Density condensations in planetary nebulae and the electron temperature

Viegas, S. M.; Clegg, R. E. S.

doi:10.1093/mnras/271.4.993

Cited by 79 publications

(80 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…In the presence of such fluctuations, the abundances derived from RLs should be more representative of the true ones because abundances relative to hydrogen derived from RLs are almost independent on T e , while those determined from CELs are strongly dependent on it. Classical photoionisation models do no predict significant temperature fluctuations but certain physical inhomogeneities in nebulae such as the presence of density variations may produce them (Viegas & Clegg 1994). Moreover, departures from a Maxwell-Boltzmann energy distribution of free electrons in nebulae in form of a "kappa-distribution" can mimic the effects of temperature fluctuations on the derived abundances (Nicholls et al 2012) and could explain their ultimate nature.…”

Section: Abundance Discrepancy and Temperature Fluctuationsmentioning

confidence: 99%

The chemical composition of Galactic ring nebulae around massive stars

Esteban

Mesa‐Delgado

Morisset

et al. 2016

Mon. Not. R. Astron. Soc.

View full text Add to dashboard Cite

We present deep spectra of ring nebulae associated with Wolf-Rayet (WR) and O-type stars: NGC 6888, G2.4+1.4, RCW 58, S 308, NGC 7635 and RCW 52. The data have been taken with the 10m Gran Telescopio Canarias and the 6.5m Clay Telescope. We extract spectra of several apertures in some of the objects. We derive C 2+ and O 2+ abundances from faint recombination lines in NGC 6888 and NGC 7635, permitting to derive their C/H and C/O ratios and estimate the abundance discrepancy factor (ADF) of O 2+ . The ADFs are larger than the typical ones of normal H ii regions but similar to those found in the ionised gas of star-forming dwarf galaxies. We find that chemical abundances are rather homogeneous in the nebulae where we have spectra of several apertures: NGC 6888, NGC 7635 and G2.4+1.4. We obtain very high values of electron temperature in a peripheral zone of NGC 6888, finding that shock excitation can reproduce its spectral properties. We find that all the objects associated with WR stars show N enrichment. Some of them also show He enrichment and O deficiency as well as a lower Ne/O than expected, this may indicate the strong action of the ON and NeNa cycles. We have compared the chemical composition of NGC 6888, G2.4+1.4, RCW 58 and S 308 with the nucleosynthesis predicted by stellar evolution models of massive stars. We find that non-rotational models of stars of initial masses between 25 and 40 M ⊙ seem to reproduce the observed abundance ratios of most of the nebulae.

show abstract

Section: Abundance Discrepancy and Temperature Fluctuationsmentioning

confidence: 99%

The chemical composition of Galactic ring nebulae around massive stars

Esteban

Mesa‐Delgado

Morisset

et al. 2016

Mon. Not. R. Astron. Soc.

View full text Add to dashboard Cite

show abstract

“…On the other hand, the accuracy of the abundances determined from collisionally excited lines could be affected by temperature or density fluctuations (Peimbert 1967;Peimbert, Storey, & Torres-Peimbert 1993;Viegas & Clegg 1994;Peimbert et al 2004) or other factors that lead to calculating forbidden line strengths using incorrect or incorrectly weighted electron temperatures. The existence of distinctly different structural components within the PNe giving rise to either only collisionally excited or only recombination lines has also been proposed (Liu et al 2000;Tsamis et al 2004).…”

Section: Introductionmentioning

confidence: 99%

Identification and Characterization of Faint Emission Lines in the Spectrum of the Planetary Nebula IC 418

Sharpee¹,

Baldwin²,

Williams³

2004

ApJ

View full text Add to dashboard Cite

We present high signal-to-noise echelle spectra of the compact high surface brightness, low ionization planetary nebula IC 418. These reveal 807 emission lines down to intensities less than 10 −5 that of Hβ for which we determine widths and relative intensities. We show that line profiles are a valuable parameter for making line identifications and in constraining the excitation mechanism of the lines. We present evidence that indicates that many supposed high-level recombination lines may in fact be excited by a process other than recombination. We contend from the detection of dielectronic recombination lines that their relatively low intensities argue against their making a significant contribution to level populations of the heavy ions in this object. Following similar analyses of other PNe we find that IC 418 shows a small discrepancy in ion abundances derived from forbidden vs. recombination lines of the heavy elements.

show abstract

“…Note that introducing a density condensation shifts the dominant oxygen ion to a less charged one, and consequently the increase in t 2 (O ++ ) is not as important as might have been thought a priori. Viegas & Clegg (1994) argued that very high density clumps (n > 10 5 cm −3 ) could mimic the effects of temperature fluctuations by collisionally deexciting the [O iii] λ5007 line. The existence of such clumps is however not confirmed by the densities derived from [Ar iv] λ4740/4711, from the ratio of fine structure [O iii] lines and from high order Balmer decrement lines (Liu et al 2000.…”

Section: Small Scale Temperature Variationsmentioning

confidence: 99%