Orbital Parameters and Binary Properties of 37 FGK Stars in the Cores of Open Clusters NGC 2516 and NGC 2422

Abstract We present orbits for 24 binaries in the field of open cluster NGC 2516 (∼150 Myr) and 13 binaries in the field of open cluster NGC 2422 (∼130 Myr) using results from a multiyear radial-velocity (RV) survey of the cluster cores. Six of these systems are double-lined spectroscopic binaries. We fit these RV variable systems with orvara, a MCMC-based fitting program that models Keplerian orbits. We use precise stellar parallaxes and proper motions from Gaia EDR3 to determine cluster membership. We impose a barycentric RV prior on all cluster members; this significantly improves our orbital constraints. Two of our systems have periods between five and 15 days, the critical window in which tides efficiently damp orbital eccentricity. These binaries should be included in future analyses of circularization across similarly-aged clusters. We also find a relatively flat distribution of binary mass ratios, consistent with previous work. With the inclusion of TESS light curves for all available targets, we identity target 378–036252 as a new eclipsing binary. We also identify a field star whose secondary has a mass in the brown dwarf range, as well as two cluster members whose RVs suggest the presence of an additional companion. Our orbital fits will help constrain the binary fraction and binary properties across stellar age and across stellar environment.

Download Full-text

The nature of the NGC 2546: Not one but two open clusters

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936294 ◽

2020 ◽

Vol 633 ◽

pp. A146 ◽

Cited By ~ 1

Author(s):

A. D. Alejo ◽

J. F. González ◽

M. E. Veramendi

Keyword(s):

Radial Velocity ◽

Binary Stars ◽

Open Cluster ◽

Open Clusters ◽

Spectroscopic Binaries ◽

Physical Parameters ◽

Distance Modulus ◽

Cluster Membership ◽

Spectroscopic Observations ◽

Astrometric Data

Context. As part of a broader project on the role of binary stars in clusters, we present a spectroscopic study of the open cluster NGC 2546, which is a large cluster lacking previous spectroscopic analysis. Aims. We report the finding of two open clusters in the region of NGC 2546. For the two star groups, we determine radial velocity, parallax, proper motion, reddening, distance modulus, and age, using our spectroscopic observations and available photometric and astrometric data, mainly from the second Gaia data release (Gaia-DR2). We also determine the orbit of four spectroscopic binaries in these open clusters. Methods. From mid-resolution spectroscopic observations for 28 stars in the NGC 2546 region, we determined radial velocities and evaluate velocity variability. To analyze double-lined spectroscopic binaries, we used a spectral separation technique and fit the spectroscopic orbits using a least-squares code. The presence of two stellar groups is suggested by the radial velocity distribution and confirmed by available photometric and astrometric data. We applied a multi-criteria analysis to determine cluster membership, and obtained kinematic and physical parameters of the clusters. Results. NGC 2546 is actually two clusters, NGC 2546A and NGC 2546B, which are not physically related to each other. NGC 2546A has an age of about 180 Myr and a distance of 950 pc. It has a half-number radius of 8 pc and contains about 480 members brighter than G = 18 mag. NGC 2546B is a very young cluster (<10 Myr) located at a distance of 1450 pc. It is a small cluster with 80 members and a half-number radius of 1.6 pc. Stars less massive than 2.5 M⊙ in this cluster would be pre-main-sequence objects. We detected four spectroscopic binaries and determined their orbits. The two binaries of NGC 2546A contain chemically peculiar components: HD 68693 is composed of two mercury-manganese stars and HD 68624 has a Bp silicon secondary. Among the most massive objects of NGC 2546B, there are two binary stars: HD 68572, with P = 124.2 d, and CD -37 4344 with P = 10.4 d.

