Electron temperature determination from nebular continuum emission in planetary nebulae and the importance of temperature fluctuations

Liu, Xiaowei; Danziger, John

doi:10.1093/mnras/263.1.256

Cited by 69 publications

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“…They compared the average temperatures derived from the Paschen continuum emission and the [OIII] lines and found differences of at least 2000 K using the two methods. Liu & Danziger (1993) derived the same result from a study of 14 planetary nebulae (PNe).…”

Section: Real Abundance Variations or Local Temperature Fluctuations?mentioning

confidence: 59%

The chemical abundances in a sample of dwarf irregular galaxies

Hidalgo-Gámez

Olofsson

Masegosa³

2001

A&A

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Abstract. Deep groundbased spectra of Hubble V and Hubble X, the two largest and brightest H ii regions in the Local Group dwarf galaxy, NGC 6822, are presented. The extinction, excitation and ionization are studied on scales as small as 4 pc. The chemical composition of some elements within the regions as well as possible small scale variations in the abundances of helium, nitrogen, oxygen and neon over the face of the two regions are investigated. The detection of the emission lines [OI] and [ClIII] are probably related to shock-heating from gas ejected from supernova explosions and planetary nebula ejections, respectively, although the contribution to the total ionization is very small. No significant differences in chemical composition was found between Hubble V and Hubble X. However, some small scale variations in the abundances of oxygen, and possibly nitrogen and helium, over the face of both H ii regions were noted, although different physical conditions could apply within the regions, such as local fluctuations in the temperature.

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Section: Real Abundance Variations or Local Temperature Fluctuations?mentioning

confidence: 59%

The chemical abundances in a sample of dwarf irregular galaxies

Hidalgo-Gámez

Olofsson

Masegosa³

2001

A&A

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“…Although t 2 cannot be directly measured, it can be estimated through the effects of the temperature fluctuations on the values of temperature or abundance obtained from different methods. By this method, values of t 2 ≈ 0.02−0.10 have been attributed to planetary nebulae (Dinerstein et al 1985;Liu & Danziger 1993;Peimbert et al 1995), galactic (Esteban et al , 1999a and extragalactic (Luridiana et al 1999;Gonzalez-Delgado et al 1994) H ii regions. However, these high values for t 2 are not reproduced by the standard photoionization models, which predict t 2 ≤ 0.02 (Gruenwald & Viegas 1995;Kingdon & Ferland 1995).…”

Section: Magnitude Of the Electron Temperature Fluctuationsmentioning

confidence: 97%

Electron temperature fluctuations in 30 Doradus

Krabbe

Copetti

2002

A&A

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Abstract. We present an observational study of the spatial variation of the electron temperature in the 30 Doradus Nebula. We used the [O iii](λ4959 + λ5007)/λ4363 ratio to estimate the electron temperature at 135 positions in the nebula across three different directions. We analysed long-slit spectrophotometric data of high signalto-noise in the range of 4100 to 5030Å obtained with the Cassegrain spectrograph attached to the 1.60 m telescope of the Laboratório Nacional de Astrofísica, Brazil. No large-scale electron temperature gradient was detected in 30 Doradus. The electron temperature estimates obtained are fairly homogeneous with a mean value of 10 270 ± 140 (3σ) K. The compatibility between the present estimates with optical and radio temperature determinations found in the literature for other positions or for the entire nebula corroborates this conclusion. Temperature fluctuations of small amplitude were observed with a variance relative to the mean of t 2 s = 0.0025 or equivalently with a dispersion of only 5%. The areas with lower surface brightness seem to present slightly higher electron temperatures. This would indicate that the bright arcs of 30 Doradus, which correspond to the densest regions, would have lower electron temperatures than the most diffuse areas.

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“…The logarithmic extinction at Hβ, c(Hβ), is normally obtained by comparing the observed Balmer decrement (in particular Hα/Hβ) to the intrinsic value given by Brocklehurst (1971) and Hummer & Storey (1987). The estimates of c(Hβ) (from the Balmer ratio) reported in the literature for NGC 6818 span the range 0.25 (Aller & Czyzak 1983, Liu & Danziger 1993 to 0.41 (Collins et al 1961). Moreover, Tylenda et al (1992) and Condon et al (1999) obtained c(Hβ) = 0.33 and 0.40, respectively, from the radio to Hβ fluxes.…”

Section: Interstellar Absorptionmentioning

confidence: 99%

The 3-D ionization structure of NGC 6818: A Planetary Nebula threatened by recombination

Benetti

Ragazzoni

Sabbadin

et al. 2003

A&A

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Abstract. Long-slit NTT+EMMI echellograms of NGC 6818 (the Little Gem) at nine equally spaced position angles, reduced according to the 3-D methodology introduced by Sabbadin et al. (2000a,b), allowed us to derive: the expansion law, the diagnostics and ionic radial profiles, the distance and the central star parameters, the nebular photo-ionization model, the 3-D reconstruction in He II, [O III] and [N II], the multicolor projection and a series of movies. The Little Gem results to be a young (3500 years), optically thin (quasi-thin in some directions) double shell (M ion 0.13 M ) at a distance of 1.7 kpc, seen almost equatorial on: a tenuous and patchy spherical envelope (r 0.090 pc) encircles a dense and inhomogeneous tri-axial ellipsoid (a/2 0.077 pc, a/b 1.25, b/c 1.15) characterized by a hole along the major axis and a pair of equatorial, thick moustaches. NGC 6818 is at the start of the recombination phase following the luminosity decline of the 0.625 M central star, which has recently exhausted the hydrogen shell nuclear burning and is rapidly moving toward the white dwarf domain (log T * 5.22 K; log L * /L 3.1). The nebula is destined to become thicker and thicker, with an increasing fraction of neutral, dusty gas in the outermost layers. Only over some hundreds of years the plasma rarefaction due to the expansion will prevail against the slower and slower stellar decline, leading to a gradual re-growing of the ionization front. The exciting star of NGC 6818 (m V 17.06) is a visual binary: a faint, red companion (m V 17.73) appears at 0.09 arcsec in PA = 190 • , corresponding to a separation ≥150 AU and to an orbital period ≥1500 years.

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Electron temperature determination from nebular continuum emission in planetary nebulae and the importance of temperature fluctuations

Cited by 69 publications

References 0 publications

The chemical abundances in a sample of dwarf irregular galaxies

The chemical abundances in a sample of dwarf irregular galaxies

Electron temperature fluctuations in 30 Doradus

The 3-D ionization structure of NGC 6818: A Planetary Nebula threatened by recombination

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