scholarly journals The Ionization of Planetary Nebulae

1968 ◽  
Vol 34 ◽  
pp. 190-204 ◽  
Author(s):  
Robert E. Williams
Keyword(s):  
Ionizing Radiation ◽  
Emission Line ◽  
Radiation Field ◽  
Planetary Nebulae ◽  
Model Atmosphere ◽  
Evolutionary Sequence ◽  
Lyman Continuum ◽  
The Mean ◽  
Central Stars

The ionization of the most abundant elements in planetary nebulae has been determined for a number of models of nebulae at different epochs in their expansion. The values used for the temperatures and radii of the central stars and the sizes and densities of the shells have come from Seaton's evolutionary sequence. The ionizing radiation field has been taken from model atmosphere calculations of the central stars by Gebbie and Seaton, and Böhm and Deinzer. Emission-line fluxes have been calculated for the models and compared with observations of planetary nebulae by O'Dell, Osterbrock's group, and Aller and his collaborators. Results indicate that the central stars have strong He+ Lyman continuum excesses, similar to those predicted by Gebbie and Seaton. The mean abundance determinations for the nebulae made by Aller are confirmed, with the exception of nitrogen, which appears to be 3 or 4 times more abundant than his value. It is also seen that the electron temperatures of the nebulae are higher than previous theoretical determinations, providing better agreement with empirically derived values.

scholarly journals Spectrophotometric studies of Planetary Nebulae with [WR] central stars

1997 ◽  
Vol 180 ◽  
pp. 269-269
Author(s):  
M. Peña ◽  
G. Stasińska ◽  
C. Esteban ◽  
R. Kingsburgh ◽  
L. Koesterke ◽  
...  
Keyword(s):  
Ionizing Radiation ◽  
Radiation Field ◽  
Planetary Nebulae ◽  
Model Atmosphere ◽  
The Other ◽  
Self Consistent ◽  
First Results ◽  
Photoionization Model ◽  
Central Stars

We present the first results of a project on PNe with [WR] nuclei whose aim is twofold. One is to search for possible spatial abundance variations inside the nebula. The other is to check whether, for each object, one can build a self-consistent photoionization model (with the code PHOTO, Stasińska 1990, A&AS, 83, 501) using, as an input, the ionizing radiation field from an expanding model atmosphere reproducing the observed stellar lines of He, C and O (Koesterke et al., these proceedings).

scholarly journals The Weak Emission Line Stars

2003 ◽  
Vol 209 ◽  
pp. 235-236
Author(s):  
Jeffrey Fogel ◽  
Orsola De Marco ◽  
George Jacoby
Keyword(s):  
Emission Line ◽  
Absorption Line ◽  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Emission Lines ◽  
Type I ◽  
Evolutionary Sequence ◽  
Lower Mass ◽  
Stellar Temperatures ◽  
Central Stars

In this paper, we study the evolution of the weak emission line central stars of planetary nebula (WELS), which are similar to the H-deficient Wolf-Rayet central stars except for systematically weaker emission lines. Our attempts at finding an evolutionary sequence for the WELS similar to what was established for Wolf-Rayet central stars, were unsuccessful. No correlation was found between any of the analysed quantities: emission and absorption line fluxes or stellar and nebular parameters from the literature. It does appear, however, that WELS have intermediate stellar temperatures (30–80 kK), and do not reside in the middle of Type I planetary nebulae, possibly indicating lower mass precursors.

Unified Model Atmosphere Studies of Central Stars of Planetary Nebulae

1993 ◽  
pp. 82-82
Author(s):  
R. Gabler ◽  
A. Gabler ◽  
R. H. Méndez ◽  
R. P. Kudritzki
Keyword(s):  
Planetary Nebulae ◽  
Model Atmosphere ◽  
Unified Model ◽  
Central Stars

scholarly journals A High Resolution Far-UV Spectral Atlas of CSPNs and Hot White Dwarfs

1993 ◽  
Vol 155 ◽  
pp. 91-91
Author(s):  
R.W. Tweedy
Keyword(s):  
High Resolution ◽  
White Dwarfs ◽  
Planetary Nebulae ◽  
Central Star ◽  
Evolutionary Sequence ◽  
Spectroscopic Analyses ◽  
Spectroscopic Information ◽  
The University ◽  
Phd Thesis ◽  
Central Stars

A high-resolution IUE spectral atlas of central stars of planetary nebulae and hot white dwarfs has been produced (part of Tweedy, 1991, PhD thesis from the University of Leicester, UK), and examples from it are shown here. It has been sorted into an approximate evolutionary sequence, based on published spectroscopic analyses, from the cool 28,000K young central star He 2–138, through the hot objects like NGC 7293 and NGC 246 at 90,000K and 130,000K respectively, down to 40,000K DA white dwarfs like GD 2, which is the chosen cutoff for this selection. Copies of a revised version of this atlas, which will include more recent spectroscopic information and also white dwarfs down to 35,000K – to include the Si III object GD 394 – will be sent to anyone who requests one.

scholarly journals Non-LTE analysis of central stars∗

1984 ◽  
Vol 105 ◽  
pp. 205-208
Author(s):  
R.P. Kudritzki ◽  
R.H. Méndez ◽  
K.P. Simon
Keyword(s):  
Emission Line ◽  
Planetary Nebulae ◽  
Present Knowledge ◽  
Indirect Methods ◽  
Central Stars

Most of our present knowledge about central stars of planetary nebulae (CPN) is obtained by indirect methods using the emission line spectra of the surrounding nebula. These methods, which apply the beautiful recombination theory, can provide us with information about temperature, distance and radius of the CPN. However, we know that these methods are subject to severe problems, which then lead to strong discrepancies in the parameters of the CPN.

