scholarly journals Collisional Excitation of the 10830 He I Line and the Population of the 23S He I State in Gaseous Nebulae

1989 ◽  
Vol 131 ◽  
pp. 212-212
Author(s):  
M. Peimbert ◽  
S. Torres-Peimbert
Keyword(s):  
Optical Depth ◽  
Planetary Nebulae ◽  
H Ii Regions ◽  
Type I ◽  
Line Intensities ◽  
Gaseous Nebulae ◽  
Radiative Transitions ◽  
Ngc 7027 ◽  
Ngc 7662 ◽  
Dust Absorption

From the study of the λλ5876, 7065 and 10830 He I line intensities in NGC 6572, NGC 6803, NGC 7009, NGC 7027, NGC 7662 and IC 418, it is found that the I(10830)/I(5876) ratio is weaker than expected. By considering estimates of the optical depth at λ10830 due to dust absorption and by determining the optical depth at λ10830 due to atomic absorption, it is argued that dust absorption of λ(10830) photons is not the cause for the low I(10830)/I(5876) ratios. By assuming that the 23S He0 state is depopulated only by radiative transitions to the 11S state and by triplet-singlet exchange collisions, it is found that its population is about a factor of two smaller than expected. This result is in agreement with a previous study of the λ3889, 4472, 5876, 6678 and 7065 line intensities in a group of thirteen Type I planetary nebulae. One of the main implications of the underpopulation of the 23S level is that the collisional effects in the N(He)/N(H) abundance ratios of planetary nebulae and 0-poor extragalactic H II regions are smaller than previously thought.

scholarly journals Helium Abundances in Gaseous Nebulae

1989 ◽  
Vol 131 ◽  
pp. 211-211 ◽  
Author(s):  
R.E.S. Clegg ◽  
J. P. Harrington
Keyword(s):  
Planetary Nebulae ◽  
H Ii Regions ◽  
Type I ◽  
Quantum Calculation ◽  
Recombination Line ◽  
Metastable Helium ◽  
Gaseous Nebulae ◽  
The Mean

New collision strengths, from a 19-state quantum calculation for He I, are used to derive revised He/H ratios in planetary nebulae (PN). Empirical formulae are given, for the correction of He I recombination line fluxes for collisional effects, and for the calculation of the population of metastable helium (He I 23S) in gaseous nebulae. The revised He abundances for PN, for four samples of published line fluxes, show a mean ratio He/H = 0.100 ±0.007 if nebulae with neutral He and Type I PN are excluded. The mean reduction due to collisional effects is only 10% for Galactic PN. It is shown that the hypothesis, that He/H should be independent of nebular temperature and density, is better satisfied when collisional effects are allowed for. The new He abundances indicate that there is very little He enrichment in Galactic PN of Types II, III, and IV, and that the enhancement of Type I PN in He over H II regions is reduced from earlier values by one third.

scholarly journals Structure

1968 ◽  
Vol 34 ◽  
pp. 456-462 ◽  
Author(s):  
R. Minkowski
Keyword(s):  
Near Infrared ◽  
Planetary Nebulae ◽  
Seyfert Galaxy ◽  
Seyfert Galaxies ◽  
Brightness Distribution ◽  
Line Intensities ◽  
Near Ultraviolet ◽  
Ngc 7027 ◽  
Expansion Pattern ◽  
Ngc 1068

My first task is to give summaries of the sessions on observations of the spectra of planetary nebulae and on the spectra of the central stars.About the spectra of planetary nebulae there is little more to say than that the observations of line intensities in the range from the near ultraviolet to the near infrared have made impressive progress. Most important is the extension of the observations into the infrared which has led to the discovery by Gillet, Low and Stein of unexpectedly high intensities in the continuous spectrum of NGC 7027 between 4μ and 14μ (75 to 22 THz). In this respect NGC 7027 and the Seyfert galaxy NGC 1068 resemble each other. Similarity of the compositions of the emission-line spectra of these two objects has been noted long ago; some lines of low ionization – [O II], [S II] –, however, are stronger in the Seyfert galaxies. The physical significance of the similarity of the infrared continua is not clear at this time, but I see no reason to reject the classification of NGC 7027 as a planetary nebula. It has a very irregular brightness distribution with much structure, but an outline which is roughly elliptical and the usual expansion pattern with a velocity of expansion of 21 km/sec.

