Investigating kinematics and dynamics of three open clusters towards Galactic anticentre (original) (raw)
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Star Clusters in the Galactic Anticenter Stellar Structure and the Origin of Outer Old Open Clusters
The Astrophysical Journal, 2004
The Galactic Anticenter Stellar Structure (GASS) has been identified with excess surface densities of field stars in several large area sky surveys, and with an unusual, string-like grouping of five globular clusters. At least two of these are diffuse, young "transitional" clusters between open and globular types. Here we call attention to the fact that four younger open or transitional clusters extend the previously identified, string-like cluster grouping, with at least one having a radial velocity consistent with the previously found GASS velocity-longitude trend. All nine clusters lie close to a plane tipped 17 • to the Galactic plane. This planar orientation is used to forage for additional potential cluster members in the inner Galaxy, and a number are found along the same plane and string-like sequence, including almost all fifteen known outer, old open clusters. Tidal accretion of a dwarf satellite galaxy on a low inclination orbit -perhaps the GASS system -appears to be a plausible explanation for the origin of the outer, old open and transitional clusters of the Milky Way. We use these clusters to explore the age-metallicity relation of the putative accreted GASS progenitor. Finally, we provide the first radial velocity of a star in the cluster BH 176 and discuss its implications.
A Gaia-based Photometric and Kinematic Analysis of the Old Open Cluster King 11
The Astronomical Journal, 2021
This paper presents an investigation of an old age open cluster King 11 using Gaia's Early Data Release 3 (EDR3) data. Considering the stars with membership probability (P µ) > 90%, we identified 676 most probable cluster members within the cluster's limiting radius. The mean proper motion (PM) for King 11 is determined as: µ x = −3.391 ± 0.006 and µ y = −0.660 ± 0.004 mas yr −1. The blue straggler stars (BSS) of King 11 show a centrally concentrated radial distribution. The values of limiting radius, age, and distance are determined as 18.51 arcmin, 3.63±0.42 Gyr and 3.33 ± 0.15 kpc, respectively. The cluster's apex coordinates (A = 267.84 • ± 1.01 • , D = −27.48 • ± 1.03 •) are determined using the apex diagram (AD) method and verified using the (µ U ,µ T) diagram. We also obtained the orbit that the cluster follows in the Galaxy and estimated its tentative birthplace in the disk. The resulting spatial velocity of King 11 is 60.2 ± 2.16 km s −1. A significant oscillation along the Z-coordinate up to 0.556±0.022 kpc is determined.
2020
We derive astrophysical and structural parameters of open clusters NGC 1245 and NGC 2099 from 2MASS JHKs and Gaia DR2 photometric / astrometric data bases. Their likely members have been determined from Gaia DR2 proper motion data. Our E(B – V) values (2MASS) are slightly smaller than the literature values, whereas our E(B – V) values (Gaia DR2) agree with the literature within the uncertainties. Their distance moduli/distances and ages are in a good agreement with the early studies. NGC 1245 has steep negative core mass function slope (MFs) (χcore = −1.24). Its halo (χhalo = +0.78) and overall (χoverall = −0.95) MFs indicate small-scale mass segregation from its core to the outer regions, due to its [trlx(overall), τoverall] = [302 Myr, 5]. The MFs of NGC 2099 is very negative steep (χcore = −2.67) in the core, and quite positive steep (χhalo = +1.41) in the halo. This kind of MF slope steeping from the core to the outskirts indicates that lowmass stars in the core are transferred ...
Study of open cluster King 13 using CCD VI, 2MASS and Gaia DR2 Astrometry
New Astronomy, 2020
In this paper, we present astrophysical parameters of the open cluster King 13 based on the V I CCD and 2MASS JHK s photometric data. This is a poorly studied cluster, for which new results have been found in the present work. To identify probable members, we use proper motion data from Gaia DR2 catalogue. The mean proper motion of the cluster is determined as −2.8±0.2 and −0.88±0.14 mas yr −1 and cluster extent is derived as 3 ′ .2. Using color-magnitude diagrams, we estimate the age and distance of the cluster as 510 ± 60 Myr and 3.84 ± 0.15 kpc respectively. Interstellar reddening E(B − V) in the direction of the cluster is determined as 0.80 ± 0.2 mag using color-color diagram. Mass function slope of the cluster is found to be comparable with the Salpeter value. The total mass of this cluster is derived as 270 M ⊙. The present analysis shows that King 13 is a dynamically relaxed cluster.
