Proper Motion and Kinematics of the Ansae in NGC 7009

Abstract

We have measured the proper motion (PM) and kinematics of the ansae in NGC 7009 using high-dispersion echelle spectra and archive narrowband Hubble Space Telescope images. Assuming that the ansae are moving at equal and opposite velocities from the central star, we obtain a system radial velocity of -53+/-2 km s^-1, the eastern ansa approaching and the western ansa receding at v_r=5.3+/-1 km s^-1 with respect to this value. The PM of the eastern ansa is 28+/-8 mas yr^-1, which, with our weighted distance to NGC 7009 of 0.86+/-0.34 kpc, gives V_exp=114+/-32 km s^-1. The electron temperature and density in both ansae were determined to be T_e~9000+/-400 K and n_e~2300+/-400 cm^-3. The dynamic age of the ansae is ~910+/-260 yr, and the implied PM of the central star is μ_CS=1+/-0.5 mas yr^-1. This is in qualitative but not quantitative agreement with previous work.