PROPER MOTION AND KINEMATICS OF THE ANSAE IN NGC 7009

摘要

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.