The structure and dynamics of young star clusters: King 16, NGC 1931, NGC 637 and NGC 189
Astrophysics and Space Science, 2008
In this paper, using 2MASS photometry, we study the structural and dynamical properties of four young star clusters viz. King 16, NGC 1931, NGC 637 and NGC 189. For the clusters King 16, NGC 1931, NGC 637 and NGC 189, we obtain the limiting radii of 7′, 12′, 6′ and 5′ which correspond to linear radii of 3.6 pc, 8.85 pc, 3.96 pc and 2.8 pc respectively. The reddening values E(B−V) obtained for the clusters are 0.85, 0.65–0.85, 0.6 and 0.53 and their true distances are 1786 pc, 3062 pc, 2270 pc and 912 pc respectively. Ages of the clusters are 6 Myr, 4 Myr, 4 Myr and 10 Myr respectively. We compare their structures, luminosity functions and mass functions (φ(M)=dN/dM ∝ M −(1+χ)) to the parameter τ=t age /t relax to study the star formation process and the dynamical evolution of these clusters. We find that, for our sample, mass seggregation is observed in clusters or their cores only when the ages of the clusters are comparable to their relaxation times (τ≥1). These results suggest mass seggregation due to dynamical effects. The values of χ, which characterize the overall mass functions for the clusters are 0.96±0.11, 1.16±0.18, 0.55±0.14 and 0.66±0.31 respectively. The change in χ as a function of radius is a good indicator of the dynamical state of clusters.
Monthly Notices of the Royal Astronomical Society, 2013
Aims. In this work we investigate the nature of 50 overdensities from the catalogue of Froebrich, Scholz, and Raftery (FSR) projected towards the Galactic anticentre, in the sector 160 • ≤ ℓ ≤ 200 • . The sample contains candidates with |b| ≤ 20 • classified by FSR as probable open cluster (OC) and labelled with quality flags 2 and 3. Our main purpose is to determine the nature of these OC candidates and the fraction of these objects that are unknown OCs, as well as to derive astrophysical parameters (age, reddening, distance, core and cluster radii ) for the clusters and to investigate the relationship among parameters.
The dynamical distance and intrinsic structure of the globular cluster omega Centauri
2005
We determine the dynamical distance D, inclination i, mass-to-light ratio M/L and the intrinsic orbital structure of the globular cluster omega Cen, by fitting axisymmetric dynamical models to the ground-based proper motions of van Leeuwen et al. and line-of-sight velocities from four independent data-sets. We correct the observed velocities for perspective rotation caused by the space motion of the cluster, and show that the residual solid-body rotation component in the proper motions can be taken out without any modelling other than assuming axisymmetry. This also provides a tight constraint on D tan i. Application of our axisymmetric implementation of Schwarzschild's orbit superposition method to omega Cen reveals no dynamical evidence for a significant radial dependence of M/L. The best-fit dynamical model has a stellar V-band mass-to-light ratio M/L_V = 2.5 +/- 0.1 M_sun/L_sun and an inclination i = 50 +/- 4 degrees, which corresponds to an average intrinsic axial ratio of 0.78 +/- 0.03. The best-fit dynamical distance D = 4.8 +/- 0.3 kpc (distance modulus 13.75 +/- 0.13 mag) is significantly larger than obtained by means of simple spherical or constant-anisotropy axisymmetric dynamical models, and is consistent with the canonical value 5.0 +/- 0.2 kpc obtained by photometric methods. The total mass of the cluster is (2.5 +/- 0.3) x 10^6 M_sun. The best-fit model is close to isotropic inside a radius of about 10 arcmin and becomes increasingly tangentially anisotropic in the outer region, which displays significant mean rotation. This phase-space structure may well be caused by the effects of the tidal field of the Milky Way. The cluster contains a separate disk-like component in the radial range between 1 and 3 arcmin, contributing about 4% to the total mass.
