Open Clusters Research Articles

Structural properties of subgroups of stars associated with open clusters

Structural properties of subgroups of stars associated with open clusters

Identifying Uncertainties in Stellar Evolution Models Using the Open Cluster M67

Stellar age estimates are often calculated by interpolating a star’s properties in a grid of models. However, different model grids will give different ages for the same star. We used the open cluster M67 to compare four different model grids: DSEP, GARSTEC, MIST, and YREC (10.5281/zenodo.12775242). Across all model grids, age estimates for main sequence stars were consistently higher than the accepted age of M67, while age estimates for red giant stars were lower. We compared model-generated age and mass values to external constraints as an additional test of the reliability of each model grid. For stars near solar age and metallicity, we recommend using the DSEP model grid to estimate the ages of main sequence stars and the GARSTEC model grid for red giant stars.

Selective tandem transformation of furfural to cyclopentanone over CoNi alloy coupled with flower like Nb2O5

The matching of hydrogenation sites and acid sites is the key to design efficient catalyst for the synthesis of cyclopentanone from lignocellulosic derived furfural. In this work, Co-Ni/Nb2O5 catalyst with three-dimensional open flower cluster structure was constructed. The results of characterization and theoretical calculation show that the introduction of Ni leads to the formation of Co-Ni alloy, tailoring the electronic properties of metal center and acidity of the catalyst. On the one hand, it effectively enhances the activation of H2, modulates the d-band structure of the metal center, thus controlling the adsorption configuration of the substrate, leading to the selective activation of carbonyl groups and avoiding the furan hydrogenation byproduct. On the other hand, it promotes the ring-opening rearrangement of intermediates. Benefiting from the synergistic effect of hydrogenation sites and acidic sites, 99.0 % yield of CPO was achieved under mild conditions (150 ℃ and 1.5 MPa for 4 h) within 6 cycles. Therefore, this study will provide a new way to realize the green manufacturing of cyclopentanone.

On the Determination of Stellar Mass and Binary Fraction of Open Clusters within 500 pc from the Sun

We investigated the stellar mass function and the binary fraction of 114 nearby open clusters (OCs) using the high-precision photometric data from Gaia Data Release 3 (Gaia DR3). We estimated the mass of member stars by using a ridge line that is better in line with the observed color–magnitude diagram, thus obtaining more accurate stellar mass and binary mass ratio (q) at the low-mass region. By analyzing the present-day mass function (PDMF) of star clusters, we found that 108 OCs follow a two-stage power-law distribution, whereas six OCs present a single power-law PDMF. Subsequently, we fitted the high(low)-mass index of PDMF ( dN/dm∝m−α ), denoted as α h(α l), and segmentation point m c. For our cluster sample, the median values of α h and α l are 2.65 and 0.95, respectively, which are approximately consistent with the initial mass function results provided by Kroupa. We utilized the cumulative radial number distribution of stars with different masses to quantify the degree of mass segregation. We found a significant positive correlation between the state of dynamical evolution and mass segregation in OCs. We also estimated the fraction of binary stars with q ≥ 0.5, ranging from 6% to 34% with a median of 17%. Finally, we provided a catalog of 114 nearby cluster properties, including the total mass, the binary fraction, the PDMF, and the dynamical state.

UOCS

Context. Evolutionary pathways of binary systems are vastly different from single stellar evolution, and thus there is a need to quantify their frequency and diversity. Thanks to their to their coeval nature, open clusters are the best test beds for unveiling the secrets of binary populations. The availability of multi-wavelength data in recent years has been critical in characterising the binary population. Aims. NGC 752 is a solar-metallicity, intermediate-age open cluster located at 460 pc. In this work, we aim to identify the optically sub-luminous white dwarfs in NGC 752 and identify the elusive blue lurkers by association. Methods. We used multi-wavelength photometry from AstroSat/UVIT, Swift/UVOT, Gaia DR3, and other archival surveys to analyse the colour-magnitude diagrams and spectral energy distributions of 37 cluster members. Results. We detected eight white dwarf companions of cluster members. Four of the systems are main sequence stars with extremely low-mass white dwarfs as their companions. Two of these main sequence stars are also fast rotators. Conclusions. The presence of low-mass white dwarfs and fast rotation signals a past mass transfer, and we classify the four main sequence stars as blue lurkers. The binary fraction in NGC 752 is estimated to be 50–70%, and it shows that the contribution of optically undetected stars is crucial in quantifying the present-day binary fraction.

