Issue |
A&A
Volume 389, Number 1, July I 2002
|
|
---|---|---|
Page(s) | 286 - 294 | |
Section | The Sun | |
DOI | https://doi.org/10.1051/0004-6361:20020528 | |
Published online | 14 June 2002 |
The stellar content, metallicity and ionization structure of HII regions *
1
Kapteyn Institute, PO Box 800, 9700 AV Groningen, The Netherlands
2
SRON, National Institute for Space Research, PO Box 800, 9700 AV Groningen, The Netherlands
Corresponding author: N. L. Martín-Hernández, leticia@astro.rug.nl
Received:
22
October
2001
Accepted:
5
April
2002
Observations of infrared fine-structure lines provide direct information
on the metallicity and ionization structure of HII regions and
indirectly on the hardness of the radiation field ionizing these
nebulae. We have analyzed a sample of Galactic and Magellanic Cloud HII
regions observed by the Infrared Space Observatory (ISO) to examine
the interplay between stellar content,
metallicity and the ionization structure of HII regions. The observed
[] 10.5/[
] 18.7
and [
] 15.5/[
] 12.8
line ratios
are shown to be highly correlated over
more than two orders of magnitude. We have compared the observed line
ratios to the results of photoionization models using different stellar
energy distributions. The derived characteristics of the ionizing star
depend critically on the adopted stellar model as well as the (stellar)
metallicity. We have compared the stellar effective temperatures
derived from these model studies for a few well-studied HII regions with
published direct spectroscopic determinations of the spectral type of
the ionizing stars. This comparison supports our interpretation that
stellar and nebular metallicity influences the observed infrared ionic
line ratios. We can
explain the observed increase in degree of ionization, as traced by
the [
]/[
] and [
]/[
] line ratios, by the hardening
of the radiation field due to the decrease of metallicity. The
implications of our results for the determination of the ages of
starbursts in starburst galaxies are assessed.
Key words: stars: atmospheres / stars: early-type / ISM: abundances / ISM: HII regions / galaxies: starburst / galaxies: individual: Milky Way / Magellanic Clouds
© ESO, 2002
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