scholarly journals The Three-Dimensional Ionization Structure and Evolution of NGC 6720, The Ring Nebula

2007 ◽  
Vol 134 (4) ◽  
pp. 1679-1692 ◽  
Author(s):  
C. R. O'Dell ◽  
F. Sabbadin ◽  
W. J. Henney
Keyword(s):  
Three Dimensional ◽  
Ionization Structure ◽  
Ring Nebula

scholarly journals Giant Arcs – Spherical Shells?

1988 ◽  
Vol 130 ◽  
pp. 598-598
Author(s):  
Avishai Dekel ◽  
Erez Braun
Keyword(s):  
Supernova Remnants ◽  
Surface Brightness ◽  
High Redshift ◽  
Three Dimensional ◽  
Circular Ring ◽  
Clusters Of Galaxies ◽  
Spherical Shells ◽  
Random Direction ◽  
Ring Nebula ◽  
Stimulated Radiation

A noticeable fact about the giant luminous arcs, which have been detected in a few high-redshift clusters of galaxies (see contributions by Petrosian and by Mellier in this volume), is that they seem to be segments of almost perfectly circular rings – in one case spanning about one third of a circle. If this is a characteristic property of these arcs, they cannot be segments of randomly-oriented three-dimensional rings, which, when viewed from a random direction, should look acircular in most cases. Perhaps the most generic source for a circular ring is a limb-brightened luminous shell – as in planetary nebulae and supernova remnants. Such shells can naturally arise, for example, from explosion-generated shocks which cooled and fragmented into stars. If the sources are shells, and the arcs are either resolved or their thickness is determined by the seeing conditions (and by the CCD pixle size), there is a very general upper-limit on the possible surface-brightness contrast between the arcs and the regions encompassed by them. For the detected arcs, without any special finetuning, this limit is ≃ 3. It might become twice as big if the shell is transparent and the interior is opaque. This limit could exclude the shell model if the preliminary claims for a detected contrast greater than 10 are confirmed. It is interesting to note that the famous ring nebula presents a similar problem. We checked several mechanisms, such as stimulated radiation, which could, in principle, enhance the observed contrast while retaining the spherical symmetry; if such a mechanism is responsible for the enhanced contrast, it should show clear imprints on the spectrum. The figure shows the surface-brightess profile for a shell of thickness d.

scholarly journals Imaging Spectrophotometry of the Ring Nebula

1993 ◽  
Vol 155 ◽  
pp. 194-194
Author(s):  
Nancy Jo Lame ◽  
Richard W. Pogge
Keyword(s):  
Emission Line ◽  
Ohio State University ◽  
State University ◽  
Ionization State ◽  
Ionization Structure ◽  
Ring Nebula ◽  
Fabry Perot ◽  
The Ohio State University ◽  
Line Imaging ◽  
Balmer Decrement

We present new results from a program of emission-line imaging spectrophotometry of planetary nebulae using the Ohio State University Imaging Fabry-Perot Spectrograph (IFPS). High-quality emission-line maps of the important diagnostic lines [NII]λλ5755,6583, [SII]λλ6717,6731, [OI]λ6300, [OIII]λ5007, Hα, and Hβ have been obtained. Maps of the ionization structure ([S II]/Hα, [N II]/Hα, [O III]/Hβ, and [O I]/[O III]), temperature in the N+ region, density in the S+ region, and Balmer decrement across the nebula are presented. These show considerable variation in ionization state, temperature and density. This detailed information will provide powerful constraints on photoionization models for the Ring Nebula.

scholarly journals Mapping the Physical and Chemical Conditions of the Ring Nebula

2016 ◽  
Vol 12 (S323) ◽  
pp. 345-347
Author(s):  
Marcelo L. Leal-Ferreira ◽  
Isabel Aleman ◽  
Andrea Gaughan ◽  
Djazia Ladjal ◽  
Toshiya Ueta ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Elemental Abundance ◽  
Emission Lines ◽  
Correction Factors ◽  
Elemental Abundances ◽  
Ring Nebula ◽  
History Of ◽  
Electronic Densities ◽  
Chemical Conditions ◽  
Physical And Chemical

