Kinematics and Proper Motion of the Ansae in NGC7009

Abstract

We have measured the expansion velocities and proper motion of the ansae in NGC7009 using high dispersion echelle spectra and archive narrow band HST images. Assuming that the ansae are moving at equal and opposite velocities from the central star we obtain an average system radial velocity of -54 +-2 km/s, the eastern ansa approaching and the western ansa receding at Vr = 5.5 +-1 km/s relative to this value. Only the proper motion of the eastern ansa could be measured, leading to 2.8 +- 0.8 arcsec/century, or Vt=130 +- 40.d km/s, where d is the distance to the nebula in kpc. Additionally, the electron temperature and density for each ansa was measured using line intensity ratios. The results are Te = 9000 K and ne = 2000 /cm3 for both ansae within the errors.