B. Louise Webster

The Kinematics of the Planetary Nebulae in the Large Magellanic Cloud

The radial velocities of a total of 94 Planetary Nebulae (PN) in the Large Magellanic Cloud (LMC) have been determined. The kinematics of the population of planetary nebulae is compared with the H I data in the context of a re-analysis of the survey by Rohlfs et al. (1984), taking into account the transverse velocity of the LMC. We find that the best solution for this transverse velocity is 275±65 km s-1, and that the LMC is near perigalacticon. This is consistent with a maximum Galactic mass of order 4.5x1011M⊙ out to 51 kpc. The rotation curve obtained after correction for this velocity implies a mass of (4.6x0.3)x 109 M⊙ within a radius of 3 degrees, or about 6x109 M⊙, total. The rotation solution for the PN population is essentially identical with that of the H I, but the vertical velocity dispersion of 19.1 km s-1 is much greater than the value of 5.4 km s-1 found for the H I. This increase in velocity dispersion is consistent with it being the result of orbital heating and diffusion operating in the LMC in a manner essentially identical with that found for the solar neighbourhood.

Evolution of Magellanic Cloud Planetary Nebulae

New evolutionary correlations have been discovered to apply to the population of Planetary Nebulae (FN) in the Magellanic Clouds. Firstly, the age of the nebular shell is found to follow a relationship T = 890[(Mneb/M⊙) (Vexp/km s-1)]0,6 yr, which is shown to be consistent with a model in which the total energy of the ionised and swept up gas drives the expansion down the density gradient in the precursor AGB wind. Secondly, a tight correlation is found between the expansion velocity and a combination of the Excitation Class and the Hβ flux. This appears to be determined by the mass of the planetary nebula nuclear star. These correlations provide strong observational support for the idea that the PN shells are ejected at low velocity during the Asymptotic Giant Branch phase of evolution, and that they are continually accelerated during their nebular lifetimes.