arXiv subjects

Jeison Alfonso

Publications and source records attributed to Jeison Alfonso.

4 recordsLinked to original sources

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.

astro-ph.GA↗

arXiv2024

Exploring Galactic open clusters with Gaia. II Dynamical Evolution and Stellar Population Properties in Fifteen Nearby Open Clusters

Stellar mass governs stellar evolution and the distribution of stellar masses plays a central role in the dynamical evolution of stellar clusters. Using high-precision astrometry and photometry from Gaia DR3, we investigate mass segregation and the present-day mass function (PDMF) in fifteen nearby open clusters. Single and binary stars are identified from the color magnitude diagram, and stellar masses for single stars are derived from a cubic spline relation with G-band magnitude, while binary component masses are estimated via a simulation-based inference method. Based on these mass estimates, mass segregation is quantified using the minimum spanning tree technique, and the PDMF is characterized through power-law fitting. We detect significant mass segregation in all clusters. Systems lacking very massive stars exhibit weaker segregation affecting a larger fraction of the population, whereas clusters hosting a small number of very massive stars show strong central concentration of these objects. The PDMF follows a power law with a slope of 2.01, consistent with the canonical Kroupa initial mass function. The strength of mass segregation correlates with the mass of the most segregated stars. Strong segregation observed in very young clusters supports a primordial origin, while older clusters display signatures of dynamical mass segregation at lower masses and evidence of binary disruption. A low-mass break in the PDMF observed in most clusters, if not due to incompleteness, may reflect early gas expulsion in initially mass-segregated systems.

astro-ph.GA↗

arXiv2024

Exploring Galactic open clusters with Gaia I. An examination in the first kiloparsec

Context. Since the first publication of the Gaia catalogue a new view of our Galaxy has arrived. Its astrometric and photometric information has improved the precision of the physical parameters of open star clusters obtained from them. Aims. Using the Gaia DR3 catalogue, we aim to find physical stellar members including faint stars for 370 Galactic open clusters located within 1 kpc. We also estimate the age, metallicity, distance modulus and extinction of these clusters. Methods. We employ the HDBSCAN algorithm on both astrometric and photometric data to identify members in the open clusters. Subsequently, we refine the samples by eliminating outliers through the application of the Mahalanobis metric utilizing the chi-square distribution at a confidence level of 95%. Furthermore, we characterize the stellar parameters with the PARSEC isochrones. Results. We obtain reliable star members for 370 open clusters with an average parallax error of 0.16 mas. We identify about 40% more stars in these clusters compared to previous work using the Gaia DR2 catalogue, including faint stars as new members with G > 17. Before the clustering application we correct the parallax zero-point bias to avoid spatial distribution stretching that may affect clustering results. Our membership lists include merging stars identified by HDBSCAN with astrometry and photometry. We note that the use of photometry in clustering can recover up to 10% more stars in the fainter limit than clustering based on astrometry only, this combined with the selection of stars filtering them out by quality cuts significantly reduces the number of stars with huge parallax error. After clustering, we estimate age, Z, and AV from the photometry of the membership lists.

astro-ph.GA↗

arXiv2023

A Gaia astrometric view of the open clusters Pleiades, Praesepe and Blanco 1

Context. Near open clusters as Pleiades, Praesepe and Blanco 1 have been extensively studied due to their proximity to the Sun. The Gaia data brings the opportunity to investigate these clusters, since it contains valuable astrometric and photometric information which can be used to update their kinematic and stellar properties. Aims. Our goal is to carry out a star membership study in these nearby open clusters employing an astrometric model with proper motions and an unsupervised clustering machine learning algorithm using positions, proper motions and parallaxes. The star members are selected from the cross-matching between both methods. Methods. We use the Gaia DR3 catalogue to determine star members using two approaches: a classical Bayesian model and the unsupervised machine learning algorithm DBSCAN. For star members we build the radial density profiles, the spatial distributions and compute the King parameters. The ages and metallicities were estimated using the BASE-9 Bayesian software. Results. We identified 958, 744 and 488 star members for the Pleiades, Praesepe and Blanco 1 respectively. We corrected the distances and built the spatial distributions, finding that Praesepe and Blanco 1 have elongated shape structures. The distances, ages and metallicities obtained were consistent with the reported in the literature. Conclusions. We obtained catalogues of star members, updated kinematic and stellar parameters for these open clusters. We found that the proper motions model can find a similar number of members as the unsupervised clustering algorithm does when the cluster population form an overdensity in the vector point diagram. It allows to select an adequate size of the proper motions region to run these methods. Our analysis found stars that are being directed towards the outskirts of the Praesepe and Blanco 1, which exhibit elongated shapes.

astro-ph.GA↗