Vertical distribution and kinematics of protoplanetary nebulae in the galaxy

Abstract

The catalogue of protoplanetary nebulae by Vickers et al. has been supplemented with the line-of-sight velocities and proper motions of their central stars from the literature. Based on an exponential density distribution, we have estimated the vertical scale height from objects with an age less than 3 Gyr belonging to the Galactic thin disk (luminosities higher than 5000 L_⊙) to be h = 146 ± 15 pc, while from a sample of older objects (luminosities lower than 5000 L_⊙) it is h = 568 ± 42 pc. We have produced a list of 147 nebulae in which there are only the line-of-sight velocities for 55 nebulae, only the proper motions for 25 nebulae, and both line-of-sight velocities and proper motions for 67 nebulae. Based on this kinematic sample, we have estimated the Galactic rotation parameters and the residual velocity dispersions of protoplanetary nebulae as a function of their age. We have established that there is a good correlation between the kinematic properties of nebulae and their separation in luminosity proposed by Vickers. Most of the nebulae are shown to be involved in the Galactic rotation, with the circular rotation velocity at the solar distance being V₀ = 227 ± 23 km s⁻¹. The following principal semiaxes of the residual velocity dispersion ellipsoid have been found: (σ₁, σ₂, σ₃) = (47, 41, 29) km s⁻¹ from a sample of young protoplanetary nebulae (with luminosities higher than 5000 L_⊙), (σ₁, σ₂, σ₃) = (50, 38, 28) km s⁻¹ from a sample of older protoplanetary nebulae (with luminosities of 4000 L_⊙ or 3500 L_⊙), and (σ₁, σ₂, σ₃) = (91, 49, 36) km s⁻¹ from a sample of halo nebulae (with luminosities of 1700 L_⊙).