Discovered a new open cluster near the poorly studied Majaess 190

We present the results of a comprehensive astrophysical study of a newly discovered open cluster, dubbed Ash-1. Using the third data release of the Gaia space mission, Gaia DR3, Ash-1 was accidentally discovered within the constellation Sagittarius in the field of the poorly studied cluster Majaess 190. Here we present the first estimates of these two clusters’ primary astrophysical properties. The membership probabilities > 0.50 were assigned to both clusters using the pyUPMASK technique. The distances were determined using the parallaxes of the clusters’ members, which were consistent with the isochrone fitting of the color-magnitude diagrams. The ages and distances of Majaess 190 and Ash-1 are found to be 4 ± 0.05 Gyr and 630 ± 20 Myr; 2130 and 1360 (±80) pc, respectively. The extinctions, heliocentric distances, mass function, luminosity function, and overall masses of the studied clusters were also computed. Based on the relaxation times, it appears that both clusters are in a state of dynamic relaxation.

Magnetic Fields in M-dwarf Members of the Pleiades Open Cluster Using APOGEE Spectra

Average magnetic field measurements are presented for 62 M-dwarf members of the Pleiades open cluster, derived from Zeeman-enhanced Fe i lines in the H band. A Markov Chain Monte Carlo methodology was employed to model magnetic filling factors using Sloan Digital Sky Survey (SDSS) IV APOGEE high-resolution spectra, along with the radiative transfer code Synmast, MARCS stellar atmosphere models, and the APOGEE Data Release 17 spectral line list. There is a positive correlation between mean magnetic fields and stellar rotation, with slow-rotator stars (Rossby number, Ro > 0.13) exhibiting a steeper slope than rapid rotators (Ro < 0.13). However, the latter sample still shows a positive trend between Ro and magnetic fields, which is given by 〈B〉 = 1604 × Ro−0.20. The derived stellar radii when compared with physical isochrones show that, on average, our sample shows radius inflation, with median enhanced radii ranging from +3.0% to +7.0%, depending on the model. There is a positive correlation between magnetic field strength and radius inflation, as well as with stellar spot coverage, correlations which together indicate that stellar spot-filling factors generated by strong magnetic fields might be the mechanism that drives radius inflation in these stars. We also compare our derived magnetic fields with chromospheric emission lines (Hα, Hβ, and Ca ii K), as well as with X-ray and Hα to bolometric luminosity ratios, and find that stars with higher chromospheric and coronal activity tend to be more magnetic.

The enigma of Li-rich giants and its relation with temporal variations observed in radial velocity and stellar activity signals

Context. Despite the large number of studies focused on the characterisation of Li-rich stars and understanding the mechanisms leading to such enrichment, their origin remains a mystery. Aims. Magnetic activity, particularly the phenomena usually associated with it (e.g. spots and plages), and the Li abundance (A(Li)) of stars, are in general thought to be connected. As of today, however, just how they are connected is unclear. In this work, we study a sample of young but evolved intermediate-mass red giants that are inhabitants of open clusters where planets have been searched for. Our aim is to use radial velocity (RV) and stellar activity indicator signals to look for relations between Li abundances and stellar activity or variability. Methods. We explored how the standard deviation (STD), peak-to-peak amplitude (PTP), mean, and median of typical stellar activity indicators (BIS, FWHM, Teff, and Hα index) change as a function of the Li content of 82 red giants. Furthermore, we computed weighted Pearson correlation coefficients (ρw) between time series of RV measurements and the stellar activity indicators for the stars in our sample. To aid our results, we also studied generalized Lomb–Scargle periodograms (GLSP) to capture possible significant periodic temporal variations in our data. Results. Our analysis indicates that the STD and PTP of BIS and FWHM, the mean and median of the Hα index, and υ sin(i) increase exponentially with A(Li) in our sample of red giants. Significant temporal variations and correlations between RVs and activity indicators also tend to be found preferentially for stars where high A(Li) is observed. Most of the Li-rich stars in our sample either show strong correlations of RV with at least one of the stellar activity indicators or reveal significant periodic temporal variations in their GLSPs of stellar activity indicators that are consistent with those found for RV.

