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arXiv2026

Comprehensive Gaia DR3-Based Astrometric, Photometric, and Kinematic Studies of the Binary Open Cluster $h$ and $χ$ Persei

In the Gaia era, a comprehensive analysis of the binary open clusters NGC 869 (h Persei) and NGC 884 (chi Persei) system has been conducted to investigate its structural, astrophysical, kinematic, and Galactic orbital properties, along with its dynamical evolution. By applying the UPMASK algorithm to Gaia astrometric data for the estimation of cluster membership probabilities, it has been determined that 808 stars in NGC 869 and 707 stars in NGC 884 exhibit the highest statistical likelihood of being cluster members. The fundamental astrophysical parameters of the clusters were inferred within a Bayesian framework using Gaia data and PARSEC stellar evolutionary isochrones, through the application of the Markov Chain Monte Carlo (MCMC) technique. The estimated parameters are: colour excess E(B-V) = 0.516 +0.17/-0.24 mag and 0.516 +0.22/-0.33 mag, distances 2376 +301/-278 and 2273 +230/-290 pc, ages log(t/yr) = 7.31 +0.17/-0.32 and log(t/yr) = 7.30 +0.13/-0.29, and metallicities [Fe/H] = -0.24 +/- 0.12 and [Fe/H] = -0.25 +/- 0.12 dex for NGC 869 and NGC 884, respectively. Since spectroscopic observations are not available for the clusters, SED analysis was employed for the member stars, yielding results consistent with those obtained using the MCMC method. Kinematic and Galactic orbital analyses suggest that the open clusters originated in nearby regions of the Galaxy. This interpretation is supported by their similar space velocities and Galactic orbital parameters. Furthermore, orbital integration over 1 Gyr indicates a potential interaction between the clusters within the next 11 Myr. This study provides strong evidence of a common origin and a possible future dynamical interaction, contributing valuable insights into the formation and evolution of binary open clusters in the Milky Way.

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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

Stellar Ancestry Unlocked: Chemical and Orbital Clues Link Metal Poor Stars to Globular Clusters and the Galaxy's Thick Disk

This study presents a detailed chemical, kinematic, and orbital dynamic analysis of five metal poor stars in the solar neighborhood: HD 2665, HD 5916, HD 122956, HD 189349, and HD 218857. Using high-resolution spectroscopic data from the ELODIE and ESPaDOnS instruments, we derived elemental abundances for 29 species (25 elements: C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Sr, Y, Zr, Ba, Ce, Nd, and Sm) via LTE based analysis with ATLAS9 model atmospheres. Notably, we report first time detections of Ce and Nd in HD2665; Al, V, Sm, and Mn in HD5916; Al in HD 122956; and C, O, S, Sc, Mn, Co, Cu, Zn, Sr, Zr, Nd, and Sm in HD 189349. Dynamical and chemical diagnostics reveal distinct origins: HD 2665 shows strong orbital and chemical similarity to GC NGC 5139 ($ω$ Cen), while HD 218857 exhibits chemodynamic signatures consistent with NGC 5634. HD 122956 aligns with NGC 6864 (M75), though intriguingly shares age, metallicity ([Fe/H]), and [Mg/Fe] ratios with NGC 6517, a cluster whose reported abundances are derived solely from one star with APOGEE $H$-band spectroscopic measurements, as no optical spectroscopic data exist for its members. In contrast, HD 5916 and HD 189349 exhibit kinematic and chemical properties consistent with the field-star population and are classified as thick disk members.

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arXiv2025

Tracing the Galactic Origins of Selected Four G-type Stars in the Solar Neighbourhood

We present a multi-method investigation of four metal-poor G-type main-sequence stars to resolve their Galactic origins. By combining high-resolution spectroscopy from PolarBase, photometric/astrometric data from Gaia DR3, and spectral energy distribution (SED) modelling, we derive precise stellar parameters, chemical abundances, kinematics and Galactic orbital parameters. The stars HD 22879, HD 144579, HD 188510, and HD 201891 show effective temperatures of 5855 +/- 110, 5300 +/- 160, 5370 +/- 60, and 5880 +/- 90 K; surface gravities of 4.40 +/- 0.18, 4.52 +/- 0.37, 4.57 +/- 0.13, and 4.48 +/- 0.18 (in cgs units); and metallicities of -0.86 +/- 0.08, -0.55 +/- 0.12, -1.60 +/- 0.07, and -1.15 +/- 0.07 dex, respectively. Kinematic analysis suggests that HD 22879, HD 144579, and HD 201891 are potential bulge-origin escapees, possibly ejected by the Galactic bar or spiral arm perturbations. HD 188510, however, shows halo-like dynamics, including a retrograde orbit. Chemical abundance trends ([alpha/Fe] vs. [Fe/H]) reveal mixed origins, challenging kinematic classifications. This discrepancy highlights the importance of integrative methodologies in Galactic archaeology. We associate HD 22879, HD 144579, and HD 201891 with the bulge globular clusters NGC 6441, NGC 5927, and NGC 6544, respectively. HD 188510's retrograde motion and low metallicity align with ejection from the halo globular cluster NGC 5139 (omega Centauri). These results illustrate the complex interplay of dynamical processes -- including bar resonances, spiral arm perturbations, and tidal stripping -- in depositing metal-poor stars into the solar neighborhood.

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arXiv2020

Multiwavelength Absolute Magnitudes and Colours of Red Clump Stars in {\it Gaia} Era

This study presents the multi-wavelength investigation of the absolute magnitudes and colours of the red clump (RC) stars selected from APOGEE and GALAH DR2 combined catalogue which is complemented with {\it Gaia} DR2 astrometric data and multi-wavelength photometric data of {\it GALEX} GR6/7, SDSS DR7, {\it Gaia} DR2, 2MASS and {\it WISE} sky surveys. The analyses are centred on the different distance estimation methods using {\it Gaia} trigonometric parallaxes, (1/$\varpi$) and Bayes statistics, and chemically defined Galactic disc populations on [$α$/Fe]$\times$[Fe/H] plane. Such investigation questions the long studied problem of the population effects on RC luminosity. Using two different distance estimation approach, (i) chemical thin and chemical thick disc RC stars are shown to have different absolute magnitudes, while colours remain the same in all photometric bands. Absolute magnitudes vary between -0.12 and +0.13 mag for the 1/$\varpi$ with the change of the Galactic population. This variation in absolute magnitudes is found to be larger for the other method. (ii) The Besan\c con population synthesis model of Galaxy for 2MASS photometry, in which the absolute magnitude difference between chemical populations were found between -0.35 and -0.40 mag from thin disc to thick disc. When results compared with each other, differences of absolute magnitudes are about three times larger in the model than observations. We confirm that the RC absolute magnitudes depend on $α$-element abundances of Galactic populations.

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