Astronomy and Astrophysics, volume 492, 463-468 (2008/12-3)
Electron temperature fluctuations in NGC346.
OLIVEIRA V.A., COPETTI M.V.F. and KRABBE A.C.
Abstract (from CDS):
The existence and origin of large spatial temperature fluctuations in HII regions and planetary nebulae are assumed to explain the differences between the heavy element abundances inferred from collisionally excited and recombination lines, although this interpretation remains significantly controversial. We investigate the spatial variation in electron temperature inside NGC346
, the brightest HII region in the Small Magellanic Cloud. Long slit spectrophotometric data of high signal-to-noise were employed to derive the electron temperature from measurements derived from localized observations of the [OIII](λ4959 + λ5007)/λ4363 ratio in three directions across the nebula. The electron temperature was estimated in 179 areas of 5"x1.5" of size distributed along three different declinations. A largely homogeneous temperature distribution was found with a mean temperature of 12269K and a dispersion of 6.1%. After correcting for pure measurements errors, a temperature fluctuation on the plane of the sky of t2s
=0.0021 (corresponding to a dispersion of 4.5%) was obtained, which indicates a 3D temperature fluctuation parameter of t2
≃0.008. A large scale gradient in temperature of the order of -5.7±1.3K/arcsec was found. The magnitude of the temperature fluctuations observed agrees with the large scale variations in temperature predicted by standard photoionization models, but is too small to explain the abundance discrepancy problem. However, the possible existence of small spatial scale temperature variations is not excluded.
ISM: HII regions - ISM: individual objects: NGC346
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