Issue |
A&A
Volume 381, Number 2, JanuaryII 2002
|
|
---|---|---|
Page(s) | 606 - 627 | |
Section | The Sun | |
DOI | https://doi.org/10.1051/0004-6361:20011504 | |
Published online | 15 January 2002 |
ISO spectroscopy of compact HII regions in the Galaxy*
II. Ionization and elemental abundances
1
Kapteyn Institute, PO Box 800, 9700 AV Groningen, The Netherlands
2
SRON, National Institute for Space Reasearch, PO Box 800, 9700 AV Groningen, The Netherlands
3
Institut d'Astrophysique de Marseille, CNRS & Univ. de Provence, BP 8, 13376 Marseille Cedex 12, France
4
Institut d'Astrophysique Spatiale, Bât. 121, Université de Paris XI, 91405 Orsay, France
5
Laboratoire d'Astrophysique, Observatoire Midi-Pyrénées, 14, Av. E. Belin, 31400 Toulouse, France
6
Department of Astronomy, 475 North Charter Street, University of Wisconsin, Madison, WI 53706, USA
7
ISO Data Centre, Astrophysics Division, ESA, Villafranca, Spain
Corresponding author: N. L. Martín-Hernández, leticia@astro.rug.nl
Received:
3
August
2001
Accepted:
18
October
2001
Based on the ISO spectral catalogue of compact HII regions by [CITE], we present a first analysis of the
hydrogen recombination and atomic fine-structure lines originated in
the ionized gas. The sample consists of 34HII regions located at
galactocentric distances between RGal = 0 and 15 kpc. The SWS recombination lines between 2 and 8
are used to estimate the
extinction law at these wavelengths for 14 HII regions. An
extinction in the K band between 0 and ~3 mag has been derived.
The fine-structure lines of N, O, Ne, S and Ar are detected in most of
the sources. Most of these elements are observed in two different
ionization stages probing a range in ionization potential up to 41 eV.
The ISO data, by itself or combined with radio data taken from the
literature, is used to derive the elemental abundances relative to
hydrogen. The present data thus allow us to describe for each source
its elemental abundance, its state of ionization and to constrain the
properties of the ionizing star(s). The main results of this study
are as follows. The ionization ratios Ar++/Ar+, N++/N+, S+3/S++ and
Ne++/Ne+, which measure the degree of ionization and to first order,
the hardness of the stellar radiation, seem to increase with RGal.
These ionization ratios correlate well with each other, implying that
the spectral hardening affects equally the full range of ionizing
energies. A Galactocentric gradient of N/O (
) is observed in the sense of a
decreasing abundance ratio with RGal in agreement with previous
studies. Abundance gradients for neon and argon are derived of the
form
and
.
These elemental gradients could be enlarged by the existing Galactic
Te gradient. Adopting a Te gradient of approximately 330
K kpc-1, the slopes in the Ne/H and Ar/H gradients become
-0.06 and -0.07 dex kpc-1, respectively. Lower limits for
the sulphur and oxygen abundances are derived. Nitrogen abundances are
derived for 16 sources.
Key words: ISM: abundances / ISM: dust, extinction / ISM: HII regions / galaxy: abundances / infrared: ISM: lines / atomic data
© ESO, 2002
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