Deep investigation of a pair of open clusters NGC 7031 and NGC 7086 utilizing Gaia DR3

Deep investigation of a pair of open clusters NGC 7031 and NGC 7086 utilizing Gaia DR3

Photometric Studies of EV Cnc and AH Cnc in the Open Cluster M67

Contact binaries at various stages of evolution unveil various operating mechanisms that drive them. We report the photometric and period variation analysis of two contact binaries EV Cnc and AH Cnc in open cluster M67. We observed the cluster from the JCBT 1.3 m telescope and utilized TESS and Kepler observations. The photometric solutions of EV Cnc and AH Cnc revealed a mass ratio of q ∼ 0.41 and ∼0.15 with an inclination of i = 42° and 87° respectively. These solutions suggest that EV Cnc is probably a semi-detached and AH Cnc is a deep low-mass ratio contact binary. The study of O − C variation analysis indicates that for both systems, the period is increasing which suggests the mass transfer is occurring from secondary to primary. In the case of AH Cnc and based on simulations by randomly varying the time of minima to fit the LITE solution, we noted the third body orbital period to be around P 3 = 26.82 ± 2.54 yr, which is different from earlier reported values and conclude that future observations are required to confirm this scenario. We compare these two systems with other similar contact binaries to get an estimate of the final configuration of the respective systems.

WIYN Open Cluster Study. XC. Barium Surface Abundances of Blue Straggler Stars in the Open Clusters NGC 7789 and M67

We investigate barium (Ba) abundances in blue straggler stars (BSSs) in two open clusters, NGC 7789 (1.6 Gyr) and M67 (4 Gyr), as signatures of asymptotic-giant-branch (AGB) mass transfer. We combine our findings with previous Ba abundance analyses of NGC 6819 (2.5 Gyr) and NGC 188 (7 Gyr). Out of 35 BSSs studied in NGC 7789, NGC 6819, and M67, 15 (43% ± 11%) are Ba enriched; no BSSs in NGC 188 are Ba enriched. The Ba abundances of enriched BSSs show an anticorrelation with cluster age, ranging from an enrichment of [Ba/Fe] ∼ +1.5 dex in NGC 7789 to [Ba/Fe] ∼ +1.0 dex in M67. The Ba-enriched BSSs all lie in the same region of the H-R diagram, irrespective of cluster age or distance from the main-sequence turnoff. Our data suggest a link between AGB donor mass and mass-transfer efficiency in BSSs, in that less massive AGB donors tend to undergo more conservative mass transfer. We find that 40% ± 16% of the Ba-enriched BSSs are in longer-period spectroscopic binaries with orbital periods less than 5000 days. Those Ba-enriched BSSs that do not exhibit radial-velocity variability suggest AGB mass transfer in wide binaries by either wind mass transfer or wind Roche-lobe overflow. Given the preponderance of long orbital periods in the BSSs of M67 and NGC 188 and the frequency of Ba enrichment in NGC 7789, NGC 6819, and M67, it may be that AGB mass transfer is the dominant mechanism of BSS formation in open clusters older than 1 Gyr.

An Analysis of Blue Straggler Stars in Open Clusters

The presence of blue straggler stars (BSSs) in open clusters (OCs) presents an opportunity to study star formation and cluster dynamics. Our paper analyzes several properties of BSSs across 161 OCs of different ages, metallicities, and sizes. Specifically, we examine the impact of cluster age and metallicity on the number of BSSs as well as the spatial distribution of BSSs within each cluster. We report a positive correlation between the age of the cluster and the number of BSSs present. This investigation into BSSs provides valuable insights into their formation as well as the dynamics and interactions within open clusters.

