arXiv subjects

Olcay Plevne

Publications and source records attributed to Olcay Plevne.

11 recordsLinked to original sources

arXiv2026

Targeting the future of spectroscopic galaxy surveys -- A cosmological study case with the Wide-field Spectroscopic Telescope

The next generation of Stage-V spectroscopic surveys are designed to measure hundreds of millions of galaxy and quasar spectra, extending precision large-scale-structure cosmology to redshifts and volumes well beyond the reach of current Stage-IV facilities. Realising this potential requires revisiting the target selection strategies and designing them explicitly around the depth, multiplexing, and survey time of the new instruments, rather than a direct extrapolation of existing recipes. This work develops and characterises new strategies for the Wide-field Spectroscopic Telescope (WST), a proposed 12-metre, highly multiplexed facility expected to operate in the 2040s. Using deep multi-band photometry, including COSMOS-field data from CLAUDS and HSC, we revisit low-redshift $z<1.6$ tracer selection of SDSS, BOSS/eBOSS, DESI and 4MOST-CRS -- Bright Galaxies, Luminous Red Galaxies, Emission Line Galaxies and quasars -- to photometric depth achievable in the WST era, and introduce a purely magnitude-limited sample (MagMax) exploiting three-dimensional colour-colour star-galaxy separation, and a set of Lyman-Break Galaxy dropout samples extending target selection to $z>2$. Using Fisher-matrix forecasts, we showcase the constraining power of a WST-like cosmological survey on BAO distance parameters $α_\parallel$ and $α_\perp$, the growth rate $f$, the evolving dark energy equation $w_0w_a$, the local-type primordial non-Gaussianity $f_{\rm NL}^{\rm loc}$, and the sum of the neutrino mass $Σm_ν$. The main outcome of this work is an optimisation framework that directly links instrumental capabilities and observing time to cosmological constraining power, providing a science-driven template applicable to the design of future generations of Stage-V spectroscopic surveys.

astro-ph.CO↗

arXiv2026

Astrophysical Parameters of 5056 Open Star Clusters from Bayesian Nested Sampling with PARSEC Isochrones

We present a homogeneous catalogue of ages, metallicities, distances, and reddenings for 5056 open clusters in the Unified Cluster Catalogue (UCC), derived uniformly from Gaia Data Release 3 (DR3) colour-magnitude diagrams via Bayesian nested sampling with PARSEC isochrones. Unlike previous large-scale catalogues, metallicity is fitted as a free parameter for every cluster rather than fixed or adopted from the literature: where available, Gaia XP spectrophotometric metallicities inform the fit (1201 clusters), while the remaining clusters are constrained by broad priors from Gaia parallaxes and the Schlegel-Finkbeiner-Davis dust map. No cluster is anchored to an external open-cluster parameter catalogue, and no per-cluster manual intervention is applied. A fit-quality metric, $η_{\rm fit}$, identifies 3807 clusters (75 per cent) with reliable colour-magnitude solutions, spanning ages of 0.004-5.9 Gyr and distances out to 17 kpc. We validate the resulting parameters against six literature catalogues and, more critically, against independent high-resolution spectroscopic metallicities from OCCAM DR19: for 132 clusters in common we find a median absolute deviation of only 0.054 dex ($-0.021 \pm 0.132$ dex mean offset), comparable to the intrinsic systematic uncertainty of isochrone-based metallicities. As a direct consequence of this fidelity, the radial metallicity gradient recovered from our XP-informed clusters ($-0.064$ dex kpc$^{-1}$) steepens towards the spectroscopically calibrated value ($-0.079$ dex kpc$^{-1}$) for the highest-quality subset - demonstrating that a purely photometric pipeline, built without reference to spectroscopy, recovers a physically meaningful abundance scale. The full catalogue and posterior chains are publicly released.

astro-ph.GA↗

arXiv2026

Honoring Paris Pişmiş' Legacy: Uniform Astrophysical Properties of 14 Understudied Clusters from Gaia DR3