Download Full-text

ML-MOC: Machine Learning (kNN and GMM) based Membership determination for Open Clusters

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab118 ◽

2021 ◽

Vol 502 (2) ◽

pp. 2582-2599

Author(s):

Manan Agarwal ◽

Khushboo K Rao ◽

Kaushar Vaidya ◽

Souradeep Bhattacharya

Keyword(s):

Machine Learning ◽

Open Cluster ◽

A Priori ◽

Gaussian Mixture ◽

Open Clusters ◽

Proper Motions ◽

Cluster Membership ◽

Priori Information ◽

Gaia Dr2 ◽

Good Agreement

ABSTRACT The existing open-cluster membership determination algorithms are either prior dependent on some known parameters of clusters or are not automatable to large samples of clusters. In this paper, we present ml-moc, a new machine-learning-based approach to identify likely members of open clusters using the Gaia DR2 data and no a priori information about cluster parameters. We use the k-nearest neighbour (kNN) algorithm and the Gaussian mixture model (GMM) on high-precision proper motions and parallax measurements from the Gaia DR2 data to determine the membership probabilities of individual sources down to G ∼ 20 mag. To validate the developed method, we apply it to 15 open clusters: M67, NGC 2099, NGC 2141, NGC 2243, NGC 2539, NGC 6253, NGC 6405, NGC 6791, NGC 7044, NGC 7142, NGC 752, Blanco 1, Berkeley 18, IC 4651, and Hyades. These clusters differ in terms of their ages, distances, metallicities, and extinctions and cover a wide parameter space in proper motions and parallaxes with respect to the field population. The extracted members produce clean colour–magnitude diagrams and our astrometric parameters of the clusters are in good agreement with the values derived in previous work. The estimated degree of contamination in the extracted members ranges between 2 ${{\ \rm per\ cent}}$ and 12 ${{\ \rm per\ cent}}$. The results show that ml-moc is a reliable approach to segregate open-cluster members from field stars.

Download Full-text

Characterising open clusters in the solar neighbourhood with the Tycho-Gaia Astrometric Solution

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731251 ◽

2018 ◽

Vol 615 ◽

pp. A49 ◽

Cited By ~ 26

Author(s):

T. Cantat-Gaudin ◽

A. Vallenari ◽

R. Sordo ◽

F. Pensabene ◽

A. Krone-Martins ◽

...

Keyword(s):

Monte Carlo ◽

Markov Chain ◽

High Probability ◽

Open Clusters ◽

Distance Modulus ◽

The Sun ◽

Proper Motions ◽

Orbital Parameters ◽

Naval Observatory ◽

Galactic Potential

Context. The Tycho-Gaia Astrometric Solution (TGAS) subset of the first Gaia catalogue contains an unprecedented sample of proper motions and parallaxes for two million stars brighter than G ~ 12 mag. Aims. We take advantage of the full astrometric solution available for those stars to identify the members of known open clusters and compute mean cluster parameters using either TGAS or the fourth U.S. Naval Observatory CCD Astrograph Catalog (UCAC4) proper motions, and TGAS parallaxes. Methods. We apply an unsupervised membership assignment procedure to select high probability cluster members, we use a Bayesian/Markov Chain Monte Carlo technique to fit stellar isochrones to the observed 2MASS JHKS magnitudes of the member stars and derive cluster parameters (age, metallicity, extinction, distance modulus), and we combine TGAS data with spectroscopic radial velocities to compute full Galactic orbits. Results. We obtain mean astrometric parameters (proper motions and parallaxes) for 128 clusters closer than about 2 kpc, and cluster parameters from isochrone fitting for 26 of them located within a distance of 1 kpc from the Sun. We show the orbital parameters obtained from integrating 36 orbits in a Galactic potential.

Download Full-text

Reanalysis of nearby open clusters using Gaia DR1/TGAS and HSOY

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731905 ◽

2018 ◽

Vol 615 ◽

pp. A12 ◽

Cited By ~ 12

Author(s):

Steffi X. Yen ◽

Sabine Reffert ◽

Elena Schilbach ◽

Siegfried Röser ◽

Nina V. Kharchenko ◽

...