Tessilator: a one-stop shop for measuring TESS rotation periods

ABSTRACT We present a software package designed to produce photometric light curves and measure rotation periods from full-frame images taken by the Transiting Exoplanet Survey Satellite (TESS), which we name ‘tessilator’. tessilator is the only publicly available code that will run a full light curve and rotation period ($P_{\rm rot}$) analysis based on just a (list of) target identifier(s) or sky position(s) via a simple command-line prompt. This paper sets out to introduce the rationale for developing tessilator, and then describes the methods, considerations, and assumptions for: extracting photometry; dealing with potential contamination; accounting for natural and instrumental systematic effects; light-curve normalization and detrending; removing outliers and unreliable data; and finally, measuring the $P_{\rm rot}$ value and several periodogram attributes. Our methods have been tuned specifically to optimize TESS light curves and are independent from the pipelines developed by the TESS Science Processing Operations Center (SPOC), meaning tessilator can, in principle, analyse any target across the entire celestial sphere. We compare tessilator$P_{\rm rot}$ measurements with TESS-SPOC-derived light curves of 1560 (mainly solar-type and low-mass) stars across four benchmark open clusters (Pisces–Eridanus, the Pleiades, the Hyades, and Praesepe) and a sample of nearby field M-dwarfs. From a vetted subsample of 864 targets we find an excellent return of $P_{\rm rot}$ matches for the first three open clusters ($\gt 85$ per cent) and a moderate ($\sim 60$ per cent) match for the 700 Myr Praesepe and MEarth sample, which validates tessilator as a tool for measuring $P_{\rm rot}$. The tessilator code is available at https://github.com/alexbinks/tessilator.

High-Nuclearity Ln210Al140 Clusters: Neonates of Open Hollow Dodecahedral Cage Families.

Open hollow dodecahedral cage clusters have long been a coveted target in synthetic chemistry, yet their creation poses immense challenges. Here we report two open hollow dodecahedral lanthanide-aluminum (Ln-Al) heterometallic cage clusters, namely, [Ln210Al140(μ2-OH)210(μ3-OH)540(OAc)180(H2O)156](ClO4)120·(MeCN)x·(H2O)y, (Ln = Dy and x = 27, y = 300 for 1; Ln = Y and x = 28, y = 420 for 2). Remarkably, the 350 metal atoms in 1 and 2 display a Keplerate-type four-shell structure of truncated icosidodecahedron@dodecahedron@dodecahedron@icosidodecahedron. The diameter of the cationic cluster in 1 is approximately 5.0 nm, with an inner cavity diameter of about 2.8 nm and a window diameter of roughly 0.66 nm. The cluster in 1 boasts an accessible inner void volume of up to 15,000 Å3. Notably, these cage clusters maintain stability in water, and the truncated icosidodecahedrons in 1 and 2 are the first of their kind synthesized to date. Given that the open hollow dodecahedral Ln-Al cage cluster has never been reported before, this work represents a member in the family of hollow open dodecahedral cages.

UOCS XIV: Study of the Open Cluster NGC 2627 Using UVIT/AstroSat

We study the intermediate-age open cluster NGC 2627, located at a distance of ∼2 kpc, using UVIT/AstroSat and other archival data. Using a machine learning-based algorithm, ML-MOC, on the Gaia DR3 data, we identify 422 cluster members, including four blue straggler stars (BSSs), one yellow straggler star (YSS), one blue lurker (BL), one red clump (RC) star, and two binary candidates with detection in both UVIT/F148W and UVIT/F169M filters. We characterise them using multiwavelength spectral energy distributions (SEDs). Out of the above nine sources, one BSS, the BL, and one binary candidate have a source nearby; hence, we did not fit their SEDs. Of the remaining six sources, we successfully fit two with single-component SEDs and four with binary-component SEDs. The binary-component SED-based parameters indicate that the hot companions of BSSs, the YSS, the RC star, and the binary candidate are extremely low-mass white dwarfs, confirming that at least four out of nine stars (44%) are formed via the mass transfer channel. We fit King’s profile function to the high-probability (p > 0.8) cluster members and estimate the cluster core radius (r C ) to be 3.84′ and the tidal radius (r t ) to be 36.85′. We find that the equal-mass binaries are most concentrated towards the cluster center, followed by the single massive stars, and single low-mass stars. The BSS population of the cluster is also found to be located within a radius r ∼ 10 × r C from the cluster center, suggesting the dynamical evolution of the cluster.