Open clusters are fundamental tracers of the chemical and dynamical evolution of the Galactic disc. This study presents a systematic characterisation of 14 understudied open clusters from the Pismis catalogue, selected for a well-defined stellar sequence in Gaia DR3 and spanning a wide range of ages and distances. Using high-precision Gaia DR3 astrometry, we provide a high-fidelity modernisation of these historical discoveries while testing our analytical framework across diverse stellar populations. Membership probabilities were determined via the unsupervised UPMASK algorithm using Gaia DR3 positions, proper motions, and parallaxes. To ensure high sample purity, the member samples entering the isochrone fits were restricted to P >= 0.90, with astrophysical parameters calculated through membership-weighted likelihoods. Fundamental properties -- age, distance, reddening, and metallicity -- were derived using a Bayesian Nested Sampling approach to isochrone fitting, chosen for its robustness against the parameter degeneracies typical of dense Galactic fields. The 14 systems exhibit a broad range of properties, with ages from approximately 11 Myr to 1.5 Gyr and distances spanning approximately 690 to 5445 pc. These refined, uniform parameters reconcile historical observations with the precision era of modern astrophysics, providing a homogeneous baseline for systems that large-scale automated surveys recover only partially. A direct cross-match against widely used automated catalogues shows that they typically contain only about a third of the members identified here, and substantially less in the most crowded fields, underscoriecific analysis. This workcontributes to a more complete census of the Galactic disc and sets out a reproducible, per-cluster licable to the manycomparable low-latitude systems still to be characterised.

astro-ph.GA↗

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$^{-1}$.

astro-ph.GA↗

arXiv2026

Unsupervised Chemo-Dynamical Dissection of the Inner Galactic Halo: Discovery of Five Accreted Substructures with SDSS-V and Gaia

The inner Galactic halo is a complex graveyard of the Milky Way's earliest accretion events, where severe orbital phase-mixing challenges traditional dynamical stream-finding techniques. We present a purely data-driven, 12-dimensional chemo-dynamical analysis of the inner halo using \textsl{SDSS-V Milky Way Mapper} (DR19) and \textsl{Gaia} DR3. Utilizing an unsupervised machine learning framework based on UMAP and HDBSCAN, we perform a blind search for clustered populations within a chemically selected \textit{ex-situ} sample of 2,185 stars without kinematic pre-selection. Our pipeline recovers nine kinematic groupings corresponding to seven known substructures (including \textsl{Gaia}-Enceladus/Sausage, the Helmi Streams, and Sequoia), validating the robustness of the high-dimensional feature space. We also report five new tightly bound candidate substructures, designated FO1--FO5 ($E_{\rm tot} \leq -1.8 \times 10^5~\mathrm{km^2~s^{-2}}$). Four candidates (FO1, FO3, FO4, FO5) are confirmed as robust chemo-dynamical overdensities, while FO2 exhibits a striking nitrogen enhancement ($[\mathrm{N/Fe}] = +0.83 \pm 0.16$) suggestive of tidal debris from a disrupted massive globular cluster. Finally, we demonstrate that high-dimensional chemical information is critical for resolving dynamical degeneracies in the crowded inner halo, differentiating structures sharing similar orbits but distinct chemistry (e.g., FO5 and Shiva), and the reverse (e.g., FO3 and the Helmi Streams). These findings confirm that the deepest regions of the Galactic potential preserve a rich record of the Galaxy's assembly history.

astro-ph.GA↗

arXiv2026

Chemical Taxonomy of $ω$~Centauri: Ten Populations Reveal a Multi-Phase Enrichment History

$ω$~Centauri, the most massive globular cluster in the Milky Way, exhibits a level of stellar population complexity that has long resisted a unified chemical characterisation. We exploit high-resolution near-infrared spectroscopy from the Milky Way Mapper survey (MWM DR19) to construct one of the largest homogeneously analysed samples of $ω$~Cen members to date. Applying Ward-linkage hierarchical clustering in a seven-dimensional chemical abundance space, without prior assumptions on population number or boundaries, we identify ten chemically distinct stellar populations. Their nucleosynthetic signatures trace four enrichment channels: iron-peak, $α$-element, CNO-cycle, and high-temperature proton-capture processes. The populations organise into two dominant groups separated by a large light-element spread at a modest iron baseline, consistent with AGB-driven self-enrichment. This dichotomy reflects distinct enrichment pathways: core-collapse supernovae establish the iron baseline, while AGB stars dominate light-element and $s$-process enrichment. A decoupled rise in $s$-process abundances relative to iron-peak elements, together with sub-dominant Type~Ia contributions across all metallicities, indicates evolution on timescales shorter than the characteristic Type~Ia delay time. One intermediate-metallicity population retains a primordial composition, providing evidence for spatially segregated enrichment within the progenitor. The most metal-rich component may trace star formation continuing after accretion into the Milky Way halo. All populations lie in the accreted regime of the $[\mathrm{Al/Fe}]$--$[\mathrm{Mg/Mn}]$ plane, supporting an ex-situ origin. These results reinforce the interpretation of $ω$~Cen as the remnant nucleus of an accreted dwarf galaxy and provide a framework for future chemo-dynamical studies.

