scholarly journals Bi-abundance photoionization models of planetary nebulae: determining the amount of oxygen in the metal-rich component

2020 ◽  
Vol 497 (3) ◽  
pp. 3363-3380 ◽  
Author(s):  
V Gómez-Llanos ◽  
C Morisset
Keyword(s):  
Heavy Element ◽  
Volume Fraction ◽  
Planetary Nebulae ◽  
Line Ratio ◽  
Small Contribution ◽  
Rich Region ◽  
Normal Region ◽  
Cold Metal ◽  
High Metallicity

ABSTRACT We study the hypothesis of high-metallicity clumps being responsible for the abundance discrepancy found in planetary nebulae between the values obtained from recombination and collisionally excited lines. We generate grids of photoionization models combining cold metal-rich clumps emitting the heavy element recombination lines, embedded in a normal metallicity region responsible for the forbidden lines. The two running parameters of the grid are the metallicity of the clumps and its volume fraction relative to the whole nebula. We determine the density and temperatures (from the Balmer jump and the [O iii] 5007/4363 Å line ratio) and the ionic abundances from the collisional and recombination lines, as an observer would do. The metallicity of the near-to-solar region is recovered, while the metallicity of the clumps is systematically underestimated by up to two orders of magnitude. This is mainly because most of the Hβ emission is coming from the ‘normal’ region, and only the small contribution emitted by the metal-rich clumps should be used. We find that a given ADF(O++) can be reproduced by a small amount of rich clumps, or a bigger amount of less rich clumps. Finally, comparing with the observations of NGC 6153, we find two models that reproduce its ADF(O++) and the observed electron temperatures. We determine the fraction of oxygen embedded in the metal-rich region (with a fraction of volume less than 1 per cent) to be roughly between 25 per cent and 60 per cent of the total amount of oxygen in the nebula (a few 10−3M⊙).

scholarly journals Chemical Abundances in Galactic Bulge Pn

1993 ◽  
Vol 155 ◽  
pp. 581-581 ◽  
Author(s):  
N.A. Walton ◽  
M.J. Barlow ◽  
R.E.S. Clegg
Keyword(s):  
Galactic Disk ◽  
Planetary Nebulae ◽  
Solar Neighbourhood ◽  
Galactic Bulge ◽  
Low Resolution ◽  
Chemical Abundances ◽  
The Mean ◽  
Optical Spectrophotometry ◽  
High Metallicity

We present abundance determinations, in particular of carbon, and C/O ratios, for 11 Galactic bulge planetary nebulae (PN) based on our low resolution UV data from IUE observations and optical spectrophotometry from the Anglo-Australian Telescope. We compare the observed abundances with those predicted by dredge-up theory for the high metallicity Galactic bulge. The sample abundances are also contrasted with the abundances found for PN in the Galactic disk. The mean C/O ratio for the bulge PN is significantly lower than that found for Galactic disk PN. Further, we present an abundance analysis of the very metal-poor bulge PN M2-29. From an analysis of the differential extinction found from the observed ratios of the He ii 1640,4686Å lines, we find that the ultraviolet reddening law towards the bulge is steeper than in the solar neighbourhood.

scholarly journals The UV and optical reddening law to the Galactic Bulge and CNO abundances in Bulge planetary nebulae

1993 ◽  
Vol 153 ◽  
pp. 337-338
Author(s):  
N.A. Walton ◽  
M.J. Barlow ◽  
R.E.S. Clegg
Keyword(s):  
Galactic Disk ◽  
Planetary Nebulae ◽  
Line Ratio ◽  
Solar Neighbourhood ◽  
Balmer Line ◽  
Galactic Bulge ◽  
The Mean ◽  
Cno Abundances ◽  
Halo Population ◽  
Selective Extinction

An analysis of the differential ultraviolet extinction towards four bulge planetary nebulae, based on the observed line ratio of He II 1640/4686Å, shows that the ultraviolet reddening law towards the bulge is much steeper than in the solar neighbourhood. An analysis of the optical reddening law for 42 bulge PN, based upon observed Balmer line ratios and Hβ to radio free-free flux ratios, is presented. The optical reddening law towards the bulge is steeper than in the local ISM, and thus the ratio of total to selective extinction, Rv = 2.29 (± 0.50), is lower than the standard solar neighbourhood value of Rv = 3.10.We present abundance determinations, in particular C/H and C/O ratios, for 11 Galactic bulge PN, based on spectrophotometry in the UV from IUE and in the optical from the Anglo-Australian Telescope. The derived abundances are compared with values for PN in the Galactic disk. The mean C/O ratio for bulge PN is significantly lower than that found for Galactic disk PNs. Additionally we present an abundance analysis of the very metal-poor halo population PN M2-29, which is located in the bulge.