Keyword(s):

Milky Way ◽

Open Cluster ◽

Star Clusters ◽

Open Clusters ◽

Parameter Estimates ◽

Cluster Membership ◽

Fitting Procedure ◽

Cluster Data ◽

The Galaxy ◽

Automatic Tool

Context. Open clusters have long been used to gain insights into the structure, composition, and evolution of the Galaxy. With the large amount of stellar data available for many clusters in the Gaia era, new techniques must be developed for analyzing open clusters, as visual inspection of cluster color-magnitude diagrams is no longer feasible. An automatic tool will be required to analyze large samples of open clusters. Aims. We seek to develop an automatic isochrone-fitting procedure to consistently determine cluster membership and the fundamental cluster parameters. Methods. Our cluster characterization pipeline first determined cluster membership with precise astrometry, primarily from TGAS and HSOY. With initial cluster members established, isochrones were fitted, using a χ2 minimization, to the cluster photometry in order to determine cluster mean distances, ages, and reddening. Cluster membership was also refined based on the stellar photometry. We used multiband photometry, which includes ASCC-2.5 BV, 2MASS JHKs, and Gaia G band. Results. We present parameter estimates for all 24 clusters closer than 333 pc as determined by the Catalogue of Open Cluster Data and the Milky Way Star Clusters catalog. We find that our parameters are consistent to those in the Milky Way Star Clusters catalog. Conclusions. We demonstrate that it is feasible to develop an automated pipeline that determines cluster parameters and membership reliably. After additional modifications, our pipeline will be able to use Gaia DR2 as input, leading to better cluster memberships and more accurate cluster parameters for a much larger number of clusters.

Download Full-text

High-resolution spectroscopy of red giants and ‘yellow stragglers’ in the southern open cluster NGC 2539

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa647 ◽

2020 ◽

Vol 494 (1) ◽

pp. 1470-1489

Author(s):

Cintia F Martinez ◽

N Holanda ◽

C B Pereira ◽

N A Drake

Keyword(s):

High Resolution ◽

Open Cluster ◽

Open Clusters ◽

Solar Neighborhood ◽

Spectroscopic Binaries ◽

High Resolution Spectroscopy ◽

Red Giants ◽

Light Elements ◽

Abundance Pattern ◽

Solar Metallicity

ABSTRACT We present a detailed high-resolution spectroscopic analysis of 12 red giant stars, in single and binaries or multiples systems, classified as members of the intermediate-age (631 Myr) open cluster NGC 2539. We used FEROS echelle spectra and the standard LTE analysis to derive the atmospheric parameters for the stars and the abundance ratios of light elements (Li, C, N), light odd-Z elements (Na, Al), α-elements (Mg, Si, Ca, Ti), Fe-group elements (Cr, Fe, Ni), and n-capture elements (Y, Zr, Ce, Nd, Eu). Our results show that the sample star of NGC 2539 has low projected rotational velocities and an almost solar metallicity, with a mean of [Fe/H] = −0.03 ± 0.07 dex. The abundance pattern displays for the analyzed stars are, in general, similar to those presented by solar neighborhood stars, including giant members of others open clusters. In particular, light elements and Na abundance pattern shows anomalies resulting from the appearance of enriched material on the stellar surface, produced by mechanisms like the first dredge-up and/or thermohaline and rotation-induced mixing. We also identified two of the spectroscopic binaries of our sample as ‘yellow stragglers’ and we determined the nature of their companions.

Download Full-text

The expectation maximization algorithm as a powerful tool to solve the stellar membership in open clusters: An application to M67

Serbian Astronomical Journal ◽

10.2298/saj0673057u ◽

2006 ◽

pp. 57-64 ◽

Cited By ~ 5

Author(s):

A. Uribe ◽

R. Barrera ◽

E. Brieva

Keyword(s):

Em Algorithm ◽

Expectation Maximization ◽

Open Cluster ◽

Expectation Maximization Algorithm ◽

Open Clusters ◽

Membership Problem ◽

Proper Motions ◽

Bivariate Normal ◽

Mixture Density ◽

The Em Algorithm

The EM algorithm is a powerful tool to solve the membership problem in open clusters when a mixture density model overlaping two heteroscedastic bivariate normal components is built to fit the cloud of relative proper motions of the stars in a region of the sky where a cluster is supposed to be. A membership study of 1866 stars located in the region of the very old open cluster M67 is carried out via the Expectation Maximization algorithm using the McLachlan, Peel, Basford and Adams EMMIX software.

