Issue |
A&A
Volume 453, Number 3, July III 2006
|
|
---|---|---|
Page(s) | 943 - 947 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20054736 | |
Published online | 28 June 2006 |
Electron temperature fluctuations in H II regions
The feasibility of t2 estimates from point-to-point observations
Laboratório de Análise Numérica e Astrofísica, Departamento de Matemática, Universidade Federal de Santa Maria, 97119-900 Santa Maria, RS, Brazil e-mail: mvfc@lana.ccne.ufsm.br
Received:
20
December
2005
Accepted:
24
February
2006
Context. The spatial electron temperature fluctuations in ionized nebulae that were initially proposed to explain the discrepancies among temperatures obtained from different sensors have been pointed to as the cause of huge inconsistencies among abundances of heavy elements calculated from recombination and forbidden emission lines. Recently, there have been some attempts of direct detection and quantification of spatial temperature fluctuations with point-to-point temperature measurements across the nebula.
Aims. In this paper, we assess the feasibility of estimating the temperature fluctuation parameter t2, the total variance of the spatial distribution of temperature relative to the mean, from the distribution of temperatures measured on the plane of the sky with different sensors.
Methods. Point-to-point measurements of the electron temperature at a series of contiguous and equally spaced rectangular apertures along a radius of homogeneous and spherically symmetric nebulae were numerically simulated for six different temperature sensors.
Results.
Variances of projected temperature distributions were obtained and compared with
total t2 for different values for the density, ionization parameter and
temperature of the ionizing star.
The projected profiles of electron temperature obtained from indicators
associated with ions occurring at large fractions of the nebula, such as
[] (
,
[
]
, and the Balmer
jump
/Hβ, are good tracers
of the internal gradient of temperature. The variances
of
the projected temperature distributions measured from these sensors correspond
to significant fractions of the total temperature variance, for typical
nebulae of the order of
30%, 25%, and 15% for
the Balmer jump and the [
] and [
] ratios, in that
order. On the other hand, the temperature profiles obtained from sensors
corresponding to low ionization ions, such as [
] (
, [
]
, and [
]
, are almost constant at the values of temperature of the outer parts of
the nebula, fail to reproduce the true temperature gradient, and have a
that is always less than 10% and is usually around
1–3% of t2.
Key words: ISM: H II regions / ISM: planetary nebulae: general
© ESO, 2006
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