scholarly journals The effect of the slit configuration on the H2 1-0 s(1) to Br γ line ratio of spatially resolved planetary nebulae

2020 ◽  
Vol 497 (3) ◽  
pp. 3180-3190
Author(s):  
Isabel Aleman
Keyword(s):  
Numerical Simulations ◽  
Planetary Nebulae ◽  
Line Ratio ◽  
Excitation Mechanism ◽  
Limited Region ◽  
Spectroscopic Observations ◽  
Spatially Resolved ◽  
Peak Emission

ABSTRACT The H2 1-0 S(1)/Br γ ratio (R(Br γ)) is used in many studies of the molecular content in planetary nebulae (PNe). As these lines are produced in different regions, the slit configuration used in spectroscopic observations may have an important effect on their ratio. In this work, observations and numerical simulations are used to demonstrate and quantify such effect in PNe. The study aims to assist the interpretation of observations and their comparison to models. The analysis shows that observed R(Br γ) ratios reach only values up to 0.3 when the slit encompasses the entire nebula. Values higher than that are only obtained when the slit covers a limited region around the H2 peak emission and the Br γ emission is then minimized. The numerical simulations presented show that, when the effect of the slit configuration is taken into account, photoionization models can reproduce the whole range of observed R(Br γ) in PNe, as well as the behaviour described above. The argument that shocks are needed to explain the higher values of R(Br γ) is thus not valid. Therefore, this ratio is not a good indicator of the H2 excitation mechanism as suggested in the literature.

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 Advances in Numerical Simulations of Gaseous Nebulae

1993 ◽  
Vol 155 ◽  
pp. 123-130 ◽  
Author(s):  
Gary J. Ferland
Keyword(s):  
Numerical Simulations ◽  
Planetary Nebulae ◽  
Stellar Atmosphere ◽  
Ionized Gas ◽  
Gaseous Nebulae ◽  
Recent Advances ◽  
New Generation

I outline recent advances in numerical simulations of gaseous nebulae. These fall into three major areas; the Opacity Project and its extensions, the role of grains within the ionized gas, and the effects of mechanical heat on the nebula. These advances, together with improvements in stellar atmosphere calculations, should lead to a new generation of more realistic simulations of conditions in planetary nebulae and predictions of their emitted spectra.

scholarly journals Spectroscopic Observations of Planetary Nebulae in the Magellanic Clouds

1968 ◽  
Vol 34 ◽  
pp. 34-35 ◽  
Author(s):  
M. W. Feast
Keyword(s):  
Planetary Nebulae ◽  
Magellanic Clouds ◽  
Preliminary Results ◽  
Spectroscopic Observations

A programme of spectroscopic observations of planetary nebulae in both Magellanic Clouds has been underway in Pretoria for some years, and some preliminary results for the LMC have been published (Feast, 1964b). More extensive observations are now available (altogether in both clouds 112 spectra of 39 objects), and these are being prepared for publication elsewhere. Below are summarized the main conclusions so far deduced.

scholarly journals Photometric and Spectroscopy Observations of Peculiar Nuclei of Planetary Nebulae

1989 ◽  
Vol 131 ◽  
pp. 309-309
Author(s):  
G. Jasniewicz ◽  
A. Acker
Keyword(s):  
Radial Velocity ◽  
Planetary Nebulae ◽  
Spectroscopic Observations ◽  
Photometric And Spectroscopic Observations ◽  
Ccd Detector ◽  
Central Stars

Photometric and spectroscopic observations of some bright central stars of planetary nebulae (PN) have been conducted between 1984 and 1987 with the following tools: differential photometer P7 (70-cm swiss telescope, La Silla c/o ESO); radial velocity scanner CORAVEL (1-m swiss telescope, Observatoire de Haute-Provence = OHP); spectrograph CARELEC with CCD detector (193-cm telescope, OHP).

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 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.

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