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

TL;DR

This study analyzes a comprehensive sample of open star clusters within 1.8 kpc to understand their properties and the structure of the Milky Way, revealing scale heights, local mass density, and cluster relations.

Contribution

It provides the first detailed statistical analysis of open clusters within 1.8 kpc, linking cluster parameters to Galactic structure and dynamics.

Findings

Average Galactic scale height for young clusters is 60 pc.

Solar offset from the Galactic plane is 6.2 pc.

Local mass density is 0.090 Msun/pc^3, indicating minimal dark matter.

Abstract

Based on an almost complete sample of Galactic open star clusters within 1.8 kpc, we perform a comprehensive statistical analysis of various cluster parameters like spatial position, age, size, mass and extinction in order to understand the general properties of the open cluster system in the Galaxy and the Galactic structure. Based on the distribution of 1241 open clusters about the Galactic plane and in different age bins, we find the average Galactic scale height as Zh = 60+/-2 pc for the youngest cluster population having Age <700 Myr, however, it increases up to 64+/-2 pc when we also include older 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 \rho_0 = 0.090+/-0.005 Msun/pc^3 and found a negligibly small amount of dark matter in the solar neighbourhood. The reddening in the direction of clusters suggests a strong correlation with their vertical distance from the Galactic plane having 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 a slope of dR/d(logM) = 2.08+/-0.10 and d(logM)/d(logT) = -0.36+/-0.05,respectively.