Electron temperature fluctuations in 30 Doradus

Abstract

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.

Electron temperature fluctuations in planetary nebulae

“…This was also found in 30 Doradus (Krabbe & Copetti 2002). A possible interpretation of such behavior is that it might be indicating an anti-correlation between [O iii] temperature and density.…”

“…Recently, direct determinations of electron temperature fluctuations have been obtained for the planetary nebulae NGC 4361 (Liu 1998) and NGC 7009 (Rubin et al 2002), and for the H ii regions 30 Doradus (Krabbe & Copetti 2002) and Orion Nebula (Rubin et al 2003;O'Dell et al 2003) from pointto-point measurements of electron temperature and very low temperature fluctuations have been measured. Up to now these four objects are the only ones for which direct estimations of electron temperature fluctuations have been published.…”

Abundance gradients in a sample of barred spiral galaxies

“…If we applied such correction over the direct oxygen abundances utilized in this paper, it would reconcile our predictions. However, theoretical and observational studies (e.g., Kingdon & Ferland 1995;Krabbe & Copetti 2002;Rubin et al 2003) have up to now failed to predict or directly detect such high levels of electron temperature fluctuations. Strong evidence against the presence of temperature fluctuations in planetary nebulae and in H  regions have been also found by Liu et al (2000Liu et al ( , 2001Liu et al ( , 2004 and Tsamis et al (2003), respectively.…”

Chemical abundances in seven galactic planetary nebulae

“…One potential explanation to these discrepancies would be the presence of temperature fluctuations inside of H II regions and planetary nebulae (Peimbert 1967). However, the observed values of electron temperature fluctuations have been lower than the ones necessary to Table 1 is only available in electronic form at http://www.edpsciences.org reconcile the abundances derived from forbidden and permitted lines (Liu 1998;Rubin et al 2002;Krabbe & Copetti 2002;Rubin et al 2003;O'Dell et al 2003;Krabbe & Copetti 2005). Other solution that was suggested by Liu et al (2000) would be the presence inside the nebula of hydrogen deficient clumps with high density and rich in heavy elements.…”