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 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 Self-Consistent Photoionization Models of Planetary Nebulae Luminescence

1993 ◽  
Vol 155 ◽  
pp. 187-187
Author(s):  
V.V. Golovaty ◽  
F Malkov
Keyword(s):  
Chemical Elements ◽  
Planetary Nebulae ◽  
Central Star ◽  
Model Atmosphere ◽  
Emission Lines ◽  
Lyman Continuum ◽  
Self Consistent ◽  
Spectral Ranges ◽  
Photoionization Model ◽  
The Continuum

The modern self-consistent photoionization model of planetary nebula luminescence is described. All of the processes which play an important role in the ionization and thermal equilibrium of the nebular gas are taken into consideration. The diffuse ionizing radiation is taken into account completely. The construction of the model is carried out for the radial distribution of gas density in the nebular envelope which is consistent with isophotal map of the nebula. The application of the model is illustrated on the example of the planetary nebulae BD+30°3639 and NGC 7293. For each nebula, the intensities of the emission lines of ten basic chemical elements in the UV, optical and IR spectral ranges are calculated and matched with observational data. Both the chemical composition of the nebular gas and the continuum of the central star at the wavelengths ≤912Å are determined during the process of model calculation. It is shown that the continuum of the central star at ≤912Å does not correspond to the blackbody spectrum but agrees with the spectrum of the corresponding non-LTE model atmosphere. The radial distributions of electron density, electron temperature and other parameters in the nebular envelopes are found. The optical thickness of the nebulae in the Lyman continuum is derived.

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 survey for hot central stars of planetary nebulae – I. Methods and first results

2016 ◽  
Vol 465 (1) ◽  
pp. 293-301
Author(s):  
Graham C. Kanarek ◽  
Michael M. Shara ◽  
Jacqueline K. Faherty ◽  
David Zurek ◽  
Anthony F. J. Moffat
Keyword(s):  
Planetary Nebulae ◽  
First Results ◽  
Central Stars

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 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.

scholarly journals Unified Model Atmosphere Studies of Central Stars of Planetary Nebulae

1993 ◽  
Vol 155 ◽  
pp. 82-82
Author(s):  
R. Gabler ◽  
A. Gabler ◽  
R. H. Méndez ◽  
R. P. Kudritzki
Keyword(s):  
High Resolution ◽  
Absorption Line ◽  
Spectroscopic Analysis ◽  
Planetary Nebulae ◽  
Model Atmosphere ◽  
Unified Model ◽  
Parallel Model ◽  
Line Profiles ◽  
Atmospheric Parameters ◽  
Central Stars

A first step in the accurate quantitative spectroscopic analysis of central stars of PN has been based on fitting the results of NLTE, hydrostatic, plane-parallel model atmosphere calculations to the observed H and He absorption-line profiles in high-resolution spectra of bright central stars (Méndez et al. 1988, A&A 190, 113 and subsequent papers). Such analyses have provided very useful determinations of the basic atmospheric parameters: Teff, log g and He abundance.

scholarly journals Reliability of semiconductor and gas-filled diodes for over-voltage protection exposed to ionizing radiation

2009 ◽  
Vol 24 (2) ◽  
pp. 132-137 ◽  
Author(s):  
Koviljka Stankovic ◽  
Milos Vujisic ◽  
Edin Dolicanin
Keyword(s):  
Ionizing Radiation ◽  
Gamma Radiation ◽  
Radiation Field ◽  
Working Conditions ◽  
The Other ◽  
Wide Spread ◽  
Other Hand ◽  
Non Linear ◽  
Insight Into

The wide-spread use of semiconductor and gas-filled diodes for non-linear over-voltage protection results in a variety of possible working conditions. It is therefore essential to have a thorough insight into their reliability in exploitation environments which imply exposure to ionizing radiation. The aim of this paper is to investigate the influence of irradiation on over-voltage diode characteristics by exposing the diodes to californium-252 combined neutron/gamma radiation field. The irradiation of semiconductor over-voltage diodes causes severe degradation of their protection characteristics. On the other hand, gas-filled over-voltage diodes exhibit a temporal improvement of performance. The results are presented with the accompanying theoretical interpretations of the observed changes in over-voltage diode behaviour, based on the interaction of radiation with materials constituting the diodes.

Model Atmospheres and Quantitative Spectroscopy of Central Stars of Planetary Nebulae

1989 ◽  
Vol 131 ◽  
pp. 273-292 ◽  
Author(s):  
R. P. Kudritzki ◽  
R.H. Méndez
Keyword(s):  
Quantitative Analysis ◽  
Planetary Nebulae ◽  
Physical Nature ◽  
Black Body ◽  
Central Star ◽  
Model Atmosphere ◽  
Stellar Atmospheres ◽  
Spectral Lines ◽  
Quantitative Spectroscopy ◽  
Central Stars

It is a good tradition in IAU Symposia about PN to have a paper on model atmospheres. However, this is always a difficult task for the authors, because the majority of the PN researchers still believe that the best model atmosphere for a Central Star is a black body. Of course, this puts a theorist in stellar atmospheres into a somewhat desperate position. However, Central Stars of Planetary Nebulae (hereafter CSPN) - as all other stars - show spectral lines. And we will try to use the opportunity of this paper to convince that - as for all other stars - the quantitative analysis of these lines on basis of model atmospheres yields extremely valuable information about the physical nature of the stars.

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