scholarly journals Spectroscopic Distances to Central Stars of Planetary Nebulae

1989 ◽  
Vol 131 ◽  
pp. 168-168 ◽  
Author(s):  
R. H. Méndez ◽  
R. P. Kudritzki ◽  
A. Herrero ◽  
D. Husfeld ◽  
H. G. Groth
Keyword(s):  
Absorption Line ◽  
Planetary Nebulae ◽  
Interstellar Extinction ◽  
Model Atmosphere ◽  
Line Profiles ◽  
Available Information ◽  
Central Stars

We present spectroscopic distances for 22 central stars of planetary nebulae. These distances have been determined using information provided by our non-LTE model atmosphere analyses of the stellar H and He absorption line profiles. In this way, no assumptions about nebular properties are necessary.Our spectroscopic distances turn out to be larger than many other frequently cited values. We show that our distances are not in contradiction with the available information about the interstellar extinction, and we describe additional evidence supporting them.

scholarly journals Spectral analysis of the O(He)-type central stars of the planetary nebulae K 1-27 and LoTr 4

2011 ◽  
Vol 7 (S283) ◽  
pp. 482-483
Author(s):  
Nicole Reindl ◽  
Ellen Ringat ◽  
Thomas Rauch ◽  
Klaus Werner ◽  
Jeffrey. W. Kruk
Keyword(s):  
Spectral Analysis ◽  
Planetary Nebulae ◽  
Agb Stars ◽  
Evolutionary Sequence ◽  
Preliminary Results ◽  
Pure Helium ◽  
R Coronae Borealis Stars ◽  
Central Stars

AbstractThe four known O(He) stars are the only amongst the hottest post-AGB stars whose atmospheres are composed of almost pure helium. Thus, their evolution deviates from the hydrogen-deficient post-AGB evolutionary sequence of carbon-dominated stars like e.g. PG 1159 stars. The origin of the O(He) stars is still not explained. They might be either post-early AGB stars or the progeny of R Coronae Borealis stars. We present preliminary results of a non-LTE spectral analysis based on FUSE and HST/COS observations.

scholarly journals Nebular abundances in galaxies: Beware of biases

2009 ◽  
Vol 5 (S262) ◽  
pp. 93-96 ◽  
Author(s):  
Grażyna Stasińska
Keyword(s):  
Ionizing Radiation ◽  
Emission Line ◽  
Structural Properties ◽  
Radiation Field ◽  
Dwarf Galaxies ◽  
Strong Line ◽  
Compact Galaxies

AbstractThe derivation of nebular abundances in galaxies using strong line methods is simple and quick. Various indices have been designed and calibrated for this purpose, and they are widely used. However, abundances derived with such methods may be significantly biased, if the objects under study have different structural properties (hardness of the ionizing radiation field, morphology of the nebulae) than those used to calibrate the methods. Special caution is required when comparing the metallicities of different samples, like, for example, blue compact galaxies and other emission line dwarf galaxies, or samples at different redshifts.

scholarly journals Shaping bipolar and elliptical Planetary Nebulae: Rotation and magnetic field

1997 ◽  
Vol 180 ◽  
pp. 226-226 ◽  
Author(s):  
Guillermo García-Segura ◽  
Norbert Langer ◽  
Michał Różyczka ◽  
Mordechai-Mark Mac Low ◽  
José Franco
Keyword(s):  
Magnetic Field ◽  
Ionizing Radiation ◽  
Radiation Field ◽  
Binary Systems ◽  
Planetary Nebulae ◽  
Stellar Rotation ◽  
Central Source ◽  
Formation And Evolution

We present hydrodynamical and magnetohydronynamical simulations for the formation and evolution of bipolar and elliptical planetary nebulae with two interacting winds. The models are performed under the hypothesis of a single central source, i.e. binary systems are not considered and a single initial wind function is used in our calculations. We explore various relevant parameters, including the effects of stellar rotation, ionizing radiation field and stellar magnetic field, and a catalogue of resulting shapes is generated.

scholarly journals Far-infrared spectroscopy of Planetary Nebulae with the KAO

1997 ◽  
Vol 180 ◽  
pp. 278-278
Author(s):  
R. H. Rubin ◽  
S.W.J. Colgan ◽  
M.R. Haas ◽  
S. D. Lord ◽  
J. P. Simpson
Keyword(s):  
Infrared Spectroscopy ◽  
Ionizing Radiation ◽  
Radiation Field ◽  
Electron Density ◽  
Flux Ratio ◽  
Planetary Nebulae ◽  
Far Infrared ◽  
Far Infrared Spectroscopy ◽  
Ionic Ratio ◽  
Ngc 7027

We present new far-infrared line observations of the planetary nebulae (PNs) NGC 7027, NGC 7009, NGC 6210, NGC 6543, and IC 4997 obtained with the Kuiper Airborne Observatory (KAO). The bulk of our data are for NGC 7027 and NGC 7009, including [Ne V] 24 μm, [O IV] 26 μm, [O III] (52, 88μm), and [Nm] 57 μm. Our data for [O III] (52, 88) and [N III] 57 in NGC 7027 represent the first measurements of these lines in this source. The large [O III] 52/88 flux ratio implies an electron density (cm–3) of log Ne[O III] = 4.19, the largest Ne ever inferred from these lines. We derive N++/O++ = 0.394±0.062 for NGC 7027 and 0.179±0.043 for NGC 6210. We are able to infer the O+3/O++ ionic ratio from our data. As gauged by this ionic ratio, NGC 7027 is substantially higher ionization than is NGC 7009 – consistent with our observation that the former produces copious [Ne V] emission while the latter does not. These data help characterize the stellar ionizing radiation field.

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