Three-Dimensional Kinematics of Classical Cepheids

TL;DR

This study uses a linear Ogorodnikov-Milne model to analyze the 3D kinematics of 832 classical Cepheids in the Milky Way, revealing residual rotations possibly linked to the Galactic disk warp.

Contribution

It applies a complete Ogorodnikov-Milne model to Gaia DR2 data to estimate Galactic rotation parameters from Cepheid kinematics, accounting for disk warp effects.

Findings

Estimated Galactic rotation around the y-axis as 0.64±0.17 km/s/kpc.

Detected residual rotation around the y-axis as 0.54±0.15 km/s/kpc.

Found positive rotation around the x-axis as 0.33±0.10 km/s/kpc.

Abstract

A linear Ogorodnikov-Milne model is applied to study the three-dimensional kinematics of classical Cepheids in the Milky Way. A sample of 832 classical Cepheids from Mr'oz et al. (2019) with distances, line-of-sight velocities, and proper motions from the Gaia DR2 catalogue is used. The Cepheid space velocities have been freed from the differential Galactic rotation found by us previously based on a nonlinear rotation model. Based on a complete Ogorodnikov-Milne model, involving the line-of-sight velocities and proper motions of stars, we have estimated the angular velocity of rotation around the Galactic $y$ axis, $\Omega_y=0.64\pm0.17$~km s$^{-1}$ kpc$^{-1}$. We think that this rotation is associated with the warp of the Galactic thin disk. Our calculations using only the proper motions of Cepheids under the assumption of no deformations due to the disk warp have shown the presence of a residual rotation around the $y$ axis with an angular velocity $\Omega_y=0.54\pm0.15$~km s$^{-1}$ kpc$^{-1}$ and the presence of a positive rotation around the $x$ axis with an angular velocity $\Omega_x=0.33\pm0.10$~km s$^{-1}$ kpc$^{-1}$.