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Register a new userPhotometric and kinematical analysis of Koposov 12 and Koposov 43 open clusters
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W. H. Elsanhoury
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We present a photometric and kinematical analysis of two and poorly studied open clusters; Koposov 12 (FSR 802) and Koposov 43 (FSR 848) by using cross-matched data from PPMXL and Gaia DR2 catalog. We use astrometric parameters to identify 285 and 310 cluster members for Koposov 12 and Koposov 43, respectively. Using the extracted member candidates and isochrone fitting to near-infrared (J, H, Ks) and Gaia DR2 bands (G, GBP, GRP), and Color Magnitude Diagrams (CMDs), we have estimated ages: log (age/yr) = 9.00 +/- 0.20 and 9.50 +/- 0.20, and distances d = 1850 +/- 43 pc and 2500 +/- 50 pc for Koposov 12 and Koposov 43, respectively, assuming Solar metallicity (Z=0.019). The estimated masses of the cluster derived using initial mass function and synthetic CMD are 364 +/- 19 M_sun and 352 +/- 19 M_sun. We have also computed their velocity ellipsoid parameters based on (3x3) matrix elements (mu_ij).
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This paper presents an investigation of an old age open cluster King 11 using Gaias Early Data Release 3 (EDR3) data. Considering the stars with membership probability ($P_{mu}$) $> 90%$, we identified 676 most probable cluster members within the clusters limiting radius. The mean proper motion (PM) for King 11 is determined as: $mu_{x}=-3.391pm0.006$ and $mu_{y}=-0.660pm0.004$ 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$pm$0.42 Gyr and $3.33pm0.15$ kpc, respectively. The clusters apex coordinates ($A=267.84^{circ} pm 1.01^{circ}$, $D=-27.48^{circ} pm 1.03^{circ}$) are determined using the apex diagram (AD) method and verified using the ($mu_U$,$mu_T$) 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 $pm$ 2.16 km s$^{-1}$. A significant oscillation along the $Z$-coordinate up to 0.556$pm$0.022~kpc is determined.
We analysed the open clusters Czernik 2 and NGC 7654 using CCD UBV photometric and Gaia Early Data Release 3 (EDR3) photometric and astrometric data. Structural parameters of the two clusters were derived, including the physical sizes of Czernik 2 being r=5 and NGC 7654 as 8 min. We calculated membership probabilities of stars based on their proper motion components as released in the Gaia EDR3. To identify member stars of the clusters, we used these membership probabilities taking into account location and the impact of binarity on main-sequence stars. We used membership probabilities higher than $P=0.5$ to identify 28 member stars for Czernik 2 and 369 for NGC 7654. We estimated colour-excesses and metallicities separately using two-colour diagrams to derive homogeneously determined parameters. The derived $E(B-V)$ colour excess is 0.46(0.02) mag for Czernik 2 and 0.57(0.04) mag for NGC 7654. Metallicities were obtained for the first time for both clusters, -0.08(0.02) dex for Czernik 2 and -0.05(0.01) dex for NGC 7654. Keeping the reddening and metallicity as constant quantities, we fitted PARSEC models using colour-magnitude diagrams, resulting in estimated distance moduli and ages of the two clusters. We obtained the distance modulus for Czernik 2 as 12.80(0.07) mag and for NGC 7654 as 13.20(0.16) mag, which coincide with ages of 1.2(0.2) Gyr and 120(20) Myr, respectively. The distances to the clusters were calculated using the Gaia EDR3 trigonometric parallaxes and compared with the literature. We found good agreement between the distances obtained in this study and the literature. Present day mass function slopes for both clusters are comparable with the value of Salpeter (1955), being X=-1.37(0.24) for Czernik 2 and X=-1.39(0.19) for NGC 7654.