scholarly journals Infrared Images and Line Profiles of Planetary Nebulae

1989 ◽  
Vol 131 ◽  
pp. 178-178
Author(s):  
M. G. Smith ◽  
T. R. Geballe ◽  
C. Aspin ◽  
I. S. Mclean ◽  
P. F. Roche
Keyword(s):  
Planetary Nebulae ◽  
Line Profiles ◽  
Infrared Images ◽  
Infrared Telescope ◽  
The United Kingdom ◽  
Fabry Perot ◽  
Ngc 7027 ◽  
Ngc 7662 ◽  
Infrared Array ◽  
Selection Of

We present high spatial resolution infrared images of the planetary nebulae NGC 7027, M2-9, BD +30 3639, NGC 7099 and NGC 7662. These were taken through a selection of broad and narrow-band line and continuum filters (including a Fabry-Pérot interferometer) using the 2D infrared array “IRCAM” on the United Kingdom Infrared Telescope, UKIRT, in July 1987. Comparison is made with recently published high-resolution VLA radio maps (Basart and Daub 1987, Ap. J., 317, 412) and mid-IR Wyoming Infrared Telescope raster-scanning maps (Bentley et al.1984, Ap. J., 278, 665).

scholarly journals Planetary nebulae in the Magellanic Clouds

1991 ◽  
Vol 148 ◽  
pp. 299-306 ◽  
Author(s):  
M. A. Dopita
Keyword(s):  
Planetary Nebulae ◽  
Central Star ◽  
Magellanic Cloud ◽  
Expansion Velocity ◽  
H Ii Regions ◽  
Type I ◽  
Chemical Abundances ◽  
Processed Material ◽  
Density Radius ◽  
Central Stars

We present a simple two-wind model for the evolution of the Magellanic Cloud planetary nebulae (PN) which reproduces the observed density / radius / ionised mass relationships, and serves to define the geometrical relationship between the ionised nebula and the star. From self-consistent photoionisation modelling of 78 Magellanic Cloud PN, we have constructed the H-R Diagram for the central stars, and have derived both the chemical abundances and the nebular parameters. We find that the central stars have masses generally between 0.55 and 0.7 M⊙. Type I PN have more massive precursors, and show clear evidence for the Third dredge-up episode and for the dredge-up of ON processed material. The expansion velocity of the nebula is closely correlated with the position of the central star on the H-R Diagram, proving that the nebula undergoes continuous acceleration. Excluding Type I PN, the mean abundances derived for the LMC and the SMC agree with those derived from H II regions and evolved, radiative SNR.

scholarly journals The discovery of heavy elements (Z > 30) in NGC 7027

1997 ◽  
Vol 180 ◽  
pp. 128-129
Author(s):  
D. Péquignot ◽  
J.-P. Baluteau
Keyword(s):  
Planetary Nebulae ◽  
Heavy Elements ◽  
H Ii Regions ◽  
Ngc 7027

An important aim of nebular spectroscopy is the identification of new elements. Since the pioneering work of Bowen (1928), who identified the “nebulium” lines with forbidden lines of abundant elements, most elements in nebulae have been discovered thanks to forbidden lines. The number of elements known in planetary nebulae and H II regions was 2, 5, 15, 17, and 20 in 1896, 1927, 1938, 1960, and 1975 respectively.

scholarly journals METALLICITY GRADIENTS IN M31, M 33, NGC 300 AND THE MILKY WAY USING ABUNDANCES OF DIFFERENT ELEMENTS

2019 ◽  
Vol 55 (2) ◽  
pp. 255-271 ◽  
Author(s):  
Miriam Peña ◽  
Sheila N. Flores-Durán
Keyword(s):  
Milky Way ◽  
Planetary Nebulae ◽  
Extreme Case ◽  
H Ii Regions ◽  
Type I ◽  
Chemical Abundances ◽  
Homogeneous Sample ◽  
Radial Migration ◽  
Chemical Gradients ◽  
M 31

Metallicity gradients derived from planetary nebulae (PNe) using O, Ne, and Ar abundances are studied and compared to those from H ii regions in the galaxies M 31, M 33, NGC 300 and the Milky Way. Galactocentric radii and chemical abundances were collected from the literature, carefully selecting a homogeneous sample for each galaxy. Metallicity gradients shown by PNe are flatter than those of H ii regions in all cases. The extreme case is M 31 where PN abundances are not related to galactocentric distances and the gradients are consistent with zero. To analyze the evolution of gradients with time we build gradients for Peimbert Type I and non-Type I PNe finding that Type I PNe show steeper gradients than non-Type I PNe and more similar to the ones of H ii regions indicating that the chemical gradients might steepen with time. Alternatively, the flat gradients for old PNe show that radial migration could have an important role in the evolution of galaxies.