Monthly Notices of The Royal Astronomical Society, 2007
We present a UBV CCD photometric study of four open clusters, NGC 7245, King 9, IC 166 and King 13, located between l=90o−135ol = 90^o - 135^ol=90o−135o. All are embedded in a rich galactic field. NGC 7245 and King 9 are close together in the sky and have similar reddenings. The distances and ages are: NGC 7245, 3.8$\pm$0.35 kpc and 400 Myr; King 9 (the most distant cluster in this quadrant) 7.9$\pm$1.1 kpc and 3.0 Gyr. King 13 is 3.1$\pm$0.3 kpc distant and 300 Myr old. King 9 and IC 166 (4.8$\pm$0.5 kpc distant & 1 Gyr old) may be metal poor clusters (Z=0.008), as estimated from isochrone fitting. The average value of the distance of young clusters from the galactic plane in the above longitude range and beyond 2 kpc ($-47\pm$16 pc, for 64 clusters), indicates that the young disk bends towards the southern latitudes.
A Photometric and Astrometric Study of the Open Clusters NGC 1664 and NGC 6939
Astronomical Journal, 2022
This study calculated astrophysical parameters, as well as kinematic and galactic orbital parameters, of the open clusters NGC 1664 and NGC 6939. The work is based on CCD ultraviolet, blue, and visual (UBV) and Gaia photometric and astrometric data from ground-and space-based observations. Considering Gaia Early Data Release 3 (EDR3) astrometric data, we determined membership probabilities of stars located in both of the clusters. We used two-color diagrams to determine the E(B − V) color excesses for NGC 1664 and NGC 6939 as 0.190 ± 0.018 and 0.380 ± 0.025 mag, respectively. Photometric metallicities for the two clusters were estimated as [Fe/H] = −0.10 ± 0.02 dex for NGC 1664 and as [Fe/H] = −0.06 ± 0.01 dex for NGC 6939. Using the reddening and metallicity calculated in the study, we obtained distance moduli and ages of the clusters by fitting PARSEC isochrones to the color-magnitude diagrams based on the most likely member stars. Isochrone fitting distances are 1289 ± 47 pc and 1716 ± 87 pc, which coincide with ages of 675 ± 50 Myr and 1.5 ± 0.2 Gyr for NGC 1664 and NGC 6939, respectively. We also derived the distances to the clusters using Gaia trigonometric parallaxes and compared these estimates with the literature. We concluded that the results are in good agreement with those given by the current study. Present-day mass function slopes were calculated as Γ = −1.22 ± 0.33 and Γ = −1.18 ± 0.21 for NGC 1664 and NGC 6939, respectively, which are compatible with the Salpeter slope. Analyzes showed that both of clusters are dynamically relaxed. The kinematic and dynamic orbital parameters of the clusters were calculated, indicating that the birthplaces of the clusters are outside the solar circle.
Kinematics of a globular cluster with an extended profile: NGC 5694
Monthly Notices of the Royal Astronomical Society, 2014
We present a study of the kinematics of the remote globular cluster NGC 5694 based on GIRAFFE@VLT medium resolution spectra. A sample of 165 individual stars selected to lie on the Red Giant Branch in the cluster Color Magnitude Diagram was considered. Using radial velocity and metallicity from Calcium triplet, we were able to select 83 bona-fide cluster members. The addition of six previously known members leads to a total sample of 89 cluster giants with typical uncertainties 1.0 km/s in their radial velocity estimates. The sample covers a wide range of projected distances from the cluster center, from ∼ 0.2 to 6.5 23 half-light radii (r h). We find only very weak rotation, as typical of metal-poor globular clusters. The velocity dispersion gently declines from a central value of σ = 6.1 km/s to σ 2.5 km/s at ∼ 2 7.1r h , then it remainins flat out to the next (and last) measured point of the dispersion profile, at ∼ 4 14.0r h , at odds with the predictions of isotropic King models. We show that both isotropic single-mass non-collisional models and multi-mass anisotropic models can reproduce the observed surface brightness and velocity dispersion profiles.