AbstractWe observed the Planetary Nebula NGC 6720 with the Gemini Telescope and the Gemini Multi-Object Spectrographs. We obtained spatial maps of 36 emission-lines in the wavelength range between 3600 Å and 9400 Å. We derived maps of c(Hβ), electronic densities, electronic temperatures, ionic and elemental abundances, and Ionization Correction Factors (ICFs) in the source and investigated the mass-loss history of the progenitor. The elemental abundance results indicate the need for ICFs based on three-dimensional photoionization models.

scholarly journals On the Chemodynamics of NGC 6888

1991 ◽  
Vol 143 ◽  
pp. 422-422
Author(s):  
C. Esteban ◽  
J.M. Vilchez
Keyword(s):  
Major Axis ◽  
Chemical Abundances ◽  
Ionized Gas ◽  
Physical Conditions ◽  
Processed Material ◽  
Ionization Structure ◽  
Ring Nebula ◽  
Solar Abundances ◽  
H Ii Region ◽  
Emission System

We present preliminary results on an extensive spectroscopical study of the WR Ring nebula NGC 6888. The observations combine high spatial (1.5 arcsec/pixel) and spectral resolution (30 to 50 km s–1) covering most of the optical range - λλ 3600 to 6800 å- at 3 different slit positions along the major axis of the nebula. The spectra of the central parts give an emission system with three different velocities: a) VLSR=-64 km s–1, b) VLSR=+18 km s–1, and c) VLSR=+78 km s–1. Assuming that NGC 6888 is in fact an expanding bubble of gas, as demonstrated by Marston and Meaburn (1988), we can identify components a) and c) as those moving towards us and receeding parts of the shell, while b) could be related to the ambient interstellar ionized gas outside the bubble. We have isolated the spectrum for each component in order to analyse the ionization structure and excitation mechanism, as well as to derive their physical conditions and chemical abundances. The use of diagnostic diagrams indicates that the nebula is basically photoionized, without any significant contribution of shock excitation in the zones studied. The ambient interstellar component shows a spectrum typical of an H II region with nearly solar abundances. In the case of the bubble components, their spectra produce [N II]/Hα line ratios which are outside the H II region box, and entering the extended planetary nebulae locus, suggesting a contribution of ejected nitrogen in the bubble. This fact is evident from the abundance analysis we have performed, finding that, with respect to the values quoted for the ambient gas, the O/H is deficient by a factor 4, N/H is 2.5 times higher, and helium is enhanced by a factor 2. These quoted values clearly indicate that a substantial fraction of the gas in the bubble is processed material ejected from the central massive star.

scholarly journals The Ionization Structure of NGC 6720 and NGC 7009

1983 ◽  
Vol 103 ◽  
pp. 522-522
Author(s):  
T. Barker
Keyword(s):  
Spectral Range ◽  
Central Star ◽  
Resonance Fluorescence ◽  
Recombination Line ◽  
Line Intensities ◽  
Ionization Structure ◽  
Ring Nebula ◽  
Central Stars ◽  
Good Agreement ◽  
Made In

Measurements of line intensities over a spectral range generally as great as 1300 Å to 11,000 Å have been made in four positions in the Ring Nebula and eight positions in NGC 7009. Ionic abudances determined from optical and UV lines are in good agreement, except that the C2+ abundance inferred from the optical 4267 Å recombination line is as much as 10 times higher than that measured from the 1906, 1909 Å CIII) lines. In both nebulae, this discrepancy is greatest nearest the central star. At the present time the most attractive explanation seems to be that the 4267 Å line is affected by resonance fluorescence due to light from central stars of planetaries.

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