Double Shells of the Planetary Nebula NGC 7009 Minor Axis

Abstract We analyzed the minor-axis spectra of elliptical planetary nebula (PN) NGC 7009 observed with Keck HIRES a 0.″862 × 10″ slit placed at about 7.″5 and away from center 14″ center. The mean densities derived integrated [S ii ] 6716/6731 Å fluxes along length indicate density range 10 3.7 –10 4.1 cm −3 , while local spectral images show large variation 2.8 4.6 : vary more substantially than values over line sight. expansion rates main outer shells obtained by are 21.7 30.0 km s −1 respectively. kinematic results lines correspond to outermost regions two not representative whole PN but closely related other emission in shell gas. conclude that contrast leads formation inner shell, change ionization state shell. suggest result successive major ejections. physical conditions central star must have been different when these first formed.