astro-ph.GA↗

arXiv2026

The structure and evolution of the Galactic high-$α$ disc I. Chemical and age orbital cartography

We present a comprehensive chemical and age orbital cartography of the Galactic high-$α$ disc using subgiant stars with precise ages, element abundances, and full phase-space information from the \textsl{LAMOST--Gaia} data set. Specifically, we map how average [Fe/H], [$α$/Fe], and age vary across present-day kinematic and orbital coordinates. We analyse the data in full and across mono-abundance populations to measure element abundance-orbital and age-orbital gradients across orbital actions and angular-momenta. Our results show that the high-$α$ disc exhibits clear and coherent gradients in [Fe/H], [$α$/Fe], and age with orbits; these gradients are much stronger and sharper in orbital space than in present-day kinematics, showing that orbital diagnostics recover the intrinsic disc structure of old disc populations more effectively than instantaneous kinematic coordinates. We find that older high-$α$ populations display qualitatively similar element abundance--orbital and age--orbital trends to stars in the low-$α$ disc, although the high-$α$ gradients are generally shallower. The presence of these ordered correlations indicates that the old high-$α$ disc is structured, and preserved a strong fossil record of its early assembly despite the Milky Way's subsequent accretion history. This result implies that later mergers did not fully erase the chemical-orbital and age-orbital structure imprinted during the high-$α$ disc's earliest formation epoch. All together, these findings indicate that the Galactic high-$α$ disc formed mainly through inside-out and upside-down growth.

astro-ph.GA↗

arXiv2025

Estimating Initial Mass of Gaia-Enceladus Dwarf Galaxy with Chemical Evolution Model

This work investigates the initial mass and chemical evolution history of the Gaia-Enceladus dwarf galaxy. We combine spectroscopic data from APOGEE with astrometric data from Gaia DR3 to identify Gaia-Enceladus candidate stars via a machine-learning pipeline using t-SNE and HDBSCAN. By focusing on kinematic and chemical parameters, especially $\mathrm{[Fe/H]}$, $\mathrm{[Mg/Fe]}$, $\mathrm{[Al/Fe]}$, and $\mathrm{[Mn/Fe]}$, we uncover a population of metal-poor, high-eccentricity stars that align with literature criteria for Gaia-Enceladus debris. We then apply the \textit{OMEGA+} chemical evolution model, incorporating MCMC fitting of the observed abundance trends in the $\mathrm{[Mg/Fe]\times[Fe/H]}$ plane. Our best-fitting model indicates a gas mass of $4.93_{-0.72}^{+0.32}\times10^9\,{M_{\odot}}$ for Gaia-Enceladus, placing it at the higher end of previously suggested mass ranges. The model scenario suggests a short star formation timescale, substantial outflows, and a rapid build-up of metals mainly driven by core-collapse supernovae, with a lesser contribution from Type~Ia supernovae. Comparison with observational data in other chemical planes (e.g., $\mathrm{[Mg/Mn]\times[Al/Fe]}$) supports this scenario, emphasizing a distinct evolution path relative to the Milky Way. Additionally, our results provide indirect evidence that star formation in Gaia-Enceladus likely ceased within the first 4 Gyr, consistent with earlier inferences of an early merger event. These findings highlight the power of chemical evolution modeling in reconstructing the origin and mass of ancient accreted systems. Overall, we show that Gaia-Enceladus, through a rapid star formation and strong outflows, contributed a significant fraction of the metal-poor stellar halo of the Milky Way.

astro-ph.GA↗

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.

astro-ph.GA↗

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.

astro-ph.SR↗

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.

astro-ph.GA↗