VVVX survey dusts off a new intermediate-age star cluster in the Milky Way disk

Context. In the last decade, many new star clusters have been discovered in heavily obscured regions of the Milky Way bulge and disk. Aims. Our primary long-term objective is to seek out additional star clusters in the poorly studied regions of the Milky Way, where detections pose significant challenges. The aim of this pursuit is to finalize the Milky Way’s globular and open cluster system census and to gain a comprehensive understanding of both the formation and evolution of these systems and our Galaxy as a whole. Methods. We report the discovery of a new star cluster, named Garro 03. We investigated this new target using a combination of near-infrared and optical databases. We employed the VISTA Variables in the Via Láctea Survey and Two Micron All Sky Survey data in the near-infrared, and the Gaia Data Release 3 and the DECam Plane Survey datasets in the optical passband. We constructed density maps and vector proper motion diagrams in order to highlight our target. We performed a photometrical analysis in order to derive its main physical parameters. Results. Garro 03 is located at equatorial coordinates RA = 14:01:29.3 and Dec = −65:30:57.0. From our photometric analysis we find that this cluster is not heavily affected by extinction with AKs = 0.25 ± 0.04 mag and AG = 1.54 ± 0.02 mag. It is located at heliocentric distance of 14.1 ± 0.5 kpc, which places Garro 03 at 10.6 kpc from the Galactic centre and Z = −0.89 kpc below the Galactic plane. We also calculated the mean cluster proper motion of (μα*,μδ)=(−4.57 ± 0.29, −1.36 ± 0.27) mas yr−1. We derived an age of 3 Gyr and metallicity [Fe/H] = −0.5 ± 0.2 by the isochrone-fitting method, employing the PARSEC models. The total luminosity was derived in the Ks and V bands, finding MKs = −6.32 ± 1.10 mag and MV = −4.06 mag. Finally, the core and tidal radii were measured constructing the Garro 03 radial density profile and fitting the King model. We obtained rc = 3.07 ± 0.98 pc and rt = 19.36 ± 15.96 pc, respectively. Conclusions. We photometrically confirm the cluster nature for Garro 03, located in the Galactic disk. It is a distant, low-luminosity, metal-rich star cluster of intermediate age. We also searched for possible signatures (streams or bridges) between Garro 03 and Garro 01, but we exclude a companionship with the present analysis. We need spectroscopic data to classify it as an old open cluster or a young globular cluster, and to understand its origin.

Chemical Cartography with APOGEE: Two-process Parameters and Residual Abundances for 288,789 Stars from Data Release 17

Stellar abundance measurements are subject to systematic errors that induce extra scatter and artificial correlations in elemental abundance patterns. We derive empirical calibration offsets to remove systematic trends with surface gravity log(g) in 17 elemental abundances of 288,789 evolved stars from the SDSS APOGEE survey. We fit these corrected abundances as the sum of a prompt process tracing core-collapse supernovae and a delayed process tracing Type Ia supernovae, thus recasting each star’s measurements into the amplitudes A cc and A Ia and the element-by-element residuals from this two-parameter fit. As a first application of this catalog, which is 8× larger than that of previous analyses that used a restricted log(g) range, we examine the median residual abundances of 14 open clusters, nine globular clusters, and four dwarf satellite galaxies. Relative to field Milky Way disk stars, the open clusters younger than 2 Gyr show ≈0.1−0.2 dex enhancements of the neutron-capture element Ce, and the two clusters younger than 0.5 Gyr also show elevated levels of C+N, Na, S, and Cu. Globular clusters show elevated median abundances of C+N, Na, Al, and Ce, and correlated abundance residuals that follow previously known trends. The four dwarf satellites show similar residual abundance patterns despite their different star formation histories, with ≈0.2–0.3 dex depletions in C+N, Na, and Al and ≈0.1 dex depletions in Ni, V, Mn, and Co. We provide our catalog of corrected APOGEE abundances, two-process amplitudes, and residual abundances, which will be valuable for future studies of abundance patterns in different stellar populations and of additional enrichment processes that affect galactic chemical evolution.

Discovery of a Barium Blue Straggler Star in M67 and “Sighting” of Its White Dwarf Companion* * This is paper XV of the UVIT Open Cluster Study (UOCS).

