Parameters of the Local Warp of the Stellar-Gaseous Galactic Disk from the Kinematics of Tycho-2 Nearby Red Giant Clump Stars

TL;DR

This study analyzes the 3D kinematics of Tycho-2 red giant clump stars to understand the local warp of the stellar-gaseous Galactic disk, revealing a rotation pattern related to the warp structure.

Contribution

It provides new measurements of the residual rotation of the ICRS/HIPPARCOS system and characterizes the kinematics of the Galactic warp using a large stellar sample.

Findings

Residual rotation vector components determined with high precision.

Kinematic peculiarities linked to the Galactic warp identified.

The warp exhibits a rotation around the Galactic X axis with specific angular velocity.

Abstract

We analyze the three-dimensional kinematics of about 82000 Tycho-2 stars belonging to the red giant clump (RGC). First, based on all of the currently available data, we have determined new, most probable components of the residual rotation vector of the optical realization of the ICRS/HIPPARCOS system relative to an inertial frame of reference, \omega_x,\omega_y,\omega_z)= (-0.11,0.24,-0.52)+/-(0.14,0.10,0.16) mas/yr. The stellar proper motions in RA have then be corrected by applying the correction \omega_z = -0.52 mas/yr. We show that, apart from their involvement in the general Galactic rotation described by the Oort constants A= 15.82+/-0.21 km/s/kpc and B=-10.87+/-0.15 km/s/kpc, the RGC stars have kinematic peculiarities in the Galactic yz plane related to the kinematics of the warped stellar-gaseous Galactic disk. We show that the parameters of the linear Ogorodnikov-Milne model that describe the kinematics of RGC stars in the zx plane do not differ significantly from zero. The situation in the yz plane is different. For example, the component of the solid-body rotation vector of the local solar neighborhood around the Galactic x axis is M_32- = -2.6+/-0.2 km/s/kpc. Two parameters of the deformation tensor in this plane, namely M_23^+ = 1.0+/-0.2 km/s/kpc and (M_33-M_22)= -1.3+/-0.4 km/s/kpc, also differ significantly from zero. On the whole, the kinematics of the warped stellar-gaseous Galactic disk in the local solar neighborhood can be described as a rotation around the Galactic X axis (close to the line of nodes of this structure) with an angular velocity (-3.1+/-0.5) < \Omega_W < (-4.4+/-0.5) km/s/kpc.