Analysis of spatial velocities of several samples of open star clusters

TL;DR

This study analyzes the kinematics of open star clusters to determine the Galaxy's rotation parameters, wave patterns, and the Sun's proximity to the corotation radius, using Fourier analysis on a large sample of young clusters.

Contribution

It provides new measurements of Galactic rotation parameters and wave characteristics in the velocities of open star clusters, indicating the Sun's near position to the corotation radius.

Findings

Galactic angular velocity $ ext{Ω}_0$ is approximately 29 km/s/kpc.

Wavelengths of velocity waves are around 2.0-2.2 kpc.

The Sun is very close to the Galaxy's corotation radius.

Abstract

An analysis of the kinematics of open star clusters (OSCs) using their characteristics from the new Hunt and Reffert catalog was conducted. Based on 4003 OSCs younger than 200 million years, the following values for the angular velocity of the Galaxy's rotation were found: $\Omega_0 = 28.99\pm0.11$ km/s/kpc, $\Omega^{'}_0 = -3.909\pm0.026$ km/s/kpc$^{2}$ and $\Omega^{''}_0 = 0.5662\pm0.018$ km/s/kpc$^{3}$, where $V_0=234.8\pm3.0$ km/s for $R_0=8.1\pm0.1$ kpc. It was found that periodicity in the radial velocities of OSCs is manifested in clusters younger than 600 Myr, while a wave in residual tangential velocities is observed only in the youngest ones, younger than 40 Myr. A spectral Fourier analysis of the radial velocities of three OSC samples with average ages of 18, 72, and 143 Myr was used to obtain the following values of the wavelength $\lambda$ and the velocity perturbation amplitude $f_R$: $\lambda=2.0$ kpc and $f_R=4.3$ km/s, $\lambda=2.2$ kpc and $f_R=8.2$ km/s, $\lambda=2.1$ kpc and $f_R=9.6$ km/s, respectively. A systematic change in the positions of the maxima and minima of the waves in the radial velocities of OSCs was found depending on the age of the sample. From the analysis of these shifts, the value of the absolute value of the difference $|\Delta\Omega|$ between the angular velocity of rotation of the spiral pattern $\Omega_p$ and the rotation velocity of the Galaxy was found, $|\Delta\Omega|=2.0\pm0.5_{stat}\pm2.3_{syst}$ km/s/kpc. Based on this, an estimate of two possible values of the corotation radius was obtained: $8.6\pm0.2$ kpc and $7.6\pm0.2$ kpc, which indicates that the Sun is very close to the corotation.