Study of open clusters within 1.8 kpc and understanding the Galactic structure

Abstract

Context. Significant progress has been made in recent years to understand the formation and evolution of our Galaxy, but we still lack a complete understanding of the Galaxy and its structure. Aims. Using an almost complete sample of Galactic open star clusters within 1.8 kpc, we aim to understand the general properties of the open cluster system in the Galaxy and probe the Galactic structure. Methods. We first extracted 1241 open clusters within 1.8 kpc of the Sun from the Milky Way Star Clusters (MWSC) catalog. Considering it an almost complete sample of clusters within this distance, we performed a comprehensive statistical analysis of various cluster parameters such as spatial position, age, size, mass, and extinction. Results. We find an average cluster scale height of z h = 60 ± 2 pc for clusters younger than 700 Myr, which increases to 64 ± 2 pc when we include all the clusters. The z h is found to be strongly dependent on R GC and age, and on an average, z h is more than twice as large as in the outer region than in the inner region of the solar circle, except for the youngest population of clusters. The solar offset is found to be 6.2 ± 1.1 pc above the formal Galactic plane. We derive a local mass density of ρ 0 = 0.090 ± 0.005 M ⊙ /pc 3 and estimate a negligibly small amount of dark matter in the solar neighborhood. The reddening in the direction of clusters suggests a strong correlation with their vertical distance from the Galactic plane with a respective slope of dE(B − V)/dz = 0.40±0.04 and 0.42±0.05 mag/kpc below and above the GP. We observe a linear mass-radius and mass-age relations in the open clusters and derive the slopes of dR/d(logM) = 2.08 ± 0.10 and d(logM)/d(logT ) = − 0.36 ± 0.05, respectively. Conclusions. The dependence of the spatial distribution of clusters on their age points to a complex interplay between cluster formation and survivability within the Galaxy. The geometrical characteristics of a significant number of clusters enabled us to understand large-scale spatial properties of the cluster systems within the Galaxy. The structural and physical parameters of clusters allowed us to check mutual correlations between the individual parameters.

A New Electron-Density Model for Estimation of Pulsar and FRB Distances

“…9 Recent estimates of  z range between +6 pc and +30 pc (Joshi et al 2016). Based on an analysis of nearby open clusters, Joshi et al (2016) obtained  = +  z 6.2 1.1 pc; we fix  z at +6.0 pc. The Galactic Cartesian coordinates of any object are (x, y,…”

“…Studies of the distribution of massive stars, molecular gas, and H II regions in the inner Galaxy (e.g., Nakanishi & Sofue 2006;Urquhart et al 2014;Anderson et al 2015) show that the gas density peaks at a Galactocentric radius of 4-5 kpc. Analyses of the z-distribution of tracers of high-density gas in the Galactic disk and spiral arms such as neutral hydrogen (H I; e.g., Kalberla et al 2007) and molecular gas (e.g., Nakanishi & Sofue 2006) give scale heights in the range 50-70 pc at Galactocentric radii of 4-6 kpc, whereas mid-infrared observations of massive stars in the Galactic disk (e.g., Urquhart et al 2014) and open star clusters (Joshi et al 2016) give scale heights less than half as large, 20-25 pc. 11 All of these tracers show an increasing scale height with increasing Galactocentric radius, with a pronounced flaring at radii 10 kpc.…”

The Ages of the Thin Disk, Thick Disk, and the Halo from Nearby White Dwarfs

“…Bonatto et al (2006) demonstrated that the scale height increases from 48±3 pc for open clusters younger than 200 Myr to 150±27 pc for clusters with ages up to 1 Gyr. Studying a larger sample of open clusters, Buckner & Froebrich (2014) and Joshi et al (2016) showed that this trend continues for older clusters; they found a scale height h 300 > pc for 2.5 Gyr and older clusters. Bovy et al (2012) used SEGUE G dwarfs to define monoabundance populations, and fit each population as a single exponential disk.…”

Photometric and kinematic study of the three intermediate age open clusters NGC 381, NGC 2360, and Berkeley 68

“…The distance and age of the Galactic OCs are important parameters in tracing the Galactic structure and chemical evolution of the Galaxy using OCs as tracers (Friel & Janes 1993;Joshi et al 2016). The CMD of the cluster play important role in identification of the member stars as well as determination of the cluster parameters like reddening, metallicity, age, and distance modulus.…”

“…The study of mass segregation in OCs can be carried out by studying mass distribution and variation in the slope of the MF with the radial distances (Lim et al 2013). The intermediate age OCs are spread in most regions of the Galactic disk and have a wide range in their ages (Joshi et al 2016), therefore, they are very important in the understanding of stellar evolution and dynamical evolution of the stars, particularly having intermediate to low masses.…”