Download Full-text

Orbit circularization time in binary stellar systems

Symposium - International Astronomical Union ◽

10.1017/s0074180900031223 ◽

1984 ◽

Vol 105 ◽

pp. 411-414 ◽

Cited By ~ 1

Author(s):

M. Mayor ◽

J.-C. Mermilliod

Keyword(s):

Time Scale ◽

Dynamical Evolution ◽

Open Clusters ◽

Spectroscopic Binaries ◽

Stellar Systems ◽

Orbital Parameters ◽

Short Period ◽

Red Giant

We have analyzed the orbital parameters of 33 red dwarf and 17 red giant spectroscopic binaries belonging to open clusters to deduce the time-scale for orbital circularization. The dynamical evolution of BD +23°635, a short period binary member of the Hyades, should result in the formation either of a cataclysmic binary or a WUMa system.

Download Full-text

Exploring open cluster properties with Gaia and LAMOST

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937131 ◽

2020 ◽

Vol 640 ◽

pp. A127

Author(s):

Jing Zhong ◽

Li Chen ◽

Di Wu ◽

Lu Li ◽

Leya Bai ◽

...

Keyword(s):

Open Cluster ◽

Open Clusters ◽

Reliable Determination ◽

Spectroscopic Parameters ◽

Orbital Parameters ◽

Spectroscopic Observations ◽

Fundamental Properties ◽

Cluster Properties ◽

Stellar Properties ◽

High Level

Context. In Gaia DR2, an unprecedented high level of precision has been reached at sub-milliarcsecond for astrometry and millimagnitudes for photometry. Using cluster members identified with the astrometry and photometry in Gaia DR2, we can obtain a reliable determination of cluster properties. However, because of the shortcomings of Gaia spectroscopic observations in dealing with densely crowded cluster regions, the RVs and metallicity values for cluster member stars from Gaia DR2 are still lacking. It is necessary to combine the Gaia data with the data from large spectroscopic surveys, such as LAMOST, APOGEE, GALAH, and Gaia-ESO. Aims. In this study our aim is to improve the cluster properties by combining the LAMOST spectra. In particular, we provide the list of cluster members with spectroscopic parameters as an add-value catalog in LAMOST DR5, which can be used to perform a detailed study for a better understanding of the stellar properties, by using their spectra and fundamental properties from the host cluster. Methods. We cross-matched the spectroscopic catalog in LAMOST DR5 with the identified cluster members in Cantat-Gaudin et al. (2018, A&A, 618, A93). We then used members with spectroscopic parameters to derive statistical properties of open clusters. Results. We obtained a list of 8811 members with spectroscopic parameters and a catalog of 295 cluster properties. The provided cluster properties include astrometric parameters, spectroscopic parameters, derived kinematic and orbital parameters, and isochrone fitting results. In addition, we study the radial and vertical metallicity gradient and age-metallicity relation with the compiled open clusters as tracers, finding slopes of −0.053 ± 0.004 dex kpc−1, −0.252 ± 0.039 dex kpc−1, and 0.022 ± 0.008 dex Gyr−1, respectively. The slopes of the metallicity distribution relation for young clusters (0.1 Gyr < Age < 2 Gyr) and the age-metallicity relation for clusters within 6 Gyr are both consistent with the literature results. In order to fully study the chemical evolution history in the disk, more spectroscopic observations for old and distant open clusters are needed for further investigation.