We report the discovery of a barium blue straggler star (BSS) in M67, exhibiting enhancements in slow neutron-capture (s-)process elements. Spectroscopic analysis of two BSSs (WOCS 9005 & WOCS 1020) and four stars located near the main-sequence turn-off using GALAH spectra, showed that WOCS 9005 has a significantly high abundance of the s-process elements ([Ba/Fe] = 0.75 ± 0.08, [Y/Fe] = 1.09 ± 0.07, and [La/Fe] = 0.65 ± 0.06). The BSS (WOCS 9005) is a spectroscopic binary with a known period, eccentricity, and a suspected white dwarf (WD) companion with a kinematic mass of 0.5 M ⊙. The first “sighting” of the WD in this barium BSS is achieved through multiwavelength spectral energy distribution (SED) with the crucial far-UV data from the UVIT/AstroSat. The parameters of the hot and cool companions are derived using binary fits of the SED using two combinations of models, yielding a WD with T eff in the range 9750–15,250 K. Considering the kinematic mass limit, the cooling age of the WD is estimated as ∼60 Myr. The observed enhancements are attributed to a mass transfer (MT) from a companion asymptotic giant branch star, now a WD. We estimate the accreted mass to be 0.15 M ⊙, through wind accretion, which increased the envelope mass from 0.45 M ⊙. The detection of chemical enhancement, as well as the sighting of WD in this system, have been possible due to the recent MT in this binary, as suggested by the young WD.

Exploring fluorine chemical evolution in the Galactic disk: The open cluster perspective

Open clusters are ideal tools for tracing the abundances of different elements because their stars are expected to have the same age, distance, and metallicity. Therefore, they serve as powerful tracers for investigating the cosmic origins of elements. This paper expands on a recent study by us, in which the element fluorine was studied in seven open clusters; here we add six open clusters and eight field stars. The primary objective is to determine the abundance of fluorine (F) to gain insight into its production and evolution. The magnesium (Mg) abundances were derived to categorize the field stars into high and low alpha disk populations. Additionally, cerium (Ce) abundances were determined to better understand the interplay between F and s-process elements. Our goal is to analyze the trend of F abundances across the Galactic disk based on metallicity and age. By comparing observational data with Galactic chemical evolution models, the origin of F can be better understood. The spectra were obtained from the high-resolution near-infrared GIANO-B instrument at the Telescopio Nazionale Galileo (TNG). For the derivation of the stellar parameters and abundances, the Python version of Spectroscopy Made Easy ( PySME ) was used. OH, CN, and CO molecular lines and band heads along with Fe I lines were used to determine the stellar parameters in the H-band region. Two HF lines in the K band ($ 2.28, and 2.33 mu m), three K-band Mg I lines ($ 2.10, 2.11, and 2.15 mu m), and two Ce II lines in the H band ($ 1.66, and 1.71 mu m) were used to derive the abundances of F, Mg, and Ce, respectively. F, Mg, and Ce abundances were derived for 14 stars from 6 OCs, as well as for 8 field stars. The F and Ce abundances were investigated as a function of metallicity, age, and galactocentric distance. We also compared our findings with different Galactic chemical evolution models. Our results indicate that asymptotic giant branch stars and massive stars, including a subset of fast rotators (whose rotation speed likely increases as metallicity decreases), are necessary to explain the cosmic origin of F. This finding is consistent with and, with the large sample size, reinforces the conclusion of our previous study.

Tidal tails of open clusters

Open clusters that emerged from the star-forming regions as gravitationally bound structures are subjected to star evaporation, ejection, and tidal forces throughout the rest of their lives. Consequently, they form tidal tails that can stretch kiloparsecs along the cluster's orbit. Cluster members are typically found by searching for overdensities in some parameter space (positions and velocities or sometimes actions and orbital parameters of stars). However, this method is not effective at identifying stars located in the tidal tails far from the open cluster cores. We present a probabilistic method for finding distant cluster members without relying on a search for overdensities and apply it to 476 open clusters. First, we simulated the dissolution of a cluster and obtained a probability distribution (likelihood) describing where cluster members are to be found. The distribution of stars from the Gaia DR3 catalogue in high likelihood regions was then compared to the simulated stellar population of the Galaxy to define the membership probability of each star. The survey of cluster members included all stars with a magnitude of $G&lt;17.5$ and larger clusters with an age of $&gt;100\ Myr $ within $3\ kpc $ from the Sun. We successfully found stars with high membership probabilities in the tidal tails of most clusters. The recovered tidal tails stretch more than a kiloparsec from the cluster cores in some cases. We analysed the morphological properties of the tidal tails and demonstrated how properly normalised membership probabilities aid systematic studies of open clusters. Finally, we have published a catalogue of stars found in the tidal tails.