scholarly journals Hydrogen Deficient Planetary Nebulae: Preliminary Results

1985 ◽  
Vol 87 ◽  
pp. 359-365 ◽  
Author(s):  
S.R. Pottasch ◽  
A. Mampaso ◽  
A. Manchado ◽  
J. Menzies
Keyword(s):  
Correction Factor ◽  
Heavy Element ◽  
Planetary Nebulae ◽  
Ionization State ◽  
Abundance Gradient ◽  
Element Abundances ◽  
Preliminary Results ◽  
Very High

AbstractNew spectra of A78 and A58 at different positions in the nebulae are presented. An abundance gradient is found in A78, extending quite close to the center. Similarly the nebulous knot near the center of A58 has considerably higher heavy element abundances than the outer regions of this nebula. The ionization state is considerably lower in A58 than A78. In A78 most of the neon is in the form of Ne+3 and Ne+4, indicating that the standard ionization correction factor as used by Jacoby and Ford, is substantially in error. Finally, the very high infrared excesses found in this nebulae are discussed.

scholarly journals The Spatio-Kinematic Structure of the CO Envelopes in Evolved Planetary Nebulae

1993 ◽  
Vol 155 ◽  
pp. 224-224
Author(s):  
R. Bachiller ◽  
P.J. Huggins ◽  
P. Cox ◽  
T. Forveille
Keyword(s):  
Angular Resolution ◽  
Planetary Nebulae ◽  
Line Ratio ◽  
High Angular Resolution ◽  
Molecular Gas ◽  
Excitation Temperature ◽  
Kinematic Structure ◽  
Ellipsoidal Shell ◽  
Polar Caps ◽  
Resolution Mapping

We report high angular resolution mapping of the CO (J=2→1 and 1→0) lines in three evolved planetary nebulae (PNe): NGC 6781, NGC 6772, and VV47. The CO 2→1 observations of the ring-like nebula NGC 6781 provide the most detailed map to date of the kinematic structure of a PN envelope. The data are well explained with a model consisting of a thin, clumpy, ellipsoidal shell, which is open at the ends and is expanding with a velocity proportional to distance from the star. The molecular shell of NGC 6772 appears similar, but the gas is more confined to an equatorial ring and is much more incomplete. The molecular gas in VV 47 is in two clumpy lobes, which are likely to be the only surviving molecular condensations from an earlier, more extended equatorial distribution of the same kind. The average CO excitation temperature of these PNe is found to be >23 K from the CO 2→1/1→0 line ratio, and the mass of molecular gas is estimated to be 0.1, 0.02, and 0.002 M⊙ in NGC 6781, NGC 6772, and VV 47, respectively. It appears that the ring-like PNe are formed from the dissociation and ionization of neutral ellipsoidal shells; destruction of the envelope begins with the rapid ionization of the least dense polar caps, and continues until the densest molecular material at the nebular waist is fully ionized.

scholarly journals Plasma diagnostics for planetary nebulae and H ii regions using N ii and O ii optical recombination lines

2011 ◽  
Vol 7 (S283) ◽  
pp. 432-433
Author(s):  
Ian A. McNabb ◽  
Xuan Fang ◽  
Xiao–Wei Liu ◽  
Peter J. Storey
Keyword(s):  
Plasma Diagnostics ◽  
Planetary Nebulae ◽  
Coupling Scheme ◽  
H Ii Regions ◽  
Diagnostic Analysis ◽  
Plasma Diagnostic ◽  
Intermediate Coupling ◽  
Physical Conditions ◽  
Cold Metal ◽  
Intermediate Coupling Scheme

AbstractWe carry out plasma diagnostic analysis for a number of planetary nebulae (PNe) and H ii regions. We use N ii and O ii optical recombination lines (ORLs) with new effective recombination coefficients calculated under the intermediate coupling scheme, for a range of electron temperatures (Te) and densities (Ne), and fitted against the most reliable measurements. Comparing Te derived from ORLs, collisionally excited lines (CELs), the hydrogen Balmer Jump, and/or He i if available, we find the relation Te (ORLs) < Te (He i) < Te (H i BJ) < Te (CELs), confirming the physical conditions in the bi-abundance model postulated by Liu et al., i.e. the nebula contains another cold, metal-rich and probably H-deficient component.