scholarly journals Accurate Abundances Determination of Planetary Nebulae

2003 ◽  
Vol 209 ◽  
pp. 376-376
Author(s):  
J. Bernard Salas ◽  
S. R. Pottasch ◽  
P. R. Wesselius ◽  
P. Marigo
Keyword(s):  
Planetary Nebulae ◽  
Central Star ◽  
Optical Data ◽  
Infrared Space Observatory ◽  
Chemical Abundances ◽  
Mixing Processes ◽  
International Ultraviolet Explorer ◽  
Ngc 7027 ◽  
Ngc 7662 ◽  
Using Data

Accurate chemical abundances for the following planetary nebulae (PNe); NGC 6537, He 2-111, NGC 6302, NGC 6445, NGC 6741, NGC 7027, NGC 7662, NGC 2440 and NGC 5315 have been derived using data from the Infrared Space Observatory (ISO) and the International Ultraviolet Explorer (IUE). Optical data from the literature has also been used. These work has been published by Pottasch et al. (2001), Bernard Salas et al. (2001 and 2002). In particular, the use of the ISO data has reduced the need for ionization correction factors. Furthermore, infrared data avoid or reduce many problems when deriving these abundances, namely: temperature fluctuations in the nebula, and extinction corrections. The electron temperature (Te) and density of the PNe has been derived. For those PNe in which the Te has been derived for several ions a trend with the ionization potential is present. Ions with high stages of ionization give higher Te, probably because they are formed close to the central star. The chemical abundances measured in these PNe give some hint of the nucleosynthesis and mixing processes experienced by their progenitor stars. In this view, a preliminary comparison with synthetic TP-AGB models is made (Bernard Salas et al. (in prep.)). NGC 7027, NGC 6741, NGC 2440, and NGC 6445 are consistent with the occurrence of the 3rd dredge-up due to both C12 and He4 enrichment. NGC 6537, NGC 6302, and He 2-111 are likely to have stellar progenitors experiencing hot bottom burning due to the low C12 and high N14 abundances.

scholarly journals Models of Planetary Nebulae

1978 ◽  
Vol 76 ◽  
pp. 161-161
Author(s):  
M. Perinotto
Keyword(s):  
Ionization Potential ◽  
Neutral Hydrogen ◽  
Planetary Nebulae ◽  
Transfer Reactions ◽  
Line Intensities ◽  
Calculated Line ◽  
Ionization Structure ◽  
Charge Transfer Reactions ◽  
Ngc 7662 ◽  
Astronomy And Astrophysics

From existing models of planetary nebulae an important discrepancy comes out with the low ionization potential ions, as N+ and 0+, whose calculated line intensities are smaller than the observed ones. In this work the effect of charge transfer reactions between single, double, and triple ionized oxygen and nitrogen with neutral hydrogen is taken into account in a model of NGC 7662. The ionization structure of oxygen and nitrogen becomes strongly modified. The computed fractional abundances of 0+ and N+ turn out substantially larger than in previous models, thus helping to reconcile the computed line emissions from low ionization potential ions with the observed ones. (Paper will appear in Astronomy and Astrophysics.)

scholarly journals The Remarkable Evolution of the Post-Agb Star FG SGE

1998 ◽  
Vol 11 (1) ◽  
pp. 363-363
Author(s):  
Johanna Jurcsik ◽  
Benjamin Montesinos
Keyword(s):  
Time Scales ◽  
Effective Temperature ◽  
Planetary Nebula ◽  
Planetary Nebulae ◽  
Central Star ◽  
Evolutionary Models ◽  
Single Star ◽  
Line Intensities ◽  
Evolutionary Changes ◽  
Evolutionary Studies

FG Sagittae is one of the most important key objects of post-AGB stellar evolutionary studies. As a consequence of a final helium shell flash, this unique variable has shown real evolutionary changes on human time scales during this century. The observational history was reviewed in comparison with predictions from evolutionary models. The central star of the old planetary nebula (Hel-5) evolved from left to right in the HR diagram, going in just hundred years from the hot region of exciting sources of planetary nebulae to the cool red supergiant domain just before our eyes becoming a newly-born post-AGB star. The effective temperature of the star was around 50,000 K at the beginning of this century, and the last estimates in the late 1980s give 5,000-6,500 K. Recent spectroscopic observations obtained by Ingemar Lundström show definite changes in the nebular line intensities. This fact undoubtedly rules out the possibility that, instead of FG Sge, a hidden hot object would be the true central star of the nebula. Consequently, the observed evolutionary changes are connected with the evolution of a single star.

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