English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We analyzed the minor axis spectra of the elliptical planetary nebula (PN)NGC 7009 observed with the Keck HIRES with a 0.862$"$ $\times$ 10$"$ slitplaced at about $\sim$7.5$"$ and 10$"$ away from the center and a 0.862$"$$\times$ 14$"$ slit at the center. The mean densities derived from theintegrated [SII] 6716/6731\r{A}, fluxes along the Keck HIRES slit lengthindicate a density range of 10$^{3.7}$ to 10$^{4.1}$ cm$^{-3}$, while the localdensities derived from the slit spectral images show a large local densityvariation of about 10$^{2.8}$ - 10$^{4.6}$ cm$^{-3}$: local densities varysubstantially more than values integrated over the line of sight. The expansionrates of the main and outer shells obtained by [SII] are about 21.7 and 30.0kms$^{-1}$, respectively. The kinematic results of the [SII] spectral linescorrespond to the outermost regions of the two shells and are notrepresentative of the whole PN but are closely related to the other emissionlines observed in the shell gas. We conclude that the density contrast leads tothe formation of the inner shell, while the change in ionization state leads tothe formation of the outer shell. We suggest that the inner main and outershells result from two successive major ejections. The physical conditions ofthe central star must have been different when these shells first formed.

Double Shells of the Planetary Nebula NGC 7009 Minor Axis