The [S II] Spectral Images of the Planetary Nebula NGC 7009: II. Major Axis

Abstract

We derived position-velocity density distribution diagrams along the major (PA = 77${}^{\circ }$) axis of the elliptical planetary nebula NGC 7009 with the Keck HIRES [SII] 6716/6731 \A, doublet spectral images. The average densities of the main shell and knots of NGC 7009 derived from the [SII] 6716/673 \A, fluxes integrated over the line of sight indicate a density range of $N_{\mathrm{e}}$ = $10^{3.4}$ to 10${}^{3.9}$ $c{m}^{-3}$, while the local densities from the volume fraction resolved in radial velocities along the line of sight show a considerably large range of about 10${}^{2.8}$ -- 10${}^{4.7}$ $c{m}^{-3}$. The derived projection angle of the major axis of the main shell is about $\psi \sim$18.3($\pm$2)${}^{\circ }$. Assuming that the main shell is an ellipsoidal shell with $a\simeq$16${}^{\prime \prime }$ and $b\simeq 6^{\prime \prime }$, we found the range of expansion velocity, radius, and latitude of four knots and a hot bubble. The four knots at the points in symmetrical positions are roughly aligned with the same axis of expansion of latitudes $\varphi \sim \pm 34.5(\pm 0.6{)}^{\circ }$: One pair expands at about 35 $km{s}^{-1}$ close to the main ellipsoidal shell, and the other expands rapidly at about 60 $km{s}^{-1}$ at a distance of $r\sim 16^{\prime \prime }$. In the latitude range $\varphi =$65 -- 75${}^{\circ }$, the hot bubble of a relatively large structure expands rapidly with a velocity of 130 -- 150 $km{s}^{-1}$. Four knots and hot bubble points that expand faster than the main shell appear to have been formed by two to three eruptions at a different epoch than the primary structure formation.

18 pages, 7 figures Accepted for publication in ApJS

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