Issue |
A&A
Volume 456, Number 1, September II 2006
|
|
---|---|---|
Page(s) | 235 - 244 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20064991 | |
Published online | 23 August 2006 |
Study of photon dominated regions in Cepheus B
KOSMA, I. Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany e-mail: bhaswati@astro.umd.edu
Received:
9
February
2006
Accepted:
9
June
2006
Aims. The aim of the paper is to understand the emission from the photon dominated regions in Cepheus B, estimate the column densities of neutral carbon in bulk of the gas in Cepheus B and to derive constraints on the factors which determine the abundance of neutral carbon relative to CO.
Methods.This paper presents
fully sampled maps of [
] at 492 GHz and
12CO 4–3 observed with KOSMA at 1´ resolution. The new
observations have been combined with the FCRAO 12CO 1–0, IRAM-30 m
13CO 2–1 and C18O 1–0 data, and far-infrared continuum data from
HIRES/IRAS. The KOSMA-τ spherical PDR model has been used to
understand the [
] and CO emission from the PDRs in Cepheus B and to
explain the observed variation of the relative abundances of both
C0 and CO.
Results.The emission from the PDR associated with Cepheus B is
primarily at VLSR between -14 and -11 km s-1. We estimate about
23% of the observed [] emission from the molecular hotspot is due
to the ionized gas in the
region. Over bulk of the material the
C0 column density does not change significantly,
cm-2, although the CO column density
changes by an order of magnitude. The observed C/CO abundance
ratio varies between 0.06 and 4 in Cepheus B. We find an
anti-correlation of the observed C/CO abundance ratio with the
observed hydrogen column density, which holds even when all
previous observations providing C/CO ratios are included.
Here we show that this observed variation of C/CO abundance with total
column density can be explained only by clumpy PDRs consisting of an
ensemble of clumps. At high H2 column densities high mass clumps,
which exhibit low C/CO abundance, dominate, while at low column
densities, low mass clumps with high C/CO abundance dominate.
Key words: ISM: clouds / ISM: dust, extinction / ISM: H ii regions / ISM: structure
© ESO, 2006
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