Strengthening Behavior and Tension–Compression Strength–Asymmetry in Nanocrystalline Metal–Ceramic Composites

2012 ◽  
Vol 134 (4) ◽  
Author(s):  
A. M. Dongare ◽  
B. LaMattina ◽  
A. M. Rajendran
Keyword(s):  
Molecular Dynamics ◽  
Volume Fraction ◽  
Md Simulations ◽  
Ceramic Composites ◽  
Embedded Atom Method ◽  
Nanocrystalline Metal ◽  
Rich Region ◽  
Embedded Atom ◽  
Metal Ceramic ◽  
Strength Asymmetry

Metal–ceramic composites are an emerging class of materials for use in the next-generation high technology applications due to their ability to sustain plastic deformation and resist failure in extreme mechanical environments. Large scale molecular dynamics simulations are used to investigate the performance of nanocrystalline metal–matrix composites (MMCs) formed by the reinforcement of the nanocrystalline Al matrix with a random distribution of nanoscale ceramic particles. The interatomic interactions are defined by the newly developed angular-dependent embedded atom method (A-EAM) by combining the embedded atom method (EAM) potential for Al with the Stillinger–Weber (SW) potential for Si in one functional form. The molecular dynamics (MD) simulations are aimed to investigate the strengthening behavior and the tension–compression strength asymmetry of these composites as a function of volume fraction of the reinforcing Si phase. MD simulations suggest that the strength of the nanocomposite increases linearly with an increase in the volume fraction of Si in the Al-rich region, whereas the increase is very sharp in the Si-rich region. The higher strength of the nanocomposite is attributed to the reduced sliding/rotation between the Al/Si and the Si/Si grains as compared to the pure nanocrystalline metal.

scholarly journals A Spatially Resolved Spectroscopic Study of NGC 7009

2003 ◽  
Vol 209 ◽  
pp. 393-394
Author(s):  
S.-G. Luo ◽  
X.-W. Liu
Keyword(s):  
High Resolution ◽  
Spectroscopic Study ◽  
Electron Temperature ◽  
Large Amplitude ◽  
Heavy Element ◽  
Line Ratio ◽  
Element Abundances ◽  
Spatially Resolved ◽  
The Difference ◽  
Recombination Spectrum

Liu et al. (1995) and Luo, Liu & Barlow (2001) determined the CNONe abundances in NGC 7009 using optical recombination lines (ORLs) and found that they are all approximately a factor of five higher than the corresponding values derived from collisionally excited lines (CELs). We have obtained new deep high resolution long-slit spectra of NGC 7009. The data have been used to map the electron temperature, density and element abundances across the nebula, using both CELs and ORLs. While the electron temperature derived from the [O III] forbidden line ratio, Te([O III]), is found to be largely constant, that derived from Balmer jump of H I recombination spectrum, Te(BJ), shows large amplitude complicated variations. The ratios of the heavy element abundances derived from ORLs to those deduced from CELs are found to be correlated with the difference between the difference between Te([O III]) and Te(BJ) – a relation previously known to exist from analyses of the integration spectra of individual nebulae (Liu et al. 2001).

scholarly journals ON THE [ArIV]/[ArIII] LINE RATIO IN PLANETARY NEBULAE

2000 ◽  
Vol 3 (01-02) ◽  
pp. 48-50
Author(s):  
R. E. Carlos Reyes ◽  
F. Elizalde ◽  
J. E. Steiner
Keyword(s):  
Planetary Nebulae ◽  
Line Ratio

Estudios espectroscópicos anteriores de las nebulosas planetarias han demostrado que la razón de línea [ArIV] / [ArIII] observada no es reproducida por los modelos de fotoionización. Mostrados que esta discrepancia desaparece si consideramos una combinación adecuada del fator de llenarlo y de perfil de la densidad radial.

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