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

High-resolution Hubble Space Telescope (HST) archive imaging andhigh-dispersion spectroscopy are used to study the complex morphological andkinematical structure of the planetary nebula, NGC 2818. We analyze narrow bandH{\alpha}, [O III], [N II], [S II] and He II images, addressing importantmorphological features. Ground-based longslit echelle spectra were obtainedcrossing NGC 2818 at five different positions to precisely determinekinematical features in the structure of the nebula. A distance of 2.5 kpc wasused to determine physical scales. Constructing models to fit the data withmodern computational tools, we find NGC 2818 is composed by: (1) a non-uniformbipolar structure with a semi-major axis of 0.92 pc (75 arcsec), possiblydeformed by the stellar wind, (2) a 0.17 pc (14 arcsec) diameter centralregion, which is potentially the remnant of an equatorial enhancement, and (3)a great number of cometary knots. These knots are preferentially located insidea radius of 0.24 pc (20 arcsec) around the central star. The ma jor axis of themain structure is oriented at i \simeq 60\degree with respect to theline-of-sight and at PA = +89\degree on the plane of the sky. Expansionvelocities of this nebula are Vpol = 105 km/s and Veq = 20 km/s, which lead toour estimate of the kinematical age of {\tau}k \simeq 8,400 \pm 3, 400 yr(assuming homologous expansion). Our observations do not support the idea thathigh velocity collimated ejections are responsible for the formation ofmicrostructures inside the nebula. We determine the systemic velocity of NGC2818 to be VHEL = +26 \pm 2 km/s.

Bubbles and Knots in the Kinematical Structure of the Bipolar Planetary Nebula NGC 2818