We present an analysis of three southern open star clusters NGC 6067, NGC 2506 and IC 4651 using wide-field photometric and Gaia DR2 astrometric data. They are poorly studied clusters. We took advantage of the synergy between Gaia DR2 high precision astrometric measurements and ground based wide-field photometry to isolate cluster members and further study these clusters. We identify the cluster members using proper motions, parallax and colour-magnitude diagrams. Mean proper motion of the clusters in RA and DEC is estimated as -1.90 pm 0.01 and -2.57 pm 0.01 mas/yr for NGC 6067, -2.57 pm 0.01 and 3.92 pm 0.01 mas/yr for NGC 2506 and -2.41 pm 0.01 and -5.05 pm 0.02 mas/yr for IC 4651. Distances are estimated as 3.01 pm 0.87, 3.88 pm 0.42 and 1.00 pm 0.08 kpc for the clusters NGC 6067, NGC 2506 and IC 4651 respectively using parallaxes taken from Gaia DR2 catalogue. Galactic orbits are determined for these clusters using Galactic potential models.We find that these clusters have circular orbits. Cluster radii are determined as 10 arcmin for NGC 6067, 12 arcmin for NGC 2506 and 11 arcmin for IC 4651. Ages of the clusters estimated by isochrones fitting are 66 pm 8 Myr, 2.09 pm 0.14 Gyr and 1.59 pm 0.14 Gyr for NGC 6067, NGC 2506 and IC 4651 respectively. Mass function slope for the entire region of cluster NGC 2506 is found to be comparable with the Salpeter value in the mass range 0.77 - 1.54 Solar mass. The mass function analysis shows that the slope becomes flat when one goes from halo to core region in all the three clusters. A comparison of dynamical age with clusters age indicates that NGC 2506 and IC 4651 are dynamically relaxed clusters.
Very precise observational data are needed for studying the stellar cluster parameters (distance, reddening, age, metallicity) and cluster internal kinematics. In turn, these give us an insight into the properties of our Galaxy, for example, by giving us the ability to trace Galactic spiral structure, star formation rates and metallicity gradients. We investigated the available Gaia DR2 catalogue of 1229 open clusters and studied cluster distances, sizes and membership distributions in the 3D space. An appropriate analysis of the parallaxto-distance transformation problem is presented in the context of getting distances toward open clusters and estimating their sizes. Based on our investigation of the Gaia DR2 data we argue that, within 2 kpc, the inverse-parallax method gives comparable results (distances and sizes) as the Bayesian approach based on the exponentially decreasing volume density prior. Both of these methods show very similar dependence of the line-of-sight elongation of clusters (needle-like shapes resulting from the parallax uncertainties) on the distance. We also looked at a measure of elongations of the studied clusters and find the maximum distance of 665 pc at which a spherical fit still contains about half of the stellar population of a cluster. It follows from these results that the 3D structure of an open cluster cannot be properly studied beyond about 500 pc when using any of mentioned standard transformations of parallaxes to distances.
Context. The origin and dynamical evolution of star clusters is an important topic in stellar astrophysics. Several models have been proposed to understand the formation of bound and unbound clusters and their evolution, and these can be tested by examining the kinematical and dynamical properties of clusters over a wide range of ages and masses. Aims. We use the Gaia-ESO Survey products to study four open clusters (IC 2602, IC 2391, IC 4665, and NGC 2547) that lie in the age range between 20 and 50 Myr. Methods. We employ the gravity index $gamma$ and the equivalent width of the lithium line at 6708 $AA$, together with effective temperature $rm{T_{eff}}$, and the metallicity of the stars in order to discard observed contaminant stars. Then, we derive the cluster radial velocity dispersions $sigma_c$, the total cluster mass $rm{M}_{tot}$, and the half mass radius $r_{hm}$. Using the $Gaia$-DR1 TGAS catalogue, we independently derive the intrinsic velocity dispersion of the clusters from the astrometric parameters of cluster members. Results. The intrinsic radial velocity dispersions derived by the spectroscopic data are larger than those derived from the TGAS data, possibly due to the different masses of the considered stars. Using $rm{M}_{tot}$ and $r_{hm}$ we derive the virial velocity dispersion $sigma_{vir}$ and we find that three out of four clusters are supervirial. This result is in agreement with the hypothesis that these clusters are dispersing, as predicted by the residual gas expulsion scenario. However, recent simulations show that the virial ratio of young star clusters may be overestimated if it is determined using the global velocity dispersion, since the clusters are not fully relaxed.
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