Download Full-text

Investigating dynamical properties of evolved Galactic open clusters

Astronomy and Astrophysics ◽

10.1051/0004-6361/201832702 ◽

2019 ◽

Vol 624 ◽

pp. A8 ◽

Cited By ~ 8

Author(s):

M. S. Angelo ◽

J. F. C. Santos ◽

W. J. B. Corradi ◽

F. F. S. Maia

Keyword(s):

Open Cluster ◽

Three Dimensional ◽

Dynamical Evolution ◽

Long Term Evolution ◽

Open Clusters ◽

Evolutionary Stage ◽

Proper Motions ◽

Stellar Content ◽

Term Evolution

Context. The stellar content of Galactic open clusters is gradually depleted during their evolution as a result of internal relaxation and external interactions. The final residues of the long-term evolution of open clusters are called open cluster remnants. These are sparsely populated structures that can barely be distinguished from the field. Aims. We aimed to characterise and compare the dynamical states of a set of 16 objects catalogued as remnants or remnant candidates. We employed parameters that are intimately associated with the dynamical evolution: age, limiting radius, stellar mass, and velocity dispersion. The sample also includes 7 objects that are catalogued as dynamically evolved open clusters for comparison purposes. Methods. We used photometric data from the 2MASS catalogue, proper motions and parallaxes from the Gaia DR2 catalogue, and a decontamination algorithm that was applied to the three-dimensional astrometric space of proper motions and parallaxes (μα, μδ, ϖ) for stars in the objects’ areas. The luminosity and mass functions and total masses for most open cluster remnants are derived here for the first time. Our analysis used predictions of N-body simulations to estimate the initial number of stars of the remnants from their dissolution timescales. Results. The investigated open cluster remnants present masses (M) and velocity dispersions (σv) within well-defined ranges: M between ∼10−40 M⊙ and σv between ∼1−7 km s−1. Some objects in the remnant sample have a limiting radius Rlim ≲ 2 pc, which means that they are more compact than the investigated open clusters; other remnants have Rlim between ∼2−7 pc, which is comparable to the open clusters. We suggest that cluster NGC 2180 (previously classified as an open cluster) is entering a remnant evolutionary stage. In general, our clusters show signals of depletion of low-mass stars. This confirms their dynamically evolved states. Conclusions. We conclude that the open cluster remnants we studied are in fact remnants of initially very populous open clusters (N0 ∼ 103−104 stars). The outcome of the long-term evolution is to bring the final residues of the open clusters to dynamical states that are similar to each other, thus masking out the memory of the initial formation conditions of star clusters.

Download Full-text

White dwarf-open cluster associations based on Gaia DR2

Astronomy and Astrophysics ◽

10.1051/0004-6361/202039276 ◽

2020 ◽

Vol 645 ◽

pp. A13

Author(s):

M. Prišegen ◽

M. Piecka ◽

N. Faltová ◽

M. Kajan ◽

E. Paunzen

Keyword(s):

Open Cluster ◽

Open Clusters ◽

Photometric Data ◽

Mass Relation ◽

Physical Processes ◽

Satellite Mission ◽

Cluster Membership ◽

Fundamental Parameters ◽

Data Release ◽

Gaia Dr2

Context. Fundamental parameters and physical processes leading to the formation of white dwarfs (WDs) may be constrained and refined by discovering WDs in open clusters (OCs). Cluster membership can be utilized to establish the precise distances, luminosities, ages, and progenitor masses of such WDs. Aims. We compile a list of probable WDs that are OC members in order to facilitate WD studies that are impractical or difficult to conduct for Galactic field WDs. Methods. We use recent catalogs of WDs and OCs that are based on the second data release of the Gaia satellite mission (GDR2) to identify WDs that are OC members. This crossmatch is facilitated by the astrometric and photometric data contained in GDR2 and the derived catalogs. Assuming that most of the WD members are of the DA type, we estimate the WD masses, cooling ages, and progenitor masses. Results. We have detected several new likely WD members and reassessed the membership of the literature WDs that had been previously associated with the studied OCs. Several of the recovered WDs fall into the recently reported discontinuity in the initial-final mass relation (IFMR) around Mi ∼ 2.0 M⊙, which allows for tighter constrains on the IFMR in this regime.

Download Full-text